Patent Application
20190145640
The present application relates to methods and systems for liquid desiccant air conditioning. For example, the ability for the system to heat and simultaneously humidify the space, for the system to heat and simultaneously dehumidify, or to cool and humidify thereby providing for more comfortable and healthier indoor air conditions than conventional systems can provide.
Desiccant dehumidification systems—both liquid and solid desiccants—have been used in parallel to conventional vapor compression HVAC equipment to help reduce humidity in spaces, particularly in spaces that require large amounts of outdoor air or that have large humidity loads inside the building space itself. (ASHRAE 2012 Handbook of HVAC Systems and Equipment, Chapter 24, p. 24.10). Humid climates, such as Miami, Fla., require a lot of energy to properly treat (dehumidify and cool) the fresh air that is required for a space's occupant comfort. Desiccant dehumidification systems—both solid and liquid—have been used for many years and are generally quite efficient at removing moisture from the air stream. However, liquid desiccant systems generally use concentrated salt solutions such as ionic solutions of LiCl, LiBr, or CaCl2 and water. Such brines are strongly corrosive to metals, even in small quantities, so numerous attempts have been made over the years to prevent desiccant carry-over to the air stream that is to be treated. In recent years, efforts have begun to eliminate the risk of desiccant carry-over by employing micro-porous membranes to contain the desiccant solution. These membrane-based liquid desiccant systems have been primarily applied to unitary rooftop units for commercial buildings. However, in addition to rooftop units, commercial buildings also use air handlers located inside technical spaces in the building for the cooling and heating of both outside air and recirculated air. There is an additional substantial market for chillers that provide cold water to coils inside the building and use evaporative cooling for high efficiency condensers. Residential and small commercial buildings often use split air conditioners wherein the condenser (together with the compressor and control system) is located outside and one or more evaporator cooling coils is installed in the space than needs to be cooled. In Asia in particular (which is generally hot and humid), the split air conditioning system is the preferred method of cooling (and sometimes heating) a space. We disclose solutions that are highly suitable for such a split approach using liquid desiccant heat exchangers.
Liquid desiccant systems generally have two separate functions. The conditioning side of the system provides conditioning of air to the required conditions, which are typically set using thermostats or humidistats. The regeneration side of the system provides a reconditioning function of the liquid desiccant so that it can be re-used on the conditioning side. Liquid desiccant is typically pumped or moved between the two sides, and a control system helps to ensure that the liquid desiccant is properly balanced between the two sides as conditions necessitate and that excess heat and moisture are properly dealt with, without leading to over-concentrating or under-concentrating of the desiccant.
During the cooling cycle, effective dehumidification can be achieved at higher evaporator temperatures, while the regeneration can fully reject the condenser energy at lower temperatures than traditional air-cooled systems. As a result, the compressor can move energy from the conditioned space at a much lower temperature differential than traditional systems. This improves the efficiency of the compressor in proportion to the reduction in the temperature difference. This drives the efficiency of the combination of compressor based cooling and heating with liquid desiccant heat exchangers.
The benefits of liquid desiccant systems as described in earlier patent applications by the Applicant (U.S. Pat. Nos. 9,243,810, 9,308,490, U.S. Patent Application Publication No. 2014-0260399, U.S. Patent Application Publication No. 2015-0338140, and U.S. Patent Application Publication No. 2016-0187011—all of which are incorporated by reference herein) have been clearly demonstrated for hot and humid climates with a large latent load. As buildings get better insulated, these latent loads increase as a percentage of total cooling loads, making effective dehumidification more important. As internal sensible loads are reduced in tighter, better insulated buildings, conditioning ventilation air becomes an even more significant part of total cooling and heating loads.
Extreme design conditions, including very humid and cool, very hot and dry, and very humid and cold require special cooling and heating solutions.
For example, at very high temperatures (>100 F) and very low humidity (<20% RH), prior liquid desiccant systems may not operate efficiently and need special controls to avoid crystallization of the desiccant. Traditional evaporative cooling systems do well at low humidities and moderate cooling requirements, but are unable to deal with extreme heat or with more humid conditions that tend to occur at least part of the time in most locations. These conditions require compressor based solutions, which are much less efficient and lose significant capacity at high temperatures and/or very high humidities. As a result, they tend to process a mix of outside and return air. Adding evaporative cooling capabilities to a liquid desiccant system creates a unit that has the benefits of both, which is not only critical for use of these systems in monsoon climates, but also raises the possibility of using a standardized system in all climate zones, which is a key requirement of large national and international users of these systems.
For ventilation air, the 920 standard C and D conditions require air to be dehumidified and heated to 70 F. Existing systems use reheat, hot gas bypass, solid desiccants or other options that significantly increase system costs and complexity. We will disclose how a small air cooled evaporator coil in the liquid desiccant system can further increase the basic efficiency of liquid desiccant systems, especially for those conditions.
Traditional cooling systems use refrigerant coils that are air cooled and are best suited for sensible cooling. Condense forming on the coil acts as an insulator that reduces its capacity. Thus, multiple coils need to be used in series to fully dehumidify and cool the air. Four and six row coils are not common. Still, traditional systems often cannot handle the full latent load without significantly overcooling the air and then reheating it, or mixing high volumes of return air with small volumes of outside air to minimize the humidity level of the mix. Especially on days where only a small amount of sensible cooling is required, the building can reach unacceptable levels of humidity. On cold and humid days, such as in the rainy season, with relative humidity levels >90% and low temperatures, heating the air would be preferred while also dehumidifying it. We will disclose how LDAC systems can do this efficiently. Many split systems provide heating by operating as a reversible heat pump system. These tend to be most useful in moderate climates where cooling and heating loads are roughly in balance. Very cold climates like the Midwest and Northeast of the US still require additional heating, often from natural gas or oil. In more moderate climates heat pump effectiveness is limited by humidity, which can lead to frost forming and the use of very inefficient defrost cycles. We will disclose how defrost can be avoided by using liquid desiccant systems.
Commercial ventilation standards (AHRI) have been upgraded and now require 20 CFM per person instead of 5 CFM. Controlled outside air is also becoming more important for residential applications as insulation improves and infiltration is reduced. Traditionally, outside air requirements were met by “infiltration”—open doors and windows and leaks. In earlier patents we have already shown how liquid desiccants can significantly improve the efficiency of such dedicated outdoor air systems or DOAS units.
The high humidity levels of outside air are difficult to meet with the thin coils used in many residential systems. Removal of condense is a special problem for split systems. Condense management has a significant impact on installation and maintenance cost. Condense lines can get plugged if not well maintained, which leads to moisture damage if not timely restored. We will disclose how liquid desiccant HX (heat exchangers) solves these problems.
Additional building humidity “guidelines” are being developed to encourage maximum, and sometimes even minimum, humidity levels mostly driven by health considerations, especially the impact on respiratory disease and allergies. We will disclose solutions that are able to maintain a narrow band of relative humidity (RH) conditions between 40 and 60% RH.
In dry climates, water cooled chillers and evaporative coolers use the evaporation energy of water to cool spaces and/or improve compressor efficiency. They often use potable water in substantial volumes. Managing the scaling effects and biological pollution of such water is a significant challenge. In locations where both humid and dry conditions occur, evaporative chillers are less effective. Standard liquid desiccant solutions do not operate well under those conditions. We will disclose how water addition can be used to simplify liquid desiccant systems and make them competitive in both dry and humid conditions. Many buildings have to deal with a variety of conditions from very hot and dry to relatively cool and humid. Buildings with high dewpoint (DP)/high RH and high dry bulb (DB)/low DP design points require costly conventional solutions, including technologies like solid desiccant wheels, heat pipes and hot gas reheat. We will disclose how liquid desiccant systems can handle these conditions effectively.
There remains a large and increasing need to provide a retrofittable, cost effective and efficient cooling system that can handle both high humidity loads with low sensible loads, as well as high sensible loads with low humidity loads for both cooling and heating. For example, existing liquid desiccant systems manage sensible loads by adding sensible cooling coils or “heat dumps” to the condenser. There are limits to the range of conditions each of these solutions can manage. This forces suppliers to offer a wide range of solutions for buildings with different design conditions in terms of outside air conditions and thermal/latent loads. We will disclose how a combination of the special dehumidification coil disclosed in U.S. Patent Application Publication No. 2016-0187011 and water addition disclosed in U.S. Patent Application Publication No. 2015-0338140 to the liquid desiccant systems disclosed in U.S. Pat. No. 9,243,810 and U.S. Patent Application Publication No. 2014-0260399 creates a compact system that can operate with superior efficiency and capacity over a very wide range of applications and design requirements. This includes making use of available exhaust air for energy recovery, which requires additional heat exchangers, or solid desiccant wheels in traditional systems, while liquid desiccant systems can recover much of the available latent and sensible potential of exhaust air without additional components.
Provided herein are methods and systems used for the efficient cooling and dehumidification of an air stream under a variety of conditions with a single solution. In accordance with one or more embodiments, the liquid desiccant flows down the face of a support plate as a falling film. In accordance with one or more embodiments, the liquid desiccant is contained by a microporous membrane and the air stream is directed in over the surface of the membrane and whereby both latent and sensible heat are absorbed from the air stream into the liquid desiccant. In accordance with one or more embodiments, the support plate is filled with a heat transfer fluid that ideally is flowing in a direction counter to the air stream. In accordance with one or more embodiments, the system comprises a conditioner that removes latent and sensible heat through the liquid desiccant into the heat transfer fluid, a regenerator that rejects the latent and sensible heat from the heat transfer fluid to another environment, and a heat dump coil that rejects excess heat to the other environment as well. In accordance with one or more embodiments, the system is able to provide cooling and dehumidification in a summer cooling mode, humidification and heating in a winter operating mode and heating and dehumidification in a rainy season mode.
In accordance with one or more embodiments, in a summer cooling and dehumidification mode, the heat transfer fluid in the conditioner is cooled by a refrigerant compressor. In accordance with one or more embodiments, the heat transfer fluid in the regenerator is heated by a refrigerant compressor. In accordance with one or more embodiments, the refrigerant compressor is reversible to provide heated heat transfer fluid to the conditioner and the cold heat transfer fluid to the regenerator. The conditioned air is heated and humidified and the regenerated air is cooled and dehumidified. In accordance with one or more embodiments, the conditioner, regenerator and a sensible coil are part of a “packaged” unit. In accordance with one or more embodiments, the conditioner is mounted against a wall in a space, the regenerator and sensible coil are mounted outside of the building. In accordance with one or more embodiments, the regenerator supplies concentrated liquid desiccant to the conditioner through a corrosion resistant, cost effective heat exchanger. In one or more embodiments, the conditioner receives 100% outside air, 100% room air, or a mixture of the two through the use of dampers and ducts. In one or more embodiments, the regenerator receives 100% outside air. In one or more embodiments, the regenerator receives 100% exhaust air from the sensible coil. In one or more embodiments, the sensible coil receives 100% outside air. In one or more embodiments, the sensible coil receives 100% exhaust air from the regenerator.
In accordance with one or more embodiments, a heat exchanger receives hot refrigerant and sends hot heat transfer fluid to a regenerator and a cold refrigerant is used to send cold heat transfer fluid to a conditioner where cool, dehumidified air is created. In accordance with one or more embodiments, water valves can be switched so that the cold heat transfer fluid is directed to a “special mode” sensible heat exchanger in a “rainy” season, or high humidity/cool mode. Wherein the hot refrigerant creates a hot heat transfer fluid for a regenerator, while at the same time the valve system is directing cold cooling fluid to the “special mode” sensible coil and the conditioner receives no or a reduced flow of heat transfer fluid so that liquid desiccant in the conditioner absorbs moisture adiabatically.
In accordance with one or more embodiments, a four way refrigerant valve and bypass valves allows the hot refrigerant to be switched to heat the previously cold heat transfer fluid in a winter operating mode, so that the conditioner receives the now hot heat transfer fluid and the cold heat transfer fluid is directed to the regenerator. In accordance with one or more embodiments, the hot heat transfer fluid can be directed through valves to a “special mode” sensible coil. In one or more embodiments, the hot refrigerant is directed through additional refrigerant valves through a dual fluid “special mode” sensible coil.
In accordance with one or more embodiments, the refrigerant valves contain a set of two 4-way and one bypass valve. In accordance with one or more embodiments, the first 4-way valve is switched so that hot refrigerant from a compressor flows to a first heat exchanger, then to the second 4-way valve, from which it flows to a heat dump coil, through an expansion valve, to a second heat exchanger before flowing back to the first 4-way valve in a summer cooling and dehumidification mode. In one or more embodiments, the first heat exchanger is coupled by means of a heat transfer fluid to a regenerator. In one or more embodiments, the regenerator is a 3-way liquid desiccant membrane regenerator. In one or more embodiments, the regenerator delivers concentrated liquid desiccant to a conditioner. In one or more embodiments, the second heat exchanger is coupled by means of a heat transfer fluid to a conditioner. In one or more embodiments, the conditioner is a 3-way liquid desiccant membrane conditioner. In one or more embodiments, the conditioner receives concentrated liquid desiccant from a regenerator. In accordance with one or more embodiments, the first 4-way valve can be switched to a winter heating and humidification mode, such that the hot refrigerant first flows to the second heat exchanger, then through an expansion valve, into the heat dump coil, through the second 4-way valve to the first heat exchanger, and through the first 4-way valve back through the compressor. In accordance with one or more embodiments, the first 4-way valve is switched so that hot refrigerant from a compressor flows to a first heat exchanger, through a second 4-way valve, through an expansion valve, and the now cold refrigerant flows through a heat dump coil where heat is added to the cold refrigerant by the coil. After which the refrigerant flows through the second 4-way valve through the bypass valve, back through the first 4-way valve and to the compressor in a rainy season heating and dehumidification mode. In one or more embodiments, the first heat exchanger is coupled by means of a heat transfer fluid to a regenerator. In one or more embodiments, the regenerator is a 3-way liquid desiccant membrane regenerator. In one or more embodiments, the regenerator delivers concentrated liquid desiccant to a conditioner. In one or more embodiments, the second heat exchanger is coupled by means of a heat transfer fluid to a conditioner. In one or more embodiments, the conditioner is a 3-way liquid desiccant membrane conditioner. In one or more embodiments, the conditioner receives concentrated liquid desiccant from a regenerator. In one or more embodiments, the conditioner is only receiving concentrated desiccant from the regenerator, but no heat transfer fluid is flowing in the rainy season mode.
In accordance with one or more embodiments, a compressor delivers a hot refrigerant through a 4-way valve into a first heat exchanger, where a hot heat transfer fluid is created in a summer cooling mode. The cooled refrigerant is then directed through a first expansion valve, where it becomes cold, to a second heat exchanger, where it creates a cold heat transfer fluid. The hot heat transfer fluid in the first heat exchanger is directed through means of a series of valves to a liquid desiccant regenerator, where a concentrated liquid desiccant is produced, as well as to a heat dump coil, where excess heat can be rejected. In one or more embodiments, the regenerator and heat dump coil are located outside a building. In one or more embodiments, the regenerator is a 3-way liquid desiccant membrane regenerator.
The cold heat transfer fluid in the second heat exchanger is directed through a series of valves to a liquid desiccant conditioner, where a concentrated liquid desiccant is received and used to dehumidify an air stream, as well as to a “special mode” sensible coil. In one or more embodiments, the “special mode” sensible coil is located next to the liquid desiccant regenerator. In one or more embodiments, the “special mode” sensible coil uses air coming from the regenerator, outside air, or through a damper, a mixture of the two. In one or more embodiments, the “special mode” sensible coil provides air to the regenerator. The air stream going into the regenerator can be outside air, exhaust air from the building, or a mixture of the two. In one or more embodiments, the conditioner is a 3-way liquid desiccant membrane conditioner. In one or more embodiments, the conditioner is located inside a building. In one or more embodiments, the conditioner is connected to ducts that supply air to the building.
In one or more embodiments, the 4-way valve can be switched so that the hot refrigerant is directed to the second heat exchanger in a winter heating and humidification mode. In one or more embodiments, the second heat exchanger delivers a hot heat transfer fluid to a conditioner, which in turn creates a warm, humid air stream for heating and humidifying a space. In one or more embodiments, the conditioner is a 3-way liquid desiccant membrane conditioner. In one or more embodiments, the regenerator is a 3-way liquid desiccant membrane regenerator. In accordance with one or more embodiments, a compressor delivers a hot refrigerant flowing through the 4-way valve to a first heat exchanger, wherein a hot heat transfer fluid is created.
The hot heat transfer fluid can be redirected by the series of valves to flow to the regenerator only in cool and high humidity, or “rainy season”, operating mode. The cooler refrigerant now flows through an expansion valve, wherein the refrigerant gets cold and flows to a second heat exchanger, wherein a cold heat transfer fluid is created. In one or more embodiments, the cooler refrigerant is directed via a series of valves to a second expansion valve, where the cold refrigerant flows through a “special mode” sensible coil, located next to the regenerator. The cold heat transfer fluid in the second heat exchanger can be now be directed to the heat transfer coil. In one or more embodiments, the regenerator receives the hot heat transfer fluid and a diluted desiccant, and provides a concentrated desiccant and a humid, warm air stream. In one or more embodiments, the concentrated desiccant is flowing to a conditioner. In one or more embodiments, the conditioner is dehumidifying an air stream. In one or more embodiments, the conditioner is not receiving a heat transfer fluid and the dehumidification takes place adiabatically. In one or more embodiments, the conditioner is a 3-way liquid desiccant membrane conditioner. In one or more embodiments, the conditioner receives concentrated liquid desiccant from a regenerator. In one or more embodiments, the regenerator is a 3-way liquid desiccant membrane regenerator. In one or more embodiments, the conditioner is only receiving concentrated desiccant from the regenerator, but no heat transfer fluid is flowing in the rainy season mode.
In accordance with one or more embodiments, a heat exchanger receives hot refrigerant and sends hot heat transfer fluid to a regenerator, while at the same time hot refrigerant is also directed to a “special mode” sensible coil and a cold refrigerant is used to send cold heat transfer fluid to a conditioner where cool, dehumidified air is created. In accordance with one or more embodiments, there is a set of 3-way and one 4-way refrigerant valves, and three bypass valves that allow the hot refrigerant to be switched to heat the previously cold heat transfer fluid in a winter operating mode, so that the conditioner receives the now hot heat transfer fluid, and the cold heat transfer fluid is directed to the “special mode” sensible coil and regenerator. In accordance with one or more embodiments, the set of refrigerant valves can also be switched so that the hot refrigerant is directed to the heat exchanger in a rainy season mode, wherein the hot refrigerant creates a hot heat transfer fluid for a regenerator, while at the same time the valve system is directing cold refrigerant to the heat dump coil, and the conditioner receives no heat transfer fluid so the liquid desiccant in the conditioner absorbs moisture adiabatically.
In accordance with one or more embodiments, the refrigerant valves contain a set of two 4-way and one bypass valve. In accordance with one or more embodiments, the first 4-way valve is switched so that hot refrigerant from a compressor flows to a first heat exchanger, then to the second 4-way valve, from which it flows to a heat dump coil, through an expansion valve, to a second heat exchanger, before flowing back to the first 4-way valve in a summer cooling and dehumidification mode. In one or more embodiments, the first heat exchanger is coupled by means of a heat transfer fluid to a regenerator. In one or more embodiments, the regenerator is a 3-way liquid desiccant membrane regenerator. In one or more embodiments, the regenerator delivers concentrated liquid desiccant to a conditioner. In one or more embodiments, the second heat exchanger is coupled by means of a heat transfer fluid to a conditioner. In one or more embodiments, the conditioner is a 3-way liquid desiccant membrane conditioner. In one or more embodiments, the conditioner receives concentrated liquid desiccant from a regenerator. In accordance with one or more embodiments, the first 4-way valve can be switched to a winter heating and humidification mode, such that the hot refrigerant first flows to the second heat exchanger, then through an expansion valve, into the heat dump coil, through the second 4-way valve to the first heat exchanger, and through the first 4-way valve back through the compressor. In accordance with one or more embodiments, the first 4-way valve is switched so that hot refrigerant from a compressor flows to a first heat exchanger, through a second 4-way valve, through an expansion valve, and the now cold refrigerant flows through a heat dump coil, where heat is added to the cold refrigerant by the coil, after which the refrigerant flows through the second 4-way valve, through the bypass valve, and back through the first 4-way valve to the compressor in a rainy season heating and dehumidification mode. In one or more embodiments, the first heat exchanger is coupled by means of a heat transfer fluid to a regenerator. In one or more embodiments, the regenerator is a 3-way liquid desiccant membrane regenerator. In one or more embodiments, the regenerator delivers concentrated liquid desiccant to a conditioner. In one or more embodiments, the second heat exchanger is coupled by means of a heat transfer fluid to a conditioner. In one or more embodiments, the conditioner is a 3-way liquid desiccant membrane conditioner. In one or more embodiments, the conditioner receives concentrated liquid desiccant from a regenerator. In one or more embodiments, the conditioner is only receiving concentrated desiccant from the regenerator, but no heat transfer fluid is flowing in the high humidity and cool rainy season mode.
In accordance with one or more embodiments, a compressor delivers a hot refrigerant through a 4-way valve into a first heat exchanger where a hot heat transfer fluid is created in a summer cooling mode. The cooled refrigerant is then directed through a first expansion valve, where it become cold, to a second heat exchanger, where it creates a cold heat transfer fluid. The hot heat transfer fluid in the first heat exchanger is directed through means of a series of valves to a liquid desiccant regenerator, where a concentrated liquid desiccant is produced, as well as to a heat dump coil, where excess heat can be rejected. In one or more embodiments, the regenerator and heat dump coil are located outside a building. In one or more embodiments, the regenerator is a 3-way liquid desiccant membrane regenerator.
The cold heat transfer fluid in the second heat exchanger is directed through a series of valves to a liquid desiccant conditioner where a concentrated liquid desiccant is received and used to dehumidify an air stream, as well as to a “special mode” sensible coil. In one or more embodiments, the “special mode” sensible coil is located next to the liquid desiccant regenerator. In one or more embodiments, the “special mode” sensible coil uses air coming from the regenerator, outside air, or through a damper a mixture of the two. In one or more embodiments, the “special mode” sensible coil provides air to the regenerator. The air stream going into the regenerator can be outside air, exhaust air from the building, or a mixture of the two. In one or more embodiments, the conditioner is a 3-way liquid desiccant membrane conditioner. In one or more embodiments, the conditioner is located inside a building. In one or more embodiments, the conditioner is connected to ducts that supply air to the building. In one or more embodiments, with one or more conditioners located inside a building, and a separate regenerator and compressor located outside the building, one or more intermediate “mid” units provide access to water addition, and simplifies flow and pressure control for heat transfer fluids and desiccants.
In one or more embodiments, the 4-way valve can be switched so that the hot refrigerant is directed to the second heat exchanger in a winter heating and humidification mode. In one or more embodiments, the second heat exchanger delivers a hot heat transfer fluid to a conditioner, which in turn creates a warm, humid air stream for heating and humidifying a space. In one or more embodiments, the cold refrigerant can be directed through a series of valves to a special mode sensible coil. In one or more embodiments, the special mode coil processes the dehumidified cold outside air from the regenerator, further cooling it sensibly, and increasing the sensible heating capacity of the liquid desiccant heat exchanger. In winter mode, this reduces the humidity provided to the space in the conditioner, ensuring that a comfortable 30-60% RH can be maintained. Dehumidification of the outside air ensures that the special mode coil does not get frost bound, avoiding the defrosting cycles, typical at moderately cold but humid outside conditions. In one or more embodiments, the additional humidity is provided by diluting the desiccant to maintain a sufficiently high RH. In one or more embodiments, addition of humidity improves overall compressor efficiency by reducing the lift at which a total enthalpy increase is realized.
In one or more embodiments, the conditioner is a 3-way liquid desiccant membrane conditioner. In one or more embodiments, the conditioner is located inside a building and processes local air. In one or more embodiments, the conditioner is connected to ducts that supply air to the building. In one or more embodiments, the cooler refrigerant is directed through a second expansion valve and the cold refrigerant is directed to the first heat exchanger, wherein a cold heat transfer fluid is created. The cold heat transfer fluid in the first heat exchanger is now directed to a regenerator, where heat and moisture are removed from an air stream, and to a “special mode” sensible dump coil, where additional heat can be picked up from the dry air exhausted from the regenerator, from a second air stream, or a mixture of the two using a damper. The air stream going into the regenerator can be outside air, exhaust air from the building, or a mixture of the two. In one or more embodiments, the regenerator and heat dump coil are located outside a building. In one or more embodiments, the regenerator and special dehumidification sensible coil are located inside a building with a duct connection for air supply from the outside, or from exhaust air from the building. In one or more embodiments, the regenerator is a 3-way liquid desiccant membrane regenerator. In accordance with one or more embodiments, a compressor delivers a hot refrigerant flowing through the 4-way valve to a first heat exchanger, wherein a hot heat transfer fluid is created.
The hot heat transfer fluid can be redirected by the series of valves to flow to the regenerator only in cool and high humidity or “rain season” operating mode. The cooler refrigerant now flows through an expansion valve, wherein the refrigerant gets cold and flows to a second heat exchanger, wherein a cold heat transfer fluid is created. In one or more embodiments, the cooler refrigerant is directed via a series of valves to a second expansion valve, where the cold refrigerant flows through a “special mode” sensible coil, located next to the regenerator. The cold heat transfer fluid in the second heat exchanger can be now be directed to the heat transfer coil. In one or more embodiments, the regenerator receives the hot heat transfer fluid and a diluted desiccant, and provides a concentrated desiccant and a humid, warm air stream. In one or more embodiments, the concentrated desiccant is flowing to a conditioner. In one or more embodiments, the conditioner is dehumidifying an air stream. In one or more embodiments, the conditioner is not receiving a heat transfer fluid and the dehumidification takes place adiabatically. In one or more embodiments, the conditioner is a 3-way liquid desiccant membrane conditioner. In one or more embodiments, the conditioner receives concentrated liquid desiccant from a regenerator. In one or more embodiments, the regenerator is a 3-way liquid desiccant membrane regenerator. In one or more embodiments, the conditioner is only receiving concentrated desiccant from the regenerator, but no heat transfer fluid is flowing in the rainy season mode.
In accordance with one or more embodiments, liquid desiccant is diluted in the conditioner. In accordance with one or more embodiments, the diluted liquid desiccant is heated up in the regenerator. In accordance with one or more embodiments, the heated desiccant evaporates water into an air stream. In accordance with one or more embodiments, the desiccant is diluted. In accordance with one or more embodiments, the dilution is done in a water transfer membrane unit, where a feed stream of tap water, seawater or other water sources with some contamination is used to dilute the desiccant. In accordance with one or more embodiments, the water transfer membrane unit uses forward osmosis to transfer water from the feed stream into the liquid desiccant. In accordance with one or more embodiments, the membrane water transfer unit uses vapor transfer membranes, similar to or identical to the ones used in the 3-way heat exchanger, to transfer water from the feed stream into the liquid desiccant. In accordance with one or more embodiments, the liquid desiccant used has been heated up in the regenerator to maximize the transfer rate. In accordance with one or more embodiments, the membrane water transfer unit is used to dilute the desiccant in the desiccant tank, or in the feed stream to the regenerator, or in the desiccant coming from the conditioner. In accordance with one or more embodiments, an available demineralized water stream is used to dilute the desiccant in the desiccant tank, in the feed stream to the regenerator, or in the desiccant coming from the conditioner.
In accordance with one or more embodiments, a liquid desiccant membrane system employs an evaporator. In one or more embodiments, the water supplied to the evaporator is potable water. In one or more embodiments, the water is seawater. In one or more embodiments, the water is waste water. In one or more embodiments, the evaporator uses a membrane to prevent carry-over of non-desirable elements from the seawater or waste water to the air stream. In one or more embodiments, the water in the evaporator is not cycled back to the top of the indirect evaporator, such as would happen in a cooling tower, but between 20% and 80% of the water is evaporated and the remainder is discarded.
In accordance with one or more embodiments, air supplied to the conditioner is sent first through an evaporative cooling pad, or similar direct evaporative cooling. This reduces the cooling load compared to only sensible cooling of the air when the dew point of air is lower than the supply absolute humidity target. In accordance with one or more embodiments, the conditioner further dehumidifies and cools air when the combination of dew point and wet bulb condition is too high to reach both the humidity and sensible cooling targets. This reduces the total load, if the air condition is lower than the target supply dew point, and always reduces the temperature difference between the evaporator and condenser of the compressor system, improving compressor efficiency. The efficiency of the Carnot cycle is directly proportional to this delta T. Since the water is absorbed as a vapor, no demineralization is required. Unlike liquid desiccant heat exchangers, the water treatment requirements for direct evaporative cooler are well understood by local contractors.
FIG. 6A1 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a summer cooling and dehumidification mode in accordance with one or more embodiments, using one 4-way and three 3-way refrigerant valves.
FIG. 6A2 shows a schematic of a chiller assisted liquid desiccant air conditioning system in a summer cooling and dehumidification mode in accordance with one or more embodiments, using one 4-way refrigerant valve with a single 3-way valve system.
FIG. 6A3 shows the chiller system of 6A2 in a cooling mode for dry conditions with one 4-way and one 3-way valve and a 3-way water circuit valve to a dual fluid air cooled coil.
FIG. 6B1 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a winter heating and frost prevention mode in accordance with one or more embodiments, using one 4-way and three 3-way refrigerant valves.
FIG. 6B2 shows a schematic of an alternative chiller assisted liquid desiccant air conditioning system in a winter heating and frost prevention mode in accordance with one or more embodiments, using one 4-way and one 3-way refrigerant valves.
FIG. 6C1 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a colder season warming and dehumidification mode in accordance with one or more embodiments, using one 4-way and three 3-way refrigerant valves.
FIG. 6C2 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a colder season dehumidification with independent temperature control mode in accordance with one or more embodiments, using one 4 -way and one 3-way refrigerant valve.
FIG. 6C3 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a colder season warming and dehumidification mode in accordance with one or more embodiments, using one 4-way and one 3-way refrigerant valve.
FIG. 8A1 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a summer cooling and dehumidification mode in accordance with one or more embodiments, using four 3-way water diverting valves.
FIG. 8A2 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a cooling mode for dry(er) conditions in accordance with one or more embodiments, using four 3-way water diverting valves.
FIG. 8B1 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a winter heating and humidification mode in accordance with one or more embodiments, using four 3-way water diverting valves.
FIG. 8B2 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a frost free winter heating mode in accordance with one or more embodiments, using four 3-way water diverting valves.
FIG. 8C1 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a colder season heating and dehumidification mode in accordance with one or more embodiments, using four 3-way water diverting valves with conditioner and air cooled coil in parallel.
FIG. 8C2 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a colder season heating and dehumidification mode in accordance with one or more embodiments, using four 3-way water diverting valves with conditioner and air cooled coil in series.
FIG. 8C3 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a colder season heating and dehumidification mode in accordance with one or more embodiments, using four 3-way water diverting valves with conditioner and air cooled coil in parallel.
FIG. 10A1 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a cooling mode with evaporation in accordance with one or more embodiments, using one 4-way and two 3-way refrigerant valves.
FIG. 10A2 shows a schematic of an exemplary chiller assisted liquid desiccant air conditioning system in a cooling and dehumidification mode with evaporation support in accordance with one or more embodiments, using one 4-way and two 3-way refrigerant valves.
The liquid desiccant is collected at the bottom of the wavy conditioner plates at 111 and is transported through a heat exchanger 113, to the top of the regenerator 102, and to point 115 where the liquid desiccant is distributed across the wavy plates of the regenerator. Return air, or optionally outside air, at 105 is blown across the regenerator plate and water vapor is transported from the liquid desiccant into the leaving air stream at 106. An optional heat source 108 provides the driving force for the regeneration. The hot transfer fluid at 110 from the heat source can be put inside the wavy plates of the regenerator similar to the cold heat transfer fluid on the conditioner. Again, the liquid desiccant is collected at the bottom of the wavy plates 102 without the need for either a collection pan or bath, so the regenerator the air flow can be horizontal or vertical. An optional heat pump 116 can be used to provide cooling and heating of the liquid desiccant. It is also possible to connect a heat pump between the cold source 107 and the hot source 108, which is pumping heat from the cooling fluids rather than the desiccant.
The liquid desiccant at 428 leaves the conditioner 403 and is moved through the optional heat exchanger 426 to the regenerator 422 by pump 425. If the desiccant lines 427 and 428 are relatively long, they can be thermally connected to each other, which eliminates the need for heat exchanger 426.
The chiller system 430 comprises a water-to-refrigerant evaporator heat exchanger 407, which cools the circulating cooling fluid at 406. The liquid, cold refrigerant at 417 evaporates in the heat exchanger 407, thereby absorbing the thermal energy from the cooling fluid at 406. The gaseous refrigerant at 410 is now re-compressed by compressor 411. The compressor 411 ejects hot refrigerant gas at 413, which is liquefied in the condenser heat exchanger 415. The liquid refrigerant at 414 then enters expansion valve 416, where it rapidly cools and exits at a lower pressure. The chiller system 430 can be made very compact since the high pressure lines with refrigerant (410, 413, 414 and 417) only have to run very short distances. Furthermore, since the entire refrigerant system is located outside of the space that is to be conditioned, it is possible to utilize refrigerants that normally cannot be used in indoor environments such as CO2, ammonia and propane. These refrigerants are sometimes preferable over the commonly used R410A, R407A, R134A because of their lower greenhouse gas potential or over R1234YF and R1234ZE refrigerants, but they are undesirable indoor because of flammability or suffocation or inhalation risks. By keeping all of the refrigerants outside, these risks are significantly reduced. The condenser heat exchanger 415 releases heat to another cooling fluid loop 419, which brings hot heat transfer fluid at 418 to the regenerator 422. Circulating pump 420 brings the heat transfer fluid back to the condenser 415. The 3-way regenerator 422 receives a dilute liquid desiccant at 428 and hot heat transfer fluid at 418. A fan 424 powered by electricity 429 brings outside air at 421 (“OA”) through the regenerator 422. The outside air picks up heat and moisture from the heat transfer fluid at 418 and desiccant at 428, which results in hot humid exhaust air (“EA”) at 423.
The compressor 411 receives electrical power 412 and typically accounts for 80% of electrical power consumption of the system. The fan 402 and fan 424 also receive electrical power 405 and 429 respectively, and account for most of the remaining power consumption. Pumps 408, 420, and 425 have relatively low power consumption. The compressor 411 will operate more efficiently than the compressor 510 in
Besides the compressor 510, the outdoor components comprise a condenser coil 516 and a condenser fan 517, as well as a 4-way valve assembly 511. The 4-way valve 512 (which for convenience has been labeled the 512-“A” position) has been positioned inside the valve body 511 so that the hot refrigerant at 513 is directed to the condenser coil 516 through line 515. The fan 517 blows outside air at 518 through the condenser coil 516, where it picks up heat from the compressor 510, which is rejected to the air stream at 519. The cooled liquid refrigerant at 520 is conducted to a set of valves 521, 522, 524 and 525, with the addition of an “O” for open or a “C” for closed. As can be seen in the figure, the refrigerant at 520 goes through the check valve 521-O and bypasses the expansion valve 522-C. Since the second check valve 524-C is closed, the refrigerant moves through line 5233 and to the second expansion valve 525-O, in which the refrigerant expands and cools. The cold refrigerant at 526 is then conducted to the evaporator 501 where it picks up heat and expands back to a gas. The gas at 509 is then conducted to the 4-way valve 511 and flows back to the compressor 510 through line 514.
In some instances the system can have multiple compressors or multiple condenser coils and fans. The primary electrical energy consuming components are the compressor 510, the condenser fan 516 and the evaporator fan 502. In general, the compressor uses close to 80% of the electricity required to operate the system, with the condenser and evaporator fans taking about 10% of the electricity each.
FIGS. 6A1-6D show how the operational range of the liquid desiccant system can be enlarged with aircooled coils to provide additional sensible cooling capacity during hot and dry conditions and additional dehumidification capacity in cool and humid conditions. How these coils are connected to the refrigerant system impacts efficiency and flexibility. Coils that are part of the refrigerant system are more efficient then coils connected via a refrigerant to liquid heat exchanger. However, this results in highly complex refrigeration systems that are difficult to operate over a broad range of conditions.
Options for adding water to the liquid desiccant are also shown. Water addition significantly improves performance and increases the ratio of sensible cooling to total cooling (SHR). As such it's an efficient alternative to the condenser coil for hot and dry conditions. Various locations where water can be added are shown. High dilution of the liquid desiccant requires thorough demineralization of the liquid desiccant to avoid deposits that can damage the heat exchangers. Additional options for mineral free dilution of liquid desiccant are disclosed.
FIG. 6A1 illustrates an alternate embodiment of a liquid desiccant system set up in a summer cooling and dehumidification mode. Similar to
Refrigerant compressor 615 compresses a refrigerant gas to high pressure and the resulting hot refrigerant at 616 is directed to a 4-way valve assembly 617. The valve 618 is in the “A” position, as before labeled 618-A In this position, the hot refrigerant gas is directed through line 619 to two heat exchangers: a refrigerant-to-liquid heat exchanger 620, and a refrigerant-to-air heat exchanger 622 through 3-way switching valve 621-A, also in the “A” position, which directs the refrigerant to the heat exchanger 622. The refrigerant leaves the heat exchanger 622 through 3-way switching valve 626-A, which is also in an “A” position, which directs the refrigerant through line 627. The refrigerant from heat exchanger 620 is combined and both streams flow to a set of valves 628, 629, 630 and 631. The check valve 628-O is open and allows the refrigerant to flow to expansion valve 631-O which expands the liquid refrigerant to become cold in line 632. Check valve 630-C is closed as is expansion valve 629-C. The refrigerant next encounters another 3-way switching valve 633-A in the “A” position. The cold refrigerant now picks up heat in the aforementioned heat exchanger 614. The warmer refrigerant then moves through line 634 to the 4-way valve 617, where it is directed back to the compressor 615 through line 635. The liquid to refrigerant heat exchanger 620 is supplied with a heat transfer fluid (usually water or glycol) through line 644 by pump 643. The heated heat transfer fluid is then directed through line 651 to a regenerator membrane module 648, which is similar in construction as the module from
The air stream at 646 is now heated by the heat transfer fluid, and picks up moisture from the diluted liquid desiccant at 645, which results in a hot, moist exhaust air stream at 646. The air stream at 646 can be exhausted. Pump 653 moves the diluted liquid desiccant from reservoir 654 to the membrane module 648, and re-concentrated liquid desiccant at 652 is moved back to the reservoir 654. A small pump 655 can provide desiccant flow between the reservoirs 610 and 654. At the same time, the air stream at 624 is directed by fan 623 through the air to refrigerant heat exchanger 622. The air stream at 624 can be made up of the exhaust air from regenerator 648 through a damper, or through a permanent alignment of the two heat exchangers. The air stream at 624/646B is sensibly heated by the refrigerant and the resulting hot air at 625 is exhausted. Refrigerant line 637 is inactive in this summer cooling mode and its use will be described under FIG. 6C1. It is possible to thermally connect desiccant lines 611 and 612 and form a heat exchanger between the two lines so that heat from the regenerator 648 is not conducted directly to the conditioner 603, which will reduce the energy load on the conditioner. Furthermore, it is possible to add a separate liquid desiccant-to-liquid desiccant heat exchanger 6556, instead of (or in addition to) thermally connecting lines 611 and 612. An optional water injection system 657 (which is further described in U.S. patent application Ser. No. 14/664,219 and published as U.S. Patent Application Publication No. 20150338140 incorporated by reference herein) inhibits overconcentration of the desiccant in certain conditions by adding water at 658 to the desiccant, which also can have the effect of making the system more energy efficient and can be located on different locations in the system depending on the conditions required.
FIG. 6A2 shows a liquid desiccant system with one four way valve and a simplified valve system in summer cooling mode. Similar to FIG. 6A1, a liquid desiccant conditioner 603 receives an air stream 601, which is moved by fan 602 through the conditioner 603. The treated air 606 is directed into the space. The conditioner 603 receives concentrated liquid desiccant 607, which, as explained in connection with
Refrigerant compressor 615 compresses a refrigerant gas to high pressure and the resulting hot refrigerant 616 is directed to a 4-way valve assembly 617. The valve 618 is in the “A” position as before labeled 618-A in the figure. In this position the hot refrigerant gas is directed through line 619 to a refrigerant to liquid heat exchanger (LCC) 620. One option is to direct it via 3 way switching valve 670 to a refrigerant to air heat exchanger 671 that rejects heat into outside airflow 672. The combined refrigerant leaves the heat exchangers 620 and optionally 671 to 3-way switching valve 680, which is also in an “A” position, and which directs the refrigerant to one way valve 618C and expansion valve 638-O, which expands the liquid refrigerant to become cold in line 632. Check valve 637-C is closed as is expansion valve 624. The cold refrigerant now picks up heat in the aforementioned three way heat exchanger 614. The warmer refrigerant then moves through line 634 to the 4-way valve 617, where it is directed back to the compressor 615 through line 635 and accumulator 615B.
The liquid-to-refrigerant heat exchanger 620 is supplied with a heat transfer fluid (which can be, e.g., water) through line 644 by pump 643. The heated heat transfer fluid is then directed through line 640 to a regenerator membrane module 648, which is similar in construction as the module from
The relative humidity of air streams is directly linked to the concentration of the lithium chloride, since the vapor pressure of the air and the vapor pressure of the liquid desiccant have to be in balance. The RH of air coming out of the regenerator and conditioner is proportional to 100%-2*concentration. Lower concentration leads to higher RHs in supply stream 606.
For locations with both humid and dry hot air, an air cooled condenser or “heat dump” coil 672 can be added to the refrigerant circuit, either in parallel or in series with the LCC 620. A heat dump coil was shown in
A LCC is typically circuited with all refrigerant path in parallel thus creating a low resistance path for vapor as shown in the drawings. Air cooled condensers typically circuit pipes in series to avoid system complexity and cost due to many joints.
Parallel circuits for LCC and air cooled coil makes managing the oil and refrigerant in the compressor system easier and increases flexibility for managing dryer conditions. Putting them in series could have an advantage for specific industrial applications with a specific and stable load pattern.
In other words, the addition of this component allows the system to remove heat collected at the evaporator in one of two places. Controlling the heat flow through the LCC and therefore the regenerator LDHX controls the amount of water removed from the desiccant. This sets the desiccant concentration and thereby the desired level of dehumidification and temperature change in the process air stream. For example by flowing more air 1072 over the heat dump coil less heat is available for the LCC and thus the desiccant concentration is lowered. This allows the conditioner LDHX to dehumidify less and sensibly cool more.
Optimizing the humidity in supply stream 606 can be managed by directing refrigerant from 617 through 619 mostly or totally to heat exchanger 672. As a result heat transfer fluid 640 coming out of heat exchanger 620 will be cooler. This reduces the ability of heat exchanger 648 to increase the concentration of the desiccant 645. As a result the air coming from heat exchanger 603 will be less dehumidified, resulting in a higher sensible heat ratio
Instead of using coil 671 and valve 619, the system can also rely on adding water to the desiccant to dilute it directly. That results in significantly higher evaporation and thus lower temperatures at heat exchanger 648, which generally will improve system efficiency. U.S. Patent Application No. 61/968,333 filed Mar. 20, 2014, which is incorporated by reference herein, describes a method to add water to the liquid desiccant. This method could also be applied here and water could be injected for example in line 652 coming out of heat exchanger 648 or in line 652 going into 648. Vapor transmission through membranes is more efficient at higher temperatures and thus such a module will be positioned in flow coming out of 648. Other methods of water addition could include commercially available forward osmosis units which could be positioned at the same location or elsewhere in the liquid desiccant system, e.g. supplying demineralized water directly into tank 610.
FIG. 6A3 shows a liquid desiccant system with an alternative refrigerant system consisting of one four way valve and one 3 way valve. With the additional features like an accumulator and receiver such a configuration can maintain refrigerant quality better. Similar to FIG. 6A1 a 3-way liquid desiccant conditioner 603 receives an air stream 601 which is moved by fan 602 through the conditioner 603. The treated air 606 is directed into the space. The conditioner 603 receives concentrated liquid desiccant 607 which, as explained in
Refrigerant compressor 615 compresses a refrigerant gas to high pressure and the resulting hot refrigerant 616 is directed to a 4-way valve assembly 617. The valve 618 is in the “A” position as before labeled 618-A in the figure. In this position the hot refrigerant gas is directed through line 619 to a refrigerant to liquid heat exchanger 620. An option is to direct it via 3 way switching valve 619 to a refrigerant to air heat exchanger 671 that rejects heat into outside airflow 672. The combined refrigerant leaves the heat exchangers 620 and optionally 671 to 3-way switching valve 618 which is also in an “A” position, which directs the refrigerant to one way valve 618C and expansion valve 638-O, which expands the liquid refrigerant to become cold in line 632. Check valve 637-C is closed as is expansion valve 624. The cold refrigerant now picks up heat in the aforementioned three way heat exchanger 614. The warmer refrigerant then moves through line 634 to the 4-way valve 617, where it is directed back to the compressor 615 through line 635 and accumulator 615B.
The liquid to refrigerant heat exchanger 620 is supplied with a heat transfer fluid (usually water) through line 644 by pump 643. The heated heat transfer fluid is then directed through line 640 to a valve 640A set in position A in which it directs the heat transfer fluid to liquid to the air cooled heat exchanger 622 where it heats up air stream 646B to 625. Air cooled heat exchanger 622 then needs to be a dual fluid heat exchanger which is cooled by refrigerant in warming/heating and dehumidification mode and by heat transfer fluid in a dry climate cooling with little or no dehumidification mode as well as heating mode. The cooled down heat transfer fluid is then send to a regenerator membrane module 648, which is similar in construction as the module from
It is also possible to thermally connect desiccant lines 611 and 612 and form a heat exchanger between the two lines so that heat from the regenerator 648 is not conducted directly to the conditioner 603, which will reduce the energy load on the conditioner. Furthermore it is possible to add a separate liquid desiccant to liquid desiccant heat exchanger 656 instead of thermally connecting lines 611 and 612.
An optional water injection system 657 (which is further described in U.S. patent application Ser. No. 14/664,219 incorporated by reference herein) prevents overconcentration of the desiccant in certain conditions by adding water 652 to the desiccant. This also can have the effect of making the system more energy efficient. Forward osmosis or different vapor transfer membrane units can be used for water injection at 657. De-ionized water can be added directly to tank 610 after reverse osmosis or another demineralization process. The exact set up of tank 610, heat exchanger 656, thermal connection 611/612, water addition module 657 and pumps 653 and 609610 can be varied based on the exact application and installation.
If air flows 646 gets too dry, the concentration of the liquid desiccant in heat exchanger 648 might get too high and desiccant can then crystalize in heat exchanger 648 U.S. Patent Application No. 61/968,333 filed Mar. 20, 2014, which is incorporated by reference herein, describes a method to add water to the liquid desiccant. This method could also be applied here and water could be injected for example in line 645 coming out of heat exchanger 648. Vapor transmission through membranes is more efficient at higher temperatures and thus such a module will be positioned in flow coming out of 643. Other methods of water addition could include commercially available forward osmosis units which could be positioned at the same location or elsewhere in the liquid desiccant system, e.g., supplying demineralized water directly into tank 610or even in the supply lines to conditioner 603 when the air 601 gets very dry. The added water can then be used to increase the humidity of the outgoing air stream 606 as well as air stream 646. During hot and dry conditions the water injection systems allows the system to do more sensible and less latent cooling. It can humidify air not only at the regenerator 648 but also at the conditioner 603 when conditions are below 40% RH or a 6-10 C dew point. During very hot and dry conditions part of the sensible load to be matched by increased evaporation by coil 603. Water injection also makes the system more energy efficient by significantly reducing condenser temperature as the regenerator is able to reject more heat through evaporation. This allows a liquid desiccant with water addition to match the efficiency of water cooled chillers. It also prevents over concentration of the desiccant and avoids the need for a crystallization protection control sequence. Water addition also creates flexibility in managing latent and sensible loads independently. And allows for humidification during hot and dry or cold and very dry conditions.
This turns the liquid desiccant unit into an evaporative cooler, significantly reducing the remaining load to be handled by compressor 615 and improving the quality of the supplied air. Increasing dew point while cooling significantly reduces load and effective system level efficiency for achieving DB targets. High evaporation at the condenser significantly reduces compressor lift, improving the Carnot efficiency of the compressor.
Contrary to traditional evaporative cooling systems, a liquid desiccant system using forward osmosis and vapor transmission can use hard water, seawater or used water streams. This is critical in water constrained environments. Moreover at high wet bulb conditions the liquid desiccant system controls supply air dew point through adjustments in airflow 646, heat transfer fluid 640 and the setting of valve 618. This prevents the humidity levels of 606 to become higher than typical targets like a 12.5 dew point. This is a significant advantage over direct evaporative systems when supply air 601 conditions change from very dry to more humid, or from warm to very hot with wet bulb conditions exceeding 15C.
The system of FIG. 6A1 is able to supply sensible cooling and dehumidification at a higher temperature then a conventional HVAC system and cool the condenser at lower temperatures then non water cooled conventional systems. As a result, the system will do this with less lift (the difference in temperature of refrigerant across the compressor 615) as a conventional system would have and thus with greater efficiency. The supply air will feel drier and more comfortable than what a conventional system will be able to deliver during humid conditions. During extremely dry events humidity can be increased for greater comfort and efficiency. Thus the systems flexibility allows a single unit to handle a wide range of cooling and heating conditions from cool and very humid to hot and very dry with minimal lift in all settings, thereby maximizing efficiency not only at standard testing conditions, but in real conditions year round anywhere. As a result suppliers will be able to further standardize units and significantly reduce their cost.
In FIG. 6B1, the system of FIG. 6A1 has been switched to a winter heating and humidification mode. The valve 618 has been switched from the “A” to the “B” position, which results in reversal of the refrigerant flow through the circuits in such a way that heat exchanger 614 now receives hot refrigerant whereas heat exchangers 622 and 620 receive cold refrigerant. Valve 628-C is now closed, expansion valve 629-O is open, valve 630-O is open and expansion valve 631-C is closed. In this mode the refrigerant system is pulling heat from air streams 646 and 624 and directing it to the conditioner 603 which is now providing heated, moist air to the space. The liquid desiccant is delivering moisture to the space and thus is getting more concentrated in the conditioner 603. The liquid desiccant is pulling moisture from the air stream 646. However, there are limits to this: if the air stream 646 is relatively dry, there may not be enough moisture available and the desiccant could become over-concentrated. U.S. Patent Application No. 61/968,333 filed Mar. 20, 2014, which is incorporated by reference herein, describes a method to add water to the liquid desiccant to prevent this from happening as will be shown in
In FIG. 6B2, the system of FIG. 6A2 has been switched to a winter heating with frost prevention and limited humidification mode. The valve 618 has been switched from the “A” to the “B” position, which results in reversal of the refrigerant flow through the circuits in such a way that heat exchanger 614 now receives hot refrigerant whereas heat exchangers 622 and 620 receive cold refrigerant. Valve 628 is open, expansion valve 629-A is open, valve 629B is open and expansion valve 638-O is closed. Instead the refrigerant flows through one way valve 637-C and receiver 618B. In this mode the refrigerant system is pulling heat from air streams 646 and 624 and directing it to the conditioner 614 which is now providing heated, moist air to the space. The refrigerant from coils 620 and 622 returns to compressor 615 via accumulator 615C. The liquid desiccant is delivering moisture to the space and thus is getting more concentrated in the conditioner 614. The liquid desiccant is pulling moisture from the air stream 646. If too much moisture is absorbed from flow 646, valve 628 can be set to close the refrigerant flow to heat exchanger 620. This will cause heat exchanger 648 to dry the cold air adiabatically, dehumidifying and heating it up. That dry air is then the input for coil 622 which further cools it sensibly. Since the dew point is well below the refrigerant temperature this can be done without frost forming on coil 622. Since defrost cycles are a major efficiency reducing factor in heat pumps this represents an important improvement for the heat pump cycle with high RH cold air. By managing the flows through valve 628 the concentration of the Liquid desiccant can be adjusted. This provides control over the RH levels supplied by heat exchanger 603. Preferably dew points should not exceed 10 C during wintertime to avoid moisture damage to building structures. The 920 standards for 7C DB and 6C WB and 2C DB and 1C WB are such high RH conditions requiring frost prevention.
The advantage of this setup is that the system now provides moist, warm air to the space which will prevent the space from becoming too dry as is the case with conventional heat pump air conditioners. This will add to user comfort since conventional air conditioning heat pumps only provide heat unless a separate humidifier is used. The other advantage of this system is that in winter the heat can be primarily pumped from the regenerator module 648. Since this module only has desiccant and heat transfer fluid, it will be able to operate at much lower temperatures than the condenser coil of a conventional heat pump system, which starts to have ice formation when the outside air temperatures reaches 32 F and the relative humidity is near 100%. Conventional heat pumps in that case will temporarily reverse cycle so that ice can be removed from the coil, meaning that they are cooling the space for a little while in reverse cycle mode. This obviously is not very energy efficient. The system of FIG. 6B1 will not have to reverse cycle if the liquid desiccant concentration is kept at concentrations of approximately 20-30%. This is possible in general as long as there is enough moisture in the outside air. At very low humidity levels (below 20% relative humidity or under 2 g/kg of moisture) there may be a need to continue to add water to the desiccant so that indoor humidity can be maintained. It is also possible to add water to the liquid desiccant which is described, for example, in U.S. Patent Application No. 61/968,333, which is incorporated by reference herein.
FIG. 6C1 shows the same system of FIG. 6A1 and 6B1, with the difference that in this special operating mode the indoor conditioner unit is 603 is set up so that it provides heating and dehumidification of the air stream. This operating mode is particularly useful in seasons where the outside air is cold and the humidity is high such as the rainy season known in Asia as the plum-rain season. This mode is achieved by switching the valve 618 into the “A” position, and switching the 3-way refrigerant valves 621, 626 and 633 from the “A” to the “B” position. The hot refrigerant now takes a different path: after exiting valve 618-A, it is directed through line 619, and heat exchanger 620. However, because valve 621-B is in the “B” position, no hot refrigerant will flow through heat exchanger 622. Instead the refrigerant flows through valves 628-O and expansion valve 631-O where it is cooled. Valve 633-B is now in the “B” position and directs the cold refrigerant to line 637 where it reaches valve 626-B also now in the “B” position. The cold refrigerant thus enters the heat exchanger 622 where it is able to pick up heat from air 646b. Valve 621-B which is also in the “B” position, now directs the warmer refrigerant gas leaving the heat exchanger 622 to line 619 and 635 where it returns to the compressor 615. This configuration effectively pumps heat through the refrigerant system from heat exchanger 622 to heat exchanger 620, thereby producing hot heat transfer fluid through line 644 which thus allows the regenerator 648 to receive hot heat transfer fluid and produce more concentrated desiccant 646. Since the heat exchanger 614 is not receiving any refrigerant and is in effect inactive, pump 613 can be shut down and the conditioner module 603 no longer receives any heat transfer fluid. As a result the air stream 601 is now exposed to the concentrated desiccant 607 but because of the lack of heat transfer fluid flow through line 605, the air will dehumidify adiabatically and warm, dry air 606 will exit the conditioner. It should be clear that other circuiting options for the refrigerant can achieve the same effect or potentially provide hot refrigerant to heat exchanger 614 which will then provide additional heating capacity. The conditioner 603 thus heats and dehumidifies the air stream 601. The diluted desiccant is now regenerated by regenerator 648 which is still receiving heat from the compressor 615 which in effect pumps it from the outside air 624.
FIG. 6C2 shows the same system of FIGS. 6A2 and 6B2, with the difference that in this special operating mode the indoor conditioner unit is 603 is set up so that it provides heating and dehumidification of the air stream. This operating mode is particularly useful in seasons where the outside air is cold and the humidity is high such as the rainy season known in Asia as the plum-rain season. This mode is achieved by switching the valve 619 so that the hot refrigerant flows to heat exchanger 620 which will then provide additional heating capacity by splitting the refrigerant in valve 618 to expansion valve 624 to heat exchanger 622 and via receiver 618B to expansion valve 6380 to heat exchanger 614. The cold refrigerant thus enters the heat exchanger 622 where it is able to pick up heat from air stream 624 which can be either outside air, or airflow 646 coming from regenerator 648. The warmed refrigerant gas leaving the heat exchanger 622 and 614 to return to the compressor 615 via valve 617 and accumulator 515b. This configuration effectively pumps heat through the refrigerant system from heat exchanger 622 and 614 to heat exchanger 620, thereby producing hot heat transfer fluid through line 642 which thus allows the regenerator 648 to receive hot heat transfer fluid and produce more concentrated desiccant 652. To cool or warm the air stream 601 conditioner 603 dehumidifies the 601 and depending on the flow 605 through heat exchanger 614 cools it or heats it nearly adiabatically. This enables the system to process air with an SHR ranging between low positive to negative. The diluted desiccant is now regenerated by regenerator 648 which is receives heat from the compressor 615 which in effect pumps it from the air stream 646 which was just heated by the regenerator. This minimizes the lift seen by the compressor 615 and maximizes its dehumidification capacity and efficiency. A variant would be to flow the outside air first through 622, dehumidifying it through condensation and then supplying the dried air 625 as input air 646 to the regenerator. This reduces the temperature needed to keep the desiccant concentrated and is another way to reduce the lift seen by compressor 615 in providing the heat needed for concentrating the desiccant.
FIG. 6C3 illustrates a special mode that allows for the air to be warmed up sensibly as well as dehumidified. This would occur when outdoor conditions are cold and very humid, as is for example the case on rainy early spring days. In mainland China this is known as the plum rain season and conditions during that time of year result in very humid and cold indoor conditions, leading to mold problems and health issues. FIG. 6C3 shows the same system of FIG. 6A2 and 6B2, with the difference that in this special operating mode the indoor conditioner unit is 603 is set up so that it provides heating and dehumidification of the air stream. This operating mode is particularly useful in seasons where the outside air is cold and the humidity is high such as the rainy season known in Asia as the plum-rain season. This mode is achieved by switching the valve 619 so that the hot refrigerant flows to heat exchanger 620. The cooled down refrigerant is then directed to expansion valve 624. The cold refrigerant thus enters the heat exchanger 622 where it is able to pick up heat from air stream 624 which can be either outside air, or air 646 coming from regenerator 648. The warmed refrigerant gas leaving the heat exchanger 622 to return to the compressor 615. This configuration effectively pumps heat through the refrigerant system from heat exchanger 622 to heat exchanger 620, thereby producing hot heat transfer fluid through line 644 which thus allows the regenerator 648 to receive hot heat transfer fluid and produce more concentrated desiccant 646. Since the heat exchanger 614 is not receiving any refrigerant and is in effect inactive, pump 613 can be shut down and the conditioner module 603 no longer receives any heat transfer fluid. As a result the air stream 601 is now exposed to the concentrated desiccant 607 but because of the lack of heat transfer fluid flow through line 605, the air will dehumidify adiabatically and warm, dry air 606 will exit the conditioner. It should be clear that other circuiting options for the refrigerant can achieve the same effect
Many of the applications involve packaged units. However the architecture of VC-LDHX systems is very flexible.
Typically one or more of the heat exchangers 603 is placed in the conditioned space with the air from the space 601 being heated or cooled. In some configurations, outside air can be ducted in.
The 3 way heat exchanger 648 is placed outside together with the compressor 615 and the heat exchangers 614, 620 and 622. The desiccant tank as well as water access for water addition as well as various water and desiccant pumps and heat transfer fluid expansion can either be placed close to a source of water addition, or at a point in the building that optimizes ease of distribution of the desiccant and transfer fluid to the conditioner. This is particularly important in the case of smaller split systems where the compressor is usually kept outside because of noise, safety etc. Water supply might not be available near the location of the outside refrigeration system. Instead the liquid desiccant system can now be placed separately, close to a source of water. And preferable a location where water damage can always be limited.
This can be a technical space with an available water supply and space for water and desiccant tanks. In large complex buildings multiple mid units are used to manage desiccant and heat transfer fluid flows and pressures to and from heat exchanger 602. This flexibility is particularly important in multistory buildings where pressure management in the heat transfer fluid and desiccant circuits is critical. Positioning of the tank is an alternative to complex flow and pressure management devices. Where exhaust air is available for heat exchanger 648, the regenerator can be put in the location where the exhaust air is available, e.g., bath rooms or kitchens with connections for water and liquid desiccant to the outside and mid units, which don't need to be collocated which is particularly important in large complex buildings like hospitals, hotels and other facilities for which energy recovery and fresh air supply are critical. This may involve some fresh air being ducted in to conditioner 603 to be mixed with space air. Alternatively some of the 603 units can be dedicated outside air suppliers using 100% outside air in spaces with large exhaust requirements like kitchens or operating rooms. The detailed configuration management of these units do not impact the basic principles disclosed here.
Refrigerant compressor 615 compresses a refrigerant gas to high pressure and the resulting hot refrigerant 616 is directed to a 4-way valve assembly 617. The valve 618 is in the “A” position as before, and is labeled 617-A. In this position the hot refrigerant gas is directed through line 619 to a refrigerant-to-liquid heat exchanger 620. The refrigerant leaves the heat exchanger 620 and is directed through line 619 to a second 4-way valve assembly 722 with the valve 723-A in an “A” position, which directs the refrigerant through line 619 and subsequently to condenser coil 620. The cooler refrigerant leaves the coil 620 through line 721 and is directed to the open valve 720-O. Expansion valve 731-C is closed and inactive in this operating mode. The refrigerant moves back to 4-way valve 722 through line 732 and is directed through line 733 and line 736 to expansion valve 738-O which expands the refrigerant. Check valve 737-C is closed and inactive. The cold refrigerant enters the heat exchanger 614 through line 739 and removes heat from the heat transfer fluid on the opposite side of the heat exchanger 614. The warmer refrigerant is then moved through line 740 and 741 to 4-way valve 617 where it is directed through line 742 back to the compressor 615. Line 734 and valve 735-C are inactive or closed respectively.
The refrigerant to liquid heat exchanger 620, receives a heat transfer fluid (usually water or a water/glycol mixture but generally any heat transfer fluid will do) pumped by pump 743 through line 744. The heat from the compressed refrigerant in line 619 is transferred in the heat exchanger 620 to the heat transfer fluid and the hot heat transfer fluid is directed through line 745 to a set of regenerator plates 648 similarly constructed to those as described in
The system of
FIG. 8A1 illustrates a hybrid approach between the systems of FIG. 6A1 and that of
In essence the coil 622 (similar to coil 622 in FIG. 6A1 and 620 in
FIG. 8A1 show a simple refrigerant system which can be a simple compressor or a standard heat pump. The liquid desiccant heat exchanger and the aircooled coils are all connected to the system via the heat transfer fluid circuit, using a valve system. This gives great flexibility in the use of the system. We will also disclose how a single air cooled coil in combination with a damper can be used for to manage hot and dry as well as cool and humid conditions.
For the cool and humid conditions, FIG. 8A1 discloses the use of an air-cooled coil in series with the regenerator. In this mode the aircooled coil provides additional cooling capacity to allow the regenerator to regenerate liquid desiccant while the conditioner provides little or no load. In extreme cool and humid conditions like the Ashrae 920D condition, the conditioner should dry the air adiabatically and the aircooled coil is the only load of the compressor. Using the air-cooled coil rather than a separate heat source, uses the high heatpump COP to generate significant heat without a large usage of energy. Cooling cool and humid outside air with the coil would lead to significant condense. By cooling the exhaust air from the regenerator, condense is minimized and lift is significantly reduced—see also 15E.
Like in
Modelling shows that water addition can further improve the effectiveness of the LDAC system by 10-20% even under hot and humid conditions. In hot and dry conditions like phoenix it actually allows liquid desiccant systems to operate, where otherwise they would be at risk of b being damaged during extremely hot and dry conditions. The efficiency can approach that of a direct evaporator, but without the problems of over humidification during high wet bulb conditions or monsoon periods where humidity is increases significantly.
Units with water addition and the aircooled advanced dehumidification coil linked to the evaporator can operate under all possible conditions.
FIGS. 8A1-8D illustrate how a single configuration can be used under a very wide range of ambient conditions and supply requirements.
In the FIG. 8A1, an air stream 601 from the space is directed by fan 602 to a set of membrane conditioner plates 603 such as were earlier described in
Similar to what was described before in
As before, Pump 641 moves the heat transfer fluid through line 840 to heat exchanger 620 and line 841. Picking up heat from the refrigerant in heat exchanger 620, the hot fluid is directed to regenerator 648, which receives an air stream 841 through fan 844 resulting in a hot exhaust air stream 646. Optionally it is directed through line 837 and valve 832-A in the “A” position so the heat transfer fluid is cooled by air stream 835 and fan 634 in coil 622 resulting in a hot exhaust air stream 625 Valve 838A is also in the “A” position and simply directs the cooled heat transfer fluid back into the fluid line 840. The air 835 can be outside air or can be the exhaust air 646 from heat exchanger 648. The regenerator 648 receives a diluted, or weak desiccant through line 844 which is re-concentrated by means of the heat transfer fluid coming in through line 831. Re-concentration is reduced by opening 832A wider, increasing airflow 835, adding outside air through a damper to the exhaust air from unit 843 and by reducing airflow 841. Less concentrated desiccant reduces dehumidification and increases sensible cooling in conditioner 603 which is critical if outside air 841 is hot and dry, or 601 is dry or both. Valve 832A and fans 834 and 842 can be used to manage the sensible heat ratio and thus the rate of dehumidification independent from sensible cooling requirements. This can be done with or without water addition through 851. The re-concentrated desiccant is directed through line 846 into optional desiccant tank 847. Pump 845 removes some diluted desiccant and moves it to the regenerator 843 through line 844. Lines 817 and 850 are not used in this mode.
FIG. 8A2 illustrates how the system of 8A1 can be used in hot and humid conditions. In the figure, an air stream 801 from the space is directed by fan 602 to a set of membrane conditioner plates 603. The conditioner 603 provides an air treatment function and delivers a supply air stream 606 to the space. The conditioner 603 receives a heat transfer fluid (cold in FIG. 8A1) through line 604, which allows conditioner 603 to cool and dehumidify the air stream 601. The warmer heat transfer fluid is directed through line 605, valve 814A (in the “A”) position and through pump 613 to heat exchanger 614 where it is cooled by a cold refrigerant. The colder heat transfer fluid is then directed through valve 815-A in the “A” position back to conditioner 603. At the same time, conditioner 603 also receives a concentrated liquid desiccant through line 607 which allows the conditioner to absorb moisture from air stream 601 as described elsewhere. The diluted desiccant is directed through line 608 to an optional collection tank 610. Concentrated desiccant is pumped from tank 610 by pump 609 back to the conditioner module 603. Weak, or diluted desiccant is directed through line 611 to optional tank 847 and concentrated desiccant is removed from tank 847 by pump 848 and delivered through line 812 back to tank 610. It is also possible to thermally connect desiccant lines 811 and 812 and form a heat exchanger between the two lines so that heat from the regenerator 843 is not conducted directly to the conditioner 603, which will reduce the energy load on the conditioner. Furthermore, it is possible to add a separate liquid desiccant to liquid desiccant heat exchanger 850 instead of thermally connecting lines 811 and 812. An optional water injection system 851 (which is further described in U.S. patent application Ser. No. 14/664,219 incorporated by reference herein) reduces the concentration of the desiccant, preventing overconcentration in certain conditions by adding water 852 to the desiccant, which also can have the effect of making the system more energy efficient. Similar to
Similar to what was described before in
As before Pump 839 moves the heat transfer fluid through line 840 to heat exchanger 824 and line 841picking up heat from the refrigerant in heat exchanger 824. The hot fluid is directed to regenerator 843 which receives an air stream 841 through fan 844 resulting in a hot exhaust air stream 849. Valve 832-A is in the “B” position so that coil 833 is not heated. Valve 838A is also in the “B” position. The regenerator 843 receives a diluted, or weak desiccant through line 844 which is re-concentrated by means of the heat transfer fluid coming in through line 831. The re-concentrated desiccant is directed through line 846 into optional desiccant tank 847. Pump 845 removes some diluted desiccant and moves it to the regenerator 843 through line 844. Lines 817850 and 837 are not used in this mode.
FIG. 8B1 shows the system in FIG. 8A1 in a frost free winter heating mode. In essence only the refrigerant valve 821-B has changed from its “A” position to its “B” position. The heat transfer fluid loops are unchanged in this operating mode. The hot refrigerant flows from the compressor 818 through line 819 to valve housing 820 into heat exchanger 816. The resulting hot heat transfer fluid in line 804 drives the conditioner to heat and humidify the air 801 in the space. The condensed refrigerant now enters check valve 828-A, flows to expansion valve 827-O which expands and cools the refrigerant. The cold refrigerant then is directed to heat exchanger 824 where it picks up heat from the heat transfer fluid flowing on the opposite side in lines 840 to 831. As a result, heat and humidity are transferred ultimately from the outside air streams 841 and 835, through open valve 832A and 838A, to airflows 834 to 836, and to the indoor space air stream 806. By using dehumidified air stream 849 as input air stream 835 to coil 833, any frost forming on coil 833 is avoided. This effect can be further strengthened and captured sensible heat can be further increased by adding a valve 832b to stop heat transfer fluid flow through liquid desiccant heat exchanger 843. As a result airflow 841 will be dehumidified adiabatically, increasing its temperature while dehumidifying airflow 841. With all the heat transfer fluid now going through coil 833 its ability to sensibly cool the warmed up dry air 849 is further increased. This increases overall efficiency by reducing the temperature difference between refrigerant 823 and 830, which drives the lift of compressor 818 Adjusting valve 832A and 832B enables adjusting the ratio of sensible and latent heating at coil 802 in order to match the sensible and latent heat load of the conditioned space. The desiccant in line 844 also picks up moisture from air stream 841 resulting in a weaker desiccant that subsequently makes its way to the conditioner where it helps humidify the air stream 806. As in FIG. 8A1, the lines 817 and 840 are not active.
FIG. 8B2 shows the system in FIG. 8A2 in a winter heating and humidification mode. Again only the refrigerant valve 821-B has changed from its “A” position to its “B” position. The heat transfer fluid loops are unchanged. The hot refrigerant flows from the compressor 818 through line 819 to valve housing 820 into heat exchanger 816. The resulting hot heat transfer fluid in line 804 drives the conditioner to heat and humidify the air 801 in the space. The condensed refrigerant now enters check valve 828-A, flows to expansion valve 827-O which expands and cools the refrigerant. The cold refrigerant then is directed to heat exchanger 824 where it picks up heat from the heat transfer fluid flowing on the opposite side in lines 840 to 831. As a result, heat and humidity are transferred ultimately from the outside air streams 841 to the indoor space air stream 806. Valve 832 and 838 are closed Optional valve 8232A has to be open. The desiccant in line 844 again picks up moisture from air stream 841 resulting in a weaker desiccant that subsequently makes its way to the conditioner where it helps humidify the air stream 806. As in FIG. 8A1, the lines 817 and 840 are not active
FIG. 8C1 illustrates an alternate operating mode wherein refrigerant valve 821 is in the “A” position as in FIG. 8A1. Hot refrigerant is again directed to heat exchanger 824 and the heat transfer fluid on the opposite side in line 840 is again heated and directed to the regenerator 843. However valves 814, 815832 and 838 have all been switched into their “B” positions. This allows the hot heat transfer fluid to be directed from the regenerator solely back to the refrigerant to liquid heat exchanger 824, but not to coil 833. Instead coil 833 receives cold heat transfer fluid created in heat exchanger 816, which is directed by pump 813 through lines 817 and 850 to the coil 833. As a result the system is effectively pumping heat between heat exchanger 816 which is coupled by the cold heat transfer fluid to coil 833 and heat exchanger 824 which is coupled by the hot heat transfer fluid to the regenerator. As before this results in the indoor air 801 being dehumidified by the concentrated desiccant supplied through line 807, and since no heat transfer fluid is flowing through line 804, this dehumidification will in effect be almost adiabatic resulting in a warm, dry air stream 806. The diluted desiccant can be transported to the regenerator 843 as described before, where the heat of the hot heat transfer fluid causes the desiccant to re-concentrate. It should be clear to those experienced in the art that other water and desiccant circuits can easily be derived that accomplish the same or similar functions. For example, by making valves 815 and or 814 adjustable the heat transfer fluid can be shared between heat exchanger 803 and coil 833. As a result the air 801 will be cooled or slightly warmed as well as deeply dehumidified as the heat captured is used by heat exchanger 843 to reconcentrate the desiccant. In this way lift can be minimized and the ratio of latent to sensible cooling can be made to match the cooling load of the space. Adjustment in the airflows either through permanent coupling of air 849 from heat exchanger 843 and 835 going into air cooled coil 833 results in lower lift and higher efficiency and capacity for compressor 818 as described above. Reversing the airflow where 841 air 836 from air coil 833 provide the supply air to heat exchanger 843 allows the system to operate at cooler temperatures and lower humidities with comparable results. The water addition options are not relevant for this mode.
FIG. 8C2 is identical to 8C1, but with coil 803 and 833 in series rather than in parallel on the heat transfer circuit. For those skilled in the art a variety of similar variations can be considered. While 8C1 gives excellent results for the important 920 D standard results, 8C2 might be appropriate where design conditions are mostly focused on warmer and humid conditions like 920 A and B and where coil 833 is only used to manage the sensible heat ratio to match the latent and sensible loads of the space by adjusting airflow 835 with fan 833. These variations are clear to those skilled in the art and important for meeting specific design conditions and supply targets for a conditioned space.
FIG. 8C2 is mostly identical to FIG. 8C1 only valves 814 and 815 are now positioned so that coils 803 and 833 are in series rather than in parallel as in FIG. 8C1. For those skilled in the art a variety of similar variations can be considered. While 8C1 gives excellent results for the important 920 D standard results, 8C2 might be appropriate where design conditions are mostly focused on warmer and humid conditions like 920 A and B and where coil 833 is only used to manage the sensible heat ratio to match the latent and sensible loads of the space by adjusting airflow 835 with fan 833. These variations are clear to those skilled in the art and important for meeting specific design conditions and supply targets for a conditioned space.
FIG. 8C3 is identical to 8C1 on the heat fluid circuit but uses the refrigerant circuit of FIG. 6A3 and FIG. 6C3 with one four way valve no three way valve. This simplified circuit provides less challenges in maintaining refrigerant quality than either circuit 8C1 or the similar circuit 6A3 and 6C3. To those skilled in the art additional variants in both the refrigerant and the water circuit can be considered. 8C2 is an example of a variant on the heat fluid circuit. Those skilled in the art understand that compressor manufacturers provide variants of reversible heat pumps on the refrigerant circuit e.g. using multiple compressors that can provide the hot and cold refrigerant to heat exchanger 816 and 824.
The cooling tower contains a wetting media 917 and also contains a basin 921 which provides cold water as well as an air intake 916 and fan 918 and an exhaust air stream 920. Make-up water is provided through line 919 and an optional valve 941-A which in the “A” position directs the make-up water to the cooling tower wetting media 917. Valve 941-A can also be switched to deliver water to a water injection unit 942, which can be used to add water to the liquid desiccant flowing in line 912. Such a water injection system is further described in U.S. patent application Ser. No. 14/664,219 incorporated by reference herein and is used to control the desiccant concentration particularly in dry conditions. Valve 941-A could also be replaced with two individual valves if water needs to be delivered to the cooling tower or injection unit at the same time which can be used in hot, dry conditions. In other embodiments, the cooling tower could be replaced with a geothermal loop, in which the heat transfer fluid of line 904 is simply pumped through a geothermal heat exchanger, which is commonly located in the ground or river or lake near the facility where the system is located.
The regenerator 926 receives a hot heat transfer fluid 925 from a heat source 924, which can be any convenient heat source such as a gas-fired water heater, solar hot water system or waste heat collection system. Valve 940-A in the “A” position directs the hot heat transfer fluid 925 to the regenerator 926. The cooler hot heat transfer fluid 936 that is leaving the regenerator is pumped by pump 937 the valve 938-A in the “A” position through line 939 back to the heat source 924. The regenerator 926 also receives a dilute (weak) desiccant through line 930 as well as an air stream 927 moved by fan or blower 928 resulting in a hot, humid exhaust air stream 929. The re-concentrated desiccant flows through line 932 back to tank 933from where it is send to the conditioner 903 where it is re-used.
It is possible to add a second stage cooling system 943 (labeled IEC Indirect Evaporative Cooler in the figure). The indirect evaporative cooling system 943 provides additional sensible cooling if desired and receives water 944 from the water supply line 919. The IEC may also be used in the various other embodiments, disclosed herein to provide additional sensible cooling to the supply air stream.
Concentrated desiccant in line 908 is now directed through optional tank 910 through line 911 to tank 933 where it is pumped by pump 931 to the regenerator. The regenerator will allow the desiccant to absorb moisture assuming that the air stream 927 has enough moisture in it and diluted desiccant will flow through line 932 and tank 933, pump 934 and water injection unit 942 to line 912 back to tank 910 where it can be directed to the conditioner 903 and continue to moisten the air stream 906. If not enough humidity is available in the air stream 927, the water injection module 942 can be used to add water to the desiccant and to eventually moisten the air stream 906 as described more fully in U.S. Patent Application No. 61/968,333.
The cooling tower wetting media assembly (917) can also be replaced with a set of membrane modules similar to the conditioner membrane modules as is shown in
FIG. 10A1 shows the liquid desiccant system of 6A2 in accordance with one or more embodiments, set up in a summer cooling and dehumidification mode. The primary difference between the two systems is that in the FIG. 10A1 system, evaporator pads are shown in air stream 1046 and 1001. Plus a damper 1065. Adding a direct evaporative cooler 1071 to 1046 humidifies and cools the air stream adiabatically. In dry hot conditions this ensures that liquid desiccant heat exchanger 1048 can reject significant heat in that air leading to air 1046 having a higher enthalpy level and higher humidity level then the incoming air 1046. Damper 1065 can be used to exhaust this air, provide outside air to sensible coil 1022 or allow the air 1046 to be used as supply air for coil for coil 1022. This enables the system to respond to the changing outside air conditions without risk of crystallization of the desiccant and with great flexibility in managing sensible and latent loads.
The desiccant 1052 coming from liquid desiccant heat exchanger 1048 is more concentrated and warmer than the air coming into the liquid desiccant heat exchanger 1048. If necessary further dilution is possible through water injection as described in 6A1 and B as well as 8A1 and B.
In a direct outside air or DOAS unit, airflow 1001 will be the same hot and dry air as 1046. A similar direct evaporator cooler 1070 can be used to humidify this air adiabatically, cooling and humidifying the air entering liquid desiccant conditioner 1003. The enthalpy of that air is identical. The conditioner needs to ensure that the supply air 1009 has a targeted dry bulb condition e.g. 55 F for DOAS air. This can significantly reduce the cooling load of conditioner 1003 which through the heat transfer fluid 1005 is linked to liquid to refrigerant heat exchanger 1014. As a result the load seen by 1015 is reduced by the enthalpy difference between air 1009 at target DB and DP and air at target DB and the DP of the outside air. For air with a WB temperature of 15C and below this can even be 100% of the load, leading to zero load for the compressor and no dilution of the desiccant. At those conditions the system of 10A functions as an evaporator. As wet bulb conditions increase above the DP target the cooling load increases until the DP of 1001 is equal or greater than the target dew point for 1006. At that point the full cooling load is carried by compressor 1015 via heat transfer fluid 1005, heat exchanger 1015, refrigerant 1042 4 way valve 1017 in position A. The rate of evaporation of coils 1070 and 1071 can be used to ensure that the ratio of sensible to latent cooling matches the load in the conditioned space.
Where 1001 is return air, there is no evaporative cooler 1070. In that case evaporative cooler 1071 adds water to the desiccant in a similar way through vapor transition similar to water injection module 1056. This turns the system into the equivalent of a water cooled chiller, significantly reducing the hot refrigerant temperature coming out of heat exchanger 1020.
In this configuration valve 1019 and coil 1072 are not required, since the evaporative coil is more efficient in reducing liquid desiccant temperatures coming into valve 1018 thereby reducing the desiccant concentration and limiting the ratio of latent to sensible cooling. This increases efficiency in very dry and hot conditions compared to a system with only coil 1071
It will be obvious to anybody trained in the art that the same evaporative cooling options can be used in any of the configuration shown in 6, 7, 8 and 9. They eliminate the need for air cooled coil 1071 for managing hot and dry conditions.
FIG. 10A2 shows how the system is adjusted to meet outside humid and cool air conditions. The water supply to 1071 is stopped. Damper 1065 directs all air to air cooled coil 1022. The system then functions identical to system 6C2. For many conditions in between the extremes of very hot and dry and very cool and humid, some evaporative cooling can improve control over the ratio of latent to sensible cooling allowing the designer familiar with the art to optimize efficiency and match building loads.
In heating mode 10B the water supply to 1071 will only be used at temperatures above zero and with air 1001 with very low dew points. Then evaporation can be used to ensure that the dew point of at least 6 C DP can be maintained in the space. Too dry air is known to cause respiratory problems and problems with wooden objects like instruments. In general however, this can be easier done with water addition through 1054. The main critical application of evaporative coolers 1071 and 1070 is for dessert like conditions that benefit from using a desiccant system in series with the evaporator to improve supply air quality, avoiding over humidification and providing optimal humidity control over a full range of sometimes rapidly changing conditions.
Dilution of the liquid desiccant significantly enhances the operational range and efficiency of liquid desiccant systems. Performance will be close to that of DEVAP systems (Desiccant Enabled evaporative cooling systems). But with a compressor system as source for cold and heat it significantly reduces size and complexity of these systems. And it provides a universal solution for all locations with electricity. Compared to evaporative systems, the water consumption can be significantly lower. The use of liquid desiccants as intermediary allows the use of membrane based modules for dilution that use the ionic differential between the highly concentrated liquid desiccant and the water feed to transfer vapor or water from the feed stream. This allows the feed stream to be salt—2% seawater versus 25% Liquid desiccant has a transfer rate very similar to water. And it demineralizes water without energy intensive reverse osmosis.
Given that the use of these membrane units is new and their cost still significant, using direct evaporators before the regenerator, the conditioner or both. The evaporators can be separate or integrated in the unit. The advantage of using evaporators is that the technology is mature, suppliers understand the water management issues involved, the transfer of the water vapor to the liquid desiccant is via the air, i.e. the risks of mineral or other pollutants to the liquid desiccant system is eliminated. In particular when combining existing condenser evaporator cooling systems with their own field support with LDAC systems, operational risks are minimized. This allows for early cost effective and low risk introduction of desiccant dilution while membrane modules are further tested and development.
The desiccant 1152 coming from liquid desiccant heat exchanger 1148 is more concentrated and warmer than the air coming into the liquid desiccant heat exchanger 1148. If necessary further dilution is possible through water injection as described in 6A1 and B as well as 8A1 and B.
In a direct outside air or DOAS unit, airflow 1101 will be the same hot and dry air as 1146. A direct evaporator cooler 1170 can be used to humidify this air adiabatically, cooling and humidifying the air entering liquid desiccant conditioner 1103. The enthalpy of that air is identical. The conditioner needs to ensure that the supply air 1109 has a targeted dry bulb condition e.g. 55F for DOAS air. This can significantly reduce the cooling load of conditioner 1103, which through the heat transfer fluid 1105 is linked to liquid to refrigerant heat exchanger 1114. As a result the load seen by 1115 is reduced by the enthalpy difference between air 1109 at target DB and DP and air at target DB and the DP of the outside air. For air with a WB temperature of 15C and below this can even be 100% of the load, leading to zero load for the compressor and no dilution of the desiccant. At those conditions the system of 10A functions as an evaporative cooler. The efficiency becomes comparable to an evaporative cooling system, but with lower water consumption, and greater flexibility in meeting target conditions even under extreme conditions. As wet bulb conditions increase above the DP target the cooling load increases until the DP of 1101 is equal or greater than the target dew point for 1106. At that point, the full cooling load is carried by compressor 1115 via heat transfer fluid 1105, heat exchanger 1115, refrigerant 1142, four way valve 1117 in position A. The rate of evaporation of coils 1170 and 1171 can be used to ensure that the ratio of sensible to latent cooling matches the load in the conditioned space.
Where 1101 is return air, there is no need for an evaporative cooler 1170.
Direct evaporator coil or pad 1171 can add humidity to the air stream going into the regenerator. This is an effective alternative for water addition especially in locations where hot and very dry conditions are frequent. The water management requirements of direct evaporators is well understood by installers and contractors. Moreover direct evaporators further reduce lift compared to water addition, by reducing the sensible temperature of the regenerator. Adding water to the air stream also eliminates any risk of damage to the conditioner and regenerators due to water addition. It's a quick fix where direct evaporators are available and can be removed when conditions allow.
In dry and hot conditions direct evaporation also ensures that liquid desiccant heat exchanger 1148 can reject significant heat in that air leading to air 1146 having a higher enthalpy level and higher humidity level then the incoming air 1146. Damper 1165 can be used to exhaust this air, while providing outside air to sensible coil 1122 or allow the air 1146 to be used as supply air for coil for coil 1122. This enables the system to respond to the changing outside air conditions without risk of crystallization of the desiccant and with great flexibility in managing sensible and latent loads. During hot and dry conditions water addition allows the system to do more sensible and less latent cooling. It can humidify air not only at the regenerator 1148 but also at the conditioner 1103 when conditions are below 40% RH or a 6-10 C dew point. During very hot and dry conditions part of the sensible load is to be matched by increased evaporation by coil 1103. Water injection also makes the system more energy efficient by significantly reducing condenser temperature as the regenerator is able to reject more heat through evaporation. This allows a liquid desiccant with water addition to match the efficiency of water cooled chillers. It also prevents over concentration of the desiccant and avoids the need for a crystallization protection control sequence. Water addition also creates flexibility in managing latent and sensible loads independently. And allows for humidification during hot and dry or cold and very dry conditions. Increasing dew point while cooling significantly reduces load and effective system level efficiency for achieving DB targets. High evaporation at the condenser significantly reduces compressor lift, improving the Carnot efficiency of the compressor.
Direct evaporation with separate direct evaporative units 1170 and 1171 is an effective alternative for water addition in locations where dry and humid conditions alternate, like phoenix or the Arabian Gulf where conditions often change within hours. The hot and humid air is cooled and humidified up to the wet bulb condition. If the wet bulb condition is higher than the targeted dew point, the three way liquid desiccant conditioner 1103 dehumidifies and cools or warms the air stream coming out of the evaporator.
Adding pads increases efficiency especially in hot and dry conditions where it can become comparable to an evaporative cooling system, but with lower water consumption, and greater flexibility in meeting target conditions even under extreme conditions. Similarly, optional direct evaporator coil or pad 1071 can add humidity to the air stream going into the regenerator. This is an effective alternative for water addition especially in locations where hot and very dry conditions are frequent. It does somewhat increase pressure drop. However it is a well understood technology and water management of direct evaporators is well understood by many contractors. Direct evaporator 1171 reduce lift by reducing the sensible temperature of the regenerator 1148. The efficiency of the Carnot cycle is directly proportional to delta T between regenerator and conditioner. The temperature of desert air entering the regenerator can be reduced to close to its wet bulb condition. The concentration of the desiccant is driven by the RH of the air coming out of the evaporator. This allows the system to maintain an RH between 40 and 60% or a dew point between 45 and 55 F which is optimal for human activities. It also ensures that the air flowing through the regenerator is never hot and dry enough to be able to crystalize liquid desiccant. For LiCl that requires air of for instance 40 C and 10% RH, i.e. hot and dry desert air.
Combining both ensures a highly efficient system for monsoon and dessert type conditions e.g. in the Western USA. Adding water to the air stream also eliminates any risk of damage to the liquid desiccant heat exchangers from scaling due to residues of mineral ions entering the desiccant stream during water injection. It's a quick fix where direct evaporators are available and can be removed when conditions allow. The cost effectiveness of these system additions are highly application and location dependent.
It will be obvious to anybody trained in the art that the same evaporative cooling options can be used in any of the configuration shown in 6, 7, 8 and 10. They eliminate the need for an air cooled coil like 1071 for managing hot and dry conditions.
Direct injection of water into the liquid desiccant is an alternative for adding direct evaporative to the incoming air streams of the conditioner 1103 and the regen 1148. A range of options for injecting water 1158 into the liquid desiccant is shown. A membrane based vapor transfer or forward osmosis unit 1158 uses water 1157 to dilute the desiccant stream. An efficient version of system 1157 is described in U.S. patent application Ser. No. 14/664,219 and is incorporated by reference herein. By using the vapor pressure caused by a differential ion content of the desiccant and the water feed flow through the micro porous membrane, this unit allows standard tap water, salt or brackish water to be used as a feed flow, which is critical especially in water restricted area. This prevents also any risk of precipitation which can occur of unprocessed water used. Water addition with other membrane systems, including forward osmosis or existing vapor transfer unit can also be used to add water to the desiccant. Direct addition of water to tank 1110 or heat exchanger 1156 is also possible depending on water quality.
The optimal position of module 1157 depends on the application and the main drivers to be considered for optimization. Maximum transfer efficiency in cooling mode is achieved in stream 1152. Direct water addition to tank 1110 or integration of the water addition unit in heat exchanger 1156, can facilitate easy connection to water sources and reductions in maintenance cost, e.g. when these units are places inside the building. Water injection in stream 1106 or 1107 is also possible for special applications to minimize risk of crystallization in the conditioner. The availability of deionized water from reverse osmosis could support direct injection in tank 1112 or 1154 through a simplified floater control system that can maintain a single concentration level. The options for water injection are shown in grey in
During very hot and dry conditions, an optional membrane enabled water injection system 1157 reduces the concentration of the desiccant in certain conditions by adding water 1158 to the desiccant. Vapor transition, forward osmosis membrane units use the difference between the high ion concentration in the desiccant and the much lower ion concentration in potable, brackish, sea and waste water to transfer pure water into the desiccant thus diluting it. This prevents any scaling of the membrane, even at high rates of water addition.
The ability of using waste or brackish water is critical for water restricted areas. Also typically LDAC units will use 40-60% less water than water cooled chillers with efficiencies that are comparable or better. Water addition module 1151 can be located in the return flow from the regenerator to maximize the efficiency of vapor or Forward osmosis transfer unit, in the supply flow to the regenerator to maximize evaporation when direct addition is used and reduce condenser temperature, in the supply to the conditioner when humidification during heating is critical. Or in the return from the conditioner, to maximize transfer effectiveness in heating mode. In this way units can be optimized for application and climate conditions.
During hot and dry conditions it allows the system to do more sensible and less latent cooling. It can humidify air not only at the regenerator 1148 but also at the conditioner 1103 when conditions are below 40% RH or a 6-10 C dew point. During very hot and dry conditions part of the sensible load to be matched by increased evaporation by coil 1103. Water injection also makes the system more energy efficient by significantly reducing condenser temperature as the regenerator is able to reject more heat through evaporation. This allows a liquid desiccant with water addition to match the efficiency of water cooled chillers.
Water injection or desiccant dilution also prevents over concentration of the desiccant and avoids the need for a crystallization protection control sequence. Water addition also creates flexibility in managing latent and sensible loads independently. And allows for humidification during hot and dry or cold and very dry conditions. Increasing dew point while cooling significantly reduces load and effective system level efficiency for achieving DB targets. High evaporation at the condenser significantly reduces compressor lift, improving the Carnot efficiency of the compressor.
During very hot and dry conditions, an optional water injection system 1157 reduces the concentration of the desiccant by adding water 1158 to the desiccant. Liquid desiccant is circulated through lines 1111 and 1112 from the three way liquid desiccant heat exchanger 1103 to the liquid desiccant heat exchanger 1148. It is stored in the main tank 1110 and pumped to 1103 with pump 1109 and to 1148 with pump 1153. The extra tank 1154 and pump 1155 are optional. Heat exchanger 1156 minimizes the energy losses from the hot desiccant being transferred to the cold side and vice versa. An optional water injection 1157 (which is further described in U.S. patent application Ser. No. 14/664,219 incorporated by reference herein) reduces the concentration of the desiccant, preventing overconcentration in certain conditions by adding water 852 to the desiccant, which also can have the effect of making the system more energy efficient. Similar to
Whether a system uses membrane water injection system 1157 or evaporative pads 1170 and 1171 depends on the cost of the systems, the quality of available water
An efficient version of system 1157 is described in U.S. patent application Ser. No. 14/664,219 and is incorporated by reference herein. By using the vapor pressure caused by a differential ion content of the desiccant and the water feed flow through the micro porous membrane, this unit allows standard tap water, salt or brackish water to be used as a feed flow, which is critical especially in water restricted area. This prevents also any risk of precipitation which can occur of unprocessed water used. Water addition with forward osmosis or traditional vapor transfer unit can also be used to add water to the desiccant. Direct addition of water to tank 1110 or heat exchanger 1156 is also possible depending on water quality.
The optimal position of module 1157 depends on the application and the main drivers to be considered for optimization. Maximum transfer efficiency in cooling mode is achieved in stream 1152. Direct water addition to tank 1110 or integration of the water addition unit in heat exchanger 1056, can facilitate easy connection to water sources and reductions in maintenance cost, e.g. when these units are places inside the building. Direct addition to stream 1107 or 1145 is also possible for special applications to minimize risk of crystallization in the conditioner.
Direct evaporator coil or pad 1170 can cool and humidify a hot and dry air stream going into the conditioner. This is an effective alternative for water addition in locations where dry and humid conditions alternate, like phoenix or the Arabian Gulf where conditions often change within hours. The hot and humid air is cooled and humidified up to the wet bulb condition. If the wet bulb condition is higher than the targeted dew point, the conditioner 1003 then dehumidifies and cools or warms the air stream as described above. The efficiency becomes comparable to an evaporative cooling system, but with lower water consumption, and greater flexibility in meeting target conditions even under extreme conditions. Similarly, optional direct evaporator coil or pad 1171 can add humidity to the air stream going into the regenerator. This is an effective alternative for water addition especially in locations where hot and very dry conditions are frequent. It does somewhat increase pressure drop. However it is a well understood technology and water management of direct evaporators is well understood by many contractors. Moreover direct evaporators further reduce lift compared to water addition, by reducing the sensible temperature of the regenerator. Combining both ensures a highly efficient system for monsoon and dessert type conditions e.g. in the Western USA. Adding water to the air stream also eliminates any risk of damage to the conditioner and regenerators due to water addition. It's a quick fix where direct evaporators are available and can be removed when conditions allow. Like the damper these system additions are application and location dependent.
Where exhaust air is available, airflow 1146 can be a mix of outside air and exhaust air. This increases efficiency by up to 30% to an ISMRE for the 920 conditions of 12+. When airflow 1101 is outside air, exhaust air can also be used for energy recovery by preconditioning 1101 using the two stage liquid desiccant system disclosed in application 61834081. Alternatively, sensible or full energy plate heat exchanger, heat pipe or an enthalpy wheel can be used. These further improve system performance by reducing the cooling or heating load between (outside) air 1101b after energy recovery going into the conditioner 1103 and supply air 1106. After preconditioning the outside air, exhaust air can be further used as input for 1148 assuming its total enthalpy is still below that of outside air. Combining full ERV improves ISMRE for direct outside air units to 30% above conventional state of the art solid desiccant systems with energy recovery.
It also shows how energy recovery can be used to reduce conditioner load and optimize refrigerant load. The enthalpy or heat exchange between the exhaust air and the incoming air can be done with plate heat exchangers, energy wheels as well as the dual liquid desiccant blocks disclosed in U.S. Pat. No. 9,470,426.
A system of LD HX with one or more sensible coils can be optimized for cost, performance and flexibility in different zones 1-8 by locating the cooling fluid coils in the incoming or outgoing regen air, in the outgoing conditioner air with the cooling fluid being either refrigerant or water/glycol or similar heat transfer fluid.
The main difference is that refrigerant coils require balancing of the circuit and managing high pressures, requiring metal HX, while the cooling fluid coils can be built with metals as well as plastics depending on the corrosiveness of the environment in which we operate.
Examples of corrosive environments could include swimming pools, salt spray locations, chemical plants and laboratories. Using all plastic low pressure heat transfer coils then has an advantage. Alternatively metal refrigerant HX can be used if covered in a protective plastic sheet.
The non-reversible compressor system will always cool heat transfer fluid 1220 and provide extra heat to heat transfer fluid 1250. But by directing these fluids to the conditioner and regenerator a reversible heat pump system results.
In the cooling mode of
The concentrated liquid desiccant 1230 is diluted by 1223. The diluted desiccant 1231 flows back to a liquid desiccant tank. The diluted desiccant is reconcentrated by drawing it 1234 with pump 1235 to liquid desiccant heat exchanger 1253. Liquid desiccant heat exchanger 1253 draws hot heat transfer fluid 1250 from liquid to liquid heat exchanger 1203. The fluid passes through valve 1251 and valve 1252 in the A position. It then heats up the liquid desiccant increasing the vapor pressure of the water in the desiccant which evaporates out humidifying airflow 1270 that is send through the heat exchanger by fan 1271. The fan can be positioned before or after the heat exchanger. The air 1270 can be outside air or exhaust air from the space or a combination. Dryer exhaust air increases evaporation and thus concentrates the desiccant at a lower temperature. Strong evaporation of the desiccant also reduces the heat fluid temperature and thus the compressor heat which makes the compressor more efficient.
The desiccant 1238 coming out of the heat exchanger 1253 returns to tank 1232. A heat exchanger can be used to reduce the heat leak from the conditioner to the compressor. Alternatively the heat exchanger can be located behind pump 1233 between desiccant lines 1230 and 1231. Instead of using a heat exchanger the two lines can also be kept side by side in a single unit to equalize the temperatures of incoming and outgoing liquid desiccant. This reduces a heat loss from the conditioner 1223 to the regenerator 1253 which increases compressor load, reducing efficiency and capacity of the system.
When cooling dry air valve 1252 can be set in B position so that hot heat transfer fluid reaches air cooled coil 1280. This coil heat transfer fluid using the air coming out of the liquid desiccant heat exchanger. The heat transfer fluid 1267 is then returned to heat exchanger 1253 where it is further cooled as the diluted liquid desiccant 1237 is reconcentrated and the evaporation energy is withdrawn from the heat transfer fluid, which is then returned to pump 1256 through valve 2155 which is in the A position. In this way the air cooled coil 1280 and the liquid desiccant heat exchanger 1253 are in series. For very dry outside conditions with a space that has a significant latent load they can be set in parallel so that the cooling of the heat transfer fluid is done in Air cooled coil 1280, while 1253 re-concentrates the desiccant and humidifies and cools the hot outside air adiabatically.
This effect can be further strengthened by injecting water 1241 through module 1240 into the desiccant 1238, as described in
The warming and dehumidification mode of
In the warming and dehumidification mode of
The air 1224 is cooled adiabatically in heat exchanger 1223, diluting the concentrated desiccant 1230. The diluted desiccant 1231 is send to heat exchanger 1253 via a tank 1232, pump 1235 and a heat exchanger 1236. In 1253 the liquid desiccant is heated by the heat transfer fluid 1250 from liquid to liquid heat exchanger 2103 with valves 1251 and 1252 in the A position. The cooled down heat transfer fluid 1272 is returned via valve 1255 in the A position to pump 1256 where it is send to liquid to liquid heat exchanger 1203. This setting is optimal for conditions similar to 920D.
With an adjustable valve 1221 the heat transfer fluid can be divided between flow 12t0 and 1220b which flows through valve 1222 in the A position to heat exchanger 1223. In this arrangement the air is both cooled and dehumidified. Part of the load for the compressor comes from this so that deeper cooling becomes possible. This leads to a greater reduction in enthalpy of air 1226. This setting is optimal for conditions similar to the 920C standard.
The process air 1224 entering heat exchanger 1223 can be air from the conditioned space 1290 or outside air or outside air that has been preconditioned with exhaust air as described in
The concentrated liquid desiccant 1230 is diluted by 1223. The diluted desiccant 1231 flows back to a liquid desiccant tank, the diluted desiccant is re-concentrated by drawing it 1234 with pump 1235 to liquid desiccant heat exchanger 1253. Liquid desiccant heat exchanger 1253 draws hot heat transfer fluid 1250 from liquid to liquid heat exchanger 1203. The fluid passes through valve 1251 and valve 1252 in the A position. It then heats up the liquid desiccant increasing the vapor pressure of the water in the desiccant which evaporates out humidifying airflow 1270 that is send through the heat exchanger by fan 1271. The fan can be positioned before or after the heat exchanger.
The desiccant 1238 coming out of the heat exchanger 1253 returns to tank 1232. A liquid to liquid heat exchanger can be used to reduce the heat leak from the conditioner to the compressor. Alternatively the heat exchanger can be located behind pump 1233 between desiccant lines 1230 and 1231. Instead of using a heat exchanger the two lines can also be kept side by side in a single unit to equalize the temperatures of incoming and outgoing liquid desiccant. This reduces a heat loss from the conditioner 1223 to the regenerator 1253 which increases compressor load, reducing efficiency and capacity of the system.
Dehumidification of the cold outside air 1270 is particularly important under standard test conditions like 7C DB and 6C WB as well as 2C DB and 1C WB. In those cases traditional heat pumps coils freeze up as the moisture in the air condenses and freezes into ice. This requires a defrost cycle that makes traditional reversible heat pumps inefficient in particular in moderate and more humid winter climates as found in the northwest and south east. By dehumidifying the air, the liquid desiccant heat exchanger enables air cooled coil 1280 to deeply cool the air without condense or ice forming Dew points will be lower than the cold temperature of the heat transfer fluid coming out of heat exchanger 1206.
The hot refrigerant in heat exchanger 1203 heats up heat transfer fluid 1250. Via valve 1251 in B position the hot fluid is send via 1265 to enter three way liquid desiccant heat exchanger 1223. The process air 1224 entering heat exchanger 1223 can be air from the conditioned space 1290 or outside air or outside air that has been preconditioned with exhaust air as described in
The cooled down heat transfer fluid returns via valve 1229 in B position and line 1264 to pump 1265 and heat exchanger 1203
The diluted liquid desiccant 1230 is concentrated by 1223. The concentrated desiccant 1231 flows back to a liquid desiccant tank. The concentrated desiccant is then diluted by drawing it through 1234 with pump 1235 to liquid desiccant heat exchanger 1253. Liquid desiccant heat exchanger 1253 cools and concentrates the liquid desiccant by adiabatically cooling airflow 1270. Processed air 1272 is warmer and much dryer then the incoming air.
The desiccant 1238 coming out of the heat exchanger 1253 returns to tank 1232. A heat exchanger can be used to reduce the heat leak from the conditioner to the compressor. Alternatively the heat exchanger can be located behind pump 1233 between desiccant lines 1230 and 1231. Instead of using a heat exchanger the two lines can also be kept side by side in a single unit to equalize the temperatures of incoming and outgoing liquid desiccant. This reduces a heat loss from the conditioner 1223 to the regenerator 1253 which increases compressor load, reducing efficiency and capacity of the system.
With extremely dry and cold outside air, water injection module 1241 can be used to dilute the desiccant, allowing the air 1224 to be humidified. In heating mode, a relative humidity of at least 30% should be maintained for comfort and health reasons. Lower humidity can cause skin problems, respiratory problems and damage objects and buildings e.g. cracking wood surfaces.
With adjustable valve 1221 in a half open position, some of the heat transfer fluid 1220 can be send via valve 1223 and line 1262 to heat exchanger 1253. There it cools air 1270 allowing even deeper dehumidification further reducing frosting risks on 1280. The surfaces of the desiccant heat exchangers do not freeze up as absorption provides sufficient heat to ensure vapor transfer into the desiccant.
The heat transfer fluid 1237 returns to heat exchanger 1206 via valve 1254 and line 1263 to pump 1224.
An alternative is to close valve 1223 and instead use 1281 to send the warmed up heat transfer fluid coming out of 1280 to heat exchanger 1253. This has a similar impact as the mechanism described above and can reduce the total number of valves by eliminating the need for 1223
In winter the heat can be primarily pumped from the regenerator module 748. Since this module only has desiccant and heat transfer fluid, it will be able to operate at much lower temperatures than the condenser coil of a conventional heat pump system, which starts to have ice formation when the outside air temperatures reaches 32 F and the relative humidity is near 100%. Conventional heat pumps in that case will temporarily reverse cycle so that ice can be removed from the coil, meaning that they are cooling the space for a little while in reverse cycle mode. This obviously is not very energy efficient. The system of
The non-reversible compressor system will always cool heat transfer fluid 1220 and provide extra heat to heat transfer fluid 1250. But by directing these fluids to the conditioner and regenerator a reversible heat pump system results.
In the cooling and dehumidification mode of
The concentrated liquid desiccant 1230 is diluted by 1223. The diluted desiccant 1231 flows back to a liquid desiccant tank. The diluted desiccant is reconcentrated by drawing it 1234 with pump 1235 to liquid desiccant heat exchanger 1253. Liquid desiccant heat exchanger 1253 draws hot heat transfer fluid 1250 from liquid to liquid heat exchanger 1203. The fluid passes through valve 1251 and valve 1252 in the A position. It then heats up the liquid desiccant increasing the vapor pressure of the water in the desiccant which evaporates out humidifying airflow 1270 that is send through the heat exchanger by fan 1271. The fan can be positioned before or after the heat exchanger. The air 1270 can be outside air or exhaust air from the space or a combination. Dryer exhaust air increases evaporation and thus concentrates the desiccant at a lower temperature. Strong evaporation of the desiccant also reduces the heat fluid temperature and thus the compressor heat which makes the compressor more efficient.
The desiccant 1238 coming out of the heat exchanger 1253 returns to tank 1232. A heat exchanger can be used to reduce the heat leak from the conditioner to the compressor. Alternatively the heat exchanger can be located behind pump 1233 between desiccant lines 1230 and 1231. Instead of using a heat exchanger the two lines can also be kept side by side in a single unit to equalize the temperatures of incoming and outgoing liquid desiccant. This reduces a heat loss from the conditioner 1223 to the regenerator 1253 which increases compressor load, reducing efficiency and capacity of the system.
When dehumidifying and warming air, refrigerant valve 1206 can be set in B position so that refrigerant reaches air cooled coil 1280 via expansion valve 1207. This coil cools the air coming out of the regenerator or via a damper outside air or a mix of the two. The refrigerant is then to the compressor. The air cooled coil 1280 and the refrigerant to heat transfer fluid heat exchanger are in parallel. The load generated by coil 1280 provides the heat needed to concentrate the liquid desiccant which is then used in conditioner 1203 to dehumidify the moist air adiabatically.
Similarly in heating mode, coil 1280 provides the load needed to heat the air in conditioner 1223, while regenerator 1252 dehumidifies cold and humid air adiabatically.
With the refrigerant to heat transfer fluid HX 1203 and coil 1280 in parallel in heating mode dry air can be dehumidified deeply allowing the liquid desiccant heat exchanger 1223 to humidify dry air 1225
The principal here is that adding heat to the evaporator side of the compressor can be used during heating mode to improve dehumidification and humidification performance.
Instead of using air cooled coil 1280, other forms of heat can also be used to provide an extra cooling load to the system. A heater is an option when the conditioned mentioned are rare and when frost free heating is not a requirement. Cooling exhaust air from the regenerator is a highly efficient solution, when this isn't possible the coil can also cool outside air.
During heating mode damper 1299 will be closed and outside air 1282 will not be added, unless temperatures when outside air temperatures are below freezing.
A dual coil for heat transfer fluid and refrigerant is another option where the heat transfer fluid can be used to improve performance during hot and dry condition as described above. Optimization of system cost and design requirements will drive the choice of those trained in the art.
The range of solutions mentioned here is not limitative. For those trained in the art additional combinations are possible depending on the requirements. Combinations with the systems disclosed in U.S. Pat. Nos. 9,243,810, 9,308,490, U.S. Patent Application Publication No. 2014-0260399, U.S. Patent Application Publication No. 2015-0338140, and U.S. Patent Application Publication No. 2016-0187011, etc. are clear to those familiar with the art.
The alternative is shown in 12F. This configuration has multiple air cooled coils 671 as advanced dehumidification oil and 622 as a heat dump coil in combination with liquid cooled refrigerant coils 614 and 620 and a reversible heat pump with compressor 615 and 4 way switch 617. This is a very complex refrigerant circuit that will be difficult to control over a wide range of operating conditions because of problems with refrigerant quality at various points in the system, as well as how to properly charge such a system. The earlier examples provide a solution to this problems by keeping the refrigerant system simple and using a system of valves to redirect the heat transfer fluid. While that is not without its own challenges, the technology is well understood.
Three configurations are particularly important for efficient and accurate humidity management in Space 1301. It will be obvious for those trained in the art that these systems can be combined with energy recovery from exhaust air 1309 for load reduction through additional desiccant modules 1310 as disclosed earlier in (U.S. Pat. No. 9,470,426). Solid desiccant wheels and plate and membrane heat exchangers can be used to recover energy at 1310 from exhaust air 1309 from the space 1301 to outside air 1307 supplied to the building. Air 1311 is then processed by the conditioner 1302 and supplied to the space. The exhaust air 1309 can be ducted to the outside or used for further energy efficiency improvement as supply air to the regenerator 1303 via duct 1312. The extra complexity of this system is warranted where energy recovery from exhaust air is critical. It does give a further improvement over the earlier disclosed energy recovery from direct use of exhaust air 1313 in the regenerator 1303. Modelling results show an improvement in the ISMRE at the 920 standard for one particular configuration from 91 b/kW without energy recovery, to 12 with energy recovery 1313 through the regenerator only to greater then 151 b/kW with dual use of exhaust air in 1312. All this while maintaining supply conditions at 55 F DP and 70-80 F DB. EER shows a similar improvement.
Where deep dehumidification is required the regenerator 1303 becomes more effective in concentrating liquid desiccant if the exhaust air from the regenerator is used to pre heat air supplied to the regenerator in an air to air heat exchanger 1314. This can be critical in evaporative cooling solutions such as shown in
Air-to-air HX 1316 can be used to reheat supply air 1317 for buildings with very large latent and very low sensible loads, e.g. swimming pools.
Precooling and post heating coils 1318 are additional options to be used in combination with the conditioner to increase the sensible cooling capacity of the system.
1330 shows a variant where an air to air coil 1331 is used to precool air 1307 with the cold air from 1302 before supplying it at 1332 to space 1301
Liquid to air Coils 1305, 1306 and 1318 and air to air heat exchangers 1310, 1314 and 1316 can further improve the performance of the liquid desiccant heat exchangers disclosed in U.S. Pat. Nos. 9,243,810, 9,308,490, U.S. Patent Application Publication No. 2014-0260399, U.S. Patent Application Publication No. 2015-0338140, and U.S. Patent Application Publication No. 2016-0187011, etc. However they come at a significant cost. The viability of these combinations are driven by customer requirements for deep dehumidification, flexibility over changing conditions and precision of cooling.
The combination of liquid desiccant coils 1302, 1303 and air to liquid HX 1305 disclosed in
De-humidification and Humidification refer to adding or subtracting humidity to the air. However for a dehumidifier, just as important is whether the relative humidity of the air is increased or decreased.
The main application for liquid desiccants has been on dehumidification of warm air. A typical application is to optimize performance of an outside air unit for the 920 conditions. These require that a single target supply condition is achieved for all four outside air conditions shown as dots in
The air cooled coil can be linked directly to the refrigerant system (7) or via the refrigerant to water heat exchangers (8) in the case of cooling mode and 9 during heating mode. In the heating mode, HX 3 provides additional sensible cooling capacity to prevent over dilution of the desiccant in 648, which could over humidify the space. The table shows how the coils and desiccant dilution devices can be used in the 8 zones of
To fully appreciate the performance of the combined system requires an understanding of how liquid desiccant systems with chillers are balanced.
a. The humidity absorbed at the conditioner 1505a needs to be identical to the humidity evaporated at the regenerator 1505b.
b. The RH at the conditioner and the RH at the regenerator are both in balance with LiCL at a concentration that is nearly the same. Typically when liquid desiccant has a concentration of 25% going into the conditioner it will come out at a concentration between 15 and 24% and will return to 25% at the regenerator. As a result the conditioners RH is likely to be 2 to 4% higher than the RH at the regen for the vapor pressures in the air to be equal to the partial vapor pressure at the surface of the liquid desiccant. The RH of the system is 1-2× Concentration ensuring the RH of the conditioner and regenerator are closely correlated within 5%.
Such a system will always supply air at a concentration somewhat below that of the input condition, given that the energy available at the regenerator is always larger than the cooling power at the conditioner. Increasing the regenerator airflow will reduce the supply temperature at 1506b, which increases the RH of 1506B compared to 1504b. This will reduce the concentration of the liquid desiccant. Since the total cooling power remains the same, the WB condition will not change, but supply conditions will shift to a cooler, more humid condition 1506a.
Increasing compressor power without changing the airflows will lead to a supply condition at a lower WB condition, but also to a lower RH at the regenerator and thus to deeper dehumidification at 1507a.
Ongoing discussion about the standard recognizes that in buildings with low latent loads and high sensible loads for example from lights, supplying outside air at temperatures below comfort conditions could be justified. When selecting dehumidifiers for hot and humid climates the MRE may be more important than the ISMRE.
Still cooling outside air to 1559 and 1579 will lead to significant condensation on the coil while providing the additional load needed to reconcentrate desiccant for 920 D and C. 920B has been shown to balance to the 1510 supply condition without additional airflow over the sensible coil. 920A can match the 70/55 1510 condition by using the coil as a heat dump (1509) increasing the RH from 1510 in
The embodiments, described in
In particular combinations with the system structures described in earlier U.S. Pat. Nos. 9,243,810, 9,308,490, U.S. Patent Application Publication No. 2014-0260399, U.S. Patent Application Publication No. 2015-0338140, and U.S. Patent Application Publication No. 2016-0187011, etc. can benefit from adding water injection modules and evaporator linked air cooled coils for special dehumidification.
Also water injection modules in dry cooling are an alternative for an air-cooled heat dump coil on the condenser circuit as described in among others
The fundamental role of the air cooled coil on the evaporator circuit to cool outside air or air from the regenerator is to provide a load for the compressor so that sufficient heat is available for the regenerator to concentrate the liquid desiccant.
Alternatively a cooling load can be provided directly by heating the heat transfer fluid directly, e.g. with gas.
Where coils are on the refrigerant circuit managing refrigerant becomes paramount. In general that is easier in parallel with a lower pressure drop. However an air cooled coil in series with the heat transfer fluid to refrigerant heat exchanger has advantages for latent management if refrigerant can be managed
Similarly replacing a single fluid air cooled coil on the evaporator circuit (adv. Dehumidification coil) with a dual fluid (heat transfer fluid/refrigerant) allows intermediate solutions, e.g. using heat transfer fluid in heating and dehumidification mode and the refrigerant circuit in heating without frost mode. Cost of (adjustable) valves can be substantial and for those skilled in the art many variants are possible to optimize price performance of the system albeit often at some cost in efficiency.
The core valve system 1810 has connections to the pumps 1824 and 1819 and inputs from LCE 1815 and LCC 1820. That water to refrigerant package 1824 has a fixed connection to the conditioner(s) via 1830 and back via 1831 and to the regenerator(s) via 1832 and a return via 1833. Air cooled coil 1813 has a third set of connections 1834 from box 1824 and 1835 as return. As a result interconnecting box 1810 and subsystem 1824 is very much simplified, while providing full control for all operational modes including heating and cooling. Simplified valve boxes can be supplied where heating and cooling or advanced dehumidification are not required. Or the relevant valves can just be disabled to reduce cost through standardization of a “valve box”
In cooling mode valves heat transfer fluid (water/glycol) flow from LCE 1815 through valve 1816 and valve 1817 to the conditioner and from the conditioner via valve 1818 back through pump 1819 to the LCE 1815. The hot cooling fluid flow from LLCC 1820 via valve 1821 and 1822 to the regenerator 1812 and back the LCE via valve 1823 and pump 1824.
In heating mode the warm heat transfer fluid goes from LCC 1820 via valve 1821 to conditioner 1811 and from there through 1818 back to pump 1820 and the LCC. The cold heat transfer fluid goes from LCE 1815 via valve 1816 to air cooled coil 1813 and then via valve 1825 to regenerator 1812. With valve 1823 set to send the cold heat transfer fluid back to pump 1819 and the LCE.
In special dehumidification mode for zone 6, the cold heat transfer fluid goes from LCE 1815 through valve 1816 to air cooled coil 1813 and from there via valve 1825 to pump 1819 and the LCE.
In zone 5 valve 1816 divides the heat transfer fluid such that about 2/3 goes through 1816 and 1813 and i/3 via 1817, conditioner 1811 and 1818 back to LCE 1815. Regen and LCE are than connected again via 1821, 1822 and 1823 via pump 1824.
In dry cooling mode LCE 1815 is only connected to the conditioner via 1816, 1817 and 1818 to 1819, but the LCC is connected to the air cooled coil 1813 and the regen 1812 via valves 1821, 1822 to coil 1813 to 1825 and regenerator 1812 through 1823 back to pump 1824. In
It shall be clear to those experienced in the art that the above description of a valve box is not intended to be limitative. Modifications can be used to optimize operations in some climate conditions, e.g. by allowing 1813 and 1812 to operate in parallel during cooling with limited dehumidification. Or by not using either 1813 or 1827. Or by adding a separate heat dump for cooling with limited dehumidification. The main idea is to have a well-defined valve box with known connections that can easily be added to a unit to increase its flexibility in responding to a full range of conditions.
In all configurations above exhaust air from the building with an RH lower than outside air can be used to improve efficiency by using it to regenerate the desiccant in the regenerator at a lower temperature. This reduces the condenser temperature of the compressor, increasing the Carnot efficiency of the regenerator
In all systems described above efficiency can be further improved by using exhaust air from the building to cool and dehumidify supply air to the conditioner through a an additional set of liquid desiccant heat exchanger as described in U.S. Pat. No. 9,470,426 reducing the load for the conditioner and then supplied to the regenerator to improve its efficiency, providing a complex but efficient solution for liquid desiccant cooling and dehumidification. Instead of the liquid desiccant heat exchanger, plate heat exchangers, solid desiccant wheels or similar energy recovery systems can be used. This tend to reduce the load seen by the liquid desiccant heat exchangers by up to 30% for the 920A standard condition, improving also overall system efficiency.
Also air supplied from the conditioner can be heated in a separate heating unit before being supplied to the building. This increases the heat capacity in winter and can be used as an alternative to process very humid and cold air when this is a rare occurrence.
Having thus described several illustrative embodiments, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to form a part of this disclosure, and are intended to be within the spirit and scope of this disclosure. While some examples presented herein involve specific combinations of functions or structural elements, it should be understood that those functions and elements may be combined in other ways according to the present disclosure to accomplish the same or different objectives. In particular, acts, elements, and features discussed in connection with one embodiment are not intended to be excluded from similar or other roles in other embodiments. Additionally, elements and components described herein may be further divided into additional components or joined together to form fewer components for performing the same functions. Accordingly, the foregoing description and attached drawings are by way of example only, and are not intended to be limiting.
This application claims priority from U.S. Provisional Patent Application No. 62/580,270 filed on Nov. 1, 2017 entitled METHODS AND SYSTEMS FOR LIQUID DESICCANT AIR CONDITIONING, which is hereby incorporated by reference.
The United States Government has rights in this invention under Contract No. DE-AC36-08G028308 between the United States Department of Energy and the Alliance for Sustainable Energy, LLC, the Manager and Operator of the National Renewable Energy Laboratory.
| Number | Date | Country | |
|---|---|---|---|
| 62580270 | Nov 2017 | US |
