The present application relates to cooling and dehumidification systems using a rotary desiccant assembly.
The rising demand for cooling is putting an enormous strain on the environment, grid infrastructure, and the global climate. Meeting the world's demand for cooling while minimizing its negative impacts will be one of the defining challenges of our time. This challenge can be addressed by redesigning today's air conditioning systems to take advantage of new materials and chemical processes.
One aspect of the disclosure provides is a cooling and dehumidification system, comprising: a rotary desiccant assembly comprising a desiccant wheel that is at least partially coated with a desiccant material, the desiccant wheel configured to rotate, thereby providing for simultaneous loading and unloading of moisture on the desiccant material.
In one example, the desiccant material is configured to be unloaded with a low grade waste heat from an air conditioning system.
In one example, the desiccant material comprises at least one of a metal-organic framework (MOF) compound, a silica gel, zeolite, or temperature-responsive hygroscopic polymer.
In one example, the desiccant material is completely coated with desiccant material.
Another aspect provides a wheel structure using desiccant material that can be unloaded with low grade waste heat such that moisture is desorbed from the desiccant material, wherein the low grade waste heat is from an air conditioning system.
Another aspect of the disclosure is an interrupted desiccant drum configured to allow removal of moisture in an air conditioning system.
Another aspect of the disclosure is a cascade cycle adsorption cooling and dehumidification system, comprising of at least two closed loop adsorption loops arranged so that heat of adsorption from a first loop drives the second loop cycle. This system is followed by an open loop drying cycle to remove moisture from the room air.
Another aspect of the disclosure is an indoor cooling unit comprising a desiccant coated heat exchanger and a separate water condensing coil arranged to cycle between a mode of loading and cooling and a mode and unloading and water condensing.
Another aspect of the disclosure is a heat exchanger, partially coated with a desiccant material, such that heat and moisture exchange occur sequentially as air passes though the device. This allows the heat of adsorption and desorption to be transferred to and from a thermal fluid.
Another aspect of the disclosure is a cascade cycle adsorption cooling and dehumidification system, comprising: at least two closed loop adsorption loops arranged so that heat from a first closed loop drives a second closed loop.
Another aspect of the disclosure is a heat exchanger, at least partially coated with a desiccant material, such that heat and moisture exchange occur sequentially as air passes though the heat exchanger.
In one example, the heat of adsorption and desorption are transferred to and from a thermal fluid, in particular heat of adsorption is transferred to the thermal fluid and heat of desorption is transferred from the thermal fluid.
Another aspect of the disclosure provides a cooling and dehumidification system, comprising: a coated desiccant wheel defining a process section configured to adsorb moisture and a regeneration section configured to desorb moisture simultaneously with the adsorption of the process section; and a direct expansion vapor compression assembly, comprising: an evaporator configured to cool a stream of hot and dry air from the process section of the coated desiccant wheel; a condenser configured to heat a stream of ambient air; and a valve configured to direct the heated stream of ambient air to the regeneration section of the coated desiccant wheel.
In one example, the coated desiccant wheel is coated with at least one of: a metal organic framework (MOF); silica gel zeolite; or temperature-responsive hygroscopic polymer.
In one example, the system has direct or indirect air supply from both a conditioned space and an ambient environment.
In one example, the direct expansion vapor compression assembly further comprises an auxiliary heater or supplementary regeneration device.
In one example, the valve comprises a three-way valve.
In one example, the coated desiccant wheel includes a substrate comprising a plastic or open cell foam structure.
In one example, the coated desiccant wheel is configured to rotate to provide continuous transfer of moisture from a process stream to a regeneration stream and simultaneous loading and unloading of moisture.
In one example, the desiccant wheel rotates at a predetermined constant or adjustable angular velocity.
Another aspect of the disclosure provides a method, comprising: drawing room return air through a process section of a coated desiccant wheel; loading the coated desiccant wheel with the room return air, resulting in hot and dry air; cooling the hot and dry air with an evaporator, resulting in cool and dry air; returning the cool and dry air to a conditioned space.
In one example, drawing room return air is performed by a fan.
In one example, ambient air is heated with low grade waste heat from an air condition system.
In one example, the method further includes: heating ambient air using a condenser, resulting in hot air; splitting the hot air, using a valve, into a first stream of air and a second stream of air; passing the first stream of air to ambient; passing the second stream of air through a regeneration portion of the coated desiccant wheel, resulting in hot and moist air; and passing the hot and moist air to ambient.
In one example, the valve is a three-way valve.
Another aspect of the disclosure a heat exchanger assembly, comprising: at least one tube configured to carry refrigerant or thermal fluid; and a plurality of fins in thermal contact with the at least one tube, wherein each of the plurality of fins comprises a coated portion and an uncoated portion.
In one example, the coated portion comprises approximately 10%-90% of each respective fin.
In one example, the coated portion comprises at least one of: a metal organic framework (MOF); silica gel zeolite; or temperature-responsive hygroscopic polymer.
In one example, the assembly operates a process cycle in which: a) air flows across the uncoated portion of the plurality of fins and is sensibly cooled by transferring heat to the refrigerant or thermal fluid; and b) after a), the air flows across the coated portion of the plurality of fins.
In one example, the assembly operates a regeneration cycle in which: a) air flows across the uncoated portion of the plurality of fins and is sensibly heated by transferring heat from the refrigerant or thermal fluid; and b) after a), the air flows across the coated portion of the plurality of fins and continues to be sensibly heated by the refrigerant or thermal fluid.
The invention description below refers to the accompanying drawings, of which:
As shown, the system (120) can include a fan (101), a heat exchanger (102), desiccant wheel (104), fan (106), electric heating coil (108), and a reservoir (112) below the heat exchanger (102).
The desiccant wheel (104) (also referred to in some examples as an enthalpy wheel or a rotary desiccant assembly or rotary desiccant device) can be a three-dimensional structure and in this example can be cylindrical or substantially cylindrical. In this regard, the desiccant wheel (104) can have a substantially planar face (104a), a substantially planar face (104b) that is parallel and opposed to the planar face (104a). The desiccant wheel (104) can include a substrate made of any type of material (such as a thin metal foil, such as aluminum, or a fiber-based substrate such as a paper, a plastic, or a ceramic) and can be coated in a desiccant material. The desiccant wheel coating can be any type of hygroscopic substance, such as any type of metal-organic framework (MOF) compounds. In other examples, the desiccant wheel can be coated with silica gel zeolite, or temperature-responsive hygroscopic polymer. The desiccant wheel can be completely or partially coated with desiccant material, as described below.
In other examples, the substrate that forms the desiccant wheel (104) can be a MOF, plastic or open cell foam, or other high surface area, low thermal mass structures. Such materials can be used as substrates in this system because the materials used regenerate at lower temperature than conventional desiccant materials.
The desiccant wheel (104) can be manufactured according to various techniques, and in one example the substrate can be 3D printed as a unitary body. In another example, the desiccant wheel (104) can be 3D printed in a plurality of pieces (e.g., a plurality of portions of the overall cylindrical shape such as a plurality of pie-shaped sections) that can be adhered or otherwise engaged with one another to form the overall cylindrical shape. Other manufacturing methods can include corrugated channels or expanded foil honeycomb.
Desiccant wheels described below can have a similar or same structure and function as the wheel described with respect to
In the process airstream, room return air (100) (depicted as 100a in
As the desiccant wheel (104) rotates, the portion of the wheel (104) that coincided with the process stream rotates to coincide with the regeneration stream. In this regard, the moisture adsorbed on the desiccant while coinciding with the process stream is released to the regeneration air (111) (depicted as 111a in
As described above, the desiccant wheel (104) can be rotated (e.g., by way of a motor or other rotational motion technique) to provide for a continuous transfer of moisture from process stream to regeneration stream and simultaneous operation of the process stream and regeneration stream, allowing for simultaneous loading and unloading of moisture with respect to the same desiccant wheel. In this regard, the desiccant wheel (104) can be rotated at a predetermined constant or approximately constant angular velocity to achieve the continuous transfer. In some examples, the rotational velocity can be adjusted or adjustable according to parameters of the system to achieve the desired moisture transfer.
In the process airstream, room return air (200) (depicted as 200a in
In the process airstream, room return air (300) (depicted as 300a in
In the refrigerant circuit, refrigerant is compressed by compressor (315) and passes through condenser coil (306) where some of the refrigerant condenses. The refrigerant then passes through throttling device (316) and condenser (313) where the remainder of the refrigerant condenses. The refrigerant then passes through throttling device (317) and evaporator (310) where some of the refrigerant evaporates. The refrigerant then passes through throttling device (318) and evaporator (303) where the remainder of the refrigerant evaporates, and returns to the suction side of compressor (315). The refrigerant can be, for example, R134a, R410a, R32, or R290. In other examples, the refrigerant can generally include hydrofluorocarbons (HFCs) or hydrocarbons (HCs).
In some embodiments, an auxiliary heater or other supplementary regeneration device is added at (307). In some embodiments, condensing coil (306) and condenser (313) are switched such that refrigerant first flows to (313), then to (306). In some embodiments, (303) and (310) are switched such that refrigerant first flows to (303), then to (310). In some embodiments, water from a municipal source, rainwater collection, or storage tank is used to cool the condenser (313) by spraying or dripping water over the coils.
In a process mode depicted in
In a regeneration mode depicted in
In some embodiments, the cooling and dehumidification system can include two units in parallel, such that while one is running in process mode, the other is running in regeneration mode. In this configuration, for the indoor unit, all the exchangers, fans, valves, etc., such as the configuration of 5A, would be disposed in a side-by-side arrangement. The outdoor unit, e.g., (408) and (410), in one example, may be implemented as shown in
In this example, the indoor cooling unit can include a desiccant coated heat exchanger and separate water condensing coil arranged to cycle between loading and cooling mode and unloading and water condensing mode, as described below.
In a process mode of
In the process cycle of
In the regeneration cycle of
The extent of the desiccant coating may vary depending on the application and may comprise the full extent (fully coated). The thickness of coating may also vary along the direction of flow. The form of heat exchanger may be a conventional radiator as shown, or a microchannel radiator in which the refrigerant carrying tube is elongated and flattened to span the full width of the exchanger.
During the process cycle, air is cooled from (600) to (601) when it passes over the uncoated portion of the exchanger. It is then dehumidified (601) to (602) as moisture adsorbs onto the desiccant when it passes over the coated portion of the exchanger. In the dehumidification process, the heat of adsorption is transferred to the refrigerant. If the heat of adsorption is greater than the heat removed by the refrigerant, some heat will transfer to the air and (602) will shift to the right of (601) in the chart. If the heat of adsorption is less than the heat removed by the refrigerant, sensible heat will be removed from the air to the refrigerant, and (602) will shift to the left of (601) on the chart. If the heat of adsorption is equal to the heat removed by the refrigerant, isothermal adsorption will occur and the line between (601) and (602) will be vertical as shown.
During the regeneration cycle, air is heated from (607) to (608) when it passes over the uncoated portion of the exchanger. It is then humidified (608) to (609) as moisture desorbs from the desiccant to the airstream. The heat to desorb the desiccant is supplied by the refrigerant. If the heat of desorption is greater than the heat supplied by the refrigerant, (609) will shift to the left of (608) on the chart. If the heat of desorption is less than the heat supplies by the refrigerant, (609) will shift to the right of (608) on the chart. If the heat of desorption is equal to the heat supplied by the refrigerant, isothermal desorption will occur and the line between (608) and (609) will be vertical as shown.
While
The system advantageously conducts cooling first then adsorbing and in heating first then desorbing.
While
In the first half-cycle of
In the second half-cycle of
In some embodiments with a rotary desiccant device, a non-contacting thermometer is used to measure the temperature of the desiccant to modulate rotational speed, fan speed, or other operational parameters.
In one example, the system 1000 can use waste heat, such as heat produced by a gas-fired water heater or solar thermal collectors. The dehumidification is enabled by the hydrogel-based system described earlier and is regenerated with the heat of adsorption from Bed 2 (1020). In the second half-cycle of
Advantageously, hydrogels such as poly(N-isopropylacrylamide) can be used for dehumidification cycles, as moderate heating has shown to fully dehydrate the hydrogels and release the capture water in the liquid state (unlike conventional adsorbents which release water in vapor state).
In this regard, hydrogels address latent cooling loads, because they enable a more direct collection of water vapor from humid air than incumbent systems. Since hydrogels release liquid water directly upon heating to the lower critical solution temperature (LCST), condensate may be collected directly from the bed, eliminating the need for a condensing coil to capture the water removed from the room air. Since heat is supplied directly to the hydrogel rather than to an intermediate airstream, heat transfer losses are minimized. These features enable reduced system size, cost, and complexity while improving efficiency of the dehumidification cycle. Like hydrogels, metal-organic frameworks (MOFs), such as MIL-100, are sponge-like, highly porous materials that have very high surface area and can be regenerated with low-grade heat.
The foregoing has been a detailed description of illustrative embodiments of the invention. Various modifications and additions can be made without departing from the spirit and scope of this invention. Features of each of the various embodiments described above may be combined with features of other described embodiments as appropriate in order to provide a multiplicity of feature combinations in associated new embodiments. Furthermore, while the foregoing describes a number of separate embodiments of the apparatus and method of the present invention, what has been described herein is merely illustrative of the application of the principles of the present invention. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention.
This application claims the benefit of U.S. Provisional Application Ser. No. 63/109,840, filed Nov. 4, 2020, entitled COOLING AND DEHUMIDIFCATION SYSTEM, the entire disclosure of which is herein incorporated by reference.
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