BACKGROUND
Technical Field
Embodiments of the subject matter disclosed herein generally relate to a system and method for cooling an input air stream, and more particularly, to a hybrid air-conditioning system that combines a heat pump having desiccant-coated heat exchangers with an indirect evaporative cooler system for more efficiently dehumidifying and cooling the incoming air.
Discussion of the Background
Energy consumption for air conditioning has been increasing exponentially due to population growth and increase of living standard. From 2000 to 2015, the energy consumption for air conditioning has increased from 3.6 EJ to 7 EJ, representing about 15% of peak electricity demand worldwide. In the Gulf Cooperation Council (GCC) countries, the cooling demand is more than 36 million Rton, and it consumes 50-70% of the peak electricity generation. Consequently, a significant portion of natural energy resources (oil and gas) produced in these countries are consumed for cooling. To tackle the challenges of global energy shortage, it is critical to reduce energy consumption of air conditioning systems
The demand for cooling is usually addressed by mechanical-vapor-compression (MVC) chillers. The energy consumption of these chillers has been measured to be around 0.85±0.03 KW/Rton. In the GCC countries, the energy consumption for chillers is over 3 times as compared to that of other regions. This is attributed to the severe weather conditions, i.e., hot and humid conditions. To remove the moisture from the air to be cooled, the evaporator's temperature (5-12° C.) has to be lower than the dew point temperature of the supplied air. Meanwhile, the condenser temperature is very high (larger than 45° C.) due to the high heat rejection temperature. As a result of the high thermal lift between the evaporator and the condenser, the energy consumption of the MVC chillers is significant for humid and hot environments.
To improve the energy efficiency of the cooling units, decoupling of sensible and latent loads has been proposed, where the latent load is associated with the humidity removal and the sensible load is associated with the heating/cooling of the dry air. Traditionally, the moisture is first removed from the incoming air stream using a dehumidifier (latent load), after which the hot and dry air is cooled (sensible load) to the desired temperature. The sensible cooling of the dry air is usually achieved using an indirect evaporative cooler (IEC) system, which uses the evaporative potential of the dry air as the driving force for cooling and consumes little energy. A well-designed IEC system can achieve a COP (coefficient-of-performance) of more than 20 when the air is dry. Therefore, the overall COP of the air conditioning system is dependent on the performance of the dehumidifier.
Existing dehumidification technologies include liquid and solid desiccant systems. Most of these systems have a COP of less than 1 due to a lack of heat recovery. Recently, it was proposed a desiccant-coated heat pump, which adds desiccant coating on the heat exchangers of conventional chillers. This system achieved a COP larger than 6. After dehumidification, the dry air can be further cooled down using a conventional mechanical chiller. Alternatively, cooling can be achieved using an indirect evaporative cooler system [1]. The IEC uses the evaporative potential between unsaturated air and water as the driving force for cooling, and only a small amount of energy is required for fans and water pumps. When the intake air humidity is low, the COP of IEC itself can be >20 [1].
As the IEC system's performance degrades when the incoming air has a high humidity, several groups have proposed to combine the IEC system with MVC. For example, several hybrid systems combining IEC and dehumidification have been reported for applications in hot and humid regions [2, 3]. However, the COP of such systems is limited by the low efficiency of the dehumidification process. Another disadvantage of such system is that the supply air temperature provided by the IEC system is usually higher than 21° C., which is more than the room supply temperature (˜21° C.). To have a quantum jump in efficacy for chillers, an out-of-box solution is essential to achieve the goals of sustainable cooling
However, all the studies in the field indicate that the hybrid process is still at an undeveloped stage with several technical gaps. Thus, there is a need for an improved system that is configured for efficient air cooling with improved dehumidification.
BRIEF SUMMARY OF THE INVENTION
According to an embodiment, there is a hybrid air conditioning system for cooling a chamber, and the hybrid system includes a desiccant-coated heat pump configured to cool, through evaporation and condensation of a refrigerant, a first air stream OA, and an indirect evaporative cooling, IEC, unit configured to cool a second air stream MA, which is related to the first air stream OA, through direct heat exchange between wet channels that are placed adjacent to dry channels. The desiccant-coated heat pump is fluidly connected to the IEC unit so that a generated supply air stream SA is dehumidified by a desiccant material coated on first and second heat exchangers of the desiccant-coated heat pump.
According to another embodiment, there is a desiccant-coated heat pump that includes a first heat exchanger having a coil coated with a desiccant material, a second heat exchanger having a coil coated with the desiccant material, a first pipe junction housing only one first air damper V1, and a second pipe junction housing only one second air damper V2. The heat pump includes no more than two air dampers.
According to yet another embodiment, there is a method for supplying cool air, to a chamber, with a desiccant-coated heat pump. The method includes setting a first air damper V1 in a first pipe junction and a second air damper V2 in a second pipe junction to a first state, wherein there are no other air dampers in the heat pump, receiving an outside air stream OA at the first pipe junction, dehumidifying and cooling the outside air stream OA with a first heat exchanger having a coil coated with a desiccant material, to generate a dried air stream DA, supplying the dried air stream DA to the chamber through a second pipe junction that houses the second air damper V2, providing a return air stream PA1 from the chamber, via the first pipe junction, to a second heat exchanger having a coil coated with the desiccant material, to regenerate the desiccant material, and discharging a humid air stream PA2 from the second heat exchanger, via the second pipe junction, to the ambient.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic diagram of a novel hybrid air conditioning system that combines a desiccant-coated heat pump with an indirect evaporative cooler system that operates during a first cycle;
FIG. 2 illustrates the desiccant-coated heat pump combined with the indirect evaporative cooler system of FIG. 1, operating during a second cycle;
FIG. 3 illustrates various parameters of the hybrid air conditioning system of FIGS. 1 and 2 and their operating values;
FIG. 4 illustrates the cooling capacity and the COP of the indirect evaporative cooler system versus the outdoor air temperature;
FIG. 5 illustrates the supply air temperature generated by the indirect
evaporative cooler system versus the outdoor air temperature;
FIG. 6A illustrates the temperature versus time characteristics for the various air streams flowing through the system of FIGS. 1 and 2 during the alternating first and second cycles;
FIG. 6B illustrates the humidity versus time characteristics for the various air streams flowing through the system of FIGS. 1 and 2 during the alternating first and second cycles;
FIG. 7 illustrates the coefficient of performance of the system shown in FIGS. 1 and 2 versus the sensible heat ratio and coefficient of performance of a desiccant-coated heat exchanger used by the system shown in FIGS. 1 and 2;
FIG. 8 is a schematic diagram of another novel hybrid air conditioning system that combines a desiccant-coated heat pump with an indirect evaporative cooler system that operates during a first cycle;
FIG. 9 illustrates the desiccant-coated heat pump combined with the indirect evaporative cooler system of FIG. 8, that operates during a second cycle;
FIG. 10 illustrates the wet and dry channels of the indirect evaporative cooler system;
FIGS. 11A and 11B show a possible implementation of the desiccant-coated heat pump with a system that uses eight air dampers for directing the air flows during the alternating cycles;
FIG. 12 illustrates how the thermal lift becomes smaller and the power consumption of the compressor of the desiccant-coated heat pump is reduced by using the system of FIGS. 11A and 11B;
FIGS. 13A and 13B show another possible implementation of the desiccant-coated heat pump with a system that uses only two air dampers for directing the air flows during the alternating cycles;
FIGS. 14A and 14B show the only two air dampers and their corresponding pipe junctions;
FIG. 15 is an overview of the implementation of the desiccant-coated heat pump with only two air dampers for directing the air flows;
FIG. 16 shows an implementation of the hybrid air conditioning system that uses a combination of the desiccant-coated heat pump of FIGS. 13A and 13B and the indirect evaporative cooler system of FIGS. 1 and 2 or FIGS. 8 and 9; and
FIG. 17 is a flow chart of a system for cooling air with one of the systems discussed above.
DETAILED DESCRIPTION OF THE INVENTION
The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to a hybrid air conditioning system that includes a desiccant-coated heat pump and an IEC system. However, the embodiments to be discussed next are not limited to cooling the air, but may also be applied to heating the air.
Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.
According to an embodiment, a novel hybrid air conditioning system includes a desiccant-coated heat pump integrated with an indirective evaporative cooler system. The heat pump includes two desiccant-coated heat exchangers, which are fluidly connected to each other through a throttling valve. The heat pump further includes a compressor, an evaporator, and a throttling valve. The two desiccant-coated heat exchangers are also fluidly connected to the compressor and a four-way valve so that when one desiccant unit is used to remove the humidity from the incoming air stream, the other unit is regenerated. Thus, the air stream flowing through the heat pump is dehumidified by the desiccant of active heat exchanger of the heat pump and the dried air stream is then provided to the IEC system for cooling, prior to being supplied to the chamber desired to be cooled. The processes taking place in this system are now discussed in more detail with regard to the figures.
FIG. 1 shows a hybrid air conditioning system 100 having the desiccant-coated heat pump 110 and the IEC system 160 fluidly connected to each other so that an air stream from the heat pump 110 is cooled in the IEC system before being supplied as the cold air to the chamber 170. The desiccant-coated heat pump 110 has two desiccant-coated heat exchangers 112 and 120, each including coils coated with a desiccant substance. The desiccant substance may be any known substance (e.g., silica gel, activated charcoal, calcium chloride, charcoal sulfate, activated alumina, montmorillonite clay, molecular sieve, etc.) that can be attached to the heat exchangers (e.g., a coil) and is able to absorb humidity. In one application, no fabric material is used inside or outside the coils, to prevent or limit biofouling. The desiccant substance may be painted or spray painted on the coils of the heat exchangers. Any other process may be used to attach the desiccant material to the coils of the heat exchangers. The detailed structure of these units is discussed later. Schematically, each heat exchanger includes a corresponding housing 112A, 120A, a corresponding air flow path 114, 122, and a corresponding heat exchanger coil 116, 124 located in the housing. The passing air flow exchanges heat with a refrigerant that circulates through the heat exchanger coil. The coils of each heat exchanger are coated with a corresponding desiccant material 118, 126. In one application, the two desiccant materials are the same. The figure shows the desiccant only partially covering the heat exchanger coils inside the corresponding housing. However, one skilled in the art would understand that the desiccant may cover any percentage of the heat exchanger coils, up to 100% of the surface.
The desiccant-coated heat pump 110 further includes an evaporator 128 (optional in one implementation; note that in one configuration, the evaporator may be omitted and the air from the IEC system 160 is supplied directly to the chamber 170), a compressor 130, a four-way valve 132, a throttling valve 134, and connection valves 136, 138. The compressor 130 ensures that a refrigerant 140 flows through a piping system 141 from one of the desiccant-coated heat exchangers 112 and 120 to the evaporator 128 and back to the compressor to heat and cool the refrigerant. The four-way valve 132 and the connection valves 136, 138 ensure that during a first cycle, the refrigerant 140 in the liquid state (i.e., cold) flows from the throttle valve 134 (1) directly to the first desiccant-coated heat exchanger 112 (to cool the incoming air stream OA) and then to the compressor 130, and also (2) directly to the evaporator 128 (to cool the supplied air stream SA), while the refrigerant 140 in the gas state (i.e., hot) flows from the compressor 130 to the second desiccant-coated heat exchanger 120 to regenerate the desiccant, as shown in FIG. 1. In a second cycle, as shown in FIG. 2, the four-way valve 132 changes its setting, the connection valve 138 is closed and the connection valve 136 is open, and now the refrigerant 140 in the liquid state (i.e., cold) flows from the throttle valve 134 (1) directly to the second desiccant-coated heat exchanger 120 (to cool the incoming air stream OA) and then to the compressor 130, and also (2) directly to the evaporator 128 (to cool the supplied air stream SA), while the refrigerant 140 in the gas state (i.e., hot) flows from the compressor 130 to the first desiccant-coated heat exchanger 112 to regenerate the desiccant. Thus, a controller 150 (e.g., a processor) may be used to automatically actuate the valves 132, 136, and 138 to implement the configuration shown in FIG. 1 during the first cycle and the configuration shown in FIG. 2 during the second cycle. This change in cycle from the first to the second one and from the second one to the first one is necessary to regenerate the used desiccant material, as the desiccant material of one the desiccant-coated heat exchanger absorbs humidity from the incoming air stream OA and when it is saturated, it needs to enter the regeneration cycle to remove that moisture. Note that for the first cycle, the warm refrigerant 140 passing through the heat exchanger coil 124 evaporates the water from the desiccant 126, and for the second cycle, the warm refrigerant passing through the heat exchanger coil 116 evaporates the water from the desiccant 118. As discussed later, an air stream PA1, for example taken from the IEC system 160, may be supplied to the heat exchanger that is being regenerated to remove the humidity from inside its housing.
FIGS. 1 and 2 also show the pipe components of the air piping system 142 that guides the outside air (i.e., air from outside the chamber 170) through the various elements of the heat pump 110 and IEC system 160 prior to being supplied the chamber 170. The air piping system 142 includes a first pipe 142-1 fluidly connecting the ambient to the interior of the housing of the first heat exchanger 112 during the first cycle and to the interior of the housing of the second heat exchanger 120 during the second cycle. This pipe provides the outside air stream OA to be dehumidified by the desiccant 118 or the desiccant 126. An air damper AD1 may be placed along the pipe 142-1 to direct the air to the first heat exchanger during the first cycle and to the second heat exchanger during the second cycle. The dried air stream DA exiting the corresponding heat exchanger 112 during the first cycle or heat exchanger 120 during the second cycle, advances along a second pipe 142-2 to the IEC system 160, as directed by a second air damper AD2. The two air dampers may be controlled by the controller 150 as necessary by the requirements of the first and second cycles.
Next, the dried air stream DA is mixed with a first return air stream RA1 (returned from the chamber 170), at a junction J1, to generate a mixed air stream MA, which flows along pipe 142-3 to an input 1641 of a dry channel 164, of the IEC system 160. The pre-cooled air stream PCA from the dry channel 164 is provided along pipe 142-4 to the input 1281 of the evaporator 128, for being further cooled. The supplied air stream SA, outputted at the output 1280 of the evaporator 128, being cooled to a desired temperature, is supplied to the input 1701 of the chamber 170. A certain amount of air is returned, from a first output 1700 along a pipe 142-5, as returned air stream RA from the chamber 170 to the IEC system 160. A portion of the returned air, for example, 10% in this embodiment, but other quantities are also possible, is directly leaked to the ambient as leaked air stream LA, from a second output 170B of the chamber. The return air stream RA is split with a damper at a junction J2, which also may be controlled by the controller 150, into the first return air stream RA1, and a second return air stream RA2. The percentages of these two streams may be 60% to 30% relative to the total amount of air removed from the chamber 170. While the first return air stream RA1 has been discussed above as being fed to the dry channel 164 along the pipe 142-6, the second return air stream RA2 is fed, along pipe 142-7, as purge air to a wet channel 162 of the IEC system 160. Thus, the second return air stream RA2 enters at the input 1621 of the wet channel 162, exchanges heat with the dry channel 164 and the air passing through the dry channel, and exits the IEC system 160 at exit 1620. The released air stream PA may be discarded into the ambient along pipe 142-7. However, in one embodiment (which is discussed later in more detail), the released air stream PA may be passed through the heat exchanger that needs to be regenerated to remove the humidity from the desiccant coating. For this case, the air stream PA1, which corresponds to the stream PA, is directed into the second heat exchanger 120 during the first cycle and the air stream PA2, which carries the humidity from the desiccant coating of the second heat exchanger 120, is released into the ambient as illustrated in FIG. 1. The same configuration is shown in the embodiment illustrated in FIGS. 8 and 9. The same is true for the first heat exchanger 112, during its regeneration cycle, as shown in FIG. 2. This implementation may also be achieved with the system shown in FIGS. 13A to FIG. 16, as discussed later.
While the air piping system 142 discussed above handles the air flow through the desiccant-coated heat pump 110 and the IEC system 160, and fluidly connects these systems only in terms of the various air streams, there is a separate piping system 141 that carries the refrigerant 140 from the compressor to the various valves, desiccant-coated heat exchangers and the evaporator, that form the unit 110. The refrigerant piping system 141 is separated from the air piping system 142, in the sense that they do not share any of their medium with each other.
During operation of the system 100, for the first half cycle, which is illustrated in FIG. 1, the desiccant material 118 coating the coils of the first heat exchanger 112 are initially dry, while those coating the coils of the second heat exchanger 120 are saturated with moisture. Thus, the first heat exchanger 112 works as the evaporator/absorber and the second heat exchanger 120 works as the condenser/regenerator. As can be seen from FIG. 1, the outdoor air stream OA is passed through the first heat exchanger 112, where part of its moisture content is absorbed by the desiccant material 118, and the condensation heat is removed by the refrigerant 140. Then the dry air stream DA is mixed with a portion of the room return air stream RA1 (60% in this embodiment, but other percentages may be used), which then sequentially passes the IEC dry channels 164 and the evaporator 128 before being supplied to room 170 as the supplied air stream SA. The IEC system 160 pre-cools the mixed air stream MA to a temperature of about 22° C., and then the evaporator 128 further cools the air stream to the supply temperature of 18° C. Another portion of the room return air RA2 (which is 30% of the total air being removed from the chamber 170 in this embodiment, but can have a different value in other embodiments) is supplied to the wet channels 162 of the IEC system 160, where water evaporates due to partial vapor pressure difference between the water surface and the air. The evaporation of the water absorbs heat, thus creating a cooling effect and lowers the air temperature in both the dry and wet channels.
The refrigerant 140, after absorbing heat from the air stream OA, is firstly directed to the compressor 130 to get compressed, and then it flows to the second heat exchanger 120 for being condensed. The released condensation heat regenerates the desiccant 126 in the second heat exchanger 120, and the removed moisture is taken away using the air stream PA1. This regeneration process happens during the first cycle. After a certain period of time, the desiccant material in the first heat exchanger 112 become saturated, while that in the second heat exchanger 120 is completely regenerated. At this time, the controller 150 instructs, as can be seen from FIG. 2, the 4-way valve 132 and the throttle valve 134 to change their status, so that the flow direction of the refrigerant changes to the following path: the second heat exchanger 120→compressor 130→first heat exchanger 112→throttling valve 134. The air stream DA leaving the second heat exchanger 120 is now mixed with the first room return air stream RA1 and supplied as the mixed air stream MA to the dry channels 164 of IEC system 160, while the air stream PA2 leaving the first heat exchanger 112 is disposed to the ambient.
One possible set of parameters that may be used with the system 100 are illustrated in the table of FIG. 3. Those skilled in the art would understand that the optimum parameters shown in this table may vary, as shown in the last column of the table. Thus, in the following, the term “about” is used to describe a possible range of values for a given parameter that falls into the Range column of the table in FIG. 3.
The IEC system 160 illustrated in FIGS. 1 and 2 has been tested under various outdoor air conditions to evaluate its performance. FIG. 4 shows how the cooling capacity of the system and the energy efficiency (measured in Rton and COP, respectively) vary with the outdoor air temperature, i.e., the temperature of the incoming air stream OA. FIG. 5 shows how the supply air temperature (i.e., the temperature of the supplied air stream SA in FIGS. 1 and 2) varies with the outdoor air temperature. It can be seen from FIG. 5 that the supply air stream SA's temperature varies from 20° C. to 25° C. when the outdoor air's temperature varies from 27° C. to 42° C. The overall cooling capacity and COP of the system 160 were measured, as shown in FIG. 4. At an outdoor (inlet to IEC system) air temperature of 42° C., it produced 1 Rton cooling, as per the design specifications of the system. The corresponding COP was also calculated and a maximum value of COP=30was found. At lower inlet air temperatures, e.g., 30° C. to 35° C., the measured COPs were found to span from 14 to 20, which is significantly higher than the conventional MVC, which exhibits a COP value of about 3.5.
The system 110 has also been designed and fabricated. The total dehumidification capacity of the system 110 was found to be 1-Rton. FIGS. 6A and 6B show the temporal profiles of the desiccant-coated unit. Outdoor air is supplied at a temperature of 26.1° C. and humidity of 14 g/kg, while the room return air RA is measured to have a temperature of 21.9° C. and humidity of 10.1 g/kg. Due to batch-wise operation of the desiccant-coated heat exchangers, the supply air conditions show a cyclic manner. At the beginning of each cycle, the supply air temperature is high at 22.4° C., and its value gradually decreases to 18.8° C. at the end of the cycle, as shown in FIG. 6A. The humidity ratio of the supply air has a peak value at the beginning of each cycle because the heat exchanger coil is still hot when switched from the regeneration mode to the dehumidification mode, as shown in FIG. 6B. After the heat exchanger coil is cooled down, the supply air humidity drops quickly to 6 g/kg. Both the temperature and humidity ratio of the supply air are lower than the requirement for thermal comfort.
Because the COP of the IEC system is high, the overall COP of the hybrid air conditioning system 100 is dependent on the COP of the desiccant-coated heat pump 110 as well as the ratio between the sensible heat and latent heat. For the system 100 shown in FIGS. 1 and 2, an overall COP of 12 to 14 may be achieved, as shown in FIG. 7, which is more than 3-fold higher than a traditional mechanical chiller-based cooling system. FIG. 7 plots the COP of the system 100 as a function of the sensible heat ratio, SHR, Qsen/(Qsen+Qlat), where Qsen is the sensible heat and the Qlat is the latent heat, and as a function of the COP of the system 110.
Thus, it is observed that the novel hybrid air conditioning system 100 advantageously achieves sustainable cooling with a high-energy efficiency. Some of the feature of this system include independent sensible and latent load control, high efficiency of dehumidification and cooling processes, and stability of system performance for varying weather conditions. In one embodiment, the system 100 has at least one of the following features:
- (1) The sensible and latent loads are decoupled and can be handled separately. A conventional MVC system removes moisture by cooling the air to below the dew point temperature (˜12° C.), which leads to a high electricity consumption in the compressor. Moreover, re-heating the air to ˜18° C. is required to meet the requirement for thermal comfort. By decoupling the sensible and latent loads, the energy efficiency for each process can be improved;
- (2) As compared to conventional dehumidification systems, the novel system 100 uses a desiccant-coated heat pump for dehumidification purpose. The condensation heat during dehumidification is recovered for the regeneration of desiccant material, which is able to increase the dehumidification's COP to more than 6;
- (3) After dehumidification, the air is cooled down by the indirect evaporative cooler system with marginal energy consumption, thus bringing significant energy savings; and
- (4) If the IEC system is unable to control the supply air's temperature, a small cooling coil (evaporator) may be employed to further cool down the air coming from the IEC system to meet the demand of thermal comfort.
In another embodiment, the hybrid air conditioning system 100 shown in FIGS. 1 and 2 may be modified, as illustrated in FIGS. 8 and 9. The modified hybrid air conditioning system 800 has the same configuration for the refrigerant piping 141, and the same components for the desiccant-coated heat pump 110. However, the air piping 142 is modified so that the air stream PA1 leaving the wet channels 162 of the IEC system 160 is passed through the heat exchanger 120 during the first cycle (see FIG. 8) and through the heat exchanger 112 during the second cycle (see FIG. 9). A system that achieves this air flow change is discussed later. The operation parameters ranges of the hybrid air conditioning 800 may be those shown in the table of FIG. 3.
An example of an implementation of the IEC system 160 is shown in FIG. 10. The IEC system 160 in this embodiment has plural walls 166 (e.g., metal walls) that define the wet and dry channels 162, 164, respectively. Note that the wet channels 162 are effectively provided with a water spray or water film 168 from an exterior water source (not shown). In one embodiment, the wet channels are run as wet as possible (i.e., the wettability in the wet surfaces is 100%) so that there are no wet and dry regions where scaling can occur. In one embodiment, the water source may be the condensed water that forms inside the evaporator 128. In this embodiment, as the condensed water is distilled water, there is less microbial contamination and thus, less chances of biofouling on the coils of the heat exchangers. During a one year run of the experimental 1-Rton unit discussed above, no scaling and/or biofouling has been observed. According to this embodiment, the room exhaust air stream RA2, which is cold and dry, flows through the wet channels 162 to cool down the mixed air stream MA in the dry channels 164. The wet channels 162 are supplied with water, which evaporates and absorbs heat from the air to further cool down the air stream MA. When the temperature in the dry channels 164 is lower than the dew-point temperature of the return air RA2, condensation occurs, and the humidity ratio of the outdoor air drops. The pre-cooled and dehumidified air stream PCA is then passed through the evaporator coils of the heat pump 110, to further bring down its temperature and humidity to the desired values and it is supplied as supply air stream SA to the room 170. Meanwhile, the exhaust air PA leaving the wet channels 162 may be discharged in the ambient for the embodiment shown in FIGS. 1 and 2, or may be provided to one of the heat exchangers 112 or 120 in the embodiment shown in FIGS. 8 and 9.
The heat pump 110 may be implemented in various ways. One possible way is discussed with regard to the embodiment illustrated in FIGS. 11A and 11B. In this embodiment, which can be used with system 800 (but can be adapted to also be used with system 100), each of the heat exchangers 112 and 120 has two inputs and two outputs, namely, first and second inputs 112-11 and 112-21 for the first heat exchanger 112, first and second outputs 112-10 and 112-20 for the first heat exchanger 112, first and second inputs 120-11 and 120-21 for the second heat exchanger 120, and first and second outputs 120-10 and 120-20 for the second heat exchanger 120. Each of the first and second heat exchangers includes 8 air dampers V1 to V8, provided within the corresponding housing 112A and 120A. Each of the air damper may be independently actuated by the controller 150 (see FIGS. 8 and 9).
Starting with FIG. 11A, which illustrates the air flow during the second cycle (see FIG. 9), air dampers V3, V4, V7, and V8 in the second heat exchanger 120 are closed while air dampers V1, V2, V5, and V6 are opened. This ensures that only the outside air stream OA flows through the second heat exchanger 120. In the first heat exchanger 112, the air dampers V3, V4, V7, and V8 are open and all other air dampers are closed so that only the air stream PA1, which leaves the wet channels 162 of the IEC 160, enters the first heat exchanger. The air flows may be enhanced with corresponding fans F1 and F2, placed upstream or downstream the system 110, in the air piping system 142. The fans may be operated independently by the controller 150.
FIG. 11B illustrates the air flows corresponding to the first cycle of FIG. 8. For this cycle, the air dampers V3, V4, V7, and V8 are open while the air dampers V1, V2, V5, and V6 are closed for the second heat exchanger 120. This ensures that only the air stream PA1 flows through the second heat exchanger 120. In the first heat exchanger 112, the air dampers V3, V4, V7, and V8 are closed and all other air dampers are opened so that only the air stream OA flows through the first heat exchanger. The arrangement shown in FIG. 11A corresponds to the second heat exchanger 120 cooling and dehumidifying the incoming air stream OA and the first heat exchanger 112 being heated to regenerate the desiccant material. The arrangement shown in FIG. 11B corresponds to the second heat exchanger 120 being heated to regenerate the desiccant material and the first heat exchanger 112 cooling and dehumidifying the incoming air stream OA.
The system 800 that is implemented with the desiccant-coated heating pump (DCHP) system 110 works in a batch-operation mode, with the two heat exchangers 112 and 120 switching their roles periodically, at the end of each cycle. The heat exchanger on the top works first as the evaporator and dehumidifier. The outdoor air stream OA (hot and humid) passes through one of the heat exchangers, where its moisture content is removed by the desiccant coated on the surface of the heat exchanger. Meanwhile, cold refrigerant flows inside the heat exchanger to cool down the desiccant and the outdoor air. The air stream DA leaving the heat exchanger becomes cold and dry, and can be directly supplied to the room or to the IEC system 160 for further cooling. The refrigerant 140 is compressed to a higher pressure and flows to the other heat exchanger. The condensation heat is released to the adsorbent for regeneration, and the room return air stream PA1 is circulated outside of the heat exchangers to take away the moistures. After a certain period, the flow direction of the refrigerant is reversed. The top heat exchanger becomes the heating and regeneration coil, while the bottom one functions as the cooling and dehumidifier coil. The air dampers V1 to V8 are also switched so that outdoor air is directed to the bottom heat exchanger while the room return air stream PA1 flows through the top coil.
Different from existing MVC systems, the DCHP implementation removes the moisture by the adsorbent (i.e., desiccant material), and the evaporator can be operated at elevated temperatures (15-18° C.) with the existing stock of compressors. The condensation heat is rejected to the room return air stream PA1, which has a low temperature, thus reducing the condenser temperature. Consequently, the thermal lift becomes smaller and the power consumption of the compressor is reduced, as shown in FIG. 12 by cycle 1200. Another source of energy saving comes from the reuse of the rejected heat of the refrigerant at the condenser for the regeneration of adsorbent-coated coil. Such a heat recovery scheme helps to reduce energy consumption of dehumidification. The DCHP can achieve a high COP of >7 [4].
However, the implementation of the heat pump 110 shown in FIGS. 11A and 11B may be affected by the large of number of air dampers V1 to V8 as some of these elements may fail, may not respond correctly to the instructions of the controller 150, and require a complicated control mechanism as each air damper requires independent control. Failure of any valve will negatively affect the normal operation of the entire system. Thus, according to a new embodiment, which is illustrated in FIGS. 13A and 13B, only two air dampers are used for directing the air streams through the heat exchangers 112 and 120 and achieving the air flow switch between the first and second cycles of the system.
More specifically, as shown in FIG. 13A, the heat exchangers 112 and 120 of the system 110 are implemented into a junction unit 1300 to supply the air stream DA directly to the chamber 170 and the return air stream PA1 is taken directly from the chamber, without the use of the IEC system 160. As discussed later, it is also possible to implement the IEC system 160 into this design. During the first cycle, the bottom heat exchanger 112 functions as the cooler and dehumidifier, while the top heat exchanger 120 is the regenerator and condenser. The outdoor air stream OA is directed to the bottom heat exchanger 112 by a single air damper V1, to get cooled and dehumidified, after which it is directly supplied to the room 170 as the supply air stream. The room return air stream PA1 enters the junction unit 1300 from the other port and passes through the top heat exchanger 120, before it is discharged to the ambient as air stream PA2. Note that the same first air damper V1 directs (1) the air stream PA1 from the chamber 170 to the second heat exchanger 120, and (2) the air stream OA, from the ambient to the first heat exchanger 112, while the second air damper V2 simultaneously directs (1) the air stream DA, produced by the first heat exchanger 112, to the chamber 170, and (2) the air stream PA2, produced by the second heat exchanger 120, to the ambient. In other words, the air dampers V1 and V2 are sized to fully occupy the corresponding pipe junctions 1310 and 1320 as shown in more detail in FIGS. 14A and 14B. Note that each pipe junction 1310 and 1320 is made by the intersection of four different pipes, a first pipe fluidly connected to the ambient, a second pipe fluidly connected to the chamber 170, a third pipe fluidly connected to the first heat exchanger 112, and a fourth pipe fluidly connected to the second heat exchanger 120. In the other half cycle, the flow direction of the refrigerant is reversed, and the roles of the heat exchangers are switched, i.e., the top heat exchanger is the cooler/dehumidifier and the bottom heat exchanger is the regenerator/condenser. The two air dampers V1 and V2 are rotated by 90° to alter the flow direction of the air flows through the system. FIG. 15 shows an overview of the junction unit 1300, which is part of the desiccant-coated heat pump 110. In this embodiment, the first heat exchanger 112 is placed in direct contact with the second heat exchanger 120, i.e., their housings touch each other. Note that the two air dampers V1 and V2 have only two states in this embodiment, the state shown in FIG. 13A, which corresponds to the first cycle, and the state shown in FIG. 13B, which corresponds to the second cycle.
While FIGS. 13A and 13B illustrate the junction unit 1300 being implemented without the IEC system 160 for cooling the chamber 170, in one embodiment, as illustrated in FIG. 16, the junction unit 1300 may be fluidly connected to the IEC system 160 before supplying the cooled air to the chamber 170 to form the system 1600, which is another implementation of the hybrid system 100. For both situations, the air dampers V1 and V2 can be driven with corresponding motors 1312 and 1322, which are controlled by the controller 150. In one application, only one motor may be used to drive both air dampers V1 and V2 as there are only two configurations that need to be achieved. Thus, in this embodiment, instead of having 8 air dampers as in the embodiment shown in FIGS. 13A and 13B, only two air dampers are used to direct the air flows during the first and second cycles for the entire hybrid air system 100. Note that the refrigerant piping 141, the compressor 130, the four-way valve 132, and the evaporator 128 of the desiccant-coated heat pump 110 are omitted in the embodiments illustrated in FIGS. 13A to 16 for simplicity. However, these elements are similar to those illustrated in FIGS. 1 and 2 and are fluidly connected to the first and second heat exchangers 112 and 120 as also shown in FIGS. 1 and 2 or FIGS. 8 and 9. In other words, the embodiments discussed herein can be combined in any way as long as the overall hybrid air conditioning system includes the desiccant-coated heat pump 110 implemented in any of the above discussed cases.
A method for supplying cool air to a chamber 170 by using the desiccant-coated heat pump 110 implemented as shown in FIGS. 13A and 13B is now discussed with regard to FIG. 17. The method includes a step 1700 of setting a first air damper V1 in a first pipe junction 1310 and a second air damper V2 in a second pipe junction 1320 to a first state, wherein there are no air dampers in the heat pump, a step 1702 of receiving an outside air stream OA at the first pipe junction 1310, a step 1704 of dehumidifying and cooling the outside air stream OA with a first heat exchanger 112 having a coil 116 coated with a desiccant material 118, to generate a dried air stream DA, a step 1706 of supplying the dried air stream DA to the chamber 170 through a second pipe junction 1320 that houses the second air damper V2, a step 1708 of providing a return air stream PA1 from the chamber 170, via the first pipe junction 1310, to a second heat exchanger 120 having a coil 124 coated with the desiccant material, to regenerate the desiccant material, and a step 1710 of discharging a humid air stream PA2 from the second heat exchanger 120, via the second pipe junction 1320, to the ambient.
The method may further include switching the first and second air dampers from the first state to a second state to reverse an air flow through the first and second heat exchangers to regenerate the desiccant material in the first heat exchanger and use the desiccant material in the second heat exchanger for drying and cooling. The method may also include flowing the dry air stream DA from the first heat exchanger though dry channels of an indirect evaporative cooler, IEC, system before providing the dry air stream DA to the chamber, and flowing the return air stream PA1 through wet channels of the IEC system before arriving at the first pipe junction.
The disclosed embodiments provide a hybrid air conditioning system that uses an indirect evaporative cooler system and a desiccant-coated heat pump for cooling and/or heating the air provided to a chamber. It should be understood that this description is not intended to limit the invention. On the contrary, the embodiments are intended to cover alternatives, modifications, and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.
Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.
This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.
REFERENCES
The entire content of all the publications listed herein is incorporated by reference in this patent application.
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- [3] Pandelidis, D., S. Anisimov, W. M. Worek, and P. Drąg, Comparison of desiccant air conditioning systems with different indirect evaporative air coolers. Energy conversion and management, 2016. 117: p. 375-392.
- [4] Y. D. Tu, R. Z. Wang, T. S. Ge & X. Zheng, Comfortable, high-efficiency heat pump with desiccant-coated, water-sorbing heat exchangers, Scientific Reports 7 (2017) 40437.
Patent Application
20240369239
