METHODS AND SYSTEMS FOR MINI-SPLIT LIQUID DESICCANT AIR CONDITIONING
A split liquid desiccant air conditioning system is disclosed for treating an air stream flowing into a space in a building. The split liquid desiccant air-conditioning system is switchable between operating in a warm weather operation mode and a cold weather operation mode.
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This application claims priority from U.S. Provisional Patent Application No. 61/783,176 filed on Mar. 14, 2013 entitled METHODS AND SYSTEMS FOR MINI-SPLIT LIQUID DESICCANT AIR CONDITIONING, which is hereby incorporated by reference.
BACKGROUNDThe present application relates generally to the use of liquid desiccants to dehumidify and cool, or heat and humidify an air stream entering a space. More specifically, the application relates to the replacement of conventional mini-split air conditioning units with (membrane based) liquid desiccant air conditioning system to accomplish the same heating and cooling capabilities as those conventional mini-split air conditioners.
Desiccant dehumidification systems—both liquid and solid desiccants—have been used 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 for example 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, 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. These membrane based liquid desiccant systems have been primarily applied to unitary rooftop units for commercial buildings. However, residential and small commercial buildings often use mini-split air conditioners wherein the condenser is located outside and the evaporator cooling coil is installed in the room or space than needs to be cooled, and unitary rooftop units are not an appropriate choice for servicing those spaces.
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 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 the desiccant.
In many smaller buildings a small evaporator coil is hung high up on a wall or covered by a painting as for example the LG LAN126HNP Art Cool Picture frame. A condenser is installed outside and high pressure refrigerant lines connect the two components. Furthermore a drain line for condensate is installed to remove moisture that is condensed on the evaporator coil to the outside. A liquid desiccant system can significantly reduce electricity consumption and can be easier to install without the need for high pressure refrigerant lines that need to be installed on site.
Mini-split systems typically take 100% room air through the evaporator coil and fresh air only reaches the room through ventilation and infiltration from other sources. This often can result in high humidity and cool temperatures in the space since the evaporator coil is not very efficient for removing moisture. Rather, the evaporator coil is better suited for sensible cooling. On days where only a small amount of cooling is required the building can reach unacceptable levels of humidity since not enough natural heat is available to balance the large amount of sensible cooling.
There thus remains a need to provide a retrofitable cooling system for small buildings with high humidity loads, wherein the cooling and dehumidification of indoor air can be accommodated at low capital and energy costs.
BRIEF SUMMARYProvided herein are methods and systems used for the efficient cooling and dehumidification of an air stream especially in small commercial or residential buildings using a mini-split liquid desiccant air conditioning system. 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 desiccant is contained by a microporous membrane and the air stream is directed in a primarily vertical orientation 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 and a regenerator that rejects the latent and sensible heat from the heat transfer fluid to the environment. In accordance with one or more embodiments, the heat transfer fluid in the conditioner is cooled by a refrigerant compressor or an external source of cold heat transfer fluid. In accordance with one or more embodiments, the regenerator is heated by a refrigerant compressor or an external source of hot heat transfer fluid. In accordance with one or more embodiments, the refrigerant compressor is reversible to provide heated heat transfer fluid to the conditioner and cold heat transfer fluid to the regenerator and the conditioned air is heat and humidified and the regenerated air is cooled and dehumidified. In accordance with one or more embodiments, the conditioner is mounted against a wall in a space and the regenerator is mounted outside of the building. In accordance with one or more embodiments, the regenerator supplies liquid desiccant to the conditioner through a heat exchanger. In one or more embodiments, the heat exchanger comprises two desiccant lines that are bonded together to provide a thermal contact. In one or more embodiments, the conditioner receives 100% room air. In one or more embodiments, the regenerator receives 100% outside air. In one or more embodiments, the conditioner and evaporator are mounted behind a flat screen TV or flat screen monitor or some similar device.
In accordance with one or more embodiments a liquid desiccant membrane system employs an indirect evaporator to generate a cold heat transfer fluid wherein the cold heat transfer fluid is used to cool a liquid desiccant conditioner. Furthermore in one or more embodiments, the indirect evaporator receives a portion of the air stream that was earlier treated by the conditioner. In accordance with one or more embodiments, the air stream between the conditioner and indirect evaporator is adjustable through some convenient means, e.g., through a set of adjustable louvers or through a fan with adjustable fan speed. In one or more embodiments, the water supplied to the indirect 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 indirect evaporator uses a membrane to prevent carry-over of non-desirable elements from the seawater or waste water. In one or more embodiments, the water in the indirect 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 one or more embodiments, the indirect evaporator is mounted directly behind or directly next to the conditioner. In one or more embodiments, the conditioner and evaporator are mounted behind a flat screen TV or flat screen monitor or some similar device. In one or more embodiments, the exhaust air from the indirect evaporator is exhausted out of the building space. In one or more embodiments, the liquid desiccant is pumped to a regenerator mounted outside the space through a heat exchanger. In one or more embodiments, the heat exchanger comprises two lines that are thermally bonded together to provide a heat exchange function. In one or more embodiments, the regenerator receives heat from a heat source. In one or more embodiments, the heat source is a solar heat source. In one or more embodiments, the heat source is a gas-fired water heater. In one or more embodiments, the heat source is a steam pipe. In one or more embodiments, the heat source is waste heat from an industrial process or some other convenient heat source. In one or more embodiments, the heat source can be switched to provide heat to the conditioner for winter heating operation. In one or more embodiments, the heat source also provides heat to the indirect evaporator. In one or more embodiments, the indirect evaporator can be directed to provide humid warm air to the space rather than exhausting the air to the outside.
In accordance with one or more embodiments, the indirect evaporator is used to provide heated, humidified air to a supply air stream to a space while a conditioner is simultaneously used to provide heated, humidified air to the same space. This allows the system to provide heated, humidified air to a space in winter conditions. The conditioner is heated and is desorbing water vapor from a desiccant and the indirect evaporator can be heated as well and is desorbing water vapor from liquid water. In combination the indirect evaporator and conditioner provide heated humidified air to the building space for winter heating conditions.
In no way is the description of the applications intended to limit the disclosure to these applications. Many construction variations can be envisioned to combine the various elements mentioned above each with its own advantages and disadvantages. The present disclosure in no way is limited to a particular set or combination of such elements.
The liquid desiccant is collected at the bottom of the wavy plates at 111 and is transported through a heat exchanger 113 to the top of the regenerator 102 to point 115 where the liquid desiccant is distributed across the wavy plates of the regenerator. Return air or optionally outside air 105 is blown across the regenerator plate and water vapor is transported from the liquid desiccant into the leaving air stream 106. An optional heat source 108 provides the driving force for the regeneration. The hot transfer fluid 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 that also on 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 thus pumping heat from the cooling fluids rather than the desiccant.
Besides the compressor 402, the outdoor components comprise a condenser coil 403 and a condenser fan 417. The fan 417 blows outside air 415 through the condenser coil 403 where it picks up heat from the compressor 402 which is rejected by air stream 416. The compressor 402 creates hot compressed refrigerant in line 411. The heat of compression is rejected in the condenser coil 403. In some instances the system can have multiple compressors or multiple condenser coils and fans. The primary electrical energy consuming components are the compressor through electrical line 413, the condenser fan electrical motor through supply line 414 and the evaporator fan motor through line 405. 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.
The liquid desiccant 528 leaves the conditioner 503 and is moved through the optional heat exchanger 526 to the regenerator 522 by pump 525. If the desiccant lines 527 and 528 are relatively long they can be thermally connected to each other, which eliminates the need for heat exchanger 526.
The chiller system 530 comprises a water to refrigerant evaporator heat exchanger 507 which cools the circulating cooling fluid 506. The liquid, cold refrigerant 517 evaporates in the heat exchanger 507 thereby absorbing the thermal energy from the cooling fluid 506. The gaseous refrigerant 510 is now re-compressed by compressor 511. The compressor 511 ejects hot refrigerant gas 513, which is liquefied in the condenser heat exchanger 515. The liquid refrigerant 514 then enters expansion valve 516, where it rapidly cools and exits at a lower pressure. It is worth noting that the chiller system 530 can be made very compact since the high pressure lines with refrigerant (510, 513, 514 and 517) 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 by way of example, CO2, Ammonia and Propane. These refrigerants are sometimes preferable over the commonly used R410A, R407A, R134A or R1234YF refrigerants, but they are undesirable indoor because of flammability or suffocation or inhaling risks. By keeping all of the refrigerants outside, these risks are essentially eliminated. The condenser heat exchanger 515 now releases heat to another cooling fluid loop 519 which brings hot heat transfer fluid 518 to the regenerator 522. Circulating pump 520 brings the heat transfer fluid back to the condenser 515. The 3-way regenerator 522 thus receives a dilute liquid desiccant 528 and hot heat transfer fluid 518. A fan 524 brings outside air 523 (“OA”) through the regenerator 522. The outside air picks up heat and moisture from the heat transfer fluid 518 and desiccant 528 which results in hot humid exhaust air (“EA”) 521.
The compressor 511 receives electrical power 512 and typically accounts for 80% of electrical power consumption of the system. The fan 502 and fan 524 also receive electrical power 505 and 529 respectively and account for most of the remaining power consumption. Pumps 508, 520 and 525 have relatively low power consumption. The compressor 511 will operate more efficiently than the compressor 402 in
As in
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.
Claims
1. A split liquid desiccant air conditioning system for treating an air stream flowing into a space in a building, said split liquid desiccant air-conditioning system being switchable between operating in a warm weather operation mode and a cold weather operation mode, the split liquid desiccant air conditioning system comprising:
- a conditioner located inside the building, said conditioner including a plurality of structures arranged in a substantially vertical orientation, each structure having at least one surface across which a liquid desiccant can flow, each structure also including a passage through which a heat transfer fluid can flow, wherein the air stream to be treated flows between the structures such that the liquid desiccant dehumidifies and cools the air stream in the warm weather operation mode and humidifies and heats the air stream in the cold weather operation mode, the conditioner further comprising a sheet of material positioned proximate to the at least one surface of each structure between the liquid desiccant and the air stream, said sheet of material permitting transfer of water vapor between the liquid desiccant and the air stream;
- a regenerator located outside the building connected to the conditioner by liquid desiccant pipes for exchanging liquid desiccant with the conditioner, said regenerator including a plurality of structures arranged in a substantially vertical orientation, each structure having at least one surface across which the liquid desiccant can flow, each structure also including a passage through which a heat transfer fluid can flow, said regenerator causing the liquid desiccant to desorb water in the warm weather operation mode and to absorb water in the cold weather operation mode to or from an air stream flowing through the regenerator;
- a reversible heat pump located outside the building coupled to the conditioner and to the regenerator by heat transfer fluid pipes, wherein the heat pump pumps heat from the heat transfer fluid flowing in the conditioner to the heat transfer fluid flowing in the regenerator in the warm weather operation mode, and wherein the heat pump pumps heat from the heat transfer fluid flowing in the regenerator to the heat transfer fluid flowing in the conditioner in the cold weather operation mode;
- an apparatus for moving the air stream through the conditioner;
- an apparatus for circulating the liquid desiccant through the conditioner and regenerator; and
- an apparatus for circulating heat transfer fluid through the conditioner and the reversible heat pump; and
- an apparatus for circulating heat transfer fluid through the regenerator and the reversible heat pump.
2. The system of claim 1, wherein the reversible heat pump comprises a refrigerant evaporator heat exchanger.
3. The system of claim 1, wherein the liquid desiccant pipes comprise a first pipe for transferring liquid desiccant from the conditioner to the regenerator and a second pipe for transferring liquid desiccant from the regenerator to the conditioner, wherein the first and second pipes are in close thermal contact to facilitate heat transfer from the liquid desiccant flowing in one of the first and second pipes to the liquid desiccant flowing in the other of the first and second pipes.
4. The system of claim 3, wherein the first and second pipes comprise an integrally formed structure.
5. The system of claim 4, wherein the integrally formed structure comprises a polymer material.
6. The system of claim 5, wherein at least a wall of the structure between the first and second pipes comprises a thermally conductive polymer.
7. The system of claim 1, wherein the conditioner is mounted on a wall inside the building.
8. The system of claim 1, wherein the conditioner has a generally flat configuration adapted to be hidden behind a computer display, television, or painting.
9. The system of claim 1, further comprising one or more additional conditioners in the building, each coupled to the regenerator and the heat pump.
10. A split liquid desiccant air conditioning system for cooling and dehumidifying an air stream flowing into a space in a building, the split liquid desiccant air conditioning system comprising:
- a conditioner located inside the building, said conditioner including a plurality of first structures arranged in a substantially vertical orientation, each structure having at least one surface across which a liquid desiccant can flow, each structure also including a passage through which a heat transfer fluid can flow, wherein the air stream flows between the structures such that the liquid desiccant dehumidifies and cools the air stream, the conditioner further comprising a sheet of material positioned proximate to the at least one surface of each structure between the liquid desiccant and the air stream, said sheet of material permitting transfer of water vapor between the liquid desiccant and the air stream;
- a regenerator located outside the building connected to the conditioner by liquid desiccant pipes for exchanging liquid desiccant with the conditioner, said regenerator including a plurality of second structures arranged in a substantially vertical orientation, each structure having at least one surface across which the liquid desiccant can flow, each structure also including a passage through which a heat transfer fluid can flow, said regenerator causing the liquid desiccant to desorb water to an air stream flowing through the regenerator;
- an indirect evaporative cooling unit coupled to the conditioner for receiving the heat transfer fluid that has flowed through the first structures and a portion of the air stream that has been dehumidified and cooled by the conditioner, said indirect evaporative cooling unit including a plurality of third structures arranged in a substantially vertical orientation, each structure having at least one surface across which water is flowed, each structure also including a passage through which the heat transfer fluid from the conditioner is flowed, wherein the portion of the air stream received from the conditioner flows between the structures such that the water is evaporated by the air stream, resulting in cooling of the heat transfer fluid which is returned to the conditioner, and wherein the air stream treated by the indirect evaporative cooling unit is exhausted to the atmosphere;
- an apparatus for moving the air stream through the conditioner and the indirect evaporative cooling unit;
- an apparatus for circulating the liquid desiccant through the conditioner and regenerator; and
- an apparatus for circulating heat transfer fluid through the conditioner and the indirect evaporative cooling unit; and
- a heat source for heating the heat transfer fluid in the regenerator.
11. The system of claim 10, wherein the liquid desiccant pipes comprise a first pipe for transferring liquid desiccant from the conditioner to the regenerator and a second pipe for transferring liquid desiccant from the regenerator to the conditioner, wherein the first and second pipes are in close contact to facilitate heat transfer from the liquid desiccant flowing in one of the first and second pipes to the liquid desiccant flowing in the other of the first and second pipes.
12. The system of claim 11, wherein the first and second pipes comprise an integrally formed structure.
13. The system of claim 12, wherein the integrally formed structure comprises a polymer material.
14. The system of claim 13, wherein at least a wall of the structure between the first and second pipes comprises a thermally conductive polymer.
15. The system of claim 10, wherein the conditioner is mounted on a wall inside the building.
16. The system of claim 10, wherein the conditioner has a generally flat configuration adapted to be hidden behind a computer display, television, or painting.
17. The system of claim 10, wherein the indirect evaporative cooling unit is located inside the building.
18. The system of claim 10, wherein the indirect evaporative cooling unit is located outside the building.
19. The system of claim 10, wherein the heat source for heating the heat transfer fluid in the regenerator comprises a gas water heater, a solar module, a solar thermal/photovoltaic module, or a steam loop.
20. A split liquid desiccant air conditioning system for heating and humidifying an air stream flowing into a space in a building, the split liquid desiccant air conditioning system comprising:
- a conditioner located inside the building, said conditioner including a plurality of first structures arranged in a substantially vertical orientation, each structure having at least one surface across which a liquid desiccant can flow, each structure also including a passage through which a heat transfer fluid can flow, wherein the air stream flows between the structures such that the liquid desiccant humidifies and heats the air stream, the conditioner further comprising a sheet of material positioned proximate to the at least one surface of each structure between the liquid desiccant and the air stream, said sheet of material permitting transfer of water vapor between the liquid desiccant and the air stream;
- a regenerator located outside the building connected to the conditioner by liquid desiccant pipes for exchanging liquid desiccant with the conditioner, said regenerator including a plurality of second structures arranged in a substantially vertical orientation, each structure having at least one surface across which the liquid desiccant can flow, each structure also including a passage through which a heat transfer fluid can flow, said regenerator causing the liquid desiccant to absorb water from an air stream flowing through the regenerator;
- an indirect evaporative cooling unit coupled to the conditioner for receiving the heat transfer fluid that has flowed through the first structures and a portion of the air stream that has been humidified and heated by the conditioner, said indirect evaporative cooling unit including a plurality of third structures arranged in a substantially vertical orientation, each structure having at least one surface across which water is flowed, each structure also including a passage through which the heat transfer fluid from the conditioner is flowed, wherein the portion of the air stream received from the conditioner flows between the structures such that the water vapor is evaporated from the water, resulting in humidification of the air stream, and wherein the air stream treated by the indirect evaporative cooling unit is exhausted inside the building;
- an apparatus for moving the air stream through the conditioner and the indirect evaporative cooling unit;
- an apparatus for circulating the liquid desiccant through the conditioner and regenerator; and
- an apparatus for circulating heat transfer fluid through the conditioner and the indirect evaporative cooling unit; and
- a heat source for heating the heat transfer fluid in the conditioner and the indirect evaporative cooling unit.
21. The system of claim 20, wherein the liquid desiccant pipes comprise a first pipe for transferring liquid desiccant from the conditioner to the regenerator and a second pipe for transferring liquid desiccant from the regenerator to the conditioner, wherein the first and second pipes are in close contact to facilitate heat transfer from the liquid desiccant flowing in one of the first and second pipes to the liquid desiccant flowing in the other of the first and second pipes.
22. The system of claim 21, wherein the first and second pipes comprise an integrally formed structure.
23. The system of claim 22, wherein the integrally formed structure comprises a polymer material.
24. The system of claim 23, wherein at least a wall of the structure between the first and second pipes comprises a thermally conductive polymer.
25. The system of claim 20, wherein the conditioner is mounted on a wall inside the building.
26. The system of claim 20, wherein the conditioner has a generally flat configuration adapted to be hidden behind a computer display, television, or painting.
27. The system of claim 20, wherein the indirect evaporative cooling unit is located inside the building.
28. The system of claim 20, wherein the indirect evaporative cooling unit is located outside the building.
29. The system of claim 20, wherein the heat source for heating the heat transfer fluid in the conditioner and the indirect evaporative cooling unit comprises a gas water heater, a solar module, a solar thermal/photovoltaic module, or a steam loop.
Type: Application
Filed: Mar 14, 2014
Publication Date: Sep 18, 2014
Applicant: 7AC Technologies, Inc. (Beverly, MA)
Inventor: Peter F. Vandermeulen (Newburyport, MA)
Application Number: 14/212,097
International Classification: F24F 3/14 (20060101);