INDIRECT EVAPORATIVE COOLER USING MEMBRANE-CONTAINED, LIQUID DESICCANT FOR DEHUMIDIFICATION

• US 20100319370A1
• Filed: 01/25/2008
• Published: 12/23/2010
• Est. Priority Date: 01/25/2008
• Status: Active Grant

• Current Assignee: Alliance For Sustainable Energy LLC
• Original Assignee: Alliance For Sustainable Energy LLC
• Inventors: Kozubal, Eric Joseph, Slayzak, Steven Joseph
• Granted Patent: US 8,769,971 B2
• Time in Patent Office: Days
• US Class Current: 62/92
• CPC Class Codes: F24F 1/0007 Indoor units, e.g. fan coil units self-contained units F24F1/02
• CPC Class Codes: F24F 1/0063 by the mounting or arrangement of the heat exchangers
• CPC Class Codes: F24F 13/30 Arrangement or mounting of heat-exchangers
• CPC Class Codes: F24F 2003/1435 comprising semi-permeable membrane
• CPC Class Codes: F24F 2003/1458 using regenerators
• CPC Class Codes: F24F 3/1411 by absorbing or adsorbing water, e.g. using an hygroscopic desiccant
• CPC Class Codes: F24F 3/1417 with liquid hygroscopic desiccants
• CPC Class Codes: F24F 3/147 with both heat and humidity transfer between supplied and exhausted air
• CPC Class Codes: F24F 5/0035 using evaporation
• CPC Class Codes: F28D 15/02 in which the medium condenses and evaporates, e.g. heat pipes heat pipes used in solar heat collectors F24S10/95; in radiators F28D1/0226; in nuclear reactors G21C15/257
• CPC Class Codes: F28D 21/0015 Heat and mass exchangers, e.g. with permeable walls
• CPC Class Codes: Y02B 30/54 Free-cooling systems

Abstract

An indirect evaporative cooler for cooling inlet supply air from a first temperature to a second, lower temperature using a stream of liquid coolant and a stream of exhaust or purge air. The cooler includes a first flow channel for inlet supply air and a second flow channel adjacent the first for exhaust air. The first and second flow channels are defined in part by sheets of a membrane permeable to water vapor such that mass is transferred as a vapor through the membrane from the inlet supply air to a contained liquid desiccant for dehumidification and also to the exhaust air as heat is transferred from the inlet supply air to the liquid coolant. A separation wall divides the liquid desiccant and the coolant but allows heat to be transferred from the supply air to the coolant which releases water vapor to the counter or cross flowing exhaust air.

Claims

1. An indirect evaporative cooler for cooling a stream of inlet supply air from a first temperature to a second, lower temperature using a stream of liquid coolant and a stream of exhaust or purge air, comprising:

a first flow channel for receiving the stream of inlet supply air; and

a second flow channel adjacent to the first flow channel and for receiving the stream of exhaust air at a temperature lower than the first temperature;

wherein the second flow channel is defined in part by a sheet of a membrane at least partially permeable to water vapor and wherein the stream of liquid coolant flows on a side of the membrane opposite the second flow channel.

2. The cooler of claim 1, wherein the liquid coolant transfers mass as vapor through the membrane to the stream of exhaust air in response to receiving heat transferred from the stream of inlet supply air in the first flow channel.

3. The cooler of claim 2, further comprising a separation wall spaced apart from the sheet of membrane defining a liquid coolant flow channel for the stream of liquid coolant, the separation wall comprising a material impermeable to the liquid coolant and conductive of the heat from the stream of inlet supply air.

4. The cooler of claim 3, further comprising a second sheet of the membrane spaced apart from separation wall on a side opposite the first sheet of the membrane, the second sheet defining in part the first flow channel and the second sheet of the membrane and the separation wall defining a desiccant flow channel for receiving a stream of liquid desiccant, and wherein water vapor is transferred from the stream of inlet supply air through the second sheet of the membrane to the stream of liquid desiccant.

5. The cooler of claim 4, wherein the membrane of the first and second sheet resists flow of the liquid coolant and the liquid desiccant through the membrane, whereby the liquid desiccant and the liquid coolant are contained from flowing into the first and second flow channels, respectively.

6. The cooler of claim 5, wherein the liquid desiccant comprises a salt solution and the liquid coolant comprises water.

7. The cooler of claim 6, wherein the liquid desiccant is a weak desiccant.

8. The cooler of claim 1, wherein the exhaust air comprises a portion of the stream of inlet supply air entering the second flow channel at about the second, lower temperature.

9. The cooler of claim 1, wherein the stream of inlet supply air flows in a first direction in the first flow channel and the stream of exhaust air flows in a second direction in the second flow channel, the second direction being in at least one of cross or counter to the second direction.

10. A mass and heat transfer assembly for use in an evaporative cooler, comprising:

a first stack comprising an upper membrane, a lower membrane, and a separation wall between the upper and lower membranes, the upper and lower membranes being permeable to water in vapor form and the separation wall being substantially impermeable to liquid and vapor;

a second stack comprising an upper membrane, a lower membrane, and a separation wall between the upper and lower membranes, the upper and lower membranes being permeable to water in vapor form and the separation wall being substantially impermeable to liquid and vapor; and

a third stack comprising an upper membrane, a lower membrane, and a separation wall between the upper and lower membranes, the upper and lower membranes being permeable to water in vapor form and the separation wall being substantially impermeable to liquid and vapor;

wherein the first stack and second stack are spaced apart to define a flow channel for receiving a first stream of air and wherein the second and third stack are spaced apart to define a flow channel for a second stream of air.

11. The assembly of claim 10, wherein the first, second, and third stacks comprise a set of stacks and wherein the assembly further comprises a two or more of the sets of stacks defining a plurality of parallel ones of the flow channels for the first stream of air and for the second stream of air.

12. The assembly of claim 10, wherein the first stream of air and the second stream of air flow in cross directions in the flow channels.

13. The assembly of claim 12, wherein the first stream of air and the second stream of air flow in counter directions in the flow channels.

14. The assembly of claim 10, further comprising a divider in the flow channel between the first and second stack and a divider in the flow channel between the second and third stack, wherein the dividers are configured to maintain a spacing of the membranes of the stacks and to allow flow of the first and second streams of air.

15. The assembly of claim 10, further comprising:

in the first stack, liquid coolant flowing between the upper membrane and the separation wall and liquid desiccant flowing between the separation wall and the lower membrane;

in the second stack, liquid desiccant flowing between the upper membrane and the separation wall and liquid coolant flowing between the separation wall and the lower membrane; and

in the third stack, liquid coolant flowing between the upper membrane and the separation wall and liquid desiccant flowing between the separation wall and the lower membrane.

16. The assembly of claim 15, wherein the liquid coolant comprises water, the liquid desiccant comprises a salt solution, and the membranes each comprise a material permeable to water molecules.

17. A method of conditioning a process air, comprising:

first directing the process air through a first flow channel;

second directing a stream of a liquid desiccant adjacent a wall of the first flow channel, the liquid desiccant being separated from the process air in the first flow channel by a membrane that contains the liquid desiccant and allows water vapor from the process air to flow into the liquid desiccant, whereby the process air is dehumidified;

concurrently with the first and second directing, third directing a stream of purge air through a second flow channel proximate to the first flow channel, the purge air being at a temperature lower than at least a portion of the process air; and

concurrently with the first, second, and third directing, fourth directing a stream of liquid coolant adjacent a wall of the second flow channel, the liquid coolant being separated from the purge air in the second flow channel by a membrane that contains the liquid coolant and allows vapor from the liquid coolant to flow into the purge air, whereby heat is released from the liquid coolant and the process air is cooled concurrent with the dehumidification.

18. The method of claim 17, wherein the stream of purge air is directed in a direction at least partially counter to a direction the process air is directed through the first flow channel.

19. The method of claim 18, wherein the stream of purge air comprises a portion of the process air after the directing through the first flow channel.

20. The method of claim 17, wherein the liquid coolant is water and the liquid desiccant is a weak desiccant comprising a salt solution and wherein the membrane contains the salt solution from flowing into the first flow channel.