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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 ex

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.

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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;a second flow channe

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;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, wherein the stream of liquid coolant flows on a side of the membrane opposite the second flow channel, and 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; anda 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. 2. The cooler of claim 1, 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. 3. The cooler of claim 2, 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. 4. The cooler of claim 3, wherein the liquid desiccant comprises a salt solution and the liquid coolant comprises water. 5. The cooler of claim 4, wherein the liquid desiccant is a weak desiccant. 6. 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. 7. 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. 8. 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; anda 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. 9. The assembly of claim 8, wherein the first, second, and third stacks comprise a set of stacks and wherein the assembly further comprises 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. 10. The assembly of claim 8, wherein the first stream of air and the second stream of air flow in cross directions in the flow channels. 11. The assembly of claim 10, wherein the first stream of air and the second stream of air flow in counter directions in the flow channels. 12. The assembly of claim 8, 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. 13. The assembly of claim 8, 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; andin 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. 14. The assembly of claim 13, wherein the liquid coolant comprises water, the liquid desiccant comprises a salt solution, and the membranes each comprise a material permeable to water molecules. 15. 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; andconcurrently 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. 16. The method of claim 15, 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. 17. The method of claim 16, wherein the stream of purge air comprises a portion of the process air after the directing through the first flow channel. 18. The method of claim 15, 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. 19. 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; anda 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,wherein the stream of liquid coolant flows on a side of the membrane opposite the second flow channel, andwherein the exhaust air comprises a portion of the stream of inlet supply air entering the second flow channel at about the second, lower temperature. 20. 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; anda 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,wherein the stream of liquid coolant flows on a side of the membrane opposite the second flow channel, andwherein 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.