Systems and methods for air dehumidification in an enclosed space

Abstract

Systems and methods for providing dehumidification to an enclosed space can include a dehumidification unit in a supply air plenum that receives return air and a regeneration unit in a scavenger air plenum that receives outdoor air. The system can operate in a wet mode and a dry mode, depending on outdoor air conditions and a relative humidity setpoint for the enclosed space. The dehumidification unit and regeneration unit are both operational in the wet mode to dehumidify the return air and regenerate dilute desiccant. In the dry mode, the dehumidification unit and regeneration unit are not needed, and dry outdoor air can be supplied to the enclosed space. A heat recovery system utilizes waste heat from either return air or scavenger air, depending on the operating mode, to heat the outdoor air before it is supplied to the enclosed space or before it is used for regenerating desiccant.

What is claimed is: 
     
         1 . A system for dehumidifying an enclosed space, the system comprising:
 a supply plenum configured to direct return air from the enclosed space through the supply plenum from a return air inlet to a supply air outlet;   a scavenger plenum configured to direct outdoor air through the scavenger plenum from an outdoor air inlet to an exhaust air outlet;   a dehumidification liquid-to-air membrane energy exchanger (LAMEE) arranged in the supply plenum and configured to selectively remove water vapor from the return air using a desiccant, the dehumidification LAMEE comprising a first desiccant flow path separated from an air flow path by a membrane, the dehumidification LAMEE configured to selectively circulate the desiccant through the first desiccant flow path and remove water from the return air in the air flow path;   a regeneration unit arranged in the scavenger plenum and configured to selectively concentrate a dilute desiccant from the dehumidification LAMEE using the outdoor air passing through the regeneration unit; and   a heat recovery system configured to heat the outdoor air in the scavenger plenum,   wherein the system is configured to operate in a wet mode in which the dehumidification LAMEE and regeneration unit are operational and a dry mode in which the dehumidification LAMEE and regeneration unit are off or bypassed, and selection of the mode depends on outdoor air conditions, and   wherein the heat recovery system uses either exhaust scavenger air or exhaust return air as a heat source, depending on the selected mode.   
     
     
         2 . The system of  claim 1  further comprising:
 one or more first dampers for controlling a flow of return air through the supply plenum; and 
 one or more second dampers for controlling a flow of outdoor air through the scavenger plenum. 
 
     
     
         3 . The system of  claim 2  wherein the one or more first dampers comprises:
 a dehumidifier damper configured to prevent or permit return air from flowing through the dehumidification LAMEE; and 
 a first redirect damper configured to prevent or permit return air from flowing from the supply plenum into the scavenger plenum and out the exhaust air outlet. 
 
     
     
         4 . The system of  claim 2  wherein the one or more second dampers comprises:
 a regeneration damper configured to prevent or permit outdoor air from flowing through the regeneration unit; and 
 a second redirect damper configured to prevent or permit outdoor air from flowing from the scavenger plenum into the supply plenum and out the supply air outlet. 
 
     
     
         5 . The system of  claim 1  wherein the dehumidification LAMEE is a first LAMEE and the regeneration unit is a second LAMEE. 
     
     
         6 . The system of  claim 1  wherein the regeneration unit comprises a direct or indirect contact air/liquid exchanger. 
     
     
         7 . The system of  claim 1  further comprising:
 a controller configured to operate the system in the wet mode and the dry mode, 
 wherein selection of the mode is a function of the outdoor air and a relative humidity (RH) of air in the enclosed space. 
 
     
     
         8 . The system of  claim 7  wherein the controller controls at least one of an air flow rate and a fan speed in the supply plenum to maintain the air in the enclosed space at or near a RH setpoint. 
     
     
         9 . The system of  claim 1  wherein the system is configured to operate in a blended mode in which the dehumidification unit and the regeneration unit are both operational to dehumidify the return air and regenerate the dilute desiccant, and supply air to the enclosed space is a mixture of dehumidified return air and outdoor air. 
     
     
         10 . The system of  claim 1  further comprising:
 a dehumidification tank in fluid connection with the dehumidification LAMEE; and 
 a regenerator tank in fluid connection with the regeneration unit, wherein a desiccant transfer loop is configured to transfer desiccant between the dehumidifier tank and the regenerator tank. 
 
     
     
         11 . The system of  claim 1  wherein the heat recovery system comprises a glycol run around loop comprising a first coil in the scavenger plenum upstream of the regeneration unit and a second coil in the scavenger plenum downstream of the regeneration unit. 
     
     
         12 . A system for dehumidifying an enclosed space, the system comprising:
 a return air plenum having a return air inlet and a supply air outlet, the return air plenum configured to direct air from the enclosed space in a first air flow path from the return air inlet to the supply air outlet;   a dehumidification unit arranged inside the return air plenum to selectively circulate a desiccant through the first desiccant flow path and remove water from the air in the first air flow path, a moisture content of the air at the supply air outlet being lower than a moisture content of the air at the return air inlet;   a scavenger air plenum having a scavenger air inlet and an exhaust air outlet, the scavenger air plenum configured to direct outdoor air in a second air flow path from the scavenger air inlet to the exhaust air outlet;   a regeneration unit arranged inside the scavenger air plenum to selectively circulate the desiccant through the regeneration unit and remove water from the desiccant to the air in the second air flow path, wherein a mass concentration of the desiccant at an outlet of the regeneration unit is higher than a mass concentration of the desiccant at an inlet of regeneration unit; and   a controller configured to operate the system in a plurality of operating modes based on conditions of the outdoor air and one or more setpoint parameters for air in the enclosed space, the plurality of operating modes comprising:
 a wet mode in which the dehumidification unit and the regeneration unit are both operational to dehumidify the return air and regenerate the dilute desiccant, and supply air to the enclosed space is dehumidified return air; 
 a blended mode in which the dehumidification unit and the regeneration unit are both operational to dehumidify the return air and regenerate the dilute desiccant, and supply air to the enclosed space is a mixture of dehumidified return air and outdoor air; and 
 a dry mode in which both the dehumidification unit and the regeneration unit are off or bypassed, and supply air to the enclosed space is outdoor air. 
   
     
     
         13 . The system of  claim 12  further comprising:
 a heat recovery system to heat the outdoor air in the second air flow path, wherein a heat source for the heat recovery system depends on the operating mode of the system. 
 
     
     
         14 . The system of  claim 13  wherein the heat source is hot exhaust air in the scavenger plenum downstream of the regeneration unit when the system is operating in the wet mode and the heat source is return air from the enclosed space when the system is operating in the dry mode. 
     
     
         15 . The system of  claim 13  wherein the heat recovery system is a glycol run around loop comprising a glycol circuit having a first coil in the scavenger air plenum upstream of the regeneration unit and a second coil in the scavenger air plenum downstream of the regeneration unit. 
     
     
         16 . The system of  claim 13  wherein condensate from the outdoor air in the heat recovery system is collected for water usage. 
     
     
         17 . The system of  claim 12  further comprising a plurality of dampers to control and vary the distribution of return air and outdoor air to the enclosed space as a function of the operating mode of the system. 
     
     
         18 . The system of  claim 17  wherein the plurality of dampers comprises:
 a regeneration damper in the scavenger air plenum upstream of the regeneration unit, wherein the regeneration damper is closed in the dry mode to redirect outdoor air from the scavenger air plenum to the supply air outlet. 
 
     
     
         19 . The system of  claim 18  wherein the plurality of dampers comprises:
 a first redirect damper between the scavenger air plenum and the return air plenum upstream of the regeneration unit, wherein the first redirect damper is open in the wet mode and blended mode to redirect at least a portion of outdoor air from the scavenger air plenum to the supply air outlet. 
 
     
     
         20 . The system of  claim 17  wherein the plurality of dampers comprises:
 a dehumidification damper in the supply air plenum upstream of the dehumidification unit, wherein the dehumidification damper is closed in the dry mode to redirect return air from the supply air plenum to the scavenger air outlet. 
 
     
     
         21 . The system of  claim 20  wherein the plurality of dampers comprises:
 a second redirect damper between the scavenger air plenum and the return air plenum upstream of the dehumidification unit, wherein the second redirect damper is open in the wet mode and blended mode to redirect at least a portion of return air in the supply air plenum to the scavenger air outlet. 
 
     
     
         22 . A method of providing dehumidification to an enclosed space using a dehumidification system, the method comprising:
 directing return air from the enclosed space through a supply plenum having a return air inlet and a supply air outlet;   selectively directing the return air through a dehumidification LAMEE arranged inside the supply plenum, a first moisture content of the return air being higher at an air inlet of the dehumidification LAMEE than a second moisture content of the return air at an air outlet of the dehumidification LAMEE;   selectively directing a desiccant through the dehumidification LAMEE such that the desiccant removes water vapor from the return air, a first concentration of the desiccant at a desiccant inlet of the dehumidification LAMEE being higher than a second concentration of the desiccant at a desiccant outlet of the dehumidification LAMEE;   directing outdoor air through a scavenger plenum having an outdoor air inlet and an exhaust air outlet;   selectively directing the outdoor air through a regeneration unit arranged inside the scavenger plenum, a first moisture content of the outdoor air being lower at an air inlet of the regeneration unit than a second moisture content of the outdoor air at an air outlet of the regeneration unit;   selectively directing the desiccant through the regeneration unit such that the outdoor air removes water vapor from the desiccant, a first concentration of the desiccant a desiccant inlet of the regeneration unit being lower than a second concentration of the desiccant at a desiccant outlet of the regeneration unit;   operating the dehumidification system in multiple modes, a mode is selected based on outdoor air conditions and a setpoint for air in the enclosed space;   selectively redirecting at least a portion of the return air in the supply plenum into the scavenger plenum as a function of the selected mode;   selectively redirecting at least a portion of the outdoor air in the scavenger plenum into the supply plenum as a function of the selected mode; and   heating the outdoor air in the scavenger plenum upstream of the regeneration unit using waste heat, wherein the waste heat is either exhaust scavenger air or exhaust return air, depending on the selected mode.   
     
     
         23 . The method of  claim 22  further comprising:
 controlling a flow of return air and desiccant through at least one of the supply plenum and the dehumidification LAMEE as a function of the selected mode; and 
 controlling a flow of outdoor air and desiccant through at least one of the scavenger plenum and the regeneration unit as a function of the selected mode. 
 
     
     
         24 . The method of  claim 23  wherein controlling the flow of return air and desiccant through at least one of the supply plenum and the dehumidification LAMEE includes controlling a position of one or more first dampers. 
     
     
         25 . The method of  claim 23  wherein controlling the flow of outdoor air and desiccant through at least one of the scavenger plenum and the regeneration unit includes controlling a position of one or more second dampers. 
     
     
         26 . The method of  claim 22  further comprising:
 selectively operating the regeneration unit during off-peak periods of operation of the dehumidification system to utilize dry outdoor air to regenerate the desiccant; and 
 storing concentrated desiccant in a regenerator tank. 
 
     
     
         27 . The method of  claim 22  wherein heating the outdoor air in the scavenger plenum upstream of the regeneration unit comprises:
 heating the outdoor air in the scavenger air plenum using a glycol run around loop comprising a first coil in the scavenger plenum upstream of the regeneration unit and a second coil in the scavenger plenum downstream of the regeneration unit, and glycol is configured to circulate between the first and second coils.