Dehumidification control in refrigerant vapor compression systems

Abstract

A method and apparatus are disclosed for controlling dehumidification of an airflow to be conditioned for supply to a climate controlled space. The airflow to be conditioned is passed over a plurality of refrigerant conveying conduits of an evaporator of a refrigerant vapor compression thereby cooling the airflow. A controller operates the refrigeration vapor compression system to maintain the airflow at a set point air temperature indicative of a desired temperature within the climate controlled space. The controller also adjusts an evaporator expansion device for controlling the flow of refrigerant through the evaporator so as to reduce the temperature of the refrigerant within the refrigerant conveying conduits of the evaporator whenever further dehumidification of the air flow to be conditioned is desired.

1 . A method for controlling dehumidification of an airflow to be conditioned for supply to a climate controlled space, said method comprising the steps of:
 passing the airflow to be conditioned over a plurality of refrigerant conveying conduits of an evaporator of a refrigerant vapor compression system thereby cooling the airflow;   operating the refrigeration vapor compression system to maintain the airflow at a set point air temperature indicative of a desired temperature within the climate controlled space; and   adjusting the evaporator expansion device so as to reduce the temperature of the refrigerant within the refrigerant conveying conduits of the evaporator whenever further dehumidification of the air flow to be conditioned is desired.   
     
     
         2 . A method as recited in  claim 1  wherein the step of operating the refrigerant vapor compression system to maintain said airflow at a set point air temperature indicative of a desired temperature within the climate controlled space includes the step of reheating said airflow having passed over the plurality of refrigerant conveying conduits of the evaporator prior to supplying said airflow to the climate controlled space. 
     
     
         3 . The method as recited in  claim 1  wherein the set point air temperature comprises a temperature in the range from a preselected air temperature minus a preselected tolerance to the preselected air temperature plus the preselected tolerance, inclusive of the end point air temperatures. 
     
     
         4 . The method as recited in  claim 1  wherein the step of adjusting the evaporator expansion device so as to reduce the temperature of the refrigerant within the refrigerant conveying conduits of the evaporator is implemented if a sensed relative humidity reflective of the relative humidity within the climate controlled space exceeds a desired set point relative humidity. 
     
     
         5 . The method as recited in  claim 4  wherein the set point relative humidity comprises a relative humidity in the range from a preselected relative humidity minus a preselected tolerance to the preselected relative humidity plus the preselected tolerance, inclusive of the end point relative humidities. 
     
     
         6 . The method as recited in  claim 1  wherein the expansion device comprises an expansion device having a selectively flow area opening therethrough. 
     
     
         7 . The method as recited in  claim 1  wherein the expansion device is an electronic expansion valve (EXV). 
     
     
         8 . The method as recited in  claim 6  wherein the step of adjusting the expansion device so as to reduce the temperature of the refrigerant within the refrigerant conveying conduits of the evaporator comprises reducing a refrigerant flow area through the expansion device. 
     
     
         9 . The method as recited in  claim 6  wherein the step of adjusting the expansion device so as to reduce the temperature of the refrigerant within the refrigerant conveying conduits of the evaporator comprises increasing a pressure drop in the refrigerant passing through the expansion device. 
     
     
         10 . The method as recited in  claim 6  wherein the step of adjusting the expansion device so as to reduce the temperature of the refrigerant within the refrigerant conveying conduits of the evaporator comprises decreasing a flow rate of refrigerant passing through the expansion device. 
     
     
         11 . The method as recited in  claim 7  wherein the step of adjusting the expansion device so as to reduce the temperature of the refrigerant within the refrigerant conveying conduits of the evaporator comprises setting a superheat setting of the expansion device to a maximum superheat setting. 
     
     
         12 . A method for controlling dehumidification of air within a climate controlled space, said method comprising the steps of:
 drawing a flow of air from the climate controlled space;   passing said airflow over a plurality of refrigerant conveying conduits of an evaporator of a refrigerant vapor compression system having a compression device, a refrigerant heat rejection heat exchanger, an expansion device and the evaporator arranged in series refrigerant flow relationship in accordance with a refrigerant vapor compression cycle, thereby cooling said airflow;   adjusting a superheat level of the expansion device so as to further reduce the temperature of the refrigerant within the refrigerant conveying conduits of the evaporator thereby increasing condensation of moisture from said airflow; and   reheating said airflow having passed over the plurality of refrigerant conveying conduits of the evaporator prior to supplying said airflow to the climate controlled space.   
     
     
         13 . The method as recited in  claim 12  wherein the step of adjusting a superheat level the expansion device so as to further reduce the temperature of the refrigerant within the refrigerant conveying conduits of the evaporator comprises setting the superheat setting of the expansion device to a maximum superheat setting. 
     
     
         14 . The method as recited in  claim 13  wherein the step of adjusting a superheat level the expansion device so as to further reduce the temperature of the refrigerant within the refrigerant conveying conduits of the evaporator further comprises the steps of:
 sensing a relative humidity of said airflow prior to passing said airflow over a plurality of refrigerant conveying conduits of the evaporator; 
 comparing the sensed relative humidity of said airflow to a set point relative humidity of a desired temperature to be maintained within the climate controlled space; and 
 maintaining the superheat level of the expansion device at the maximum superheat setting so long as the sensed relative humidity of said airflow exceeds said set point relative humidity. 
 
     
     
         15 . The method as recited in  claim 14  wherein the set point relative humidity comprises a relative humidity in the range from a preselected relative humidity minus a preselected tolerance to the preselected relative humidity plus the preselected tolerance, inclusive of the end point relative humidities. 
     
     
         16 . A method as recited in  claim 12  wherein the step of reheating said airflow having passed over a plurality of refrigerant conveying conduits of the evaporator prior to supplying said airflow to the climate controlled space includes the steps of:
 sensing a temperature of said airflow having passed over a plurality of refrigerant conveying conduits of the evaporator; 
 comparing the sensed temperature of said airflow to a set point temperature indicative of a desired temperature to be maintained within the climate controlled space; and 
 reheating said airflow to the set point temperature prior to supplying the airflow to the climate controlled space. 
 
     
     
         17 . The method as recited in  claim 16  wherein the step of reheating said airflow to the set point temperature comprises reheating said airflow to a temperature in the range from a preselected air temperature minus a preselected tolerance to the preselected air temperature plus the preselected tolerance, inclusive of the end point air temperatures of the range. 
     
     
         18 . A method as recited in  claim 12  further comprising the steps of:
 providing a variable speed fan for drawing a flow of air from the climate controlled space and passing said airflow over a plurality of refrigerant conveying conduits of an evaporator; and 
 operating said variable speed fan in a low speed mode during dehumidification of said airflow. 
 
     
     
         19 . A method as recited in  claim 12  further comprising the step of bypassing a portion of said airflow around the evaporator whereby the bypass portion does not pass in heat exchange relationship with the refrigerant flowing through the refrigerant conveying conduits of the evaporator. 
     
     
         20 . A method as recited in  claim 12  further comprising the steps of:
 providing the evaporator with a first set and second set of independent refrigerant conveying conduits; and 
 selectively closing one of the first set and the second set of refrigerant convening conduits to enhance dehumidification. 
 
     
     
         21 . An apparatus for supplying conditioned air to a climate controlled space comprising:
 a refrigerant vapor compression system including a compression device, a refrigerant heat rejection heat exchanger, an electronic expansion valve, and an evaporator heat exchanger arranged in series refrigerant flow relationship in accordance with a refrigerant vapor compression cycle;   an evaporator fan for passing a flow of air to be conditioned over a plurality of refrigerant conveying conduits of the evaporator heat exchanger in heat exchange relationship with the refrigerant thereby cooling the airflow flow of air to be conditioned; and   a controller operatively associated with the refrigerant vapor compression system, said controller configured to operate the refrigeration vapor compression system to maintain the airflow at a set point air temperature indicative of a desired temperature within the climate controlled space, and to adjust the electronic expansion valve so as to reduce the temperature of the refrigerant within the refrigerant conveying conduits of the evaporator whenever further dehumidification of the air flow to be conditioned is desired.   
     
     
         22 . The apparatus as recited in  claim 21  wherein the controller adjusts a superheat setting of the electronic expansion valve to a maximum superheat setting so as to reduce the temperature of the refrigerant within the refrigerant conveying conduits of the evaporator whenever further dehumidification of the air flow to be conditioned is desired.