Method and system to vary suction temperature to postpone frost formation

Abstract

A cooling system includes an evaporator coil and a compressor fluidly coupled to the evaporator coil. A circulation fan is arranged to direct air through the evaporator coil and through a discharge air duct into a conditioned space. At least one sensor is disposed in at least one of the discharge air duct, the conditioned space, and the evaporator coil. An HVAC controller is electrically coupled to the at least one sensor and electrically coupled to the compressor. The HVAC controller is configured to receive a measurement of an HVAC parameter from the at least one sensor, determine if the HVAC parameter indicates frost formation on the evaporator coil, and, responsive to a determination that the HV AC parameter indicates frost formation on the evaporator coil, raise a saturated suction temperature of the evaporator coil.

What is claimed is: 
     
         1 . A cooling system, comprising:
 an evaporator coil;   a compressor fluidly coupled to the evaporator coil;   a circulation fan arranged to direct air through the evaporator coil and through a discharge air duct into a conditioned space;   at least one sensor, the at least one sensor being disposed in at least one of the discharge air duct, the conditioned space, and the evaporator coil;   an HVAC controller electrically coupled to the at least one sensor and electrically coupled to the compressor;   wherein the HVAC controller is configured to:
 receive a measurement of an HVAC parameter from the at least one sensor; 
 determine if the HVAC parameter indicates frost formation on the evaporator coil; and 
 responsive to a determination that the HVAC parameter indicates frost formation on the evaporator coil, raise a saturated suction temperature of the evaporator coil. 
   
     
     
         2 . The cooling system of  claim 1 , wherein the at east one sensor is a first temperature sensor. 
     
     
         3 . The cooling system of  claim 2 , wherein the first temperature sensor is disposed at a location that is selected from a group consisting of:
 in the evaporator coil; and   on an exterior surface of the evaporator coil.   
     
     
         4 . The cooling system of  claim 3 , wherein the HVAC parameter is at least one of:
 the saturated suction temperature of the evaporator coil; and   a surface temperature of the evaporator coil.   
     
     
         5 . The cooling system of  claim 1 , wherein the at least one sensor is at east one of:
 a second temperature sensor disposed in the conditioned space; and   a flow meter disposed in the discharge air duct.   
     
     
         6 . The cooling system of  claim 5 , wherein the HVAC parameter is at least one of:
 a discharge air temperature measured by the second temperature sensor; and   a discharge air velocity measured by the flow meter.   
     
     
         7 . The cooling system of  claim 1 , comprising an evaporator pressure regulator (“EPR”) fluidly coupled between the evaporator coil and the compressor, the EPR being electrically coupled to the HVAC controller. 
     
     
         8 . The cooling system of  claim 7 , wherein, responsive to the determination that the HVAC parameter indicates frost formation on the evaporator coil, the HVAC controller is configured to signal the EPR to reduce flow of a refrigerant from the evaporator coil to the compressor thereby raising the saturated suction temperature of the evaporator coil. 
     
     
         9 . The cooling system of  claim 1 , wherein, responsive to the determination that the HVAC parameter indicates frost formation on the evaporator coil, the HVAC controller is configured to signal the compressor to modulate a speed of the compressor thereby raising the saturated suction temperature of the evaporator coil. 
     
     
         10 . The cooling system of  claim 9 , wherein the HVAC controller is configured to at least one of:
 reduce the speed of the compressor; and   cycle the compressor between an activated state and a deactivated state.   
     
     
         11 . A method for operating a refrigerated display case, the method comprising:
 measuring, by at least one sensor, an HVAC parameter;   determining, by an HVAC controller electrically coupled to the at least one sensor, if the HVAC parameter indicates frost formation on an evaporator coil; and   responsive to a determination that the  1 -IVAC parameter indicates frost formation on the evaporator coil, signaling, by the HVAC controller, an evaporator pressure regulator (“EPR”) to reduce a flow of refrigerant from an evaporator coil to a compressor thereby raising a saturated suction temperature of the evaporator coil.   
     
     
         12 . The method of  claim 11 , wherein:
 the at least one sensor is a first temperature sensor disposed proximate the evaporator coil; and   the HVAC parameter is at least one of the saturated suction temperature of the evaporator coil and a surface temperature of the evaporator coil.   
     
     
         13 . The method of  claim 11 , wherein:
 the at least one sensor is a second temperature sensor disposed in a conditioned space; and   the HVAC parameter is a discharge air temperature.   
     
     
         14 . The method of  claim 11 , wherein:
 the at least one sensor is a flow meter; and   the HVAC parameter is a discharge air velocity.   
     
     
         15 . A method for operating a refrigerated display case, the method comprising:
 measuring, by at least one sensor, an HVAC parameter;   determining, by an HV AC controller electrically coupled to the at least one sensor, if the HVAC parameter indicates frost formation on an evaporator coil; and   responsive to a determination that the HVAC parameter indicates frost formation on the evaporator coil, signaling, by the HVAC controller, a compressor to modulate a speed of the compressor thereby raising a saturated suction temperature of the evaporator coil.   
     
     
         16 . The method of  claim 15 , wherein:
 the at least one sensor is a first temperature sensor disposed proximate the evaporator coil; and   the HVAC parameter is at least one of the saturated suction temperature of the evaporator coil and a surface temperature of the evaporator coil.   
     
     
         17 . The method of  claim 15 , wherein:
 the at least one sensor is a second temperature sensor disposed in a conditioned space; and   the HVAC parameter is a discharge air temperature.   
     
     
         18 . The method of  claim 15 , wherein:
 the at least one sensor is a flow meter; and   the HVAC parameter is a discharge air velocity.   
     
     
         19 . The method of  claim 15 , wherein responsive to the signaling the speed of the HVAC controller is reduced. 
     
     
         70 . The method of  claim 15 , wherein, responsive to the signaling, the compressor is cycled between an activated state and a deactivated state.