Evaporator heat exchanger for preventing ice build-up

Abstract

A system includes a compressor for increasing the pressure of a refrigerant; a condenser heat exchanger arranged downstream of the compressor for receiving a high pressure refrigerant output from the compressor and for transferring heat from the high pressure refrigerant to a source of water; an expansion device for reducing the pressure of a refrigerant; and an evaporator heat exchanger for extracting heat from ambient air. The evaporator heat exchanger includes a first tube bank having a first inlet arranged to receive a high pressure refrigerant output from the condenser and a first outlet fluidly coupled to the expansion device; and a second tube bank having a second inlet arranged to receive a low pressure refrigerant output from the expansion device, and a second outlet fluidly coupled to an inlet of the compressor.

What is claimed is: 
     
         1 . An air-to-water heat pump system comprising:
 a compressor for increasing the pressure of a refrigerant;   a condenser heat exchanger arranged downstream of the compressor for receiving a high pressure refrigerant output from the compressor and for transferring heat from the high pressure refrigerant to a source of water;   an expansion device for reducing the pressure of a refrigerant; and   an evaporator heat exchanger for extracting heat from ambient air, the evaporator heat exchanger comprising:   a first tube bank having a first inlet arranged to receive a high pressure refrigerant output from the condenser, and a first outlet fluidly coupled to the expansion device; and   a second tube bank having a second inlet arranged to receive a low pressure refrigerant output from the expansion device, and a second outlet fluidly coupled to an inlet of the compressor;   wherein the first and second tube banks are arranged in close proximity to one another such that, in use, heat from the high pressure refrigerant passing through the first tube bank is transferred to the second tube bank in order to limit and/or prevent ice build-up on an external surface of the second tube bank.   
     
     
         2 . The air-to-water heat pump system as claimed in  claim 1 , wherein a gap exists between the first and second tube banks, the gap being 1 mm or less in size, preferably 0.5 mm or less in size. 
     
     
         3 . The air-to-water heat pump system as claimed in  claim 1 , wherein the first tube bank is arranged in a heat exchange relationship with ambient air such that, in use, heat is transferred from the high pressure refrigerant to the ambient air, thereby cooling the high pressure refrigerant and warming the ambient air; and/or
 wherein the second tube bank is arranged in a heat exchange relationship with ambient air such that, in use, heat is transferred from the ambient air to the low pressure refrigerant, thereby warming the low pressure refrigerant and cooling the ambient air.   
     
     
         4 . The air-to-water heat pump system as claimed in  claim 1 , wherein the first and/or second tube bank comprises one or more rows arranged in parallel with one another and fluidly coupled to one another in series. 
     
     
         5 . The air-to-water heat pump system as claimed in  claim 5 , wherein each row of the first and/or second tube bank comprises a plurality of first and/or second tubes connected in series with one another, optionally wherein the plurality of first and/or second tubes are arranged in a serpentine or coil shape. 
     
     
         6 . The air-to-water heat pump system as claimed in  claim 1 , wherein the first and/or second tube banks comprise a plurality of refrigerant circuits. 
     
     
         7 . The air-to-water heat pump system as claimed in  claim 1 , wherein the first tube bank comprises a first plurality of fins and the second tube bank comprises a second plurality of fins, the first plurality of fins and the second plurality of fins being in close proximity to one another. 
     
     
         8 . The air-to-water heat pump system as claimed in  claim 1 , wherein the system is configured such that the freeze limit of the system is less than or equal to 10° C., preferably less than or equal to 7° C., the freeze limit being the minimum ambient temperature at which ice will not form on the heat exchanger. 
     
     
         9 . The air-to-water heat pump system as claimed in  claim 1 , wherein the system is configured such that, in use, the temperature of the external surface of the first tube bank is at least 10° C. higher than the temperature of the external surface of the second tube bank. 
     
     
         10 . The air-to-water heat pump system as claimed in  claim 1 , comprising a fan arranged to create a flow of air over the evaporator heat exchanger, preferably wherein the fan is configured to flow air over the first tube bank before the air flows over the second tube bank. 
     
     
         11 . A method of preventing and/or limiting the build-up of ice on an evaporator heat exchanger in situ in an air-to-water heat pump, the method comprising:
 passing a high pressure refrigerant through a first tube bank of the evaporator heat exchanger in order to cool the high pressure refrigerant though heat exchange between the high pressure refrigerant and ambient air;   reducing the pressure of the cooled high pressure refrigerant, so as to provide a low pressure refrigerant; and   passing the low pressure refrigerant through a second tube bank of the evaporator heat exchanger in order to warm the low pressure refrigerant through heat exchange between the low pressure refrigerant and ambient air;   wherein the first and second tube banks are arranged in close proximity to one another such that heat from the high pressure refrigerant passing through the first tube bank is transferred to the second tube bank in order to heat at least a portion of an external surface of the second tube bank, thereby limiting and/or preventing ice from building up on the external surface of the second tube bank.   
     
     
         12 . The method as claimed in  claim 11  comprising:
 increasing the pressure of the refrigerant with a compressor, thereby providing the high pressure refrigerant, before passing the refrigerant to a condenser heat exchanger; and 
 prior to passing the refrigerant to the first tube bank, using the condenser heat exchanger to cool the high pressure refrigerant through heat exchange between the high pressure refrigerant and a water source, thereby warming the water source. 
 
     
     
         13 . The method as claimed in  claim 12 , drawing air over the first and second tube banks, preferably wherein the air is drawn over the first tube bank before flowing over the second tube bank. 
     
     
         14 . The method as claimed in  claim 12 , wherein the refrigerant is R-32 refrigerant or propane. 
     
     
         15 . A method of manufacturing an air-to-water heat pump system, comprising connecting, in series:
 a compressor for increasing the pressure of a refrigerant,   a condenser heat exchanger for receiving a high pressure refrigerant output from the compressor and for transferring heat from the high pressure refrigerant to a source of water,   a first tube bank of an evaporator heat exchanger, the evaporator heat exchanger being for extracting heat from ambient air,   an expansion device for reducing the pressure of a refrigerant received from the first tube bank of the evaporator heat exchanger, and   a second tube bank of the evaporator heat exchanger,   wherein the first and second tube banks of the evaporator heat exchanger are arranged in close proximity to one another such that, in use, heat from a high pressure refrigerant passing through the first tube bank will be transferred to the second tube bank in order to limit and/or prevent ice build-up on an external surface of the second tube bank.