Vapor compression system with defrost system

Abstract

A vapor compression system including a circuit having operably coupled thereto, in serial order, a compressor, an interior heat exchanger, a second heat exchanger, an expansion device, an exterior heat exchanger, and an accumulator. A first bypass line extends from circuit between interior exchanger and second exchanger to between expansion device and third exchanger. A second bypass line extends from circuit between the exterior exchanger and accumulator to accumulator, and is operably coupled to second exchanger. A bypass expansion device is operably coupled to second bypass line. A first valve is coupled to first bypass line, and a second valve is coupled to second bypass line. During a defrost cycle first valve is in a first position wherein refrigerant flowing from interior exchanger flows to exterior exchanger through first bypass line, and second valve is in a second position wherein refrigerant flowing from exterior exchanger flows through second bypass line.

1 . A vapor compression system for use with a refrigerant to heat or cool an interior space defined by a structure, the system comprising: 
 a fluid circuit having operably coupled thereto, in serial order, a compressor, a first heat exchanger located in the interior space, a second heat exchanger, an expansion device, a third heat exchanger located exterior to the structure, and an accumulator;    a first bypass line extending from a first point in said fluid circuit between said first heat exchanger and said second heat exchanger to a second point in said fluid circuit between said expansion device and said third heat exchanger;    a second bypass line extending from a third point in said fluid circuit between said third heat exchanger and said accumulator to a fourth point in said fluid circuit between said third point and said accumulator, said second bypass line being operably coupled to said second heat exchanger;    a bypass expansion device operably coupled to said second bypass line between said third point and said second heat exchanger;    a first valve disposed in said fluid circuit between said first heat exchanger and said second heat exchanger and in communication with said first bypass line, said first valve having a first position wherein at least a substantial amount of the refrigerant flowing from said first heat exchanger flows to said third heat exchanger through said first bypass line without passing through said second heat exchanger and said expansion device thereby defrosting said third heat exchanger, and a second position wherein the refrigerant flowing from said first heat exchanger flows to said second heat exchanger though said fluid circuit without passing through said first bypass line; and    a second valve disposed between said third heat exchanger and said accumulator, said second valve having a first position restricting the flow of refrigerant from said third heat exchanger to said accumulator through said fluid circuit without flowing through said second bypass line, and a second position wherein the refrigerant flowing from said third heat exchanger flows through said second bypass line and thereby passes through said bypass expansion device and said second heat exchanger before entering said accumulator, and 
 wherein during an operating cycle said first valve is in the second position and said second valve is in the first position; and wherein during a defrost cycle said first valve is in the first position and said second valve is in the second position.  
   
   
   
       2 . The vapor compression system of  claim 1  wherein the refrigerant is carbon dioxide.  
   
   
       3 . The vapor compression system of  claim 1  wherein said first valve is a three-way valve and is disposed at said first point.  
   
   
       4 . The vapor compression system of  claim 1  wherein said second valve is a three-way valve and is disposed at said third point.  
   
   
       5 . The vapor compression system of  claim 1  wherein said first and second valves are electronically controlled valves.  
   
   
       6 . The vapor compression system of  claim 5  further comprising a controller operably coupled to said first and second valves and a sensor operably coupled to said controller, said sensor sensing the temperature of the refrigerant at a location between said third heat exchanger and said compressor in said fluid circuit and communicating said temperature to said controller, said controller switching said system from said operating cycle to said defrost cycle when said temperature falls below a pre-determined value.  
   
   
       7 . The vapor compression system of  claim 6  wherein said controller switches said first valve from the second position to the first position at initial start-up of the system.  
   
   
       8 . The vapor compression system of  claim 1  further comprising a controller operably coupled to said first and second valves and a sensor operably coupled to said controller, said sensor sensing the pressure of the refrigerant flowing from said third heat exchanger and communicating said pressure to said controller, said controller switching said system from said operating cycle to said defrost cycle when said pressure falls below a pre-determined value.  
   
   
       9 . A method for defrosting a heat exchanger of a vapor compression system, the method comprising the steps of: 
 circulating a refrigerant during an operational cycle through, in serial order, a compressor, a first heat exchanger located in an interior space defined by a structure, a second heat exchanger, an expansion device, a third heat exchanger located exterior to the structure, and an accumulator; and    circulating the refrigerant during a defrost cycle through, in serial order, the compressor, the first heat exchanger, the third heat exchanger, a bypass expansion device, the second heat exchanger, and the accumulator, 
 wherein during the defrost cycle at least a substantial amount of the refrigerant flowing from the first heat exchanger flows through a first bypass line to the third heat exchanger without passing through the second heat exchanger to thereby defrost the third heat exchanger, and wherein during the operational cycle the refrigerant flowing from the first heat exchanger bypasses the first bypass line and flows to the second heat exchanger without passing through the first bypass line.  
   
   
   
       10 . The method of  claim 9  further comprising the step of sensing the temperature of the refrigerant exiting said third heat exchanger and switching the system to the defrost cycle when the temperature of the refrigerant falls below a pre-determined value.  
   
   
       11 . The method of  claim 9  wherein during the defrost cycle the refrigerant flowing from said third heat exchanger flows through a second bypass line to the bypass expansion device and the second heat exchanger before entering the accumulator.  
   
   
       12 . The method of  claim 9  wherein the refrigerant is carbon dioxide.  
   
   
       13 . The method of  claim 9  further comprising the step of sensing the pressure of the refrigerant in said third heat exchanger and switching the system to the defrost cycle when the pressure falls below a pre-determined value.  
   
   
       14 . The method of  claim 9  further includes the step of circulating the refrigerant during a start-up cycle through, in serial order, the compressor, the first heat exchanger, the third heat exchanger, and the accumulator, wherein during the start-up at least a substantial amount of the refrigerant flowing from the first heat exchanger flows through a first bypass line to the third heat exchanger without passing through the expansion device.  
   
   
       15 . A vapor compression system for use with a refrigerant to heat or cool an interior space defined by a structure, the system comprising: 
 a fluid circuit having operably coupled thereto, in serial order, a compressor, a first heat exchanger located in the interior space, a second heat exchanger, an expansion device, a third heat exchanger located exterior to the structure, and an accumulator;    a first bypass line fluidly coupled to said fluid circuit, said first bypass line providing fluid communication between said first heat exchanger and said third heat exchanger without passing through said second heat exchanger and said expansion device;    a second bypass line fluidly coupled to said fluid circuit, said second bypass line being in thermal communication with said second heat exchanger, said second bypass line providing fluid communication between said third heat exchanger and said accumulator;    a bypass expansion device operably coupled to said second bypass line between said third heat exchanger and said second heat exchanger;    a first valve operably coupled to said first bypass line, said first valve having a first position restricting the flow of refrigerant to said second heat exchanger and communicating the refrigerant to said first bypass line, and a second position restricting the flow of the refrigerant through said first bypass line and communicating the refrigerant toward said second heat exchanger;    a second valve operably coupled to said fluid circuit between said third heat exchanger and said accumulator, said second valve having a first position restricting the flow of the refrigerant through said second bypass line and wherein the refrigerant flows to said accumulator without flowing through said bypass expansion device and said second heat exchanger, and a second position wherein the refrigerant flowing from said third heat exchanger flows through said second bypass line and thereby passes through said bypass expansion device and said second heat exchanger before entering said accumulator, and 
 wherein during an operating cycle said first valve is in the second position and said second valve is in the first position; and wherein during a defrost cycle said first valve is in the first position and said second valve is in the second position.  
   
   
   
       16 . The vapor compression system of  claim 15  wherein the refrigerant is carbon dioxide.  
   
   
       17 . The vapor compression system of  claim 15  further comprising a controller operably coupled to said first and second valves and a sensor operably coupled to said controller, said sensor sensing the temperature of said third heat exchanger and communicating said temperature to said controller, said controller switching said first valve to said first position and said second valve to said second position when said temperature falls below a pre-set level.  
   
   
       18 . The vapor compression system of  claim 15  wherein said controller switches said first valve from said second position to said first position at initial start-up of the system.  
   
   
       19 . The vapor compression system of  claim 15  further comprising a controller operably coupled to said first and second valves and a sensor operably coupled to said controller, said sensor sensing the pressure of the refrigerant in said third heat exchanger and communicating said pressure to said controller, said controller switching first valve to said first position and said second valve to said second position when said pressure falls below a pre-set level.