Abstract:
A heat pump system includes a hot gas bypass defrost mechanism which enables normal heat pump operation at low ambient air temperatures, and may be used for heating swimming pools. The bypass defrost mechanism is activated by sensing a drop in compressor suction line pressure, which occurs at low ambient temperatures when frost forms on an evaporator in the heat pump, which disrupts normal heat pump operation. The defrost mechanism includes a circuit that redirects a portion of hot refrigerant discharged by a compressor directly to the evaporator, thereby bypassing other heat pump components and defrosting the evaporator.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority of U.S. Provisional Patent Application Ser. No. 60/721,479, filed Sep. 28, 2005, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention is directed to heat pump systems. More particularly, the present invention is directed to vapor compression heat pump systems with hot gas bypass defrosting for low ambient air temperature operation.  
       BACKGROUND OF THE INVENTION  
       [0003]     The evaporator element of a vapor compression heat pump system is subject to a degradation in operating efficiency due to the frosting of the evaporator coils. Frosting occurs when the water vapor, in the ambient air surrounding the chilled evaporator, condenses on the outer surfaces of the evaporator and freezes. One method utilized to defrost the evaporator, is to reverse the heat pump cycle, wherein the evaporator becomes the condenser. Another method utilized to defrost the evaporator, is to direct a portion of the high temperature and pressure refrigerant vapor, herein referred to as hot gas, that is discharged from the compressor, directly through the evaporator, bypassing the condenser.  
         [0004]     The hot gas bypass defrost method is frequently utilized in heat pump systems which do not require a reversal of the cycle in normal operation (i.e., the heating function is not required to become a cooling function), and the hot gas bypass defrost method is often the least complex method for defrosting the evaporator in such heat pump systems. In addition, the hot gas bypass defrost method avoids cooling the heated fluid during the defrosting operation because the functioning of the condenser is never reversed to function as the evaporator.  
         [0005]     The frosting of the evaporator generally increases with decreases in the temperature of the ambient air surrounding the evaporator. Therefore, decreases in ambient air temperatures also decrease the ability of the heat pump systems to operate normally.  
         [0006]     What is needed, but has yet to be provided, is a heat pump system having a hot gas bypass defrost mechanism, which operates normally at low ambient air temperatures. This and other needs/objectives are addressed by the present invention. Additional advantageous features and functionalities of the present invention will be apparent from the disclosure which follows, particularly when reviewed in conjunction with the accompanying drawings.  
       SUMMARY OF THE INVENTION  
       [0007]     A heat pump is provided which includes a compressor, a condenser, a compressor discharge line connecting the compressor to the condenser, an expansion device, a condenser discharge line connecting the condenser to the expansion device, an evaporator, an expansion device discharge line connecting the expansion device to the evaporator, a suction line connecting the evaporator to the compressor, and a by-pass valve having an inlet, which is in fluid communication with the compressor discharge line, and an outlet, which is in fluid communication with the expansion valve discharge line. Controlling means are provided for controlling the by-pass valve so as to adjust the by-pass valve between an open position and a closed position in response to pressure in the suction line, so as to defrost the evaporator. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     For a more complete understanding of the present invention, reference is made to the following detailed description of various exemplary embodiments considered in conjunction with the accompanying drawings, in which:  
         [0009]      FIG. 1  is a schematic diagram of a heat pump, illustrating a hot gas bypass defrost circuit equipped with a capacity control discharge valve mechanism;  
         [0010]      FIG. 2  is an elevational view of the capacity control discharge valve mechanism shown schematically in  FIG. 1 ;  
         [0011]      FIG. 3  is a schematic diagram of the heat pump shown in  FIG. 1 , illustrating a hot gas bypass defrost circuit equipped with a solenoid valve mechanism;  
         [0012]      FIG. 4  is an electrical schematic of the solenoid valve mechanism shown in  FIG. 3 ;  
         [0013]      FIG. 5  is a perspective view of an exterior design for the heat pump illustrated in  FIGS. 1-4 ;  
         [0014]      FIG. 6  is a front elevational view of the heat pump shown in  FIG. 5 ;  
         [0015]      FIG. 7  is a side elevational view of the heat pump shown in  FIG. 5 ; and  
         [0016]      FIG. 8  is an exploded perspective view of the heat pump illustrated in  FIGS. 5-7 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     Tests conducted on a heat pump adapted to heat swimming pool water have demonstrated that the heat pump, operating at low ambient temperatures in the range of from about 40 degrees to about 50 degrees Fahrenheit (° F.), usually encounters frosting of the entire evaporator, which produces a reduction in the compressor suction pressure, thereby causing the heat pump compressor low-pressure switch to cease operation of the compressor. Tests have also demonstrated that, in order for the heat pump to continue to operate at low ambient air temperatures, the compressor suction pressure is required to be maintained at, or above, about 50 pounds per square inch (psi) and compressor suction temperature is required to be maintained above about 32° F.  
         [0018]     A first exemplary embodiment of the present invention is illustrated in  FIGS. 1-2 . Referring now to  FIG. 1 , a heat pump system  10  includes a refrigerant circuit  12  and a defrost circuit  14 . The refrigerant circuit  12  is constructed and operates in a manner similar to that of a conventional heat pump. The refrigerant (not shown) which flows though the heat pump  10  may be any suitable compressible refrigerant, such as carbon dioxide or a hydrocarbon refrigerant.  
         [0019]     The refrigerant circuit  12  includes in serial order and operatively coupled, a compressor  16 , a condenser  18 , an expansion device  20 , and an evaporator  22 . The compressor  16 , condenser  18 , expansion device  20 , and evaporator  22  are fluidly interconnected by a compressor discharge line  24 , a condenser discharge line  26 , an expansion device discharge line  28 , and a compressor suction line  30 . The expansion device may be a thermostatic expansion valve (TXV) or other suitable expansion device.  
         [0020]     When the heat pump  10  is operating, the refrigerant in the refrigerant circuit  12  flows continuously, and in serial order, through the compressor  16 , the compressor discharge line  24 , the condenser  18 , the condenser discharge line  26 , the expansion device  20 , the expansion device discharge line  28 , the evaporator  22 , the suction line  30 , and again through the compressor  16 . More particularly, the low pressure and temperature refrigerant vapor exiting the evaporator  22  is drawn by suction pressure into the compressor  16  where the refrigerant is compressed and discharged from the compressor  16  as hot gas, and then flows through the compressor discharge line  24  and through the condenser  18 . As the hot gas flows through the condenser  18 , thermal energy is removed from the refrigerant and transferred to a fluid, such as swimming pool water, surrounding the condenser  18 , wherein the hot gas is condensed to a liquid. The refrigerant then flows through the condenser discharge line  26  and through the expansion device  20 , which reduces the pressure of the liquid refrigerant. The refrigerant then flows through the expansion device discharge line  28  and through the evaporator  22 , wherein thermal energy is transferred from the ambient air surrounding the evaporator  22  to the evaporator  22 . The liquid refrigerant in the evaporator  22  is then evaporated into a vaporous state. The refrigerant vapor, exiting the evaporator  22 , then flows through the compressor suction line  30  and is again drawn by suction pressure into compressor  16 , where the cycle is repeated.  
         [0021]     Because thermal energy is transferred from the ambient air surrounding the evaporator  22 , water vapor in the ambient air condenses on the chilled outer surface of the evaporator  22 , forming frost. When sufficient quantities of frost are formed on the outer surface of the evaporator  22 , the heat transfer functioning of the evaporator  22  becomes impaired. The defrost circuit  14  is employed to defrost the evaporator  22  and restore the normal heat transfer functioning of the evaporator  22 . The defrost circuit  14  directs a portion of the hot gas, which is discharged from the compressor  16 , directly into the evaporator  22 , thereby bypassing the condenser  18  and the expansion device  20 . The defrost circuit  14  includes a capacity control discharge valve  32 , which will be described in greater detail below.  
         [0022]     Referring to  FIGS. 1-2 , in general, but  FIG. 2 , in particular, the capacity control discharge valve  32  has an inlet  34 , an outlet  36 , and an equalization tube connection  38 . The valve  32  may be any suitable capacity control discharge valve such as Valve Model No. ASDRSE-2-0/80 manufactured by the Sporlan Valve Company (Washington, Mo.). An inlet line  40  is in fluid communication with the discharge valve inlet  34  and the compressor discharge line  24 , for conveying hot gas to the valve  32 . An outlet line  42  is in fluid communication with the valve outlet  36  and the expansion device discharge line  28 , for conveying hot gas from the valve  32  to the expansion device discharge line  28 . An equalization tube  44  is in fluid communication with the suction line  30  and the connection  38 , for communicating the suction pressure to the valve  32 .  
         [0023]     In operation, when the evaporator  22  becomes frosted, the suction pressure at the compressor suction line  30  is reduced, it being understood that the pressure at the connection  38  is substantially the same as the pressure in the suction line  30 . When the valve  32 , which is normally closed, senses the suction line pressure at the connection  38  to be lower than a selected pressure value (e.g., 60 psi in this embodiment), the valve  32  is opened proportionately, such proportionate opening being greater for lower sensed pressures at the connection  38 . More particularly, when the discharge valve  32  is opened, a portion of the hot gas flows from the discharge line  24 , in serial order, through the inlet line  40 , the discharge valve  32 , the outlet line  42 , and the evaporator  22 , thereby bypassing the condenser  18  and the expansion device  20 . The opening of the valve  32  thereby defrosts the evaporator  22 , and simultaneously raises the suction pressure, thus enabling the evaporator  22 , the compressor  16 , and the heat pump  10  to operate at low ambient air temperatures in a normal manner. During the aforesaid operation of the valve  32 , a portion of the hot gas continues to flow through the condenser  18 , thereby continuing to transfer thermal energy to the fluid (such as swimming pool water) surrounding the condenser  18 , thus continuing to heat such fluid.  
         [0024]     Referring to the Graph 1 and Table 1 below, laboratory tests have demonstrated that the heat pump  10  operates normally at ambient air temperatures as low as 40° F. 
         
 
                     TABLE 1                       TEST RESULT OBSERVATIONS:       Graph 1 shows the testing results of the defrost mechanism,       wherein a manual shut off valve was installed to activate and       deactivate the discharge valve mechanism of the heat pump:       Graph 1: From left to right:                                ---&gt;Room temperature went from 80 F. to 50 F. without defrost       mechanism, suction temperature sank below frozen point       ---&gt;Defrost mechanism was activated, suction temperature rose above       frozen point       ---&gt;Room temperature went down to 45 F. and defrost mechanism was       turned off. Suction temperature went down to about 26 F.       ---&gt;Room temperature maintained at 45 F. and the defrost mechanism       was activated. Suction temperature rose above frozen point       ---&gt;Room Temperature went down to 40 F. with defrosting mechanism       activated. Suction temperature maintain around the frozen point       ---&gt;Defrost was turned off, suction temperature took a dive       ---&gt;Room went down to 35 F. and defrost mechanism was activated,       suction temperature maintained at about 27 to 28 F.                 From the test results, the unit can operate at 40 F. ambient without frost issues. The unit will begin          # to frost once the ambient temperature is below 40 F. depending on the humidity conditions. As we can see        # that the suction pressure still maintained about 50 psi even the room went to 40 F. and about 48 psi when the        # room went to 35 F. So the unit would continue to operate with ambient in 30s, but the low-pressure switch        # will shut down the unit once severe frost covered large part of the coil.           
 
         [0025]     Another exemplary embodiment of the present invention is illustrated in  FIGS. 3-4 . Elements illustrated in  FIGS. 3-4  which correspond to the elements described above with reference to  FIGS. 1-2  have been designated by corresponding reference numerals increased by one hundred, while new elements are designated by odd-numbered reference numerals in the one hundreds. The embodiment of the present invention shown in  FIGS. 3-4  operates and is constructed in a manner consistent with the embodiment of  FIGS. 1-2 , unless it is stated otherwise.  
         [0026]     Referring to  FIG. 3 , a heat pump system  110  includes a refrigerant circuit  112  and a defrost circuit  114 . The defrost circuit  114 , which operates in conjunction with a high pressure switch  115  disposed in a compressor suction line  130 , includes a solenoid valve  117 , which is disposed between an inlet line  140  and an outlet line  142 .  
         [0027]      FIG. 4  illustrates a transformer  119  for powering the valve  117 . Wires  121  (shown as solid lines) electrically interconnect the valve  117 , the switch  115 , and the transformer  1   19 .  
         [0028]     In operation, the switch  115  senses the suction pressure at the compressor suction line  130 . More particularly, the switch  115  is set up to open at a selected suction line pressure value (e.g., 60 psi in this embodiment). When the suction line  130  pressure is higher than 60 psi, the switch  115  is open, the transformer  119  is not activated, and the valve  117  is not energized. When the valve  117  is not energized, the valve  117  is closed to the flow of hot gas therethrough. When the switch  115  senses the suction line  130  pressure to be lower than 60 psi, the switch  115  is closed, the transformer  119  is activated, and the valve  117  is energized. When the valve  117  is energized, the valve  117  is opened to the flow of hot gas therethrough. As described above, the bypass flow of hot gas defrosts the evaporator  122  while simultaneously raising the pressure in the suction line  130 , thereby enabling the heat pump  110  to operate at low ambient air temperatures in a normal manner.  
         [0029]     Elements of the present invention are illustrated in  FIGS. 5-8 . Elements illustrated in  FIGS. 5-8  which correspond to the elements described above with reference to  FIGS. 1-2  have been designated by corresponding reference numerals increased by two hundred, while new elements are designated by odd-numbered reference numerals in the two hundreds. The embodiment of the present invention shown in  FIGS. 5-8  operates and is constructed in a manner consistent with the embodiment of  FIGS. 1-2 , unless it is stated otherwise.  
         [0030]     Referring to  FIGS. 5-7 , there is shown a heat pump  210  having an exterior design  211 . Referring to  FIG. 8 , there are shown disassembled elements of the heat pump  210 , including a compressor  216 , a condenser  218 , an expansion device  220 , and an evaporator  222 . Referring still to  FIG. 8 , there are shown disassembled elements of the heat pump  210 , including a fan top assembly  223 , an evaporator support  225 , an evaporator guard  227 , a base pan assembly  229 , a side panel  231 , a control box assembly  233 , and a cover assembly  235 .  
         [0031]     It will be understood that the embodiments of the present invention described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications, including those discussed above, are intended to be included within the scope of the invention as defined in the appended claims.