Abstract:
A thin-profiled gas cooler and chassis suitable for a transcritical heat pump water heater are provided. The heat pump system includes a chassis for supporting such system components as a gas cooler and evaporator. The dimensions of the gas cooler are designed to minimize the impact that the gas cooler has on the cooling capacity of the evaporator by reducing the amount of air flow that the gas cooler blocks. This is achieved by reducing the depth that the gas cooler extends into the chassis cavity. As a result, the height and/or width of the gas cooler is increased compared to other similar volume gas coolers is providing comparable water heating capacity.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a gas cooler and chassis for a transcritical heat pump water heater.  
         [0002]     One type of transcritical heat pump water heater uses a heat pump cycle that utilizes CO 2  as the working fluid. The heat pump may be located indoors or on the exterior of a building, for example, mounted on a roof top of a building. Numerous components are located within a chassis that supports the components, which includes for example a compressor, a gas cooler, an expansion device, an evaporator, an accumulator, and other various components.  
         [0003]     In a CO 2  heat pump water heating system, super critical CO 2  rejects heat in the gas cooler to water, and sub-critical CO 2  absorbs heat in the evaporator from the outdoor air. The heat pump system must operate desirably under a wide range of conditions. For example, the outdoor air temperature may vary from −10° F. in the winter to the 120° F. in the summer. A draft fan is usually used to force the airflow through the evaporator fin side to supply heat to the refrigerant flowing in the tube side of the evaporator. Insuring the maximum possible flow through the evaporator enables the heat pump to operate desirably throughout various airflow conditions.  
         [0004]     Previously, the gas cooler was designed only to efficiently achieve its function without consideration to the gas cooler&#39;s impact on the efficiency of other components. The gas cooler is often packaged as a rather large box-like component having insulation around the interior fluid passages to reduce heat loss. The box extends a significant distance into the cavity defined by the chassis, which also houses the various heat pump components. As a result, the gas cooler blocks and significantly inhibits the air flow through the chassis compromising the efficiency of the heat pump evaporator and ability of the evaporator to perform desirably under the various operating conditions. Therefore, what is needed is an improved gas cooler and chassis arrangement that minimizes the negative impact of the gas cooler on the evaporator as well as system performance, i.e. minimizing airflow blockage.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention relates to a gas cooler and chassis integration design suitable for a transcritical heat pump water heater. The heat pump system includes a chassis for supporting such system components as a gas cooler and evaporator. The gas cooler includes a water supply and return opening and a refrigerant inlet and outlet opening with associated passages running through the gas cooler. The water and refrigerant passages are positioned in relationship to one another such that heat from the compressed refrigerant is transferred to the water flowing through the water passage to provide heated water to a water tank.  
         [0006]     The dimensions of the gas cooler are designed to minimize the impact that the gas cooler has on the cooling capacity of the evaporator by reducing the amount of air flow that the gas cooler blocks. This is achieved by optimizing the way to package the gas cooler, for example, by reducing the depth that the gas cooler extends into the chassis cavity. As a result, the height and/or width of the gas cooler is increased compared to other similar volume gas coolers while still providing comparable water heating capacity. As a result, a shorter length of the evaporator coils is affected by the blocked airflow.  
         [0007]     A typical heat pump chassis includes spaced apart vertical and horizontal walls supported by the vertical and horizontal supports that define the dimension of the chassis. The walls and supports generally define an outer shape. The chassis provides not only support to the components of the heat pump water heater but also forms the access interface for operation and maintenance purpose. Various components of the heat pump are arranged and interconnected inside the chassis to form a closed refrigerant loop. In one example, a face of the gas cooler is located adjacent to a substantial portion of the wall, for example, greater than 50 percent.  
         [0008]     In an example shown, four sides of the gas cooler are located proximate to the spaced apart horizontal and vertical supports providing a gas cooler having a thin profile that does not extend very deeply into the chassis cavity. Additionally, the gas cooler may provide one of the exterior sides of the chassis, eliminating a separate wall used in the prior art. Preferably, the depth of the gas cooler is less than the width and/or the height. Also, the chassis may incorporate one or more guides so that the thin-profiled inventive gas cooler may be removably received within a portion of the housing preferably proximate to an outer wall of the chassis.  
         [0009]     Accordingly, the present invention provides an improved gas cooler and chassis arrangement that minimizes the negative impact the gas cooler has on the evaporator and system performance by blocking the airflow to the evaporator.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     Other advantages of the present invention can be understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0011]      FIG. 1  is a perspective view of a prior art heat pump water heater with several of the walls removed to provide an unobstructed view to the chassis cavity.  
         [0012]      FIG. 2  is a schematic of a prior art air source heat pump water heater system.  
         [0013]      FIG. 3  is a partial perspective view of the inventive gas cooler in relationship to the heat pump system chassis.  
         [0014]      FIG. 4  is a partial perspective view of the inventive heat pump chassis having structure permitting the thin-profiled gas cooler to be removably received within the chassis near the exterior. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]      FIGS. 1 and 2  depict prior art heat pump systems.  FIG. 1  illustrates a heat pump water heater  110  having a chassis  112  constructed from multiple vertical  114  and horizontal  116  supports forming a box-like structure for housing the components of the heat pump system  110 . Walls  118  are typically supported on the supports  114  and  116  to enclose the components and protect them from the exterior environment. However, the walls  118  are also considered vertical and horizontal supports and together define an outer shape. One of the walls  118  supports a fan  154  for moving air through the chassis to ensure desired operation of an evaporator located within. Maximizing the air flow through the evaporator enables desired heat pump performance during extreme operating conditions.  
         [0016]     As can be seen in  FIG. 1 , the prior art gas cooler  124  extends a considerable depth into the cavity of the chassis  112  such that it obstructs a significant amount of air flow inhibiting the desired operation of the evaporator. The gas cooler  124  is shown supported on the floor and is only proximate to a small portion of one of the vertical supports  114  and a portion of one of the horizontal support  116 . The prior art gas cooler  124  is adjacent to significantly less than half of the area defined between the vertical  114  and horizontal  116  support on one side of the chassis  112 . Moreover, the width, height and depth of the gas cooler  124  are approximately equal providing a cube or box-like structure.  
         [0017]      FIG. 2  illustrates an example prior art vapor compression system  120  that includes a compressor  122 , a heat rejecting heat exchanger (a gas cooler in transcritical cycles)  124 , an expansion device  126 , and a heat accepting heat exchanger (an evaporator)  128 . Refrigerant circulates through the closed circuit system  120 .  
         [0018]     The refrigerant exits the compressor  122  at a high pressure and a high enthalpy. The refrigerant then flows through the gas cooler  124  at a high pressure. A fluid medium  130 , such as water or air, flows through a heat sink  132  of the gas cooler  124  and exchanges heat with the refrigerant flowing through the gas cooler  124 . In the gas cooler  124 , the refrigerant rejects heat into the fluid medium  130 , and the refrigerant exits the gas cooler  124  at a low enthalpy and a high pressure. A water pump  134  pumps the fluid medium through the heat sink  132 . The cooled fluid medium  130  enters the heat sink  132  at the heat sink inlet or return  136  and flows in a direction opposite to the direction of the flow of the refrigerant. After exchanging heat with the refrigerant, the heated water  138  exits the heat sink  130  at the heat sink outlet or supply  140 . The heated water can be stored in a water tank  164 . In one example, the water tank  164  is sized to meet expected peak demand at all times. The refrigerant then passes through the expansion valve  126 , which expands and reduces the pressure of the refrigerant. The expansion device  126  can be an electronic expansion valve or other known type of expansion device.  
         [0019]     After expansion, the refrigerant flows through the passages  180  of the evaporator  128  and exits at a high enthalpy and a low pressure. In the evaporator  128 , the refrigerant absorbs heat from the outdoor air  144 , heating the refrigerant. The outdoor air  144  flows through a heat sink  146  and exchanges heat with the refrigerant passing through the evaporator  128  in a known manner. The outdoor air  144  enters the heat sink  146  through the heat sink inlet or return  148  and flows in a direction opposite to or cross to the direction of flow of the refrigerant. After exchanging heat with the refrigerant, the cooled outdoor air  150  exits the heat sink  146  through the heat sink outlet or supply  152 . The temperature difference between the outdoor air  144  and the refrigerant in the evaporator  128  drives the thermal energy transfer from the outdoor air  144  to the refrigerant as the refrigerant flows through the evaporator  128 . A fan  154  moves the outdoor air  144  across the evaporator  128 , maintaining the temperature difference and evaporating the refrigerant. The refrigerant then reenters the compressor  122 , completing the cycle.  
         [0020]     The system  120  transfers heat from the low temperature energy reservoir (ambient air) to the high temperature energy sink (heated hot water). The transfer of energy is also achieved with the aid of electrical energy input at the compressor  122 , fan  154  and pump  134 .  
         [0021]     The system  120  can also include an accumulator  156 . The accumulator  156  stores excess refrigerant from the system  120  to control the high pressure of the system  120 , and therefore the coefficient of performance.  
         [0022]     Referring to  FIG. 3 , the inventive thin-profiled gas cooler  24  is shown mounted to the chassis  12 . The depth D of the gas cooler  24  is significantly less than the height H 2  and width W 2  of the gas cooler. Moreover, the height H 2  and width W 2  are approximately equal to the height H 1  and width W 1  defined by the vertical  14  and horizontal  16  supports of the chassis  12 . That is, it is preferable that the dimensions of the gas cooler  24  are sized such that the sides of the gas cooler  24  extend to the vertical  14  and horizontal  16  supports to the greatest extent possible. In this manner, the depth D is reduced to the smallest dimension to minimize any obstruction the gas cooler creates from extending into the cavity chassis  12 , which inhibits the airflow through the evaporator  28  located within the chassis  12 .  
         [0023]     Furthermore, as depicted in  FIG. 3 , the gas cooler  24  provides the exterior side or wall  18  thereby eliminating the need of a separate chassis wall. It should also be understood that the gas cooler may provide just a portion of the exterior wall  18 . A sheet of material is connected to the gas cooler  24  in such a configuration to complete the exterior wall  18 . Although the gas cooler  24  is shown in  FIG. 3  as providing a side wall, the gas cooler  24  may also provide the top or bottom wall of the chassis  12 .  
         [0024]     The inventive features of the gas cooler  24  and its relationship relative to the chassis  12  may be expressed in any number of ways. Referring to  FIG. 4 , for example, the area A 2  of the outer side of the gas cooler  24  is adjacent to a substantial portion of the area A 1  of the chassis which, in the example shown, is defined by an area bounded by the vertical  14  and horizontal  16  supports on one side of the chassis, preferably next to the wall  18 . The gas cooler  24  is shown removed from the chassis.  
         [0025]     In one example, the area A 2  is at least 50 percent of the area A 1 . In the example shown in  FIG. 4 , the area A 2  is approximately equal to the area A 1 . Expressed in another way, the width W 2  and/or height H 2  are substantially greater than the depth D of the gas cooler  24 , for example, twice the length. While the inventive gas cooler  24  is shown arranged near a side wall, one of ordinary skill will appreciate that it may also be arranged at the top or bottom of the chassis  12 .  
         [0026]     Referring to another feature of  FIG. 4 , the inventive gas cooler  24  is removably installed into the chassis  12  at one side adjacent to a wall  18 . In the example shown, the gas cooler  24  is top loaded into the chassis  12 , but it may also be side- or bottom-loaded. One or more guides  70  are used to locate the gas cooler  24  in a desired location during installation of the gas cooler  24  into the chassis  12 . In the example shown, opposing sides of the gas cooler  24  are retained by opposing vertical members  14  and opposing vertical guides  70 .  
         [0027]     It should also be understood that the removable gas cooler configuration shown in  FIG. 4  may also provide the exterior wall  18  in a similar manner to that shown in  FIG. 3 .  
         [0028]     The inventive gas cooler  24  reduces the blockage of air to the evaporator coil so that the negative impact on the evaporator and subsequently the water heat performance is minimized. In addition, the configuration of the gas cooler  24  within the chassis  12  provides user access to the components within the chassis, in particular, the arrangement shown in  FIG. 4 .  
         [0029]     The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.