Abstract:
A plate heat exchanger can reduce thermal contact between a second fluid (water and a third fluid (low-temperature, low-pressure two-phase refrigerant) to enhance thermal efficiency. A plate heat exchanger ( 1   b ) includes a heat transfer plate group ( 102   a ) that performs heat exchange between a first fluid of high-temperature, high-pressure gas refrigerant and a second fluid of a heating target fluid; and a heat transfer plate group ( 102   b ) that performs heat exchange between a first fluid of low-temperature, high-pressure liquid refrigerant and a third fluid of low-temperature, low-pressure two-phase liquid refrigerant. The heat transfer plate group ( 102   a ) forms refrigerant channels including a stack of plates, has a configuration that a flow of the first fluid of high-temperature, high-pressure gas refrigerant and a flow of the second fluid are alternately aligned in the refrigerant channels, and causes the second fluid to flow in the outermost refrigerant channel.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a plate heat exchanger that performs heat exchange between refrigerant and heating target fluid, and a heat pump outdoor unit including the same. 
       BACKGROUND ART 
       [0002]    A heat pump outdoor unit for performing hot-water supply or a cooling/heating operation includes a system using a plate heat exchanger as a condenser and a subcooler. Examples of the plate heat exchanger include a plate heat exchanger serving as both a condenser and a subcooler. For example, in a proposed plate heat exchanger, a boundary plate is provided in a heat transfer unit to define two heat exchange units (a condensation unit and a subcooling unit) (see, for example, Patent Literature 1). 
       CITATION LIST 
     Patent Literature 
       [0003]    Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2005-106385 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0004]    In the plate heat exchanger proposed in Patent Literature 1, a first fluid (high-temperature, high-pressure gas refrigerant) that is a heating fluid and a second fluid (water) that is a heating target fluid, both being to exchange heat with each other, flow in the first heat exchange unit (condensation unit). A first fluid (low-temperature, high-pressure liquid refrigerant) that is a heating fluid and a third fluid (low-temperature, low-pressure two-phase refrigerant) that is a heating target fluid, both being to exchange heat with each other, flow in the second heat exchange unit (subcooling unit). In a case where the first heat exchange unit (condensation unit) and the second heat exchange unit (subcooling unit) are included in the same plate heat exchanger, the second fluid (water) and the third fluid (low-temperature, low-pressure two-phase refrigerant) exchange heat with each other through the boundary plate in a portion of the plate heat exchanger so that the temperature of the second fluid (water) decreases and, thereby, thermal efficiency decreases. 
         [0005]    The present invention has been made to solve the problems described above, and provides a plate heat exchanger that can suppress thermal contact between the second fluid (water) and the third fluid (low-temperature, low-pressure two-phase refrigerant b ) and enhance thermal efficiency. 
       Solution to Problem 
       [0006]    The present invention provides a plate heat exchanger including: a first heat transfer plate group that performs heat exchange between a first fluid of high-temperature, high-pressure gas refrigerant and a second fluid of a heating target fluid; and a second heat transfer plate group that performs heat exchange between a first fluid of low-temperature, high-pressure liquid refrigerant and a third fluid of low-temperature, low-pressure two-phase liquid refrigerant, wherein the first heat transfer plate group forms a plurality of refrigerant channels constituted by a stack of plates, has a configuration that a flow of the first fluid of high-temperature, high-pressure gas refrigerant and a flow of the second fluid are alternately aligned in the refrigerant channels, and causes the second fluid to flow in an outermost one of the refrigerant channels, and the second heat transfer plate group forms a plurality of refrigerant channels constituted by a stack of plates, has a configuration that a flow of the first fluid of low-temperature, high-pressure liquid refrigerant and a flow of the third fluid are alternately aligned in the refrigerant channels, and causes the first fluid of low-temperature, high-pressure liquid refrigerant to flow in one of the refrigerant channels adjacent to the first heat transfer plate group. 
       Advantageous Effects of Invention 
       [0007]    According to the present invention, a flow of the first refrigerant and a flow of the second refrigerant are alternately aligned in the refrigerant channels of the first heat transfer plate group, and the second fluid flows in the outermost refrigerant channel. In the refrigerant channels of the second heat transfer plate group, a flow of the first refrigerant and a flow of the second refrigerant are also alternately aligned, and the first fluid of low-temperature, high-pressure liquid refrigerant flows in the refrigerant channel adjacent to the first heat transfer plate group. Thus, the first fluid of low-temperature, high-pressure liquid refrigerant flows between the second fluid and the third fluid. Thus, thermal contact between the second fluid and the third fluid can be suppressed, and a temperature difference between the fluids decreases so that the amount of heat transfer from the second fluid can be reduced, and thermal efficiency can be enhanced. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is a refrigerant circuit diagram of a heat pump hot-water supply apparatus according to Embodiment 1 of the present invention. 
           [0009]      FIG. 2 a    is a left side view of the plate heat exchanger illustrated in  FIG. 1 . 
           [0010]      FIG. 2 b    is a front view of the plate heat exchanger illustrated in  FIG. 1 . 
           [0011]      FIG. 2 c    is a right side view of the plate heat exchanger illustrated in  FIG. 1 . 
           [0012]      FIG. 2 d    is a rear view of the plate heat exchanger illustrated in  FIG. 1 . 
           [0013]      FIG. 3  is a disassembled perspective view of the plate heat exchanger illustrated in  FIG. 1 . 
           [0014]      FIG. 4  schematically illustrates a flow of fluid in the plate heat exchanger illustrated in  FIG. 1 . 
           [0015]      FIG. 5  is a cross-sectional view taken along line A-A in  FIG. 2   b.    
           [0016]      FIG. 6  is a partially enlarged view of a heat transfer plate group ( 102   a,    102   b ) illustrated in  FIG. 5 . 
           [0017]      FIG. 7 a    is a full view of a heat transfer plate ( 101   a ) illustrated in  FIG. 6 . 
           [0018]      FIG. 7 b    is a full view of a heat transfer plate ( 101   b ) illustrated in  FIG. 6 . 
           [0019]      FIG. 8 a    is a full view of a side plate ( 105   a ) illustrated in  FIG. 6 . 
           [0020]      FIG. 8 b    is a full view of a side plate ( 105   b ) illustrated in  FIG. 6 . 
           [0021]      FIG. 9 a    is a full view of a reinforcing plate ( 104   a ) illustrated in  FIG. 6 . 
           [0022]      FIG. 9 b    is a full view of a reinforcing plate ( 104   b ) illustrated in  FIG. 6 . 
           [0023]      FIG. 10 a    is a full view of an isolation plate ( 106   a ) illustrated in  FIG. 6 . 
           [0024]      FIG. 10 b    is a full view of an isolation plate ( 106   b ) illustrated in  FIG. 6 . 
           [0025]      FIG. 11  is a full view of an intermediate reinforcing plate ( 107   b ) illustrated in  FIG. 6 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
       [0026]      FIG. 1  is a refrigerant circuit diagram of a heat pump hot-water supply apparatus according to Embodiment 1 of the present invention. The heat pump hot-water supply apparatus illustrated in  FIG. 1  includes a heat pump outdoor unit (heat pump unit)  2  and a water circuit  9 , The heat pump outdoor unit  2  includes a compressor  3 , a first heat exchanger  4 , a second heat exchanger  5 , electronic expansion valves  6   a  and  6   b,  and a third heat exchanger  7 . Operations of these components will be described below. 
         [0027]    (1) The compressor  3  compresses refrigerant  8  by using electric power and increases an enthalpy and a pressure of the refrigerant  8 . 
         [0028]    ( 2 ) The first heat exchanger  4  performs heat exchange between the compressed refrigerant  8  (first fluid b ) and a heating target fluid (second fluid). 
         [0029]    (3) The electronic expansion valve  6   a  adiabatically expands a part (refrigerant  8   a ) of the refrigerant  8  from the first heat exchanger  4 . The electronic expansion valve  6   a  corresponds to a first expansion valve of the present invention. 
         [0030]    (4) The second heat exchanger  5  performs heat exchange between the refrigerant  8  (first fluid) from first heat exchanger  4  and the refrigerant  8   a  (third fluid) that is a part of the refrigerant  8  and subjected to pressure reduction through the electronic expansion valve  6   a.  The third fluid is gasified through the heat exchange and is sucked into the compressor 
         [0031]    (5) The electronic expansion valve  6   b  adiabatically expands the refrigerant  8  from the second heat exchanger  5 . The electronic expansion valve  6   b  corresponds to a second expansion valve of the present invention. 
         [0032]    (6) The third heat exchanger  7  performs heat exchange between the refrigerant  8  from the electronic expansion valve  6   b  and an external heat source. Although not shown, the heat pump outdoor unit  2  may include other attachments such as a receiver for storing excess refrigerant  8 . 
         [0033]    The compressor  3  to the third heat exchanger  7  described above constitute a refrigeration cycle mechanism in which the first fluid circulates. A plate heat exchanger  1  is used as the first heat exchanger  4 . In this manner, heat (heat absorbed in the third heat exchanger  7 ) of an external heat source is transferred by the plate heat exchanger  1  so that the second fluid flowed into the plate heat exchanger  1  is heated. Examples of a medium used as the external heat source (a target of heat exchange in the third heat exchanger  7 ) include various media such as air and geothermal heat. The plate heat exchanger  1  can be used for any type of the heat pump outdoor unit  2  using an external heat source. In Embodiment 1, the plate heat exchanger  1  includes the second heat exchanger  5  in addition to the first heat exchanger  4 , that is, includes two heat exchangers. 
         [0034]    The heat pump outdoor unit  2  uses, for example, water  10  as the second fluid. The water  10  circulates in the water circuit  9 . The example illustrated in  FIG. 1  employs an indirect heating technique. The water  10  flows into the plate heat exchanger  1 , which is the first heat exchanger  4 , is heated by the first fluid (refrigerant  8 ), and flows out of the plate heat exchanger  1 . After having flowed from the plate heat exchanger  1 , the water  10  flows into a heating appliance  11 , such as a radiator or a floor heating, connected by pipes constituting the water circuit  9  to be used for indoor temperature control. The water circuit  9  includes a water-to-water heat exchange tank  12  for heat exchange between the water  10  and clean water  13  so that the clean water  13  heated by the water  10  can be used as water for domestic use, such as bathing or shower. 
         [0035]    A configuration of the plate heat exchanger  1  illustrated in  FIG. 1  will now be described. 
         [0036]      FIG. 2 a    is a left side view of the plate heat exchanger illustrated in  FIG. 1 ,  FIG. 2 b    is a front view of the plate heat exchanger illustrated in  FIG. 1 ,  FIG. 2 c    is a right side view of the plate heat exchanger illustrated in  FIG. 1 , and  FIG. 2 d    is a rear view of the plate heat exchanger illustrated in  FIG. 1 . 
         [0037]    As illustrated in  FIGS. 2 a    to  2   d,  the plate heat exchanger  1  includes nozzles  103   a  to  103   g.  As illustrated in  FIG. 2   b,  the three nozzles  103   a,    103   d,  and  103   e  are attached to the front face of the plate heat exchanger  1 . As illustrated in  FIG. 2   d,  the four nozzles  103   b,    103   c,    103   fe,  and  130   g  are attached to the rear face of the plate heat exchanger  1 . The first fluid flowed through the nozzle  103   a,  which is a first fluid inlet, flows out from two outlets, that is, the nozzle  103   b  that is a first outlet and the nozzle  103   c  that is a second outlet. A passage in which the first refrigerant flows is a first channel. As will be described in detail later, the first fluid flows out of the nozzle  103   b  after having exchanged heat with the second fluid and the third fluid. The first fluid flows out of the nozzle  103   c  after having exchanged heat with the second fluid (not having exchanged heat with the third fluid). The second fluid flowed through the nozzle  103   d  that is a second fluid inlet, flows out of the nozzle  103   e  that is a second fluid outlet. A passage in which the second fluid flows is a second channel. The third fluid flowed through the nozzle  103   f  that is a third fluid inlet, flows out of the nozzle  103   g  that is a third fluid outlet. A passage in which the third fluid flows is a third channel. The first channel, the second channel, and the third channel constitute channels that are independent of each other. 
         [0038]      FIG. 3  is a disassembled perspective view of the plate heat exchanger illustrated in  FIG. 1 . As illustrated in  FIG. 3 , in the plate heat exchanger  1 , a reinforcing plate  104   a  to which the nozzles  103   a,    103   d,  and  103   e  are attached, a side plate  105   a,  a heat transfer plate group  102   a  (a heat transfer plate  101   a,  a heat transfer plate  101   b, . . . ,  a heat transfer plate  101   a,  and a heat transfer plate  101   b ) corresponding to the first heat exchanger  4 , an isolation plate  106   a,  an intermediate reinforcing plate  107 , an isolation plate  106   b,  a heat transfer plate group  102   b  (a heat transfer plate  101   a,  a heat transfer plate  101   b  . . . , a heat transfer plate  101   a,  and a heat transfer plate  101   b ) corresponding to the second heat exchanger  5 , a side plate  105   b,  a reinforcing plate  104   b  to which the nozzles  103   b,    103   c,    103   f,  and  103   g  are attached, are stacked in this order. 
         [0039]    Then, flows of the first to third fluids in the plate heat exchanger  1  will be described. 
         [0040]      FIG. 4  schematically illustrates a flow of the fluids in the plate heat exchanger  1  illustrated in  FIG. 1 . 
         [0041]    The first fluid (refrigerant  8 ) flows from the nozzle  103   a  into the heat transfer plate group  102   a,  passes through channel holes formed in the isolation plate  106   a,  the intermediate reinforcing plate  107 , and the isolation plate  106   b,  and flows into the heat transfer plate group  102   b.  The first fluid flowed into the heat transfer plate group  102   b  is divided into a first fluid that exchanges heat with the third fluid (refrigerant  8   a ) and flows out of the nozzle  103   b  and a first fluid (which is to be a third fluid subjected to an expansion process) that does not exchange heat with the third fluid (refrigerant  8   a ) and flows out of the nozzle  103   c.  The second fluid (heating target fluid) flows into the heat transfer plate group  102   a  from the nozzle  103   d,  and flows out of the nozzle  103   e.  The third fluid flows into the heat transfer plate group  102   b  from the nozzle  103   f,  and flows out of the nozzle  103   g.    
         [0042]    The heat transfer plate group  102   a  corresponds to a first heat transfer plate group of the present invention. The heat transfer plate group  102   b  corresponds to a second heat transfer plate group of the present invention. The refrigerant flowed from the nozzle  103   a  corresponds to a first fluid of high-temperature, high-pressure gas refrigerant of the present invention. The second fluid (heating target fluid) flowed from the nozzle  103   d  corresponds to a second fluid of a heating target fluid of the present invention. The third fluid flowed from the nozzle  103   f  corresponds to a low-temperature, low-pressure third fluid of the present invention. The first fluid that has exchanged heat in the heat transfer plate group  102   a  and flowed into the heat transfer plate group  102   b  corresponds to a low-temperature, high-pressure first fluid of the present invention. 
         [0043]    Referring now to  FIGS. 5 to 11 , a configuration of the plate heat exchanger  1  will be specifically described. 
         [0044]      FIG. 5  is a cross-sectional view corresponding to an A-A section in  FIG. 2 . Regarding to  FIG. 5 , the term “corresponding to” is used for the following reason. For simplicity of description in  FIG. 5 , a total of ten heat transfer plates  101   a  and  101   b  constituting the heat transfer plate groups  102   a  and  102   b  are used. Thus, since  FIG. 5  is not identical to  FIG. 2 , the term “corresponding to” is used.  FIG. 6  is a partially enlarged view of the heat transfer plate groups  102   a  and  102   b  illustrated in  FIG. 5 . The top and bottom in description with reference to  FIG. 5  or  FIG. 6  respectively refer to the top and bottom in the illustrated positional relationship. 
         [0045]    As illustrated in  FIGS. 5 and 6 , as a main configuration of the plate heat exchanger  1  according to Embodiment 1, the heat transfer plates  101   a  and  101   b  are stacked so that the heat transfer plate groups  102   a  and  102   b  form channels for heat exchange between the first fluid and the second fluid and between the first fluid and the third fluid. The isolation plate  106   a,  the intermediate reinforcing plate  107 , and the isolation plate  106   b  are disposed between the heat transfer plate groups  102   a  and  102   b.  A fundamental part  108  of the plate heat exchanger  1  (hereinafter referred to as a fundamental part  108 ) is constituted by disposing the side plate  105   a  on top of the heat transfer plate group  102   a  and the side plate  105   b  at the bottom of the heat transfer plate group  102   b.  The reinforcing plate  104   a  is disposed on top of the fundamental part  108  and the reinforcing plate  104   b  is disposed at the bottom of the fundamental part  108  so that the fundamental part  108  is sandwiched between the reinforcing plate  104   a  and the reinforcing plate  104   b.  The reinforcing plates  104   a  and  104   b  have nozzle attachment ports (nozzle holes). The nozzles  103   a,    103   d,  and  103   e  are attached to the nozzle attachment ports of the reinforcing plate  104   a.  The nozzles  103   b,    130   c,    103   f,  and  103   g  are attached to the nozzle attachment ports of the reinforcing plate  104   b.  In  FIG. 5 , the nozzles  103   c,    103   d,  and  103   f  are behind the nozzles  103   b,    103   e,  and  103   g,  and thus, are not shown. 
       Heat Transfer Plate  101   a  and Heat Transfer Plate  101   b    
       [0046]      FIG. 7 a    is a full view of the heat transfer plate  101   a.    FIG. 7 b    is a full view of the heat transfer plate  101   b.  The heat transfer plate  101   a  illustrated in  FIG. 7 a    and the heat transfer plate  101   b  illustrated in  FIG. 7 b    have the same size and the same thickness. Each of the heat transfer plates  101   a  and  101   b  has channel holes  109   a  to  109   d  at four corners thereof. Corrugated shapes  110   a  and  110   b  for stirring fluid are disposed between the channel holes  109   a  and  109   d  and the channel holes  109   b  and  109   c  in the longitudinal direction of the heat transfer plate  101   a  ( 101   b ). The corrugated shape  110   a  of the heat transfer plate  101   a  is inverted 180 degrees (upside down) from the corrugated shape  110   b  of the heat transfer plate  101   b.  That is, the corrugated shape  110   b  is at a position by rotating the corrugated shape  110   a  180 degrees in the direction indicated by an arrow with respect to a point P. The channel holes  109   a  and  109   b  of the heat transfer plate  101   a  and peripheral portions thereof in  FIG. 7 a    are located at lower levels than the channel holes  109   c  and  109   d  and peripheral portions thereof in the vertical direction (i.e., at deeper positions in the vertical direction on the drawing sheet). Similarly, in the heat transfer plate  101   b  illustrated in  FIG. 7   b,  the channel holes  109   c  and  109   d  and peripheral portions thereof are located at lower levels than the channel holes  109   a  and  109   b  and peripheral portions thereof in the vertical direction (i.e., at deeper positions in the vertical direction on the drawing sheet). 
       Channel Formation by Heat Transfer Plates  101   a  and  101   b    
     Heat Transfer Plate Group  102   a    
       [0047]    The heat transfer plates  101   a  and  101   b  are stacked so that the corrugated shape  110   a  and the corrugated shape  110   b  are in point-contact with each other. The point-contact portions are brazed to serve as “pillars” forming channels. For example, a channel for the second fluid (e.g., pure water, tap water, or water containing an antifreeze) is formed by stacking the heat transfer plate  101   a  and the heat transfer plate  101   b  in this order. A channel for the first fluid (e.g., a refrigerant, typified by R410A, for use in an air-conditioning apparatus) is formed by stacking the heat transfer plate  101   b  and the heat transfer plate  101   a  in this order. Layers of “second fluid-first fluid” are formed by stacking the heat transfer plate  101   a,  the heat transfer plate  101   b,  and the heat transfer plate  101   a  in this order. Subsequently, the number of stacked heat transfer plates is increased so that channels for “second fluid-first fluid-second fluid-first fluid, . . . ” are alternately formed (see  FIGS. 4 and 6 ). The stacked heat transfer plates  101   a  and  101   b  described above constitute the heat transfer plate group  102   a  as illustrated in  FIGS. 5 and 6 . At this time, the number of heat transfer plates  101   a  and  101   b  is an even number, and the stack starts at the heat transfer plate  101   a  and ends at the heat transfer plate  101   b.  Thus, the second fluid flows in the outermost member of the heat transfer plate group  102   a.    
       Heat Transfer Plate Group  102   b    
       [0048]    In a manner similar to the heat transfer plate group  102   a,  the heat transfer plates  101   a  and  101   b  are stacked to constitute the heat transfer plate group  102   b.  A channel for the first fluid is formed by stacking the heat transfer plate  101   b  and the heat transfer plate  101   a  in this order. A channel for the third fluid is formed by stacking the heat transfer plate  101   a  and the heat transfer plate  101   b  in this order. Layers of “first fluid-third fluid-first fluid” are formed by stacking the heat transfer plate  101   a,  the heat transfer plate  101   b,  and the heat transfer plate  101   a.  Subsequently, channels for “first fluid-third fluid-first fluid . . . ” are alternately formed by increasing the number of stacked heat transfer plates (see  FIGS. 4 and 6 ). The stacked heat transfer plates  101   a  and  101   b  described above constitute the heat transfer plate group  102   b  as illustrated in  FIGS. 5 and 6 . At this time, the number of heat transfer plates  101   a  and  101   b  is an even number, and the stack starts at the heat transfer plate  101   b  and ends at the heat transfer plate  101   a.  Thus, the first fluid flows in the outermost member (i.e., the channel closest to the heat transfer plate group  102   a ) of the heat transfer plate group  102   b.    
       Side Plates  105   a  and  105   b    
       [0049]      FIG. 8 a    is a full view of the side plate  105   a  illustrated in  FIG. 6 .  FIG. 8 b    is a full view of the side plate  105   b  illustrated in  FIG. 6 . The side plate  105   a  and the side plate  105   b  are flat plates that have sizes and thicknesses similar to those of the heat transfer plates  101   a  and  101   b,  each have channel holes  109   a  to  109   d  at the four corners thereof, and do not have corrugated shape  110   a,    110   a.  As illustrated in  FIG. 5 , the side plate  105   a  is disposed on top of the heat transfer plate group  102   a,  and the side plate  105   b  is disposed at the bottom of the heat transfer plate group  102   b,  thereby constituting the fundamental part  108 . As illustrated in  FIGS. 8 a    and  8   b,  each of the channel holes  109   a  and  109   b  of the side plate  105   a  has a narrowing portion  111   a,  and each of the channel holes  109   c  and  109   d  of the side plate  105   b  has a narrowing portion  111   b.    
       Narrowing Portions  111   a  to  111   d    
       [0050]    As illustrated in  FIGS. 5, 8   a,  and  8   b,  the side plate  105   a  has recessed narrowing portions  111   a  formed by a narrowing process around the channel holes  109   a  and  109   b,  and the side plate  105   b  has projected narrowing portions  111   b  formed by a narrowing process around the channel holes  109   c  and  109   d.  The narrowing portions  111   a  and  111   b  are brazed to portions around the channel holes  109   a  and  109   b  of the heat transfer plates  101   a  and  101   b  so that pillars are formed around the channel holes of the heat transfer plate  101   a  and the side plates  105   a  and  105   b,  thereby increasing the strength thereof. 
         [0051]    As illustrated in  FIG. 5 , the narrowing portions  111   a  of the side plate  105   a  form a heat nontransfer space  112   a  formed by the side plate  105   a  and the heat transfer plate  101   a  and prevent the first fluid from flowing therein. The heat nontransfer space  112   a  is a space formed by a plane and the corrugated shape ( 110   b ), and has poor heat conduction. Thus, it is possible to prevent the first fluid from flowing into the heat nontransfer space  112   a  so that excessive heat transfer and a decrease in flow rate of refrigerant can be prevented. Similarly, the narrowing portions  111   b  of the side plate  105   b  form a heat nontransfer space  112   b  formed by the side plate  105   b  and the heat transfer plate  101   a  and prevent the third fluid flow flowing therein. 
       Reinforcing Plate (Pressure-resistant Plate)  104   a  and  104   b    
       [0052]      FIG. 9 a    is a full view of the reinforcing plate  104   a  illustrated in  FIG. 6 .  FIG. 9 b    is a full view of the reinforcing plate  104   b  illustrated in  FIG. 6 . As illustrated in  FIG. 5 , the reinforcing plate  104   a  is attached to the top of the fundamental part  108 , and the reinforcing plate  104   b  is attached to the bottom of the fundamental part  108 . Each of the reinforcing plates  104   a  and  104   b  has a thickness about five times as large as those of the heat transfer plates  101   a  and  101   b  and the side plate  105 , for example. In the plate heat exchanger  1 , each of the reinforcing plates  104   a  and  104   b  has three channel holes  109   a,    109   c,  and  109   d  as illustrated in  FIG. 9 . 
         [0053]    In the reinforcing plate  104   a,  the nozzles  103   a,    103   d,  and  103   e  are brazed to the channel holes  109   a,    109   c,  and  109   d,  respectively, at the side opposite to the heat transfer plate group  102   a.  In the reinforcing plate  104   b,  the nozzles  103   b,    130   c,    103   f,  and  103   g  are brazed to the channel holes  109   a,    109   c,  and  109   d,  respectively, at the side opposite to the heat transfer plate group  102   b.  The reinforcing plates  104   a  and  104   b  enable the plate heat exchanger  1  to withstand fatigue due to a variation of a pressure caused by a fluid flowing in the fundamental part  108  and a force occurring due to a difference between the pressure of the plate heat exchanger  1  and an atmospheric pressure. 
       Isolation Plates  106   a  and  106   b    
       [0054]      FIG. 10 a    is a full view of the isolation plate  106   a  illustrated in  FIG. 6 . FIG. 
         [0055]      10   b  is a full view of the isolation plate  106   b.  As illustrated in  FIG. 5 , the isolation plate  106   a  is disposed at the bottom of the heat transfer plate group  102   a,  and the isolation plate  106   b  is disposed on top of the heat transfer plate group  102   b.  The isolation plate  106   a  is a flat plate that has a size and a thickness similar to those of the heat transfer plate  101   a  ( 101   b ), has a channel hole  109   b,  and does not have the corrugated shape  110   a.  The isolation plate  106   a  has a narrowing portion  111   c  at the side facing the heat transfer plate group  102   a,  and as illustrated in  FIG. 5 , is brazed to peripheral portions of the channel holes  109   a  and  109   b  of the heat transfer plate  101   b  lastly stacked in the heat transfer plate group  102   a  to prevent the first fluid from flowing into a heat nontransfer space  112   c.  Similarly, the isolation plate  106   b  is also a flat plate that has a size and a thickness similar to those of the heat transfer plate  101   b  ( 101   a ), has a channel hole  109   b,  and does not have the corrugated shape  110   b.  The isolation plate  106   b  has a narrowing portion  111   d  at the side facing the heat transfer plate group  102   b,  and as illustrated in  FIG. 5 , is brazed to peripheral portions of the channel holes  109   c  and  109   d  of the heat transfer plate  101   b  to prevent the third fluid from flowing into the heat nontransfer space  112   d.    
       Intermediate Reinforcing Plate  107   
       [0056]      FIG. 11  is a full view of the intermediate reinforcing plate  107  illustrated in  FIG. 6 . As illustrated in  FIG. 11 , the intermediate reinforcing plate  107  has the same shape and the same thickness as those of the reinforcing plates  104   a  and  104   b,  and has a channel hole  109   b.  The intermediate reinforcing plate  107  is sandwiched between the isolation plate  106   a  and the isolation plate  106   b,  and can withstand a force occurring due to a difference between the pressure of the second fluid and the pressure of the third fluid. 
         [0057]    The heat transfer plate group  102   a  and the heat transfer plate group  102   b  are brazed with the isolation plate  106   a,  the intermediate reinforcing plate  107 , and the isolation plate  106   b  sandwiched therebetween so that the plate heat exchanger  1  can serve as both the first heat exchanger  4  and the second heat exchanger  5 . Since the outermost member of the heat transfer plate group  102   a  is the second fluid, and the outermost member of the heat transfer plate group  102   b  is the first fluid, a channel configuration of a fluid flow schematically illustrated in  FIG. 4  is formed so that the second fluid does not contact the third fluid at a low temperature. Thus, a decrease in the outlet temperature of the second fluid can be suppressed so that thermal efficiency of the plate heat exchanger  1  can be enhanced. 
       REFERENCE SIGNS LIST 
       [0058]      1  plate heat exchanger,  2  heat pump outdoor unit,  3  compressor,  4  first heat exchanger,  5  second heat exchanger,  6   a,    6   b  electronic expansion valve,  7  third heat exchanger,  8 ,  8   b  refrigerant,  9  water circuit,  10  water,  11  heating appliance,  12  water heat exchange tank,  13  clean water,  101   a  heat transfer plate,  101   b  heat transfer plate,  102   a  heat transfer plate group,  102   b  heat transfer plate group,  103   a  to  103   g  nozzle,  104   a,    104   b  reinforcing plate,  105   a,    105   b  side plate,  106   a,    106   b  isolation plate,  107  intermediate reinforcing plate,  108  fundamental part,  109   a  to  109   c  channel hole,  110   a,    110   b  corrugated shape,  111   a  to  111   d  narrowing portion,  112   a  to  112   d  heat nontransfer space.