Patent Publication Number: US-2017356681-A1

Title: Refrigeration and heating system

Description:
BACKGROUND OF THE INVENTION 
     In order to increase the efficiency of a refrigeration system by recovering the heat rejected by the refrigeration system combined refrigeration and heating systems are provided in which the heat generated by the refrigeration system is not rejected as waste heat to the environment but delivered to a heating system to be used for heating a building and/or service water etc. 
     At low ambient temperatures, e.g. in winter, only a comparatively low cooling capacity is needed. As a result, the compressor(s) of the refrigeration system will run only in part load providing only a comparatively low heating capacity. Full load with all compressors running at full speed, which causes the system&#39;s heating capacity to be at its maximum, will take place only rarely, namely during the hottest days of summer, when usually only a reduced amount of heat is needed. 
     As in case of low ambient temperatures, less cooling capacity but increased heating capacity is needed, the heat provided by the refrigeration process may not be sufficient to meet the heating demands. 
     It therefore would be beneficial to provide an improved combined refrigeration and heating system and a method of operating such a system allowing to meet increased heating demands even when less cooling capacity is needed. 
     DISCLOSURE OF THE INVENTION 
     A refrigeration and heating system according to an exemplary embodiment of the invention comprises a refrigeration circuit and a heating circuit, which are coupled by a coupling heat exchanger configured for transferring heat from a refrigerant circulating within the refrigeration circuit to a heating fluid circulating within the heating circuit. The refrigeration circuit comprises in the direction of flow of the circulating refrigerant: at least one compressor; a refrigeration circuit side of a coupling heat exchanger; at least one gas cooler; at least one expansion device; and at least one evaporator. The heating circuit comprises: a heating circuit side of the coupling heat exchanger; at least one heat consumer; and at feast one controllable heating fluid bypass valve, which allows at least a portion of the heating fluid to flow directly from an outlet to an inlet of the heating circuit side of the coupling heat exchanger bypassing the at least one heat consumer. The refrigeration and heating system further comprises a control unit, which is configured for selectively opening the at least one heating fluid bypass valve in order to meet increased heating demands. 
     A method of operating a refrigeration and heating system according to an exemplary embodiment of the invention comprises the steps of
         circulating a refrigerant through a refrigeration circuit;   circulating a heating fluid through a heating circuit; the heating circuit and the refrigeration circuit being thermally coupled by means of a coupling heat exchanger allowing heat to transfer from the refrigeration circuit to the heating circuit; and   increasing the temperature of the refrigerant leaving the coupling heat exchanger by allowing at least a portion of the heating fluid to flow directly from an outlet to an inlet of the heating circuit side of the coupling heat exchanger bypassing the at least one heat consumer in order to meet increased heating demands.       

     A refrigeration and heating system according to another exemplary embodiment of the invention comprises a refrigeration circuit and a heating circuit, which are coupled by a coupling heat exchanger configured for transferring heat from a refrigerant circulating within the refrigeration circuit to a heating fluid circulating within the heating circuit. The refrigeration circuit comprises in the direction of flow of the circulating refrigerant: at least one compressor, a heat exchanger bypass valve, which is provided as an adjustable mixing valve, a refrigeration circuit side of a coupling heat exchanger, at least one gas cooler, at least one expansion device and at least one evaporator. The heating circuit comprises a heating circuit side of the coupling heat exchanger and at least one heat consumer. The coupling heat exchanger is configured for transferring heat from the refrigerant flowing through the refrigeration circuit side to the heating fluid flowing through the heating circuit side. The refrigeration and heating system further comprises a control unit, which is configured for selectively controlling the heat exchanger bypass valve for allowing at least a portion of the refrigerant to bypass the refrigeration circuit side of a coupling heat exchanger for increasing the temperature of the refrigerant upstream the gas cooler in order to meet increased heating demands. 
     A method of operating a refrigeration and heating system according to an exemplary embodiment of the invention comprises the steps of
         circulating a refrigerant through a refrigeration circuit;   circulating a heating fluid through a heating circuit; the heating circuit and the refrigeration circuit being thermally coupled by means of a coupling heat exchanger allowing heat to transfer from the refrigeration circuit to the heating circuit; and   increasing the temperature of the refrigerant circulating within the refrigeration circuit by allowing at least a portion of the refrigerant to bypass the coupling heat exchanger in order to meet increased heating demands.       

     According to an idea of the invention the refrigeration process is made less efficient by increasing the temperature of the refrigerant circulating within the refrigeration circuit. This can be achieved either by delivering a portion of the heating fluid leaving the coupling heat exchanger directly back into the coupling heat exchanger by means of a heating fluid bypass valve connected between then outlet side and the inlet side of the coupling heat exchanger&#39;s heating circuit side or by allowing at least a portion of the refrigerant circulating within the refrigeration circuit to bypass the coupling heat exchanger. When the temperature of the refrigerant within the refrigeration circuit is increased, enhanced operation of the compressor(s) is needed in order to meet the required cooling demands. This results in more thermal heat, which may be used for heating purposes, being created without increasing the cooling capacity. 
     For a system using carbon dioxide as a refrigerant it has been found that in average 33% more heating capacity can be generated, by maintaining the pressure and increasing the temperature of the refrigerant entering the gas cooler. In addition the thermal heat can be regulated without capacity stages. The additional heat generated by the compressor(s) can either be used for reducing the size of an external (e.g. electrical) heat source, which is used in state of the art systems in order to meet high heating demands, or even make an external heating source obsolete. As existing equipment can be used with only minor modifications, the implementation costs are low. 
    
    
     
       SHORT DESCRIPTION OF THE FIGURES 
         FIG. 1  shows a refrigeration and heating system  2   a  according to a first exemplary embodiment of the invention; and 
         FIG. 2  shows a refrigeration and heating system  2   b  according to a second exemplary embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE FIGURES 
     In the following, exemplary embodiments of the invention will be described in more detail with reference to the enclosed figures: 
       FIG. 1  shows a schematic view of a refrigeration and heating system  2   a  according to a first exemplary embodiment of the invention. 
     The refrigeration and heating system  2   a  comprises a refrigeration circuit  4  and a heating circuit  20  thermally coupled with each other by a coupling heat exchanger  8 , which is configured for transferring heat from the refrigeration circuit  4  to the heating circuit  20 . 
     The refrigeration circuit  4  in particular comprises in the direction of flow of a circulating refrigerant: a plurality of compressors  6   a ,  6   b ,  6   c  fluidly connected in parallel for compressing and circulating a fluid refrigerant through the refrigeration circuit  4 ; a coupling heat exchanger bypass valve  34  allowing to selectively direct the flow of refrigerant leaving the compressors  6   a ,  6   b ,  6   c  either to a refrigeration circuit side  8   a  of a coupling heat exchanger  8 , which couples the refrigeration circuit  4  to the heating circuit  20 , or to bypass said coupling heat exchanger  8  in order to direct the flow of refrigerant leaving the plurality of compressors  6   a ,  6   b ,  6   c  directly to the inlet side  10   a  of at least one gas cooler  10 , which is fluidly connected to the outlet side of the coupling heat exchanger  8 . The outlet side  10   b  of the at least one gas cooler  10  is connected via a gas cooler bypass valve  24 , which will be described in more detail further below, to the inlet side of a high pressure control device  12 , which is configured for expanding the refrigerant from the high pressure generated by the compressors  6   a ,  6   b ,  6   c  to a lower medium pressure, before it enters into a receiver  26 , which is configured for separating gas phase refrigerant collecting at the top of the receiver  26  from liquid refrigerant, collecting at the bottom of the receiver  26 . The bottom of the receiver is fluidly connected to a medium pressure expansion device  14  and an evaporator  16  fluidly connected downstream of the medium pressure expansion device  14  for evaporating the expanded refrigerant thereby absorbing heat from the environment and providing the desired cooling capacity. The outlet side of the evaporator  16  is fluidly connected to the inlet lines  7   a ,  7   b ,  7   c  of the compressors  6   a ,  6   b ,  6   c  closing the refrigeration cycle. 
     The compressors  6   a ,  6   b ,  6   c  may be individually switched on and off allowing to vary their combined performance. Optionally, at least one of the compressors  6   a ,  6   b ,  6   c  may be provided as a variable speed compressor  6   a  allowing to continuously vary its performance in order to adjust the capacity provided by the compressors  6   a ,  6   b ,  6   c  even more precisely. 
     A flash gas line  28  comprising a flash gas valve  30  and an optional heat exchanger  32 , which is configured for allowing heat exchange between the flash gas flowing through the flash gas line  28  and the liquid refrigerant leaving the bottom of the receiver  26 , fluidly connects an upper portion of the receiver  26  to inlet lines  7   a ,  7   b ,  7   c  of the compressors  6   a ,  6   b ,  6   c  allowing, by controlling the flash gas valve  30 , flash gas to selectively exit from the top of the receiver and to flow to the inlet side of the compressors  6   a ,  6   b ,  6   c . Selectively delivering flash gas from the receiver  26  to the inlet lines  7   a ,  7   b ,  7   c  of the compressors  6   a ,  6   b ,  6   c  allows to adjust the pressure with the receiver  26 . 
     An optional gas cooler bypass line  18 , which connects between the inlet side  10   a  of the gas cooler  10  and the gas cooler bypass valve  24  arranged between the outlet side  10   b  of the gas cooler  10  and the high pressure control device  12 , allows to selectively bypass the gas cooler  10  by opening the gas cooler bypass valve  24  in case so much heat is transferred from the refrigerant circuit  4  to the heating circuit  20  by means of the coupling heat exchanger  8  that no further cooling of the circulating refrigerant is necessary. 
     The heating circuit  20  comprises in the direction of flow of a circulating heating fluid a heating circuit side  8   b  of the coupling heat exchanger  8  and at least one heat consumer  22  for consuming the transferred heat, e.g. for heating water and/or (parts of) a building. 
     The coupling heat exchanger  8  is in thermal connection with the refrigerant circuit side  8   a  of the coupling heat exchanger  8  allowing heat to transfer from the refrigerant circulating within refrigeration circuit  4  and flowing through the refrigeration circuit side  8   a  of the coupling heat exchanger  8  to the heating fluid circulating within the heating circuit  20  and flowing through the heating circuit side  8   b  of the coupling heat exchanger  8 . At least one heating fluid pump  36  may be provided for supporting the circulation of the heating fluid through the heating circuit  20 . 
     According to an exemplary embodiment of the invention, at least one heating fluid bypass valve  23  is connected in parallel to the at least one heat consumer  22  allowing to partially bypass said at least one heat consumer  22  by at least partially opening the at least one heating fluid bypass valve  23  for allowing fluid to flow from the outlet side of the coupling heat exchanger&#39;s  8  heating circuit side  8   b  of the coupling heat exchanger  8  to the inlet side of said heating circuit side  8   b  of the coupling heat exchanger  8  without being cooled by delivering heat to the at least one heat consumer  22 . As a result, the temperature within the coupling heat exchanger  8  will increase and the temperature of the refrigerant leaving the refrigeration circuit side  8   a  of the coupling heat exchanger  8  will increase, as well. 
     The increased temperature of the refrigerant will result in more flash gas being produced downstream of the high pressure control device  12 , and as a result, the refrigeration circuit  4  will operate with less efficiency. In order to maintain the desired refrigeration capacity at the evaporator  16 , the performance of the compressors  6   a ,  6   b ,  6   c  has to be increased, e.g. by switching on additional compressors  6   a ,  6   b ,  6   c  or increasing the rotational speed of an adjustable compressor  6   a ,  6   b ,  6   c . An increased operation of the compressors  6   a ,  6   b ,  6   c  will add more thermal energy into the refrigeration and heating system  2   a , which is used for providing the desired heat at the heat consumer(s)  22 . 
     The refrigeration and heating system  2   a  further comprises a control unit  38  for controlling the compressors  6   a ,  6   b ,  6   c , the switchable valves  12 ,  24 ,  30 ,  34  of the refrigeration circuit  4  and in particular the heating fluid bypass valve  23  in order to provide the desired cooling and heating capacities. The control unit  38  may control the compressors  6   a ,  6   b ,  6   c  and valves  12 ,  23 ,  24 ,  30 ,  34  by means of electrical wires, which are not shown in the figure for reasons of clarity, or by means of wireless connections (WLAN; Bluetooth etc.). 
     In order to enable the control unit  38  to control the compressors  6   a ,  6   b ,  6   c  and valves  12 ,  23 ,  24 ,  30 ,  34  appropriately, at least one of a refrigerant pressure sensor  40 , a refrigerant temperature sensor  42 , a heating fluid temperature sensor  44  and an ambient air temperature sensor  46  may be provided, allowing the control unit  38  to control the compressors  6   a ,  6   b ,  6   c  and valves  12 ,  23 ,  24 ,  30 ,  34  based on the temperatures and/or pressures measured by said sensor(s)  40 ,  42 ,  44 ,  46 . A refrigerant pressure sensor  40  may in particular be located upstream the high pressure control valve  12 . 
       FIG. 2  shows a schematic view of a refrigeration and heating system  2   b  according to a second exemplary embodiment of the invention. 
     The features of the refrigeration and heating system  2   b  which are identical to the features of the first embodiment shown in  FIG. 1  are denoted with the same reference signs and will not be discussed in detail again. 
     In the refrigeration and heating system  2   b  according to the second embodiment the heat exchanger bypass valve  34  is provided as an adjustable mixing valve  34 , which may be controlled by the control unit  38  to selectively allow a portion of the refrigerant to bypass the coupling heat exchanger  8  in order to increase the temperature of the refrigerant upstream the gas cooler  10 . 
     As the temperature of the refrigerant may be regulated by means of the heat exchanger bypass valve  34 , the heating fluid bypass valve  23 , which has been described in the context of the first embodiment, is optional and may be omitted in the refrigeration and heating system  2   b  according to the second embodiment. 
     Furthermore, in said second embodiment, as it is shown in  FIG. 2 , a flash gas compressor line  29  fluidly connects between an upper portion of the receiver  26  and the inlet side  7   d  of an additional flash gas compressor (economizer compressor)  6   d . The output side of said flash gas compressor  6   d  is connected with the outputs sides of the other compressors  6   a ,  6   b ,  6   c . Providing a separate flash gas compressor  6   d  allows for an efficient compression of the flash gas delivered from the refrigerant receiver  26 . 
     A flash gas compressor  6   d  and the flash gas compressor line  29  as shown in  FIG. 2  may by employed in the first embodiment comprising a heating fluid bypass valve  23  instead of an adjustable head exchanger bypass valve  34 , as well. The flash gas compressor  6   d  and the flash gas compressor line  29  may be employed alternatively or in addition to the flash gas line  28  comprising the flash gas valve  30  as shown in  FIG. 1 . 
     Further Embodiments 
     A number of optional features are set out in the following. These features may be realized in particular embodiments, alone or in combination with any of the other features: 
     In an embodiment the bypass valve is a continuously adjustable valve allowing to selectively adjust the flow of heating fluid bypassing the heat consumer(s) with high accuracy. 
     In an embodiment the refrigeration circuit comprises a gas cooler bypass line and a gas cooler bypass valve allowing refrigerant to selectively bypass the gas cooler(s) in case the temperature of the refrigerant leaving the coupling heat exchanger is low enough so that no further cooling of the refrigerant is necessary. 
     In an embodiment a refrigerant receiver is provided downstream of the gas cooler for separating gas phase refrigerant from liquid phase refrigerant and storing said refrigerant. Such a separation, which allows to deliver only liquid refrigerant to the expansion device which is located upstream of the evaporator, will enhance the efficiency of the refrigeration circuit. 
     In an embodiment a high pressure control device is provided upstream of the refrigerant receiver in order to expand the refrigerant leaving the gas cooler before entering the receiver. 
     In an embodiment a flash gas line fluidly connects between an upper portion of the refrigerant receiver and an inlet line of the at least one compressor for allowing flash gas, which collects at the top of the receiver, to flow from the receiver directly to the inlet side of the compressor(s) bypassing the medium expansion device(s) and the evaporator(s). 
     In an embodiment a flash gas valve provided in the flash gas line allows to control and regulate the flow of flash gas through the flash gas line and to adjust the pressure within the receiver. 
     Additionally or alternatively a flash gas compressor line may fluidly connect the upper portion of the refrigerant receiver with an inlet line of an additional flash gas compressor. 
     In an embodiment an additional flash gas heat exchanger allows heat exchange between the flash gas flowing through the flash gas line and refrigerant leaving from the bottom of the receiver. This heat exchange may improve the efficiency of the refrigeration circuit even further. 
     In an embodiment the control unit for controlling the at least one compressor, the heating fluid bypass valve and/or the gas cooler bypass valve comprises a microcomputer which is configured for running an appropriate program controlling the operation of the combined refrigeration and heating system. 
     In an embodiment the refrigeration and heating system further comprises at least one of a refrigerant pressure sensor, a refrigerant temperature sensor, a heating fluid temperature sensor and/or an ambient air temperature sensor functionally connected to the control unit for allowing the control unit to control the compressors, the heating fluid bypass valve and/or the gas cooler bypass valve based on the measured temperatures and/or pressures in order to optimally adjust the operation of the refrigeration and heating system. 
     In an embodiment the refrigerant comprises carbon dioxide, which provides an efficient, inflammable, non-toxic and environmentally acceptable refrigerant, which partly operates in transcritical conditions. The heating fluid in particular may include water, which may in particular comprise an anti-corrosive additive. 
     In an embodiment the method of operating a refrigeration and heating system includes the step of controlling a controllable valve, which is connected between the outlet and the inlet of the heating circuit side of the coupling heat exchanger, for selectively allowing a portion of the heating fluid to flow directly from an outlet to an inlet of the heating circuit side of the coupling heat exchanger bypassing the at least one heat consumer. 
     In an embodiment the method of operating a refrigeration and heating system includes the step of controlling an adjustable heat exchanger bypass valve for selectively allowing a portion of the heating fluid to bypass the coupling heat exchanger in order to increase the temperature of the refrigerant circulating within the refrigeration circuit. 
     In an embodiment the method may further include measuring the temperature of the refrigerant circulating within the refrigeration circuit and/or the temperature of the heating fluid circulating within the heating circuit and controlling the controllable valve, the adjustable heat exchanger bypass valve and/or the at least one compressor based on the measured temperature of the circulating refrigerant and/or the measured temperature of the heating fluid, respectively, in order to set an optimal operating point of the refrigeration circuit. 
     Alternatively or additionally the method may further include measuring the pressure of the refrigerant circulating within the refrigeration circuit, in particular upstream the high pressure control valve and controlling the controllable bypass valve, the adjustable heat exchanger bypass valve and/or the at least one compressor based on the measured pressure in order to set the optimal point of operation of the refrigeration circuit. 
     In an embodiment the method may further comprise measuring the ambient temperature and controlling the controllable valve based on the measured ambient temperature and/or determining the heating and/or cooling demands and controlling the controllable valve, the adjustable heat exchanger bypass valve and/or the at least one compressor based on said demands. 
     The method may also include to determine the heating and/or cooling demands and controlling the controllable valve, the adjustable heat exchanger bypass valve and/or the at least one compressor based on said demands. 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition many modifications may be made to adopt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention include all embodiments falling within the scope of the dependent claims. 
     REFERENCES 
     
         
           2   a ,  2   b  refrigeration and heating system 
           4  refrigeration circuit 
           6   a ,  6   b ,  6   c  at least one compressor 
           6   d  flash gas compressor 
           7   a ,  7   b ,  7   c ,  7   d  compressor inlet lines 
           8  coupling heat exchanger 
           8   a  refrigeration circuit side of the heat exchanger 
           8   b  heating circuit side of the heat exchanger 
           10  gas cooler; 
           10   a  inlet side of the gas cooler; 
           10   b  outlet side of the gas cooler; 
           12  high pressure control device 
           14  medium pressure expansion device 
           16  evaporator 
           18  gas cooler bypass line 
           20  heating circuit 
           22  heat consumer 
           23  heating fluid bypass valve 
           24  gas cooler bypass valve 
           26  refrigerant receiver 
           28  flash gas line 
           29  flash gas compressor line 
           30  flash gas valve/medium pressure control valve 
           32  flash gas heat exchanger 
           34  heat exchanger bypass valve/adjustable mixing valve 
           36  heating fluid pump 
           38  control unit 
           40  refrigerant pressure sensor 
           42  refrigerant temperature sensor 
           44  heating fluid temperature sensor 
           46  ambient air temperature sensor