Abstract:
A method for providing controllable amounts of heat recovery from a refrigerant circuit includes the steps of providing a cooling circuit comprising a compressor, a condenser, an expansion device and an evaporator connected in series by refrigerant flow lines; providing a heat recovery circuit comprising a heat recovery heat exchanger, the heat recovery circuit being connected to the cooling circuit so that the heat recovery heat exchanger is in parallel with the condenser, and the heat recovery heat exchanger being in heat exchange relationship with a fluid to be heated based upon an end-user demand for heat; and selectively flowing refrigerant through the condenser of the cooling circuit and the heat recovery heat exchanger of the heat recovery circuit so as to maintain temperature of the fluid within a temperature hand around a set point provided by the end user.

Description:
CROSS REFERENCE TO PROVISIONAL APPLICATION 
       [0001]    This application claims the benefit of the filing date of co-pending and commonly owned provisional application Ser. No. 60/615,440, filed Sep. 30, 2004. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a refrigeration system and method for providing heat recovery on a flexible basis as desired by the end-user. 
         [0003]    Cooling circuits of refrigeration units frequently include heat recovery units which allow heat from refrigerant discharged by the compressor to be used for heating other fluids. One example of use of this type of system would be in heating water for satisfying the hot water requirements of a building. This advantageously allows the use of such heat to satisfy other energy needs. 
         [0004]    The needs of various different buildings or other end-users in connection with the amount of heat provided to other fluids from the refrigerant circuit can vary substantially from end-user to end-user, and further can vary significantly over time for any end-user. 
         [0005]    Unfortunately, refrigeration systems with heat recovery circuits are not capable of providing sufficient flexibility to meet the various demands of different end-users, and further the time-changing demands of individual end-users. 
         [0006]    It is the primary object of the present invention to provide a system and method which address these needs. 
         [0007]    Other objects and advantages of the present invention will appear hereinbelow. 
       SUMMARY OF THE INVENTION 
       [0008]    In accordance with the present invention, the foregoing objects and advantages have been readily attained. 
         [0009]    According to the invention, a method is provided for providing controllable amounts of heat recovery from a refrigerant circuit, which method comprises the steps of providing a cooling circuit comprising a compressor, a condenser, an expansion device and an evaporator connected in series by refrigerant flow lines; providing a heat recovery circuit comprising a heat recovery heat exchanger, the heat recovery circuit being connected to the cooling circuit so that the heat recovery heat exchanger is in parallel with the condenser, and the heat recovery heat exchanger being in heat exchange relationship with a fluid to be heated based upon an end-user demand for heat; and selectively flowing refrigerant through the condenser of the cooling circuit and the heat recovery heat exchanger of the heat recovery circuit so as to maintain temperature of the fluid within a temperature band around a set point provided by the end user. 
         [0010]    In further accordance with the present invention, the system may further comprise a plurality of cooling circuits and a plurality of heat recovery circuits, and the selectively flowing step may suitably comprise selectively flowing refrigerant through heat recovery heat exchangers of one or more of the heat recovery circuits. 
         [0011]    The foregoing system and method allow flexible heating of fluid with the heat recovery heat exchanger to satisfy different and changing heat recovery needs of different end-users with a single system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    A detailed description of preferred embodiments of the present invention follows, with reference to the attached drawings, wherein: 
           [0013]      FIG. 1  schematically illustrates a single circuit adapted for cooling and heat reclaim operation according to the invention; 
           [0014]      FIG. 2  schematically illustrates a multiple-circuit system embodiment according to the invention; and 
           [0015]      FIG. 3  illustrates operation of a system in accordance with the present invention to maintain temperature of a fluid within a particular band utilizing the heat recovery operation of the system of a present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The invention relates to a refrigeration system which includes at least one heat recovery circuit. The system can selectively operate in a conventional cooling mode, and in heat recovery mode to provide transfer of heat from heated refrigerant fluid to a fluid which is desired to be heated. One example of such a fluid is water to meet the hot water requirements of an end-user, for example, the hot water requirements of a building. The system of the present invention can be used to heat fluids such as this water, and functions in such a way that widely varying needs can be met with the same system. Specifically, the system can be used to supply heated fluid at a broad range of different temperature setpoints, and within a selectable range of the setpoint. 
         [0017]      FIG. 1  shows a system  10  which includes refrigeration circuit having a compressor  12 , a condenser  14 , an expansion device  16  and an evaporator  18 . While the lines which connect these various components will be further discussed below, it should be readily appreciated that these components when operated in series define a typical refrigeration circuit. Compressed refrigerant from compressor  12  is sequentially passed through condenser  14  and expansion device  16  to evaporator  18 , wherein the refrigerant cools a stream of air as desired. Refrigerant from evaporator  18  then returns to compressor  12  to complete the circuit. The refrigerant exiting the compressor has a temperature which is sufficiently high that heat can be effectively transferred to other fluids, for example to water which must be heated to a temperature sufficient for meeting typical domestic, commercial or industrial hot water needs. 
         [0018]      FIG. 1  further shows a heat recovery heat exchanger  20  which is positioned to receive refrigerant from system  10  and exchange heat from the refrigerant to a separate stream of fluid (shown in  FIG. 2  which is described below) so as to heat this fluid as desired. This fluid may be water for supplying the hot water needs of a building, or any other fluid which can advantageously make use of heat transferred to same from the refrigerant. 
         [0019]      FIG. 1  also shows a control unit  22  which is adapted for controlling the system  10  to operate in various different modes as will be further discussed below. 
         [0020]    In order to operate as desired in accordance with the present invention, system  10  is controlled so as to flow refrigerant from compressor  12  to either condenser  14  or heat recovery heat exchanger  20 . When refrigerant flows from compressor  12  to heat recovery heat exchanger  20 , the high-temperature refrigerant advantageously transfers heat through heat exchanger  20  to the fluid to be heated as desired. 
         [0021]    A series of valves  24 ,  26 ,  28  and  30 , are positioned along lines of system  10  and operated by control unit  22  so as to direct flow from compressor  12  to condenser  14  or heat recovery heat exchanger  20 , and also to direct flow from these components as desired. Thus, flow from compressor  12  passes through a compressor discharge line  32  to a first branch  34  which extends through valve  24  to condenser  14 , and through a second branch  36  which extends through valve  28  to heat recovery heat exchanger  20 . From condenser  14 , discharge goes through condenser discharge line  38  through a first branch  40  which flows to expansion device  16 , and a second branch  42  which flows through valve  26  and line  44  to evaporator  18 . Flow from evaporator  18  passes through line  46  to compressor  12 . 
         [0022]      FIG. 1  also shows check valves  54 ,  56 , which advantageously serve to maintain flow through the lines of system  10  as desired. 
         [0023]    Co-pending and commonly owned U.S. patent application Ser. No. 10/957,181, filed Sep. 30, 2005, discloses a method of managing refrigerant charge in a system such as that illustrated in  FIG. 1 , and discloses methods whereby refrigerant charge stored in whichever of condenser  14  and heat recovery heat exchanger  20  is not currently active is used to help maintain a sub-cooling or saturation temperature within a range or setpoint. This application (Ser. No. 10/957,181) is incorporated herein, in its entirety, by reference. 
         [0024]    In cooling mode, the system is operated as described above, with the valves set to operate without flow through heat recovery heat exchanger  20 . During this operation, while condenser  14  gives off heat to an outside location as is well known, heat exchanger  20  stores charge and evaporator  18  cools a stream of air to be conditioned as is well known. 
         [0025]    In heat recovery mode, flow from compressor  12  passes through line  36  to valve  28  which is open so that refrigerant enters heat recovery heat exchanger  20 . In heat exchanger  20 , refrigerant gives off heat to a fluid to be heated, for example water. From heat exchanger  20 , flow passes to a condenser discharge line  48  and, from there, passes through line  52  to expansion device  16  and then to evaporator  18 . A sensor  58  can advantageously be positioned along the refrigerant lines, preferably just upstream of evaporator  16 , and is utilized to determine properties of the refrigerant at that point. 
         [0026]    Control unit  22  is operatively communicated with each of valves  24 ,  26 ,  28  and  30 , as well as sensor  58  and advantageously expansion device  16 , as shown by the dashed lines in  FIG. 1 . Control unit  22  is advantageously programmed to control the position of the various valves discussed above based upon information from sensor  58 , and thereby to determine position of the various valves so as to operate in cooling mode without the heat recovery heat exchanger, or in heat recovery mode, and to cycle between these modes as needed. According to the invention, by cycling between cooling mode and heat recovery mode, a desired amount of heat between 0 and 100% of the system capability can be transferred to the fluid to be heated. In the embodiment of  FIG. 2  to be discussed below, control unit  22  is preferably also utilized and would be connected and programmed in similar manner to provide desired amounts of heat recovery. In this embodiment, programming of control unit  22  would preferably further include stepped or otherwise controlled amounts of change in heat recovery mode. In other words, control unit  22  in the embodiment of  FIG. 2  could be programmed to change or cycle one circuit at a time in order to maintain a desired temperature of the heat receiving fluid. 
         [0027]    Valves  26 ,  30  are used to selectively recover charge stored in whichever one of condenser  14  and heat exchanger  20  is not active. This charge can help to control the subcooling or saturation temperature of refrigerant measured at sensor  58 . When charge is to be recovered from condenser  14 , valve  26  is opened to allow charge to flow through lines  42 ,  44  to evaporator  18 , and when charge is to be recovered from heat exchanger  20 , valve  30  is opened to allow charge to flow from heat exchanger  20  through line  50  to evaporator  18 . 
         [0028]      FIG. 2  shows a further system in accordance with the present invention, with the additional showing being that two different circuits  10 A and  10 B are provided, each of which selectively communicate with evaporator  18  and heat recovery heat exchanger  20 . In this embodiment, circuits  10 A and  10 B flow to the same evaporator  18  and the same heat recovery heat exchanger  20 , although other configurations are possible and well within the broad scope of the present invention. 
         [0029]    The system of  FIG. 2  can be operated with circuits  10 A,  10 B operated independently in similar fashion to the operation of the system of  FIG. 1 . Each circuit  10 A,  10 B has the same type of components as discussed above regarding  FIG. 1 . Thus, further description of these components is not repeated here. 
         [0030]      FIG. 2  shows heat recovery heat exchanger  20  with a heat exchange line  60  which would carry the fluid to which heat is being provided. 
         [0031]    It should readily be appreciated that, depending upon the needs of an end-user, the system of  FIG. 2  can be operated with one or both of the circuits in heat recovery mode, and that this will serve to better provide the desired reclaim heat to the end-user. 
         [0032]      FIG. 3  shows an example of operation of the present invention. As shown, an end-user would select a set point for desired temperature of fluid to be treated using the heat recovery heat exchanger. A reasonable tolerance is utilized to set a band around the set point, and temperature measurements of the fluid are made.  FIG. 3  shows the change over time of the temperature in such a system, and begins with the heat reclaim heat exchanger not in use. As the temperature of the fluid (labeled “condenser water temperature” in  FIG. 3 ) gradually declines, it eventually hits the lower threshold of the band around the set point. The system is programmed such that, when the lower threshold is hit, valves are controlled to operate at least one circuit in a heat recovery mode to provide heat to the fluid and thereby keep the fluid temperature within the band.  FIG. 3  shows the temperature of the fluid increasing accordingly after operation in heat recovery mode. When the temperature hits an upper threshold of the range surrounding the set point, the compressor circuit which was being operated in heat reclaim mode is switched off, and the temperature of the fluid again drops. 
         [0033]    This cycle is repeated, switching heat reclaim mode on when the temperature reaches a lower threshold and switching heat reclaim mode off when the temperature reaches a high level of the band. 
         [0034]      FIG. 3  shows a simple illustration for a system having only one heat recovery heat exchanger. It should be appreciated that with a multiple circuit system, different ranges within the broad operating band could be adapted to trigger adding more circuits to heat recovery mode and/or removing one of a plurality of circuits operating in heat recovery mode so as to provide more flexibility in maintaining the heated fluid temperature as desired. 
         [0035]    In this regard, according to the invention, control unit  22  is programmed to operate the system in cooling and heat recovery or reclaim modes, and suitable programming for a two circuit system is described below. In this description, condenser  14  is referred to as an air cooled condenser since the condenser is normally cooled by outside air, and the heat recovery heat exchanger is referred to as a water cooled condenser since this condenser is cooled by the fluid to which heat is being transferred, which in one embodiment is water. 
         [0036]    The software or programming of control unit  22  controls the changeover from operation in air cooled to reclaim or reclaim to air cooled modes of operation. In air cooled operation, condenser  14  is considered active, as a major portion of refrigerant is passed through same, and heat recovery heat exchanger  20  is considered inactive, as refrigerant flows through this heat exchanger only in incidental amounts, for example due to an imperfect valve. The inverse of this definition also applies to use of the term “active”, that is, in heat reclaim mode the substantial portion of refrigerant flows through heat recovery heat exchanger, and only incidental amounts of refrigerant flow to condenser  14 . 
         [0037]    Changeover from reclaim to air cooled can be caused by: a manual reclaim select change due to a local, remote or other command on the unit. A changeover can also be caused by a heat reclaim temperature change while reclaim has been selected. According to the invention, an algorithm is provided for monitoring the entering reclaim sensor temperature and comparing it with the reclaim setpoint so as to determine if reclaim is active or not. 
         [0038]    If a reclaim function is currently active, or has been selected, the reclaim shall become active when the entering reclaim temperature comes below the reclaim setpoint. 
         [0039]    Based on a difference between reclaim entering water temperature and the reclaim setpoint, control unit  22  determines if one or two circuits are required to provide heat reclaim capacity. In this manner, control unit  22  maintains the temperature of fluid as close as possible to the desired setpoint, and also avoids frequent changing from air cooled to reclaim or reclaim to air cooled cycles. Programming for control unit  22  can further be illustrated with reference to the below table. 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 # of 
                 # of circ&#39;ts 
               
               
                   
                 reclaim 
                 circ&#39;ts in 
                 in reclaim 
               
               
                 hr_ewt 
                 select 
                 reclaim 
                 STATUS CHANGE 
               
               
                   
               
             
             
               
                 — 
                 no 
                 0 
                 −2 
               
               
                 hr_ewt &lt; rsp − hr_deadb/2 
                 yes 
                 — 
                 +2 
               
               
                 rsp − hr_deadb/2 &lt; hr_ewt &lt; 
                 yes 
                 0 
                 +1 
               
               
                 rsp − hr_deadb/4 
               
               
                 rsp − hr_deadb/2 &lt; hr_ewt &lt; 
                 yes 
                 1 
                 Unchanged 
               
               
                 rsp − hr_deadb/4 
               
               
                 rsp − hr_deadb/4 &lt; hr_ewt &lt; 
                 0 
                 — 
                 Unchanged 
               
               
                 rsp + hr_deadb/4 
               
               
                 rsp + hr_deadb/4 &lt; hr_ewt &lt; 
                 0 
                 1 
                 Unchanged 
               
               
                 rsp + hr_deadb/2 
               
               
                 rsp + hr_deadb/4 &lt; hr_ewt &lt; 
                 0 
                 2 
                 −1 
               
               
                 rsp + hr_deadb/2 
               
               
                 hr_ewt &gt; rsp + hr_deadb/2 
                 0 
                 — 
                 −2 
               
               
                   
               
             
          
         
       
     
         [0040]    According to the invention, pumpdown sessions are periodically utilized to recover refrigerant volumes stored in the non-active heat exchanger. Further according to the invention, it is preferred that both circuits shall not initiate a pumpdown session at the same time. Each circuit therefore has its own reclaim function, and the description below is applied for both circuit. 
         [0041]    For a change from non-reclaim to reclaim operation, the following procedure is preferred: 
         [0042]    Verify the circuit has run for more than 2 minutes in cooling mode. 
         [0043]    Turn on the reclaim condenser pump if reclaim select is enabled. 
         [0044]    Verify that condenser flow is established: if not after 1 minute delay has elapsed, reclaim operation shall be aborted and an alarm shall be displayed. 
         [0045]    Check whether reclaim water entering requires the circuit to go to a heat reclaim session and whether the number of air cooled to reclaim changeovers is not higher than 4 per hour and whether the last changeover did not occur within a 7 minute delay. 
         [0046]    Wait until saturated condensing temperature minus saturated suction temperature is higher than 10° F. (10° C.). 
         [0047]    Start the air condenser pumpdown sequence by opening the water condenser entering valve, and closing the air condenser valve 3 s later. 
         [0048]    After a 1 minute duration or as soon as the subcooling is greater than 13° F., reclaim operation is effective. 
         [0049]    For a change from reclaim to non-reclaim mode, changeover is preferred according to the following procedure: 
         [0050]    Start a water condenser pumpdown sequence by opening the air condenser entering valve, and closing the water condenser valve 3 s later. 
         [0051]    If reclaim select is no longer active, turn off condenser pump. 
         [0052]    According to the invention, a function is preferably run, for example at every 3 second interval, in order to adjust subcooling correctly during reclaim operation (a longer interval is not recommended). 
         [0053]    During a heat recovery operation, too much charge (high subcooling) can cause high a condensing temperature, and it is necessary to inject gas into the air condenser by opening the entering air condenser valve for example by opening the valve once, for about 3 s, and repeating every 20 s. 
         [0054]    During heat recovery operation, missing gas (refrigerant) can cause poor heating performance and/or low subcooling. In order to address this, gas is injected into the water condenser by opening the leaving air condenser valve once, for about 3 s, every 20 s (This is an air condenser pumpdown as refrigerant is still resident in the air condenser because its capacity is typically larger than the reclaim condenser capacity). Such a pumpdown is efficient only if the delta pressure between air and suction pressure is correct. Gas injection should not be done if reclaim water temperature is high or saturated condensing temperature is not too high or superheat is not too low. 
         [0055]    In this regard, the fluctuation or difference between the high and low points of the range is dependent, among other things, upon the power capacity of the fluid which is receiving the heat. In other words, the more water which is passed through the heat exchanger, the more gradual will be the change in temperature of this water. Thus, an end-user can determine what level of stability is desired in connection with the temperature of the outgoing liquid, and can adjust the amount of water passing through the heat reclaim heat exchanger based upon same. As one non-limiting example, Table 1 below sets forth a series of different stabilities along with volume of the water needed in connection with same. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Stability 
                 Volume 
               
               
                   
                   
               
             
             
               
                   
                 2° C. 
                 40 l/kW 
               
               
                   
                 3° C. 
                 30 l/kW 
               
               
                   
                 4° C. 
                 20 l/kW 
               
               
                   
                 5° C. 
                 15 l/kW 
               
               
                   
                   
               
             
          
         
       
     
         [0056]    It should readily be appreciated that the system and method of the present invention advantageously provides for extremely flexible specification of heated fluid requirements of an end-user. 
         [0057]    It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.