Abstract:
A system pressure actuated charge compensator for use with a heat pump having a liquid service valve and a vapor service valve. The charge compensator comprises a holding tank having first and second ports, a first pressure tap coupled to the first port and removeably coupleable to the vapor service valve, and a second pressure tap coupled to the second port and removeably coupleable to the liquid service valve. A heat pump system and a method of manufacturing a charge compensator are also provided.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention is directed, in general, to air conditioning systems and, more particularly, to a field-installed, system pressure actuated charge compensator not requiring brazing. 
     BACKGROUND OF THE INVENTION 
     In heat pump systems, the volume ratio is the internal volume of the outdoor coil versus the internal volume of the indoor coil. The indoor and outdoor coils in conventional heat pump systems are of the appropriate size to run efficiently in cooling and heating mode. When upgrading older heat pump systems from a low SEER rating to SEER  13  or higher in order to improve cooling performance, an imbalance can occur as the volume ratio changes. When the indoor coil volume is smaller than the outdoor coil volume, the system has a high volume ratio. Conversely, when the indoor coil volume is greater than the outdoor coil volume, the system has a low volume ratio. These conditions create an imbalance in the amount of refrigerant charge needed as the heat pump changes from heating to cooling mode, i.e., the system needs more refrigerant during the cooling cycle than during the heating cycle. Existing charge compensators comprise a tank with a vapor tube passing through the tank, but the vapor tube is not open to the tank. The tank inner volume is connected to the liquid line and the excess charge is thermally drawn into the tank when the tube is cold during the heating mode; the charge is thermally driven out during the cooling mode when the tube is warm during the cooling mode. This type of compensator, if used in the field, must be brazed into the system to assure that the system is vapor tight. This requires that the refrigerant charge be removed, the system be opened, the compensator brazed in place by a technician, and the total system be evacuated and recharged. 
     Accordingly, what is needed in the art is a charge compensator that does not require brazing the compensator into the liquid and vapor lines. 
     SUMMARY OF THE INVENTION 
     To address the above-discussed deficiencies of the prior art, the present invention provides, in one aspect, a charge compensator that is pressure activated for use with a heat pump having a liquid service valve and a vapor service valve. The charge compensator comprises a holding tank having first and second ports, a first pressure tap coupled to the first port and removeably coupleable to the vapor service valve, and a second pressure tap coupled to the second port and removeably coupleable to the liquid service valve. A heat pump system and a method of manufacturing a charge compensator are also provided. 
     The foregoing has outlined features of the present invention so that those skilled in the pertinent art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the pertinent art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the pertinent art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  illustrates a schematic view of one embodiment of a charge compensator kit for field installation constructed according to the principles of the present invention; 
         FIG. 2  illustrates a schematic view of an external unit of a heat pump system having installed thereon the charge compensator kit of  FIG. 1 ; and 
         FIG. 3  illustrates a schematic view of an alternative embodiment of a charge compensator kit for field installation constructed according to the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring initially to  FIG. 1 , illustrated is a schematic view of one embodiment of a charge compensator kit  100  for field installation constructed according to the principles of the present invention. In a preferred embodiment, the charge compensator kit  100  comprises a liquid tank  110  having a first port  111 , a second port  112 , a first pressure tap  121 , a second pressure tap  122 , a vapor line  130 , a liquid line  140 , a check valve  150 , a thermostatic expansion valve (TXV)  160 , a TXV sensing bulb  170 , and a sensing line  175 . The first and second pressure taps  121 ,  122 , respectively, have for service work first and second auxiliary ports  123 ,  124 , respectively. The vapor line  130  fluidly couples the first port  111  and the first pressure tap  121 . The liquid line  140  fluidly couples the second port  112  and the second pressure tap  122 . The first and second pressure taps  121 ,  122 , respectively are removeably coupleable to service valves (not shown) of a heat pump system. For the purposes of this discussion, removeably coupleable means that the first and second pressure taps  121 ,  122  are threaded and therefore may be removed from the system with conventional mechanical tools and without the need for brazing or de-brazing of the system. The check valve  150  is interposed the first port  111  and the first pressure tap  121 . The thermostatic expansion valve  160  is interposed the second port  112  and the second pressure tap  122 . The TXV sensing bulb  170  is coupled to the TXV  160  by the sensing line  175 . The first and second ports  111 ,  112  open into an interior of the liquid holding tank  110 . In contrast, the prior art relied upon a tube passing through an interior of the tank from the first port to the second port and not open to the interior of the tank. The prior art relied upon a passive action of the temperature of the refrigerant passing through the tube to withdraw from or return excess refrigerant to the system. 
     Referring now to  FIG. 2 , illustrated is a schematic view of an external unit  200  of a heat pump system having installed thereon the charge compensator kit  100  of  FIG. 1 . The heat pump external unit  200  comprises an outdoor coil or heat exchanger  210 , a system common vapor line  220 , a vapor service valve  230 , a system common liquid line  240 , and a liquid service valve  250 . The first pressure tap  121  removeably couples to the vapor service valve  230  by threading. In a like manner, the second pressure tap  122  removeably couples to the liquid service valve  250  by threading. The TXV sensing bulb  170  mechanically couples to an exterior of the vapor line  220  and is covered with insulation  260 . The insulation  260  assures that the TXV sensing bulb  170  is sensing the temperature of the vapor line and excludes other outside influences, such as sunlight. 
     To install the charge compensator kit  100  on the heat pump external unit  200 , the system refrigerant charge is first pumped into the outdoor heat exchanger  210 . The second pressure tap  122  is removeably coupled to the liquid service valve  250  and the first pressure tap  121  is removeably coupled to the vapor service valve  230 . The TXV sensing bulb  170  is coupled to the vapor line  220  and is covered with insulation  260 . When the physical installation is complete, the system may be evacuated through first and second auxiliary ports  123 ,  124  on the first and second pressure taps  121 ,  122  as required. The refrigerant charge is then released from the outdoor heat exchanger  210  and the system is ready for operation. 
     The proposed field installed system works based on the pressure difference between the common liquid refrigerant line  240  and the common vapor refrigerant line  220 . In the cooling mode the common vapor pressure is lower than the common liquid pressure. Conversely, the common vapor pressure is higher in the heating mode. During operation of the heat pump system in heating mode, excess refrigerant charge is routed into the tank  110  through the liquid line  140  and the TXV  160  controlled by the TXV sensing bulb  170 . Note that the vapor line does not pass through the tank  110 , but rather opens into the tank  110 . This allows the tank to operate as a reservoir and therefore is actively controlled by operation of the TXV  160  in contrast to the passive operation in the prior art of relying on the temperature of the refrigerant passing through the central vapor line to withdraw from or return excess refrigerant to the system. This provides a more accurate relationship of available charge to the required refrigerant capacity. During operation of the heat pump system in cooling mode, refrigerant charge held in the tank  110  is released into the vapor line  130  through the check valve  150 . During the heating mode, the vapor line  220  is at a higher pressure than the liquid line  140 ; this allows liquid refrigerant to accumulate in the tank  110 . 
     Referring now to  FIG. 3 , illustrated is a schematic view of an alternative embodiment of a charge compensator kit  300  for field installation constructed according to the principles of the present invention. In a preferred embodiment, the charge compensator kit  300  comprises a liquid tank  310  having a first port  311  and a second port  312 , a first pressure tap  321 , a second pressure tap  322 , a vapor line  330 , a liquid line  340 , a check valve  350 , and a liquid line solenoid valve  360 . The liquid tank  310 ; first and second pressure taps  321 ,  322 , respectively; vapor line  330 ; liquid line  340 , and check valve  350  are installed and function identically to their analogous parts of the charge compensator kit  100  of  FIG. 1 . However, flow through the liquid line  340  is controlled by the liquid line solenoid valve  360  powered by  24  VAC instead of the TXV  160 , which can be directed by the central thermostat. 
     Thus, a field-installed charge compensator kit has been described. The charge compensator kit may be installed on the vapor and liquid service valves of an external heat pump heat exchanger so as to compensate for different charges required for heating vs. cooling when the indoor and outdoor heat exchangers are of different sizes. This condition is regularly encountered when the outdoor heat exchanger is upgraded to improve cooling performance. 
     Although the present invention has been described in detail, those skilled in the pertinent art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.