Abstract:
A heat transfer system including mechanical and electrical components for use with a mechanical air conditioning system to enable the system to efficiently reject heat to a water source, such as a pool or spa while simultaneously cooling an interior space. The air conditioning system incorporates three primary heat transfer coils in a mechanical refrigeration cycle to provide comfort cooling to an interior space while rejecting heat to either the atmosphere or a water source, such as a swimming pool. In an alternate heat pump embodiment, the system is capable of operating in an additional mode to absorb heat from the atmosphere and reject heat to the interior space.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to mechanical heat transfer systems, such as air conditioning systems, and more particularly to a apparatus and method for converting an otherwise conventional residential or commercial air conditioning system into a heat transfer system capable of cooling an interior space while simultaneously heating a body of water, such as water from a swimming pool. 
     2. Description of the Background Art 
     Mechanical air conditioning and refrigeration systems, for absorbing heat from one source and rejecting heat to another source, are well known in the art. In a conventional mechanical air conditioning system, a pair of heat exchangers are fluidly connected in a refrigeration circuit through which a heat transfer medium (hereinafter &#34;refrigerant&#34;) flows. In a typical system an evaporator coil is in heat transfer communication with interior space, and a condenser coil is in heat transfer communication with a suitable heat sink, such as ambient air from the atmosphere. Mechanical air conditioning systems are well known in the art. Such systems may be either &#34;packaged,&#34; wherein all of the necessary components are packaged in a single unit, or &#34;split systems,&#34; wherein typically the evaporator is remotely located with respect to the compressor and condenser. 
     Furthermore, the background art reveals heat transfer systems directed to rejecting heat into a water source, such as a swimming pool, to raise and maintain the temperature of the pool water at a comfortable level. The heat transfer systems of the background art recognize the efficiency of utilzing the waste heat of condensation, which would otherwise be rejected to the atmosphere without being put to any beneficial use, to heat water from a pool or spa for recreational purposes. In warm climates, the use of the swimming pool may be limited to those months where the ambient temperature is sufficient to warm the swimming pool water to a comfortable level, especially pools that are not exposed to direct sunlight. In colder climates, swimming pool water must be continually heated in order to provide comfortable aquatic recreation. In addition, there exists a number of other needs and uses for warmed water, including domestic hot water and water used for irrigation or other commercial purposes. 
     A number of references are directed to providing a mechanical system for rejecting heat to a water source. For example, U.S. Pat. No. 5,560,216, issued to Holmes, discloses a combination air conditioner and pool heater. U.S. Pat. No. 5,184,472, issued to Guilbault et al., discloses an add-on heat pump swimming pool control. U.S. Pat. No. 4,232,529, issued to Babbitt et al., discloses a mechanical refrigeration system for selectively heating swimming pool water. Babbitt et al. discloses three operating modes for selectively transferring heat. In the first mode, heat is transferred from the atmosphere to pool water. In a second mode, heat is transferred from a conditioned space to the atmosphere. In a third mode, heat is transferred from the conditioned space to pool water. 
     There are, however, a number of inherent disadvantages present in the prior art systems. Specifically, the prior art systems fail to disclose a system or method for routine modification of installed air conditioning systems for converting a straight cool system into a system capable of selectively heating pool water. Accordingly, there exists a need for a retrofit kit for mechanical air conditioning systems, for universal use with existing or new equipment, for converting the system to enable rejected heat to be used to warm pool water. Furthermore, additional energy savings would be realized if such a modification were capable of converting a straight cool air conditioning system into a heat pump such that the interior space served by the system could be efficiently heated, such that the energy savings of a heat pump were realized. 
     In addition, most mechanical air conditioning systems suffer from limitations in connection with the need to maintain an adequate supply of lubricating oil in the compressor. Specifically, oil used to lubricate the compressor is routinely carried by the refrigerant through the refrigerant lines. Furthermore, systems having hermetic compressors do not have a crankcase oil return connection and must rely on the refrigerant to return sufficient oil to the compressor. When the distance between certain components (e.g. evaporator and compressor) is substantial, care must be taken to insure the compressor is not starved for oil and that sufficient oil is returned to the compressor through the refrigerant lines. Accordingly, systems with heremetic compressors have historically been limited to applications having relatively short refrigerant line length requirements. As a result, it is recognized in the background art that hermetic compressors are prone to premature compressor failure in applications wherein the heat transfer coils are substantially spaced and connected by long refrigerant line runs. The oil return problem is most pronounced in complex heat transfer systems, such as those capable of rejecting heat to multiple sources, due to the spacing of components and existence of extended refrigerant line lengths. Accordingly, there exists a need for insuring that an adequate supply of lubricating oil is returned to a hermetic compresser in complex heat transfer systems. 
     A further disadvantage realized by most heat transfer systems results when oil, carried by refrigerant through the system, accumulates on the interior tube walls of the heat transfer coils and acts as a heat transfer insulator thereby degrading heat transfer efficiency. Accordingly, there exists a need for a mechanical air conditioning system capable of rejecting heat to a water source wherein heat transfer efficiency is maximized, and long runs of refrigerant tubing may be accommodated, by substantially eliminating the accumulation of lubricating oil from the heat transfer surfaces by separating entrained oil from compressed gas and returning the separated oil back to the compressor. 
     SUMMARY OF THE INVENTION 
     A heat transfer system including mechanical and electrical components for use in a mechanical air conditioning system to enable the system to efficiently utilize waste heat by rejecting the heat to a water source, such as a pool or spa, while simultaneously cooling and dehumidifying an interior space. The air conditioning system incorporates three primary heat transfer coils in a mechanical refrigeration cycle to provide comfort cooling to an interior space while rejecting heat to either the atmosphere or a water source, such as a swimming pool. 
     According to one embodiment of the present invention, a technician is able to convert a conventional air conditioning system by the addition of a few modular components. A first modular component contains refrigerant accessories, a second modular component contains a refrigerant-to-water heat exchanger and accessories, and a third modular component contains controls. Converting an existing air conditioning system merely requires the connection of each of the first two components in-line in the refrigerant piping network, and the electrical connection of the third component. 
     An air conditioning system according to the present invention includes the following primary mechanical heat transfer components: a refrigeration compressor; a first refrigerant-to-air heat transfer coil (hereinafter &#34;evaporator&#34;) in heat transfer communication with an interior space; a second refrigerant-to-air heat transfer coil (hereinafter &#34;condenser&#34;) in heat transfer communication with the atmosphere; and, a refrigerant-to-water heat exchanger in heat transfer communication with a water source. The system further incorporates controls for optimizing efficiency while maintaining pool water temperature at or near a desired set point. 
     A system according to the present invention is capable of the following two primary modes of operation. In the first mode of operation, the evaporator and condenser are active, and the refrigerant-to-water heat exchanger is inactive. In this mode, heat is absorbed from the interior space via the evaporator, and rejected to the atmosphere via the air cooled condenser. In the second mode of operation, the evaporator and the refrigerant-to-water heat exchanger are active, and the condenser is inactive. In this mode of operation, heat is absorbed from the interior space via the evaporator and rejected to water via the refrigerant-to-water heat exchanger. 
     In an alternate heat pump embodiment the system is further able to operate by absorbing heat from the atmosphere and rejecting heat to the interior space. In addition, other alternate embodiments provide for selective suction-liquid heat exchange to improve system efficiency and provide for refrigerant storage. 
     It is therefore an object of the present invention to provide a highly efficient heat transfer system. 
     A further object of the present invention is to provide a residential heat transfer system for cooling an interior residential space while heating pool water. 
     In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a heat transfer system according to the present invention, wherein heat is rejected to the atmosphere; 
     FIG. 2 is a schematic representation of a heat transfer system according to the present invention, wherein heat is rejected to water; 
     FIG. 3 is a schematic representation of an alternate embodiment of the present invention; 
     FIG. 4 is a schematic representation of another alternate embodiment of the present invention; 
     FIG. 5 is a schematic representation of the heat pump alternate embodiment in cooling mode; 
     FIG. 6 is a schematic representation of the heat pump alternate embodiment in heating mode. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 depict schematic representations of the preferred embodiment of a mechanical heat transfer system according to the present invention, generally referenced as 10, in each of the two primary operating modes. The system includes a condensing unit 20 having a compressor 22, and a condensing section consisting of a refrigerant-to-air heat transfer coil 24 and a fan 26. Condensing unit 20 may be a self contained condensing unit as normally found in a split system, or may comprise the compressor and condensing section of a packaged unit. Compressor 22 may be a compressor of any suitable type such as hermetic, reciprocating, rotary, scroll, screw, etc., and is preferably electrically powered. Compressor 22 includes a compressed gas output 22a in fluid communication, via refrigerant tubing 28, with an oil separator 32 contained within a first housing 30. 
     Oil separator 32 functions to separate substantially all of the oil entrained in the compressed refrigerant gas flowing from compressor 22. Oil separator 32 substantially reduces the amount of oil reaching the low side of the system (e.g. suction side) and helps maintain the oil charge in the compressor. Oil separator 32 includes a refrigerant output 32a fluidly connected via refrigerant tubing 34 to the input of a control valve 36, having a first outlet 36a and a second outlet 36b. Control valve 36 is preferably a heat reclaim valve, also known as a hot gas bypass valve, and is capable of selectively diverting compressed gas entering the valve inlet to either outlet 36a or 36b. 
     The first outlet 36a of valve 36 is fluidly connected via refrigerant tubing 38 to an inlet 24a of condenser 24. Condenser 24 further includes an output 24b which is fluidly connected, via refrigerant tubing 40 and check valve 42, to a liquid receiver 44 at receiver inlet 44a. Receiver 44 further includes a liquid refrigerant outlet 44b fluidly connected, via refrigerant tubing 46 and metering device 48, to an inlet 62a of evaporator coil 62 housed in air handling unit 60. In the preferred embodiment, schematically depicted in FIGS. 1 and 2, metering device 48 is a thermostatic expansion valve, however, the use of any suitable metering device, such as a capillary tube metering device, is considered within the scope of the invention. Air handling unit 60 is in heat transfer communication with an interior space and further includes a fan 64 for forcing air from the interior space across evaporator coil 62. Liquid refrigerant from receiver 44 is caused to expand within evaporator coil 62 and exits coil outlet 62b in a superheated vapor state. 
     Coil outlet 62b is fluidly connected, via refrigerant tubing 68 to a suction accumulator 70 at accumulator inlet 70a. As seen in FIG. 1, accumulator inlet 70a further communicates with an oil return outlet 32b via oil return line 33, whereby lubricating oil from oil separator 32 is mixed with refrigerant gas entering the accumulator and returned to the refrigerant gas stream returning to compressor 22 via accumulator 70. Accumulator 70 functions to prevent liquid refrigerant from returning to the compressor, and is fluidly connected, at outlet 70b, to the compressor suction inlet 22b, via refrigerant tubing 72. 
     Control valve 36 further includes an outlet 36b fluidly connected to a refrigerant-to-water heat exchanger, generally referenced as 80, at heat exchanger inlet 80a, via refrigerant tubing 76. In the preferred embodiment, refrigerant-to-water heat exchanger 80 comprises a coaxial tube heat exchanger having a corrosion resistant material, such as cupronickel or stainless steel, inner tube housed within an outer tube, such as a carbon steel jacket. As is apparent, however, any suitable heat exchanger material is considered within the scope of the invention. Heat exchanger 80 further communicates with a water source, such as a pool 100, whereby water is circulated through the heat exchanger 80, and specifically within the corrosion resistant inner tube, in heat transfer communication with refrigerant supplied by tubing 76, which refrigerant flows through the outer jacket. The refrigerant and water flow through heat exchanger 80 in counterflow so as to maximize the heat transfer efficiency. 
     As best depicted in FIG. 2, water from pool 100 flows through circulating pump 102 and enters heat exchanger 80 at 80b, whereafter a portion of the water flows through heat exchanger 80 while the remaining water flows through a pressure regulating by-pass valve 82. In the preferred embodiment, by-pass valve 82, compensates for pressure variations in inlet water pressure and maintains adequate water flow through heat exchanger 80 wherein the pool water is heated by refrigerant flowing from tubing 76. All of the pool water then exits the heat exchanger at 80a and returns to the pool as depicted in FIG. 2. Thereafter, condensed refrigerant exits heat exchanger 80 at 80b and travels through check valve 78 and refrigerant tubing 79 to the inlet 44a of liquid receiver 44. 
     The present invention contemplates that it may be desirable to configure the mechanical components referenced herein above in separate housings to facilitate an efficient installation. For example, the figures depict a first housing 30 containing oil separator 32, heat reclaim valve 36, check valve 42, receiver 44, accumulator 70, and associated refrigerant conduit. It is further contemplated that it is desirable to fill any remaining space within housing 30 with a suitable insulating foam (not shown) to prevent problems associated with condensation forming on various surfaces (e.g. external surfaces of accumulator 70). A second housing 81 may contain heat exchanger 80, bypass valve 82, liquid refrigerant check valve 78, and associated refrigerant and water conduit. Each housing has clearly marked refrigerant tubing and water connections for ease of installation. Accordingly, a technician is able to install components of the present invention using conventional refrigerant and water piping techniques. 
     I. First Operating Mode 
     In the first operating mode, wherein there is no demand for pool heat, evaporator coil 62 and condenser coil 24 are active, and the refrigerant-to-water heat exchanger 80 is inactive. In this mode, heat is absorbed from the interior space via the evaporator, and rejected to the atmosphere via the air cooled condenser coil. Specifically, as best depicted in FIG. 1, compressed refrigerant gas exits compressor 22 at 22a and passes through oil separator 32 wherein substantially all of the entrained oil is removed from the refrigerant. The refrigerant gas then flows to heat reclaim valve 36 which is configured to direct the refrigerant gas to valve outlet 36a. The refrigerant thus flows through condenser coil 24, wherein the refrigerant is condensed thereby rejecting heat to the atmosphere. The condensed refrigerant thereafter flows through tubing 40 and check valve 42 to liquid receiver 44. Liquid refrigerant exits receiver 44 and passes through metering device 48 and evaporator coil 62, wherein the liquid refrigerant evaporates thereby absorbing heat from the interior space. Refrigerant gas exiting the evaporator through tubing 68 mixes with oil from oil return line 33, enters accumulator 70 whereafter oil laden refrigerant gas return to the compressor 22 via suction line 72. 
     II. Second Operating Mode 
     In the second operating mode, wherein there is a demand for pool heat, evaporator 62 and heat exchanger 80 are active, and the condenser 24 is inactive. In this mode, heat is absorbed from the interior space via the evaporator, and rejected to the pool water via the refrigerant-to-water heat exchanger 80. Specifically, as best depicted in FIG. 2, compressed refrigerant gas exits compressor 22 at 22a and passes through oil separator 32 wherein substantially all of the entrained oil is removed from the refrigerant. The refrigerant gas then flows to control valve 36 which is configured to direct the refrigerant gas to valve outlet 36b. The refrigerant thus flows through heat exchanger 80, wherein the refrigerant is condensed thereby rejecting heat to the pool water flowing therethrough. The condensed refrigerant thereafter flows through check valve 78 and tubing 79 to liquid receiver 44. Liquid refrigerant exits receiver 44 and passes through metering device 48 and evaporator coil 62, wherein the liquid refrigerant evaporates thereby absorbing heat from the interior space. Refrigerant gas exiting the evaporator through tubing 68 mixes with oil from oil return line 33, enters accumulator 70 whereafter oil laden refrigerant gas return to the compressor 22 via suction line 72. 
     III. Alternate Embodiments 
     A. Suction-Liquid Heat Exchanger 
     As seen in FIG. 3, the present invention contemplates an alternate embodiment wherein a suction-liquid heat exchanger, generally referenced as 90, is incorporated and the liquid receiver is eliminated. In this embodiment, the suction-liquid heat exchanger 90 is used to improve overall system efficiency and reduce condensation and exterior rust formation on the compressor. 
     Generally, suction-liquid heat exchangers subcool the liquid refrigerant and superheat the suction gas, thereby increasing the efficiency of the system and enabling the refrigerant to absorb a greater amount of heat in the evaporator coil and permitting the use of longer refrigerant liquid lines. In addition, the use of a suction-liquid heat exchanger provides sufficient liquid refrigerant storage capacity to allow for the elimination of the liquid receiver. In the alternate embodiment depicted in FIG. 3, a suction-liquid heat exchanger 90 is included in the confines of the first housing 30. The invention further contemplates that the suction-liquid heat exchanger will include a liquid inlet 90a and first and second liquid outlets, 90b and 90c respectively, in addition to a suction gas inlet 90e and outlet 90f. 
     According to the first alternate embodiment suction-liquid heat exchanger configuration, refrigerant vapor exiting the evaporator coil is routed through the suction-liquid heat exchanger by proper connection to the suction gas inlet 90e and the suction gas outlet 90f. Furthermore, liquid refrigerant (from either the condenser coil 24, or from heat exchanger 80) is supplied to the heat exchanger liquid inlet 90a via conduit 79. Thus, by connecting the first liquid outlet 90b to the refrigerant tubing 46 supplying the evaporator, and leaving the second liquid outlet 90c capped, the liquid and vapor refrigerant are brought into heat transfer communication and the liquid is subcooled. It has been found that liquid refrigerant, which has been subcooled using a suction-liquid heat exchanger, requires the insulation of the liquid line 46 from the first liquid outlet 90b to the metering device 48 to prevent condensation from forming on the liquid line. Accordingly, the first liquid outlet is utilized only when the liquid line 46 is either insulated or capable of being insulated in the field. On the other hand, by connecting the second liquid outlet 90c to the refrigerant tubing 46 supplying the evaporator 62, the liquid refrigerant vapor is not brought into direct heat transfer contact with the vapor refrigerant; however, the suction-liquid heat exchanger still provides a containment volume for storing liquid refrigerant thereby eliminating the need for a separate liquid receiver. As is apparent, the second liquid outlet 90c should be utilized when the liquid line is to remain uninsulated. 
     B. Alternate Suction-Liquid Heat Exchanger 
     As best depicted in FIG. 4, the alternate embodiment includes an second structure for achieving the suction-liquid heat exchanger heat transfer effect. Specifically, the second alternate embodiment achieves the suction-liquid heat exchange by inclusion of a helical coil of copper refrigerant tubing 71 around the suction accumulator 70 and in heat transfer contact with the exterior surface thereof. Accordingly the suction-liquid heat exchanger heat transfer effect is achieved by routing liquid refrigerant through the helical coil 71 surrounding accumulator 70 whereby the liquid refrigerant is subcooled and the refrigerant vapor within the accumulator is superheated. As with the first alternate embodiment, the second alternate embodiment contemplates the use of both primary and secondary liquid outlet connections, 71a and 71b respectively. Connection of the primary liquid outlet 71a causes refrigerant to flow through the helical coil, while connection of the secondary liquid outlet 71b causes liquid refrigerant to substantially by-pass the helical coil; the helical coil however, remains available for storage of liquid refrigerant. Accordingly, the primary liquid outlet should be utilized only when the liquid line is either insulated or capable of being insulated in the field. On the other hand, by connecting the secondary liquid outlet to the refrigerant tubing supplying the evaporator, the liquid refrigerant vapor is not brought into direct heat transfer contact with the vapor refrigerant; however, the suction-liquid heat exchanger still provides a containment volume for storing liquid refrigerant thereby eliminating the need for a separate liquid receiver. As is apparent, the secondary liquid outlet should be utilized when the liquid line is to remain non-insulated. 
     C. Heat Pump Embodiment 
     FIGS. 5 and 6 depict an alternate embodiment wherein the system is capable of functioning as a heat pump. Specifically, the embodiment shown in FIGS. 5 and 6 includes additional refrigeration accessories including a reversing valve 110. FIG. 5 depicts the alternate embodiment in a &#34;cooling&#34; mode, wherein coil 62 functions as an evaporator. This alternate embodiment includes all of the components disclosed in the preferred embodiment shown in FIG. 1. In addition, the following components are added: reversing valve 110, check valve 120, check valve 42&#39;, check valve 130 and metering device 140. 
     As best depicted in FIGS. 5 and 6, reversing valve 110 includes in inlet port 110a, and three outlet ports 110b-d respectively. Inlet 110a is fluidly connected to the oil separator outlet 32a. Reversing valve outlet 110b is fluidly connected to evaporator coil 62 at 62b, reversing valve outlet 110c is fluidly connected to accumulator inlet 70a, and reversing valve outlet 110d is fluidly connected to the inlet of control valve 36. Check valve 120 is fluidly connected in parallel with metering device 48. Check valve 130 and metering device 140 are fluidly connected in parallel with check valve 42&#39;. 
     The cooling mode is depicted in FIG. 5. In the cooling mode, there is no demand for pool heat, evaporator coil 62 and condenser coil 24 are active, and the refrigerant-to-water heat exchanger 80 is inactive. In this mode, heat is absorbed from the interior space via the evaporator, and rejected to the atmosphere via the air cooled condenser coil. Specifically, as best depicted in FIG. 5, compressed refrigerant gas exits compressor 22 at 22a and passes through oil separator 32 wherein substantially all of the entrained oil is removed from the refrigerant. The refrigerant gas then flows to reversing valve inlet 110a which is in fluid communication with reversing valve outlet port 110d (note also the reversing valve ports 110b and 110c are in fluid communication). Accordingly, compressed refrigerant gas exits port 110d and is directed to heat reclaim valve 36 which is configured to direct the refrigerant gas to valve outlet 36a. The refrigerant thus flows through condenser coil 24, wherein the refrigerant is condensed thereby rejecting heat to the atmosphere. The condensed refrigerant thereafter flows through tubing 40 and check valve 42&#39; to liquid receiver 44. Liquid refrigerant exits receiver 44 and passes through metering device 48 and evaporator coil 62 (note that check valve 120 prevents refrigerant from bypassing metering device 48), wherein the liquid refrigerant evaporates thereby absorbing heat from the interior space. Refrigerant gas exiting the evaporator through tubing 68, passes through reversing valve ports 110c and 110b respectively and is then routed to accumulator inlet 70 wherein it mixes with oil from oil return line 33, and enters accumulator 70 whereafter oil laden refrigerant gas return to the compressor 22 via suction line 72. 
     The heat pump heating mode is depicted in FIG. 6. In the heat pump heating mode, there is no demand for pool heat, but there is demand for heat in the interior space served by evaporator 62. Accordingly, in the heat pump heating mode evaporator 62 (functioning as a condenser) and condenser 24 (functioning as an evaporator) are active and heat exchanger 80 is inactive. In this mode, heat is absorbed from the atmosphere via condenser 24, and rejected to the interior space via evaporator 62. Specifically, as best depicted in FIG. 6, compressed refrigerant gas exits compressor 22 at 22a and passes through oil separator 32 wherein substantially all of the entrained oil is removed from the refrigerant. The refrigerant gas then flows to the reversing valve inlet 110a which communicates with outlet port 110b. Accordingly, the compressed refrigerant gas flows to evaporator coil outlet 62b (functioning as an inlet), through coil 62, wherein the compressed gas condenses to liquid, and exits the coil at 62a and bypasses metering device 48 via check valve 120. The liquid refrigerant then passes through receiver 44 and tubing 40 and bypasses check valve 42&#39; via check valve 130 and metering device 140, whereafter the refrigerant passes through coil 24 and evaporates thereby absorbing heat from the atmosphere. The refrigerant gas then passes through control valve 36 and reversing valve ports 110d and 110c whereafter the refrigerant gas enters accumulator 70 at 70a on route to compressor suction inlet 22b. 
     As should be apparent, the heat pump embodiment may further incorporate the suction-liquid heat exchanger configurations disclosed herein. 
     IV. Control 
     The system includes a thermostat located in the interior spaced served by the air handling unit 60. The thermostat includes a temperature sensor (T-1) and an interior space set-point (SP-1) adjustment. In addition, heat exchanger 80 includes pool water inlet and outlet temperature sensors (T-2 and T-3 respectively), and the system provides for a user adjustable pool water set-point (SP-2). Furthermore, heat exchanger 80 incorporates a pressure differential switch (SW-1) connected across the heat exchanger water inlet and outlet. A refrigerant temperature sensor (T-4) is connected to refrigerant line 79 leaving heat exchanger 80. 
     Upon a demand for cooling of the interior space (e.g. T-1&gt;SP-1), the following components are energized: evaporator fan 64, compressor 22, and condenser fan 26. In addition, pool pump 102 is energized so that a pool water temperature reading can be obtained by pool water inlet sensor T-2. If the pool water temperature is below set-point (e.g. T-2&lt;SP-2), and pressure differential switch SW-1 detects a sufficient pressure differential across the pool water inlet and outlet, thereby indicating that there is sufficient pool water flow through heat exchanger 80, then condenser fan 26 is de-energized and hot gas by-pass valve 36 is energized thereby routing compressed refrigerant gas through heat exchanger 80 (e.g. pool heating mode). As should be apparent, de-energizing condener fan 26 results in substantial energy savings. Once the pool water reaches set-point (e.g. T-2≧SP-2), the condenser fan 26 is re-energized and control valve 36 is de-energized, thereby routing compressed refrigerant gas through condenser 24. 
     A. Alarm Conditions and Monitoring 
     SW-1 (normally open)--detects sufficient pool water flow. Prevents energizing of control valve 36 and de-energizing of condenser fan 26 if sufficient pool water flow is not detected. 
     T-2 (pool water inlet temperature sensor)--detects the temperature of the pool water entering the heat exchanger. If pool water inlet temperature is below 60° F. (adjustable) then the system is prevented from operating in the pool heating mode. 
     T-3 (pool water outlet temperature sensor)--detects the temperature of the pool water leaving the heat exchanger. If pool water outlet temperature is higher than 120° F. (adjustable) then the system is prevented from operating in the pool heating mode. 
     T-4 (refrigerant temperature sensor)--detects the temperature of the liquid refrigerant leaving the heat exchanger. If the refrigerant temperature is higher than 130° F. and the difference between the temperatures sensed by T-2 and T-3 is less than 10° F. fault light is illuminated indicating the need to clean the heat exchanger. 
     B. Energy conservation 
     The invention further contemplates control logic for tracking the amount of time during which pool pump 102 is energized during a 24 hour period. It is recognized that a typical pool pump should run approximately 8 hours per day to insure adequate water filtration. In a preferred embodiment, the invention will energize the pool pump to run in parallel with compressor 22. Under that control configuration, in the event that the compressor, and hence the pool pump, fails to accumulate a predetermined amount of run time (e.g. 8 hours) in a 24 hour period, the system will energize the pool pump sufficiently prior to the expiration of the 24 hour period to insure a full, e.g. 8 hours, of run time. 
     The instant invention has been shown and described herein in what is considered to be the most practical and preferred embodiment. It is recognized, however, that departures may be made therefrom within the scope of the invention and that obvious modifications will occur to a person skilled in the art.