Abstract:
A thermal energy transfer unit is used in conjunction with a conventional Freon based heat pump system. One or several thermal energy transfer units are operatively interconnected to one or several Freon based heat pump systems and share a common energy storage tank. Each thermal energy transfer unit converts energy from a compressor and condensing coil of the conventional heat pump system and stores it in the common energy storage tank when electricity is in low demand. Each thermal energy transfer unit retrieves stored energy from the common storage tank and provides air conditioning without the use of the compressor when electricity is in high demand. Each thermal energy transfer unit can be disabled to allow the heat pump units to perform as if they and the energy storage tank were not connected. One or all of the units can be disabled without affecting the performance or purpose of the others.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a heating and cooling units of the type employing a heat pump for maintaining an environment enclosed by a structure at a selectively desired comfort range. 
         [0003]    2. Description of the Prior Art 
         [0004]    Air-conditioning can be defined as the control of temperature, humidity, purity, and motion of air in an enclosed space, independent of outside conditions. There are a number of technologies which exist in the prior art to control the environmental conditions of an enclosed space, ranging from simple evaporative systems which provide cooling in an enclosed space by evaporation of water from a fixed media, to more advanced techniques that employ more sophisticated air-conditioning technology. 
         [0005]    In traditional air conditioning systems employed for many years in commerce, a refrigerant, normally consisting of a Freon compound (carbon compounds containing fluorine and chlorine or bromine), in a volatile liquid form, is passed through a set of evaporator coils located in the space to be cooled. The refrigerant evaporates and, in the process, absorbs the heat contained in the air in the enclosed space. When the cooled air reaches its saturation point, its moisture content condenses on fins placed over the coils. The water runs down the fins and drains. The cooled and dehumidified air is returned into the room by means of a blower. During this process, the vaporized refrigerant passes into a compressor where it is pressurized and forced through condenser coils, which are in contact with the outside air. Under these conditions, the refrigerant condenses back into a liquid form and gives off the heat it absorbed inside the enclosed space. This heated air is expelled to the outside, and the liquid recirculates to the evaporator coils to continue the cooling process. 
         [0006]    In some units, the two sets of coils can reverse functions so that in winter, the inside coils condense the refrigerant and heat rather than cool the room or enclosed space. These units are referred to as a “heat pump” in the discussion which follows. 
         [0007]    Both the above described traditional mechanical refrigeration air conditioning systems and heat pumps require work in the form of the energy required to operate the associated mechanical compressor in the systems. Although air-conditioning units of these types are widely used in the industry, they are typically relatively expensive to operate as they use relatively large amounts of electrical power 
         [0008]    As previously mentioned, another system of cooling air in an enclosed space is simply by means of passing air through water for cooling the air by means of evaporation. These systems are known in the industry as “evaporative coolers.” Although evaporative coolers are less expensive to operate, they do not recirculate the air in the same manner as a Freon based air conditioner, and are not as effective in operation when the humidity in the environment rises. Furthermore, over time, evaporative coolers tend to use large amounts of water, and provide a buildup of humidity within the structure which can lead to mildew buildup and other problems. 
         [0009]    Alternate systems of cooling the interior of a structure include the use of chilled water. Water may be cooled by refrigerant at a central location and run through coils at other places. Water may be sprayed over selected media which then has air blown through it. Although large commercial systems of this type are currently used in industry, they use large amounts of water, which may not be practical for dryer regions of the country where water is less abundant and may not be economically feasible for smaller installations. 
         [0010]    In recent years, the utility electrical industry has incorporated reduced electrical rates in off-peak hours when demand is low. As a result, the electrical consumer has found it advantageous to purchase and “store” the energy needed for air conditioning in the off-peak hours and use it during peak hours. This typically involves the use of an insulated tank of some sort. There are many methods of storing and retrieving thermal energy from an insulated tank. All require an insulated tank that contains a substance in which the thermal energy is stored. 
         [0011]    One method utilizes a liquid that simply stores the thermal energy by reducing the temperature of the liquid. For example, if this liquid is water, one pound of water stores approximately one BTU per degree of Fahrenheit temperature reduction. The energy is stored by removing heat from the liquid by various methods. The energy is recovered by circulating the cooled liquid into a heat exchanger during peak hours where it absorbs heat because of the low temperature of the liquid. 
         [0012]    Another method of thermal energy storage involves the freezing of the liquid inside the insulated tank to its solid state by various methods. The heat stored per pound of liquid is much greater because of the change of state of the liquid to solid. If water is the liquid, one pound of water stores approximately 144 BTU&#39;s per degree of Fahrenheit temperature reduction, the phenomenon being referred to as the latent heat. The energy is recovered from storage by circulating a substance (sometimes the same melted liquid) through or around the cold solid transferring heat to the solid until it is all melted back to its liquid state. 
         [0013]    Another method of thermal energy storage is a combination of the two previously described methods. Thermal energy is stored by transferring heat out of a liquid until a portion of the liquid solidifies to a solid state resulting in a slurry of solid particles floating in a liquid. Thermal energy is retrieved by circulating the liquid of the slurry to the area to be cooled where heat is added to the cool liquid. The heat is rejected to the particles of solid floating in the slurry. 
         [0014]    Because of problems involved in creating the above slurry and thus storing thermal energy, another method has evolved which uses sealed spherical balls containing a liquid that changes to its solid state to store thermal energy. These balls are contained in a liquid that freezes at a much lower temperature than the liquid contained in the balls. Energy is stored by removing heat from the low temperature liquid until the liquid inside the balls changes to the solid state. Energy is recovered by circulating the low temperature liquid to the area to where heat is added and then rejected to the melting of the liquid inside the balls. U.S. Pat. No. 4,768,579, issued to Patry, is an example of this method. 
         [0015]    All of these methods have advantages and disadvantages, depending upon the particular end applications, methods of storing and retrieving heat, and commercial considerations of tank size, tank location, etc. All of these methods retrieve the stored energy by circulating a liquid to transfer the heat removed from the air conditioned area to the tank containing the material in which thermal energy is stored. 
         [0016]    Past efforts for this method of conversion and storage of thermal energy have generally used a conventional condensing unit. Thus, past efforts for this method have typically used a coil submerged in liquid contained in the insulated tank for the thermal energy conversion and storage. These submerged coils had Freon flow through them to freeze the liquid to its solid state for energy storage. The same coil was used for stored energy recovery by flowing Freon through the coil where it condensed to its liquid state, thus adding heat to the frozen liquid in the tank. There were various deficiencies with this type of system, however. For example, these systems generally require the water that is frozen and the coil inside it to be located near the Freon compressor because of pressure losses in the Freon tubing between the compressor and the coil, compressor lubricating oil loss and entrapment in long runs of Freon tubing between the coil and compressor. The additional cost and inconvenience of the copper tubing connecting the coil and the compressor must be taken into consideration when the two are located apart at a relatively great distance. 
         [0017]    Additionally, even though the above described “heat pump” technology using the reversible flow of a compressible refrigerant has been available for many years, the existing heat pump systems, particularly those intended for smaller system installations, have not taken advantage of the technique of storing thermal energy in a tank and the use of chilled water as an auxiliary energy source for use during peak energy consumption hours of the day. There exists, therefore, a need for an improved apparatus and method for allowing a conventional Freon based heat pump system to store and then retrieve thermal energy in the tank using any of the above cited methods of thermal energy storage, depending upon the particular situation at hand. 
       SUMMARY OF THE INVENTION 
       [0018]    It is therefore one object of the invention to provide a unique thermal energy transfer unit which can be used with a thermal energy storage tank and which can be adapted to a conventional heat pump installation. 
         [0019]    It is another object to provide such a system which does not necessarily require the thermal energy storage tank to be located in close proximity to the heat pump. 
         [0020]    It is another objective of this invention to provide a thermal energy transfer unit and storage system for a heat pump which can be easily retrofitted to an existing heat pump system without requiring changing the plumbing located inside the structure to be cooled or heated. 
         [0021]    It is another objective of this invention to provide a thermal energy storage tank and apparatus which allows the transfer of thermal energy from the existing condensing unit of the heat pump to the remote thermal energy storage tank during off-peak hours, while allowing recovery of this energy from the storage tank during peak hours. 
         [0022]    In accordance with the teachings of the present invention, there is provided an improved method for heating and cooling a structure using a conventional Freon based heat pump system. In the system of the invention, a first refrigerant based heat exchanger located within the structure is provided which is capable of acting as either an evaporator or a condenser and adapted to absorb thermal energy from a structure in a cooling mode and supply thermal energy to the structure in a heating mode. A second refrigerant based heat exchanger located outside the structure is provided which is also capable of acting as either an evaporator or a condenser and adapted to absorb thermal energy from ambient atmosphere in a one mode and being adapted to transfer thermal energy to ambient atmosphere in a different mode. A refrigerant distribution loop containing a compressible Freon based refrigerant connects the first and second heat exchangers in fluid flow communication. A refrigerant compressor is provided to cycle the refrigerant through the refrigerant distribution loop and the first and second heat exchangers. The system also includes a reversing valve for converting the system from one of the aforesaid heating and cooling modes to the other of the modes by reversing the flow of Freon based refrigerant in the refrigerant flow loop. 
         [0023]    The improvements provided by the method of the invention include the provision of a thermal energy transfer unit in heat exchange relationship to the refrigerant distribution loop for applying energy conversion and storage to the Freon based heat pump system associated with the structure as the flow of Freon is reversed in the refrigerant flow loop during the cycling of the heating and cooling modes of operation of the system. The preferred thermal energy transfer unit includes a non-freezing liquid thermal storage media located in a thermal storage tank. The thermal energy transfer unit is utilized to transfer heat from the thermal storage media in the thermal storage tank to the first heat exchanger of the Freon based heat pump system. Heat can be transferred from inside air within the structure to the thermal storage media in the thermal storage tank without the compressor of the conventional heat pump system operating. Thereafter, the first heat exchanger can be allowed to transfer heat from the inside air of the structure to outside air in the same manner that such heat transfer was accomplished before the thermal energy transfer unit and thermal storage tank were added to the existing Freon based heat pump system. 
         [0024]    The second refrigerant based heat exchanger in the heat pump system includes an outside coil which acts as the evaporator in the system when the system is in the heating mode for heating the structure, and wherein the outside coil tends to ice up during the heating mode operation, normally requiring a thawing step between the cooling and heating modes of the system. In the method of the invention, the outside coil is thawed without the use of electric heating elements by reversing the flow of refrigerant in the refrigerant loop, thereby causing the outside coil to act as a condenser, the heat transfer between the refrigerant loop in the heat pump system and the storage media in the thermal storage tank being used to cool the thermal storage media and make ice in the thermal storage tank 
         [0025]    In the improved system of the invention, the thermal storage tank is connected at an inlet and at an outlet to a fluid flow line. A fluid pump is provided for pumping non-freezing liquid to and from the storage tank to the thermal energy transfer unit. The preferred system includes an external heating element which is in heat exchange contact with the flow line to heat the non-freezing liquid being circulated to the storage tank during the thawing step of the heat pump system. 
         [0026]    The thermal energy transfer unit of the invention allows normal air conditioning to be performed by the operation of the heat pump compressor and condensing coil as if the thermal energy transfer unit were not present, in which case heat is neither being added to nor extracted from the non freezing liquid in the storage tank and the liquid pump in the fluid flow line is not running. 
         [0027]    The thermal energy storage tank which is used in the method of the invention can use any of a variety of media for storing energy. For example, the media can be selected from among: chilling a non-freezing liquid such as a water/glycol solution; using an ice on pipe storage tank; using an ice ball storage tank; and using an ice slurry method for storing thermal energy. 
         [0028]    The preferred thermal energy transfer unit includes at least one auxiliary heat exchanger for transferring heat from a conventional heat pump system having a mechanical compressor in a closed loop refrigeration circuit to a non-freezing liquid medium that, in turn, transfers that heat to or from at least one thermal storage tank. A pump is provided for circulating the non-freezing liquid medium. A valve control circuit controls the flow of the non-freezing liquid medium to the conventional heat pump system to enable the transfer of heat to the thermal storage tank without the mechanical compressor of the heat pump system running. The valve control circuit includes a series of valves which are used to start, stop and regulate the flow of heat from the conventional heat pump system to or from the thermal storage tank, the valve control circuit also functioning to allow heat to be transferred by the heat pump system as if the thermal energy transfer unit and thermal storage tank were not present in the system. The thermal energy transfer operates to duplicate the operation of a conventional air conditioner condensing unit while operating in the cooling mode, but without the conventional air conditioner condensing unit operating. A plurality of thermal energy transfer units can be used in association with a plurality of heat pump systems to transfer heat to or from one or more shared thermal energy storage tanks. 
         [0029]    These and other aspects of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a simplified schematic representation of a conventional Freon based heat pump system shown operating in the air conditioning mode. 
           [0031]      FIG. 2  is a simplified schematic view, similar to  FIG. 1 , but showing the conventional heat pump system operating in the heating mode. 
           [0032]      FIG. 3  is a simplified schematic diagram of the heat pump system of  FIG. 1  but with Applicant&#39;s improved thermal energy transfer unit and thermal energy storage tank and with the system operating in the normal air conditioning mode. 
           [0033]      FIG. 4  is a view similar to  FIG. 3 , but with the system operating in the normal heating mode. 
           [0034]      FIG. 5  is a view of the improved system of the invention in which no heating or cooling is occurring within the structure, the thermal energy storage media being cooled in the thermal energy storage tank. 
           [0035]      FIG. 6  is a schematic representation of the operation of the system of the invention where the compressor of the conventional heat pump is not running and air conditioning of the structure is being achieved by circulating cold, non-freezing liquid from the thermal energy storage tank to an auxiliary heat exchanger which, in turn, is in a heat exchange relationship with the Freon being circulated in the heat pump system. 
           [0036]      FIG. 7  is a simplified schematic of the operation of the conventional heat pump system in the thaw out mode where the external heat exchanger coil is being defrosted. 
           [0037]      FIG. 8  is a schematic representation of another mode of operation of Applicant&#39;s system in which the external heat exchanger coil of the heat pump is being defrosted by cooling the media in the thermal energy storage tank. 
           [0038]      FIG. 9  is a view similar to  FIG. 8 , but shows the addition of a heating coil on the fluid flow line in order to raise the temperature of the non-freezing liquid while the system simultaneously defrosts the external heat exchanger coil of the conventional heat pump. 
           [0039]      FIG. 10A  is a table illustrating the component status of each of the operative components of the systems described in the drawings. 
           [0040]      FIG. 10B  is a continuation of the table of  FIG. 10A . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    The nature of the present invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting examples that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processes and manufacturing techniques are omitted so as to not unnecessarily obscure the more important features of the invention described herein. The examples used are intended merely to facilitate an understanding of ways in which the invention may be practiced and to further enable those of skill in the art to practice the various embodiments of the invention. Accordingly, the examples should not be construed as limiting the scope of the claimed invention. 
         [0042]      FIG. 1  is a simplified schematic representation of a conventional Freon based heat pump system which is used to air condition or heat a structure such as the building ( 14  in  FIG. 1 ). In  FIG. 1 , the system is shown in the normal air conditioning mode. In the discussion which follows, the term “Freon air conditioning” is intended to describe any conventional mechanical compression refrigeration or air conditioning system using a compressible refrigerant and an expansion device in a closed circuit to achieve a cooling effect by the liquid/vapor phase change of the compressible refrigerant. The term “Freon” is intended to be descriptive of that general class of refrigerants containing different chlorofluorocarbons, or CFCs, which are widely used in commerce and industry. The CFCs are a group of aliphatic organic compounds containing the elements carbon and fluorine, and, in many cases, other halogens (especially chlorine) and hydrogen. Freons are colorless, odorless, nonflammable, noncorrosive gases or liquids. Thus, a number of compressible refrigerants of the same general class will be known to those skilled in the relevant industries and that the term “Freon” is used in the discussion which follows merely as a shorthand for describing this general class of refrigerants. 
         [0043]    The building  14  has an inside heat exchange coil  9 , an inside expansion device  12 , a check valve  13  and a motorized air mover  10  located inside the building. The coil  9 , expansion valve  12  and check valve  13  are all located in a refrigerant flow loop  37  in which Freon refrigerant is being circulated. In the normal air conditioning mode, the air  11  inside the building  14  is moved past the inside coil  9  when the motorized air mover  10  is running. The components shown in  FIG. 1  which are located inside the building structure  14  are referred to in the discussion which follows as a “first refrigerant based heat exchanger” or “inside heat exchanger” capable of acting as either an evaporator or a condenser and adapted to absorb thermal energy from a structure in a cooling mode and supply thermal energy to the structure in a heating mode. 
         [0044]    The system of  FIG. 1  also has what will be referred to herein as a “second refrigerant based heat exchanger” or “outside heat exchanger” which is also capable of acting as either an evaporator or a condenser and adapted to absorb thermal energy from ambient atmosphere in a one mode and being adapted to transfer thermal energy to ambient atmosphere in a different mode. The second heat exchanger includes a refrigerant compressor  1 , an outside coil  4 , an outside air mover  5 , an expansion valve  6  and a check valve  7 . The components other than the air mover are all in fluid communication in the refrigerant flow loop  37  containing the compressible Freon based refrigerant. Outside air  8  is moved past the outside coil  4  when the motorized air handler  5  is on and running. A reversing valve  2 , located outside the building structure in association with the second heat exchanger is provided for reversing the flow of refrigerant in the refrigerant flow loop, as will be described in greater detail. 
         [0045]    In the air conditioning mode, the first and second heat exchangers operate to transfer heat from the inside air within the structure to the outside air. The compressor  1  is the prime mover and comes on when the inside air temperature rises. The compressor  1  pulls the Freon from the inside (evaporator) coil  9  through the refrigerant flow loop  37 , through the reversing valve  2  and loop leg  39 , to the compressor, where it is in a low pressure and vapor state. The compressor  1  compresses the vapor, causing the vapor to leave the compressor through the loop leg  41  at a high pressure and an elevated temperature in the vapor state. The compressed Freon then flows to the outside heat exchanger coil  4  through the connecting conduit. In this mode of operation, the outside coil  4  acts as a condensing coil. As outside air moves across the outside (condensing) coil  4 , the elevated temperature of the Freon vapor in the condensing coil  4  causes heat to transfer to the outside air. In this manner all of the heat absorbed from the inside air and all the additional heat added to the Freon in the form of work during the compression cycle is rejected to the outside air. As this heat is rejected to the outside air, the Freon within the outside (condensing) coil  4  condenses to its liquid state at this elevated pressure. As a result, the Freon leaves the condensing coil  4  as a high pressure liquid through the refrigerant flow line and travels past check valve  7  through the loop leg  43  inside the structure  14  to be cooled and to the expansion device, in this case inside expansion valve  12 . The expansion valve  12  holds back pressure on the liquid. 
         [0046]    There are several different types of expansion devices that can be used, all of which cause the pressure entering the device to be much higher than the discharge. The Freon leaves the expansion device  12  at a low pressure through the loop leg  45  of the refrigerant flow loop and travels to the inside coil  9 , which in this mode of operation acts as an evaporator coil. Inside the evaporator coil  9 , the Freon starts to vaporize because of its low pressure and added heat. As it vaporizes, the temperature of the Freon decreases until it is lower than the inside air moving past the coil  9 . Because of this low temperature, heat is transferred from the inside air to the Freon as it vaporizes. The inside (evaporator) coil  9  and the motorized air mover  10  are sized such that all the Freon is vaporized in the evaporator coil  9 . The Freon leaves the evaporator coil  9  through the loop leg  45  of the refrigerant flow loop and returns to the compressor  1  after passing through the reversing valve  2 , where it again repeats the cycle. Typically the temperature of the inside air is monitored. When the inside air temperature reaches a desired set point, the compressor  1  and motorized air movers  5  and  10  are turned off. When the inside air temperature rises they are turned on. 
         [0047]      FIG. 2  is a schematic diagram of the previously described conventional heat pump system but showing the system in the heating mode, rather than in the previously described air-conditioning mode. In the operation being illustrated in  FIG. 2 , the flow of the compressible refrigerant in the refrigerant flow loop is reversed by the action of the reversing valve  2 . The outside and inside coils,  4  and  9  respectively, then operate in exactly the opposite manner to that previously described so that the air mover  10  transfers heat to the air inside the structure. In other words, the reversing valve  2  redirects the discharge from the compressor  1  so that high pressure vapor passes through the inside coil  9 . Freon leaves the coil  9  as a high pressure liquid. The Freon then goes through the check valve  13  which is parallel to the closed expansion valve  12  and is directed to the expansion valve  6  located on the outside of the building structure. It passes in as a high pressure liquid, but out as a cold, low pressure vapor. The refrigerant then passes through the outside coil  4 , whereby the outside air is, in effect, being cooled. 
         [0048]    The operation of this type of conventional heat pump system will be familiar to those skilled in the HVAC industries. One advantage of such a system is that practically all of the work going into the compressor  1  ends up as heat energy in the inside coil  9  located inside the building structure. 
         [0049]      FIG. 3  is a simplified schematic illustration showing the previously described heat pump system to which has been added a thermal energy transfer unit (TETU)  100  and an associated thermal energy storage tank  32 . The thermal energy transfer unit (TETU)  100  consists of a means to transfer heat to or from a non-freezable liquid which is being circulated to and from the thermal energy storage tank  32 . The other components of the system include an auxiliary heat exchanger  20 , an expansion device  22 , a means of pumping liquid Freon  18 , a means of pumping the non-freezable liquid  19  and the associated flow valves and check valves needed to control the Freon flow. 
         [0050]    It is important to note that the term “non-freezing liquid” is intended in the description which follows to describe a different thermal media from the Freon type refrigerant being circulated in the conventional heat pump system. The term “non-freezing liquid” is used herein to describe a generally non-compressible liquid, such as a water/glycol solution which is pumped by means of the positive displacement liquid pump  19  in  FIG. 3 . The non-freezing liquid is in heat exchange relationship with the Freon flow loop  37  by means of the auxiliary heat exchanger coil  20 , but the non-freezing liquid does not undergo a phase change from vapor to liquid, as is occurring in the primary Freon based heat pump circulation loop. 
         [0051]    The thermal energy storage tank may contain any of a number of known thermal energy storage media materials as described, for example, in Applicant&#39;s issued U.S. Pat. No. 7,152,413. These include, for example, lowering the temperature of a liquid located within an insulated tank; by chilling a non-freezing liquid such as a water/glycol solution; using an ice on pipe storage tank; using an ice ball storage tank; and using an ice slurry method for storing thermal energy. 
         [0052]    The primary purpose of Applicant&#39;s TETU is to provide a method for:
       1. transferring heat from a thermal storage media in the thermal storage tank  32  to the heat pump system where it is rejected to outside air;   2. transfer heat from the inside air of the building structure  14  to the thermal storage media in the thermal storage tank  32  without the compressor of the heat pump system operating; and to   3. allow the inside and outside heat exchangers of the heat pump system to transfer heat from the inside air of the building structure to outside air in the same way which has been described in  FIG. 1  before the TETU  100  and storage tank  32  were added to the system.       
 
         [0056]    Each of these stages of operation of the system of the invention will now be described in greater detail. For convenience, the operation of the various valves and other components present in the refrigerant flow loop and which are used to control the flow of compressible refrigerant and non-freezing liquid during the operation of the system are summarized in the tables presented in  FIGS. 10A and 10B  of the drawings. 
         [0057]    In  FIG. 3 . the system is acting with the heat pump being in the normal air conditioning mode. Refrigerant flow is passing into the receiver  26 . Because valve  24  is open, refrigerant passes to the expansion valve  12  located within the building structure to provide a cooling effect, as if the TETU were not present in the system. In other words, except for the presence of the TETU, the operation of the first and second heat exchangers is the same as previously described with respect to  FIG. 1  of the drawings with the inside coil  9  acting as an evaporator coil and the outside coil  4  acting as a condenser coil. 
         [0058]      FIG. 4  depicts the operation of the system with the heat pump acting in the normal heating mode as if the TETU  100  were not present in the system. In this mode, the expansion valve  12  is by-passed so that high pressure vapor passes through valves  13  and  31  to the receiver  26 . Note that the flow of refrigerant is exactly reversed from that described with respect to the normal air conditioning mode of  FIG. 3 . Valves  24  and  29  are open, allowing flow through check valve  28  back to the expansion valve  6  of the first heat exchanger of the heat pump system, as if the TETU were not present in the system. 
         [0059]      FIG. 5  depicts the operation of the system with the heat pump being used in a refrigeration mode in conjunction with the TETU to create cold storage in the thermal energy storage tank  32 . The refrigerant flow comes out of the first heat exchanger of the heat pump with the coil  4  of that exchanger acting in the condensing mode, the flow passing through valve  27  to the receiver  26 . High pressure liquid passes through valve  23  to the expansion valve  22  to the auxiliary heat exchanger coil  20 . Freon is returned to the first heat exchanger of the heat pump with the heat pump acting as if it were in the air conditioning mode. Meanwhile, the liquid pump  19  is circulating non-freezing liquid from the thermal energy storage tank  32  in heat exchange relationship with the coil  20  of the auxiliary heat exchanger to cool the non-freezing liquid. Note that the second (inside) heat exchanger of the heat pump is not active during this mode of operation. 
         [0060]      FIG. 6  of the drawings depicts the operation of the system of the invention in providing air conditioning to the inside of the building structure, but without the compressor  1  and first heat exchanger of the heat pump running. This would be the normal operating mode of the system during peak air conditioning times of the day. Pump  19  is again circulating non-freezing liquid from the thermal energy storage tank  32  through one side of the auxiliary heat exchanger  20 . Low pressure vapor from the refrigerant loop passes from inside the building structure to the other side of the auxiliary heat exchanger  20  where it is condensed to the liquid state at low pressure. The low pressure liquid then passes to the Freon pump  18 , through check valve  17 , through solenoid valve  16  and through check valve  15 . Since check valve  31  is closed, high pressure liquid flows to the expansion valve  13  inside the structure and through coil  9  where it provides cooling to the inside air. Refrigerant is circulated back to the suction of the TETU and the cycle repeats. The advantage of operating the system in this manner is that, since the compressor  1  is not being used, air conditioning can be provided to cool the inside of the structure at a relatively low wattage. 
         [0061]      FIG. 7  is a simplified schematic of a conventional heat pump, similar to  FIGS. 1 and 2  which illustrates one problem which can occur with the operation of a conventional heat pump, particularly during winter time operation. For example, assume the outside air temperature is 40° F. and the system is operating in the heating mode shown in  FIG. 2 . In this mode of operation, the heat pump is, in effect, air conditioning the outside air. If the coil  4  becomes too cold, it will literally freeze up. To keep this from happening, the unit is switched to the “defrost mode” shown in  FIG. 7 . In this mode, the system switches back to the air conditioning mode to thaw the outside coil  4 . However, since the system is now cooling the air inside the structure, it is generally necessary to include an auxiliary heating element, such as the electric heating element  30  shown in  FIG. 7  to heat the inside air which is being distributed inside the structure. 
         [0062]      FIG. 8  shows an improved method of handling the thaw out cycle of the conventional heat pump system. In the operation of the system shown in  FIG. 8 , the system cools the thermal energy storage media (makes ice) in the thermal energy storage tank  32  while the outside coil  4  is being defrosted. Note that since the second heat exchanger located inside the structure is not being utilized, that no cold air is being distributed inside the structure. This solution eliminates the need to provide auxiliary electric heating elements inside the structure and saves electricity. 
         [0063]    Depending upon the ambient temperatures and other variables, the thermal energy storage tank could eventually fill with ice. As a result,  FIG. 9  illustrates the identical system to  FIG. 8 , but with the addition of an auxiliary heating coil  33 . Coil  33  can be used to heat the non-freezing liquid being circulated by the pump  19  back to the temperature it was before the thawing cycle was started. Even though the system shown in  FIG. 9  utilizes an auxiliary heating coil  33 , it is still more efficient than the conventional system shown in  FIG. 7  because it is more efficient to heat a liquid than to attempt to heat air. As an example, a 3 ton air conditioning system requires about 11-12 Kwatts of electricity for the operation of the heating coil  30  shown in  FIG. 7 . The same size system requires only about 3 Kwatts of energy using the method illustrated in  FIG. 9 . 
         [0064]    An invention has been provided with several advantages. The thermal energy transfer unit can be retrofitted to an existing Freon based heat exchanger without the requirement that the storage tank be located in close proximity to the condensing unit or that the plumbing inside the associated building structure be modified. The thermal energy transfer unit can be retrofitted to several condensing units while sharing a single remote thermal energy storage tank, also allowing the storage tank to use any of a variety of known thermal storage media for storing thermal energy. The thermal energy transfer unit is used to transfer thermal energy from the existing condensing unit to the shared remote thermal energy storage tank during off-peak hours, while allowing recovery of this energy from the common tank during peak hours. 
         [0065]    The TETU uses a non-freezing liquid that never freezes in operation and transfers heat to and from the common storage tank. The liquid is circulated to and from the storage tank and the TETU by means of a pump that is located either at the tank or in the TETU. The TETU can include one or several heat exchangers which transfer heat from the non-freezing liquid to the Freon being circulated by the condensing unit when storing energy in the tank. The TETU uses this same heat exchanger, or others, to transfer the heat in the Freon to the non-freezing liquid (and thus to the tank) when air conditioning is performed without the condensing unit running. This heat transfer, without the use of the condensing unit, is accomplished by condensing the Freon to its liquid state and then pumping the liquid Freon into the building to absorb heat where it vaporizes. After the Freon absorbs heat and vaporizes inside the structure it returns to the heat exchanger(s) where it transfers its heat to the non-freezing liquid and condenses to its liquid state. The TETU also includes a pump means for pumping the liquid Freon when air conditioning is required without the condensing unit. The TETU allows normal air conditioning to be performed by the operation of the condensing unit as if the TETU were not present. In this case, heat is neither being added nor extracted to the non-freezing liquid and the non-freezing liquid pump is not running. The TETU is provided with appropriate valving and controls to accomplish these three functions. 
         [0066]    While the invention has been shown in several of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof.