Patent Publication Number: US-2003221436-A1

Title: Recoverable ground source heat pump

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001] This invention uses the transmission of my pending application in foreign country (China), application number: 01118555.4 filed Jun. 1, 2001.  
       BACKGROUND—FIELD OF INVENTION  
       [0002] This invention relates to heat pump for heating and cooling, specifically to such heat pump with ground source.  
       BACKGROUND—DESCRIPTION OF PRIOR ART  
       [0003] Ground Source Heat Pump System  
       [0004] Ground source heat pump uses ground soil, sand, rock, and/or water as a medium to provide energy for heating in winter. A minor energy input can produce 3-5 times as much heating energy in the winter through subtracting thermal energy from the ground. In the summer, the ground medium is used as a “heat sink” to receive the heat dissipation from the refrigeration device. Due to its great savings in operational costs in comparison with conventional heating and cooling devices, ground source heat pump has been used more and more for heating and cooling, but nevertheless all the closed loop heat pump system using ground medium (soil, sand and/or rock) heretofore have a number of critical disadvantages:  
       [0005] (1) The underground heat exchange system requires extensive drilling and/or trenching plus a significant amount of pipe loop material. This results in a higher initial cost. The loop system must be large enough to provide sufficient heat transfer efficiency and energy storage capacity to ensure an acceptable temperature elevation of the ground medium during the entire summer season (cooling) and winter season (heating). This limits greatly the overall cost effectiveness of ground source heat pumps.  
       [0006] (2) For the same reason, in order to keep the temperature change of the ground medium to a moderate level after a season&#39;s heat injection or heat abstraction, there must be sufficient ground space to build a large heat exchange system. This greatly restricts the application of ground source heat pumps for buildings without a large open space, especially for multi-story and high-rise buildings.  
       [0007] (3) Because of the need to limit initial cost and to apply the system to buildings with small open space, there is a greater risk that the system will under perform. This poor performance could manifest as higher energy consumption and/or insufficient heating/cooling output due to the temperature being too high in the cooling fluid out of the ground heat exchange system in the cooling mode, or too low in the heating fluid in the heating mode. This risk is significantly increased when there is insufficient site information, poor understanding of local geological conditions, or little design experience. To retroactively correct such a poor performing system requires significant additional cost.  
       [0008] (4) The worst situations of poor design includes freezing of the circulation fluid, which can be caused by continuous heat extraction from the ground. In order to minimize this risk, antifreeze solution is generally used in most pipe loops in northern locations where the system operates primarily in the heating domain. Use of antifreeze solution causes one or more of the following problems: (a) environmental pollution, (b) increased health and safety risk, (c) corrosion of equipment, and (d) increase the initial cost.  
       [0009] Energy Storage System  
       [0010] Most energy storage system materials have moderate melting temperatures so that the great amount of latent heat during the phase change can be used. The most popular storage medium is water. Cooling of water to make ice in the off-peak hours and using ice to cool building space is the most common energy storage system. It can significantly reduce the operational cost by using cheaper electricity in the off-peak hours, but the disadvantages are obvious:  
       [0011] (1) Similar to the ground source heat pump, the ice storage system is also always associated with a larger additional cost. There has been much effort to develop a cheaper storage medium and a cheaper mechanical system. However, the additional cost is still significant.  
       [0012] (2) The storage medium must be cooled to a temperature below its freezing point in order to use the latent heat capacity of the medium released and absorbed during phase change. Cooling the storage medium to an unnecessarily low level is not efficient from the energy saving point of view.  
       [0013] (3) Low temperature of the storage medium (for instance, 0° C. for water) will release low temperature cold air to the building in the day time. The low temperature air supply may cause water to condense on the surface of duct work and terminal units (diffusers, fan/coil units). Special effort must be made to prevent damage from the moisture and condensation to the building wall and ceiling.  
       [0014] (4) Most energy storage systems are designed only for space cooling but not for heating. For example, the ice-ball storage system may be able to extract sufficient energy from water-to-ice phase change to store “cold”, but the heat storage in the same volume of water is far less from the energy needed for heating of the building space.  
       SUMMARY  
       [0015] In accordance with the present invention, a ground source heat pump system with recovery and storage functions that uses electricity in off-peak hours to storage energy to, or abstract energy from the ground medium to service in on-peak hours.  
       OBJECTIVES AND ADVANTAGES  
       [0016] In addition to the objectives and advantages of the conventional closed loop heat pump using ground medium (soil, sand, and/or rock), the objectives and advantages of the present invention are:  
       [0017] (1) To provide a ground source heat pump with significantly reduced initial cost due to the dramatic reduction in the size of the underground heat exchanger. For conventional ground source heat pump, there is a minimal requirement for underground loop size to assure that the medium can cumulatively receive or release enough energy to last the entire season. Using the present invention, the minimal requirement for underground loop size is to ensure that the medium can cumulatively receive or release enough energy to last only one or a few days. This gives the designer much more flexibility in sizing the underground heat exchanger, and increases the design safety factor, thus reducing risk and liability.  
       [0018] (2) To provide a ground source heat pump system which requires much less ground space for the same reason as explained in the above paragraph, and can be used for buildings without large ground space, especially for large multi-story and high rise buildings  
       [0019] (3) To provide a ground source heat pump system with much better reliability through the control of ground medium temperature. The ground circulation fluid temperature can be controlled and maintained at a moderate level through the recovery function of the system during off-peak-hours. Extremely high circulation fluid temperature in the summer and low temperature in the winter can be avoided. The risk of the circulation fluid freezing will be eliminated.  
       [0020] (4) To provide a ground source heat pump using off-peak-hours electricity to reduce operational cost that is equivalent to the reduction in operational cost of a phase-change energy storage system, but with a lower initial cost than a phase-change energy storage system.  
       [0021] (5) To provide a ground source heat pump using off-peak-hours electricity to reduce operational cost that is equivalent to the reduction in operational cost of a phase-change energy storage system, but results in more efficient performance than a phase-change energy storage system because the medium does not have to be cooled to an unnecessarily low temperature.  
       [0022] (6) To provide a ground source heat pump using off-peak-hours electricity to provide cooled air at a moderate temperature and thus eliminate the problem of water condensation in ductwork and/or terminal units (diffusers or fan-coil units). Potential damage to ceiling and wall due to water and moisture can be avoided.  
       [0023] (7) To provide a ground source heat pump which can use off-peak-hours electricity in a manner similar to a phase change storage system but which can serve both heating and cooling in comparison with the phase change storage system which can only serve for cooling.  
       [0024] Further objectives and advantages of my invention will become apparent from a consideration of the drawings and ensuing descriptions. 
     
    
    
     DRAWING FIGURES  
     [0025] In the drawings, closely related figures have the same number but different alphabetic suffixes.  
     [0026]FIG. 1. Shows a heat pump system with recovery and energy storage functions where two air force heat exchangers serve as out-door and in-door heat transfer equipment, respectively.  
     [0027]FIG. 1A. Shows the operation of the system of FIG. 1 in cooling mode during service period in on-peak hours (summer).  
     [0028]FIG. 1B. Shows the operation of the system of FIG. 1 in recovery period with off-peak electricity after cooling service in on-peak hours (summer).  
     [0029]FIG. 1C. Shows the operation of the system of FIG. 1 in heating mode during service period in on-peak hours (winter).  
     [0030]FIG. 1D. Shows the operation of the system of FIG. 1 in recovery period with off-peak electricity after heating service in on-peak hours (winter).  
     [0031]FIG. 2. Shows an alternative embodiment where the out-door heat exchanger in FIG. 1 is replaced with a fluid-to-fluid heat exchanger.  
     [0032]FIG. 3. Shows an alternative embodiment where the in-door heat exchanger in FIG. 1 is replaced with a fluid-to-fluid heat exchanger. Terminal units are fan-coil units instead of diffusers.  
     [0033]FIG. 4. Shows an alternative embodiment where the out-door heat exchanger in FIG. 1 is replaced with a fluid-to-fluid heat exchanger, and furthermore, in-door heat exchanger in FIG. 1 is substituted with a fluid-to-fluid heat exchanger. Terminal units are fan-coil units instead of diffusers.  
     [0034]FIG. 5. Shows an additional embodiment of FIG. 1, where heat exchangers are routed in different way.  
     [0035]FIG. 5A. Shows the operation of the system of FIG. 5 in cooling mode during service period in on-peak hours (summer).  
     [0036]FIG. 5B. Shows the operation of the system of FIG. 5 in recovery period with off-peak electricity after cooling service in on-peak hours (summer).  
     [0037]FIG. 5C. Shows the operation of the system of FIG. 5 in heating mode during service period in on-peak hours (winter).  
     [0038]FIG. 5D. Shows the operation of the system of FIG. 5 in recovery period with off-peak electricity after heating service in on-peak hours (winter).  
     [0039]FIG. 5E. Shows the direct use of ground loop water for heating and cooling of the building space, with system configuration as described in FIG. 5.  
     [0040]FIG. 6. Shows an alternative looping of heat pump system with two forced air-to-fluid heat exchangers as in-door and out-door heat transfer equipment. 
    
    
     REFERENCE NUMERALS IN DRAWINGS  
     [0041] The two typical heat exchangers used in heat pump systems are condenser and evaporator. They are referred in this application as out-door heat exchanger and in-door exchanger, respectively, since the system in my invention is designed to perform reverse operation for different modes (heating and cooling) and different periods of time (service and recovery). This means that the out-door and in-door heat exchangers will function as both condenser and evaporator depending upon the direction of fluid flow. Heat pump loop excluding evaporator and condenser is compacted as a unit set  1 .  
                                                      1   Refrigeration unit                                     1a   refrigerant compressor               1b   four-way reversing valve               1c   expansion device               1d   hot water unit               1e   supplementary electric heater                             2   Out-door heat exchanger                                     2a   forced air-to-fluid heat exchanger               2b   fluid-to-fluid heat exchanger                             3, 6, 9   Circulation water pumps           4   Cooling tower           5   In-door heat exchanger                                     5a   forced air-to-fluid heat exchanger               5b   fluid-to-fluid heat exchanger                             7   In-door terminal units                                     6a   air diffusers               6b   fan-coil units                             8   Earth-side heat exchanger           10   Ground heat exchanger           11, 12   Reversing valves           13   Reversing air valve                      
 
     DESCRIPTION—FIGS.  1 ,  1 A,  1 B,  1 C AND  1 D—PREFERRED EMBODIMENT  
     [0042] A preferred embodiment of the ground source heat pump system with recovery and energy storage functions is illustrated in FIG. 1. The refrigeration loop is shown as, but not limited to, a mechanical compression cycle. Refrigeration loop consists of the compressor  1   a , reversing valve  1   b , expansion device  1   c , optional hot water unit  1   d  and optional supplementary electrical heating units  1   e . The refrigeration loop is closed with two heat exchangers: out-door heat exchanger  2  and in-door heat exchanger  5 . In-door heat exchanger  5  is attached with terminal units  7 .  
     [0043] Out-door heat exchanger  2  conducts heat transfer between refrigerant and out-door air, and the in-door heat exchanger  5  conducts heat transfer between refrigerant and in-door space. The earth-side heat exchanger  8  conducts heat transfer between the refrigerant and the ground loop fluid. Ground loop fluid is driven by water pump  9  to circulate through earth-side heat exchanger and underground medium (soil, rock, and/or sand). The ground loops  10  can be buried horizontally or vertically in the ground at a variety of depths.  
     [0044] Two reversing valves,  11  and  12 , connect with the inlet and outlet pipes of the heat exchangers  2   a ,  5   a ,  8 , and expansion device  1   c . More specifically in this embodiment, valve  11  connects with one end of the out-door heat exchanger  2   a , one end of the expansion device  1   c , and one end of the earth-side heat exchanger  8 , while the other reversing valve  12  connects with the other end of the earth-side heat exchanger  8 , in-door heat exchanger  5   a , expansion devices  1   c  and the supplementary heating device  1   e , if it is available.  
     [0045]FIGS. 1A, 1B,  1 C, and  1 D show different operational modes of the heat pump system described in FIG. 1. Detailed explanations are given as follows.  
     [0046] Operation FIG. 1A  
     [0047]FIG. 1A shows the operation of the heat pump system described in FIG. 1 in cooling mode during service period in on-peak hours (summer).  
     [0048] In cooling mode, the compressed hot refrigerant first passes through heat exchanger  1   d  and release thermal energy to the water, if the unit has a hot water option. In this situation, the domestic hot water is free of cost since it is heated with “waste” thermal energy, which is dissipated to the environment in the summer. Refrigerant, with a certain temperature drop after releasing thermal energy to tap water, then goes to out-door heat exchanger  2   a  and has further energy transfer. Heat is moved from heat exchanger  2   a  by forced air convection.  
     [0049] The reversing valve  11  is in the status shown in FIG. 1A so that the refrigerant out of the out-door heat exchanger  2   a  flows to the earth-side heat exchanger  8  for further cooling. Fluid, driven by pump  9 , circulates within the closed loops  10  and transfers heat from earth-side heat exchanger  8  to the ground medium (soil, rock and/or sand). The heat exchanger loops  10  can be horizontally or vertically buried underground, or can be any other kind of heat exchanger buried in ground. The underground medium with a moderate year-round temperature works as a “heat sink” and can absorb a certain amount of heat from the refrigerant. After giving thermal energy to the atmosphere in out-door heat exchanger  2   a  and ejecting heat to underground medium through earth-side heat exchanger  8 , the refrigerant, with a significant temperature drop but still warm and with high pressure, flows through reversing valves  12  and is then routed to expansion device  1   c . Warm refrigerant with high pressure passing through the expansion device  1   c  reduces its pressure and causes a corresponding reduction in temperature. The low-temperature, low-pressure refrigerant then flows to in-door heat exchanger  5   a . Warm air from internal space and/or fresh air from external space is forced to flow across the heat exchanger  5   a  and then to flow to the internal building space through duct work attached to the heat exchanger. Cold air is distributed through the in-door terminal units, that functions as diffusers  7   a  in this application.  
     [0050] Refrigerant, with temperature recovered after receiving energy from the in-door space through in-door heat exchanger  5   a , then returns to the compressor  1   a  for another cycle. It passes through the optional supplementary electric heater  1   e , but in this cooling mode, the heater is off, and there is no heat exchange between refrigerant and the environment.  
     [0051] Operation FIG. 1B  
     [0052]FIG. 1B shows the operation of the above heat pump system during the recovery period using off-peak-hour electricity providing cooling service during on-peak hours (summer).  
     [0053] During cooling operation, the underground medium keeps receiving energy from the refrigerant and its temperature may significantly increase depending on the cooling load of the building and also on the ground loop size. The ground loop does not necessarily to be sized to receive heat from or provide heat to the heat pump without substantial temperature increase of the underground medium after the operation of an entire season. The recovery model shown in FIG. 1B is used for the cases where the loop is not as large as required in conventional ground source heat pump design for a season&#39;s operation for different reasons including (a) saving initial cost; (b) limitation of the ground space for loop installation; (c) using off-peak hour electricity to save operational cost.  
     [0054] While the temperature of the returning fluid from the ground loops  10  substantially increases after a period of operation, the system will manually or automatically shift to the recovery cycle in the off-peak hours as shown in FIG. 1B. In the recovery mode, the reversing valve  1   b  in the refrigeration side remains in the same position as in the cooling mode show in FIG. 1A, but both reversing valves  11  and  12  are in opposite positions. Refrigerant out of the out-door heat exchanger  2   a  is routed to the expansion device  1   c  through reversing valve  11 . As described in FIG. 1A, the refrigerant passing through the expansion device will cause a temperature reduction and a corresponding pressure drop. The low-temperature, low pressure refrigerant then passes through the in-door heat exchanger  5   a  first, and provides cold air to the building space through duct work and diffusers  7   a . This ensures that even in the recovery cycle in the off-peak hours, the cooling of the building space is still the priority and remains secure. Refrigerant at this point still has a moderately low temperature. It then secondly goes to the earth-side heat exchanger  8  via valves  12 . The cold refrigerant will receive energy from circulation fluid in the earth-side heat exchanger  8 . The energy is withdrawn from the underground medium through ground loops  10 , and then the ground medium is cooled and “recovers” from heat accumulation. Refrigerant out of the earth-side heat exchanger  8  then returns to the compressor for another cycle.  
     [0055] During the operation, the temperature of the fluid which is circulating between the earth-side heat exchanger and the ground loop needs to be monitored in order to optimize the operational strategies, including when to start the recovery cycle and when to stop the recovery cycle. The system operational strategies mainly depend on the water temperature of the ground loop, electricity price structure as a function of time, heat pump operational performance, the underground materials, and weather conditions.  
     [0056] Operation FIG. 1C  
     [0057]FIG. 1C shows the operation of the system of FIG. 1 in heating mode during service period in on-peak hours (winter).  
     [0058] In the winter, the heat pump system is shifted to heating mode shown in FIG. 1C. In heating mode, the reversing valve  1   b  is in an opposite position to the cooling mode shown in FIG. 1A. The compressed refrigerant passes through the hot water exchanger  1   d  first, if it is available. It must be noted that at this time, hot water will use extra electricity and will not be free of cost.  
     [0059] A supplementary electric heater  1   e  is shown as an option. Compressed high temperature refrigerant receives further energy from the electric heater, if it is installed. Valves  11  and  12  are in the same position as in the cooling mode. Valve  12  routes the refrigerant coming out of the electric heater  1   e  directly to the in-door heat exchanger  5   a . After giving heat to the in-door space, the refrigerant is led to the expansion device  1   e  by valve  11 . The expanded low-temperature and low-pressure refrigerant passes through the earth-side heat exchanger  4 . Ground loops  10  abstract energy from the underground medium and warm up the refrigerant before it goes back to compressor for another cycle. Out-door heat exchanger  2   a  will be manually or automatically turned off or bypassed if the temperature of refrigerant out of the earth-side heat exchanger  4  is higher then the ambient temperature. An additional reversing valve can be used to shift the out-door heat exchanger  2   a  prior to the earth-side heat exchanger if the ambient temperature is higher then both the ice point and the temperature of refrigerant coming out of the expansion devices.  
     [0060] Operation FIG. 1D  
     [0061]FIG. 1D shows the operation of the system of FIG. 1 in recovery period using off-peak electricity after heating service in on-peak hours (winter).  
     [0062] The temperature of the underground medium material decreases as the system extracts energy from it. The lower the ground temperature, the lower the system heating efficiency. When the fluid temperature is approaching the freezing point, the system is close to its operational limit and will not function properly. An appropriate threshold for the fluid temperature can be defined based on the electricity price and system performance. When the temperature of the ground circulation fluid reaches the threshold, the system will return to recovery cycle during the next off-peak hours. The supplementary electric heater  1   e  is needed if the ambient temperature during the off-peak hours (usually in the winter night) is near the ice point, and the out-door air cannot provide sufficient energy to recover underground heat losses. The refrigerant re-heated by supplementary electric heater  1   e  then flows to the in-door heat exchanger  5   a  via reversing valve  12 . Thermal energy is transferred to the building spaces through duct work and diffusers. This assures the space heating while the system is trying to warm up the underground medium. The refrigerant, after leaving the in-door heat exchanger  5   a , is still at a moderate temperature, and flows to the earth-side heat exchanger  8  and transfers the remainder of the energy to the circulating fluid which moves the heat to ground. The underground medium is then warmed up with the lower cost electricity during off-peak hours. After flowing through the heat exchange in the earth-side heat exchanger  8 , refrigerant is routed to expansion devices  1   c . The expanded low-temperature and low-pressure refrigerant then returns to the compressor through the out-door heat exchanger  2   a . A high ambient temperature will be helpful for the low-temperature (mostly below the ice point) refrigerant to gain energy from the atmosphere. Generally speaking, the more significant difference between the electricity rates in off-peak and on-peak hours, the more complete recovery is suggested until the ground circulating fluid heated to a higher level. The elevation of the underground medium temperature means storage of energy given by off-peak-hours electricity. Higher underground temperature will more energy storage will greatly improve the heating efficiency.  
     DESCRIPTION—FIG.  2 —PREFERRED EMBODIMENT  
     [0063]FIG. 2. shows an alternative embodiment where the out-door heat exchanger in FIG. 1 is replaced with a fluid-to-fluid heat exchanger. Circulation fluid (water) is driven by pump  3  to flow through fluid-to-fluid out-door heat exchanger  2  and a cooling tower  4 . The cooling tower  4  is used to dissipate heat to the atmosphere. The cooling tower can be air-cooled or water-cooled. Configuration of the remaining parts is the same as the system in FIG. 1.  
     DESCRIPTION—FIG.  3 —PREFERRED EMBODIMENT  
     [0064]FIG. 3. shows an alternative embodiment where forced air-to-fluid in-door heat exchanger  2   a  in FIG. 1 is replaced with a fluid-to-fluid heat exchanger  2   b . Heat transfer between refrigerant and the in-door space is conducted by fluid circulating through in-door heat exchange  5   b  and the terminal units  7   b . Here the terminal units are fan-coil units  7   b  instead of diffusers  7   a  as shown in FIG. 1.  
     DESCRIPTION—FIG.  4 —PREFERRED EMBODIMENT  
     [0065]FIG. 4. shows an alternative embodiment where the forced air-to-air out-door heat exchanger  2   a  in FIG. 1 is replaced with a fluid-to-fluid heat exchanger  2   b , and furthermore, forced air-to-fluid in-door heat exchanger  5   a  in FIG. 1 is substituted with a fluid-to-fluid heat exchanger  5   b . Again, fan-coil units  7   b , instead of diffusers  7   a , are used to dispute cold or warm air to the building space.  
     DESCRIPTION—FIGS.  5 ,  5 A,  5 B,  5 C,  5 D, AND  5 E—ALTERNATIVE EMBODIMENT  
     [0066]FIG. 5. show an alternative embodiment of FIG. 4, where heat exchangers are routed in different way.  
     [0067] In this application, two reversing valves  11 , and  12 , are not installed in refrigerant loop, but in the water circulation loops. Four ends of the valve  11  are connected with cooling tower  4 , out-door heat exchanger  2   b , ground loops  10 , and another reversing valve  12 , respectively. Another reversing valve  12  is connected with in-door terminal units  7   b , in-door heat exchanger  5   b , ground loops  10 , and the other reversing valve  11 . The ground loop is directly connected to the two reversing valves, and the earth-side heat exchanger  8  in FIG. 4 is omitted. Three water pumps  3 ,  6 , and  9  are used to circulate fluid (water) to pass through the out-door loop, in-door loop, and ground loop, respectively.  
     [0068] Operation—FIGS. 5A, 5B,  5 C,  5 D, AND  5 E  
     [0069]FIGS. 5A, 5B,  5 C,  5 D, and  5 E show a different operation model of the heat pump system described in FIG. 5. The operation is very similar to the operation described in FIGS. 1A, 1B,  1 C and  1 D. Here only the flow routings are listed for different cycles.  
     [0070]FIG. 5A, Cooling in summer, during on-peak-hour service:  
     [0071] Refrigeration loop: Compressor  1   a -&gt;hot water heat exchanger  1   d -&gt;out-door heat exchanger  2   b -&gt;expansion devices  1   c -&gt;in-door heat exchanger  5   b -&gt;supplementary electric heater  1   e -&gt;compressor  1   a    
     [0072] Out-door heat exchange loop (circulated by pump  3  and  9 ): Out-door heat exchanger  2   b -&gt;cooling tower  4 -&gt;ground loops  10 -&gt;out-door heat exchanger  2   b    
     [0073] In-door heat exchange loop (circulated by pump  6 ): In-door heat exchanger  5   b -&gt;terminal units (fan-coils)  7   b -&gt;In-door heat exchanger  5   b    
     [0074]FIG. 5B, Recovery of underground temperature—off-peak hours (electricity, after a period of cooling operation in on-peak hours in summer):  
     [0075] Refrigeration loop (same as the cooling loop in FIG. 5A): Compressor  1   a -&gt;hot water heat exchanger  1   d -&gt;out-door heat exchanger  2   b -&gt;expansion devices  1   c -&gt;in-door heat exchanger  5   b -&gt;supplementary electric heater  1   e -&gt;compressor  1   a    
     [0076] Out-door heat exchange loop (circulated by pump  3 ): Out-door heat exchanger  2   b -&gt;cooling tower  4 -&gt;out-door heat exchanger  2   b . (It must be noted that the ground loops  10  are not connected to out-door circulation loop here. The cooling tower  4  is the only heat exchanger to remove thermal energy from refrigerant)  
     [0077] In-door heat exchange loop (circulated by pump  3  and  6 ): In-door heat exchanger  5   b -&gt;terminal units (fan-coils)  7   b -&gt;ground loops  10  -&gt;In-door heat exchanger  5   b  (Here the ground loops  10  are connected to the in-door loop through the reversing of valve  11  and  12 . In the loop circulation, fluid (water) first receives energy from indoor hot air, and then receive heat from underground medium through the closed loops  10  until the heat accumulation during the cooling cycle is fully released, or recovered).  
     [0078]FIG. 5C, Heating in winter, during the service period of on-peak hours:  
     [0079] Refrigeration loop: Compressor  1   a -&gt;hot water heat exchanger  1   d -&gt;supplementary electric heater  1   e -&gt;in-door heat exchanger  5   b -&gt;expansion devices  1   c -&gt;out-door heat exchanger  2   b -&gt;compressor  1   a    
     [0080] Out-door heat exchange loop (circulated by pump  3  and  9 ): Out-door heat exchanger  2   b -&gt;cooling tower  4 -&gt;ground loops  10 -&gt;out-door heat exchanger  2   b  (It must be noted that the cooling tower is the place where refrigerant abstracts heat from the atmosphere, before it goes to the ground loops  10  to extract energy from the underground medium. The refrigerant has to pass through the cooling tower first to receive energy in a low temperature level while it is just comes out the expansion device, and with temperature of itself below the ice point.)  
     [0081] In-door heat exchange loop (circulated by pump  6 ): In-door heat exchanger  5   b -&gt;terminal units (fan-coils)  7   b -&gt;In-door heat exchanger  5   b    
     [0082]FIG. 5D, Recovery of the underground temperature—off-peak hours (after a period of heating operation in on-peak hours in winter):  
     [0083] Refrigeration loop (same as the heating loop in FIG. 5C): Compressor  1   a -&gt;hot water heat exchanger  1   d -&gt;supplementary electric heater  1   e -&gt;in-door heat exchanger  5   b -&gt;expansion devices  1   c -&gt;out-door heat exchanger  2   b -&gt;compressor  1   a    
     [0084] Out-door heat exchange loop (circulated by pump  3 ): Out-door heat exchanger  2   b -&gt;cooling tower  4 -&gt;out-door heat exchanger  2   b . (It must be noted that the ground loops  10  are not connected to out-door circulation loop. The cooling tower  4  is the only heat exchanger to gain energy from the environment for the refrigerant)  
     [0085] In-door heat exchange loop (circulated by pump  3  and  6 ): In-door heat exchanger  5   b -&gt;terminal units (fan-coils)  7   b -&gt;ground loops  10 -&gt;In-door heat exchanger  5   b  (Here the ground loops  10  are connected to the in-door loop through the reversing of valves  11  and  12 . In the loop circulation, fluid (water) first receives energy from in-door heat exchanger  2   b . The energy is basically generated by supplementary electric heater  1   e , and partially subtracted from atmosphere through cooling tower  4 . After dissipating energy to the building space through in-door heat exchanger  5   b , the fluid goes to fan-coil units  7   b , and the fluid is still in a relatively high temperature. Part of remaining energy then dissipates to the underground medium through loops  10 . The underground medium keeps receiving energy from circulation fluid until the energy subtraction during the building heating period in on-peak hours is fully recharged, or recovered. In this model, the energy is generated mainly by off-peak-hour electricity and stored within the underground medium, and released during the on-peak hours.  
     [0086] Operation—FIG. 5E  
     [0087] Using us off-peak electricity to heat the underground medium, it is sometimes even an economic strategy to heat the underground medium to a sufficient high level so that the heating in on-peak hours can directly come from the ground circulating fluid. In this embodiment show in  6 E, the refrigerant loop is not necessarily operated, while the fluid is circulated by pump  6  and  9  between the in-door heat exchange  5   b  and the ground loops  10 . The operation cost will be based up on, again, the electricity price structure in operation time sections.  
     [0088] While using off-peak electricity to cool down the underground medium, it is also possible to cool the medium into a sufficient lower level so that it can be directly used during the on-peak cooling service hours. The refrigeration system can be shut down, and only the circulation pumps  6  and  9  move the fluid from ground loops  10  to indoor heat exchanger  5   b , as shown in FIG. 5E.  
     DESCRIPTION—FIG.  6 —ALTERNATIVE EMBODIMENT  
     [0089]FIG. 6. shows an alternative looping of the heat pump system with two forced air-to-fluid heat exchangers used as in-door and out-door heat transfer equipment.  
     [0090] In this application, the system is simplified to use only two heat exchangers, out-door heat exchanger  2   b  and in-door heat exchanger  5   a . Heat exchanger  2   b  has to be fluid-to-fluid type and connected to ground loops  10 . The in-door heat transfer equipment  7   a  must be an air-to-fluid heat exchanger. The duct work attached to the heat exchanger  7   a  is divided into to directions. A reversing valve  13  is installed to change the direction of the forced air to in-door or out door space.  
     OPERATION DESCRIPTION AND BENIFTS  
     [0091] A specific operation strategy needs define two important operation parameters, including how frequently the recovery cycle needs to work, and what a temperature level it has to be recovered up to. All this operation optimization needs to be done based on the electricity prices, initial cost for underground loops, actual pipe size and heat transfer capacity, and the heat pump equipment performance characteristics.  
     [0092] Apparently, with the recovery and energy storage function, the yearly seasonal heat accumulation in the year around will not be problem. A much small size of ground heat exchanger can perform as well as a large size conventional system. The operation cost, since more using of off-peak electricity may be less then the conventional ground source heat pump systems. For most conventional ground source heat pump, antifreeze solution is needed to avoid the freezing of circulation fluid in the winter, especially when operating in the North regions. Antifreeze solution, and the resultant environmental, safety and erosion problems, are eliminated in this invention.  
     CONCLUSION, RAMIFICATIONS, AND SCOPE  
     [0093] Thus the reader can see that this invention provides a recoverable ground source heat pump system with energy storage function, which can reduce the initial cost of the underground loop, require less underground space, minimize the operational cost through using off-peak hours electricity, assure the performance of operational, and avoid using of antifreeze solution in to ground circulation fluid, which may cause environmental, safety and erosion problems.  
     [0094] While my above description contains many specificities, these should not be constructed as limitation on the scope of the invention, but rather as an exemplification of one preferred embodiment thereof. Many other variations are possible. For example,  
     [0095] 1. The refrigeration unit can be a mechanical compressing system as shown in the sample embodiments. It can also be any of other refrigeration apparatus including absorption refrigeration, electric-magnetic refrigeration, thermal-electric refrigeration, et al.  
     [0096] 2. The ground heat exchanger can be any type of heat exchanger which is buried in the ground medium (sand, soil, and/or rock) or laid under the asphalt or concrete pavement. The heat exchanger can be closed pipe loop(s) buried underground vertically or horizontally. The ground heat exchanger can also be heat transfer equipment or loop laid on the bottom of surface waters.  
     [0097] 3. The reversing valves can be four-way as show in the sample embodiment, or two-way, or simple one way valves but mechanically combined to reach the same open/close function. The valve can be manually operated, or automatically operated with control units. The control units can be programmable so that the system operation can be timely optimized based on all, or part of the information including electricity price, heat pump performance, ground heat transfer capacity, and the sensed temperature of the ground circulation fluid.  
     [0098] 4. The routing of the system in recovery model after heating or cooling service shown in the embodiments are just some examples. Many other loops can be routed.  
     [0099] 5. Heat exchangers can be any type to contact heat transfer between liquid and air. The terminal units can be duct work and diffuser, or fan-coil units or any other air distribution and heat transfer units.  
     [0100] 6. Supplementary heating is mainly provided by electricity, but it can also be other energy sources including solar, oil, coal, gas, and propane, which would be used in on-peak hours.  
     [0101] The scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.