Patent Application
20060288724
The present invention relates to heating and cooling apparatus, and more particularly to a heating and cooling system having geothermal and air-to-air subcircuits.
Air-to-air heat pumps have been in widespread use throughout the United States for many years. These units operate to exchange heat between outdoor air and inside air. For example, a conventional heat pump can operate in either a heating mode during which heat is drawn from the outdoor air and used in heating the inside of the building or in a cooling mode during which heat is drawn from inside the building and released into the outdoor air. Because these systems transfer rather than generate heat, they are generally more efficient than conventional heating and cooling systems.
Air-to-air heat pumps are available in a variety of designs. A typical air-to-air heat pump includes an outdoor air coil unit located outside of the building, an indoor air coil unit located within the building, a plurality of refrigerant lines for interconnecting the indoor and outdoor units, a compressor for moving refrigerant through the system and a control system for controlling operation of the heat pump. In the heating mode, liquid refrigerant enters the outdoor coil unit where it evaporates, thereby drawing heat from the external air into the refrigerant. The gas refrigerant flows from the outdoor coil unit through the refrigerant lines to the indoor coil unit. In the indoor coil unit, the gas refrigerant condenses back into a liquid, thereby releasing heat drawn from the outdoor air into the building. The liquid refrigerant then flows back to the outdoor coil unit to continue the cycle.
In the cooling mode, the process works essentially in reverse. Liquid refrigerant flows into the indoor coil unit where it evaporates to draw heat from the indoor air. The gas refrigerant flows through the refrigerant lines to the outdoor coil unit. In the outdoor coil unit, the refrigerant condenses, thereby releasing heat into the outdoor air. The liquid refrigerant then returns via the refrigerant lines to the indoor coil unit to continue the cycle.
Experience has revealed that when an air-to-air heat pump is operated in the heating mode at close to freezing temperatures, frost can form on the evaporator. This can significantly impair operation of the heat pump. Frost forms on the evaporator when the evaporator draws sufficient heat from the air surrounding the evaporator to freeze the moisture contained in the air. Frosting is typically not a problem at temperatures significantly above or below freezing because at higher temperatures there is enough heat in the air to prevent the moisture from freezing and at lower temperatures the moisture in the air is already frozen so it does not accumulate on the evaporator.
A number of methods have been developed to address the problem of frosting. For example, a number of conventional systems draw heat from inside the building to defrost the evaporator. These systems typically include an indoor coil that draws heat into the refrigerant from inside the building and then pumps the refrigerant through the external evaporator to remove the frost. This approach suffers in that it significantly reduces the efficiency of the heating system because heat is removed from the inside of building to defrost the evaporator. Drawing heat from inside the building can also generate an undesirable cold draft through the duct work. As another example, some systems include an electric heater located next to the evaporator. When the evaporator becomes frosted, the electric heater is turned on to remove the frost. This type of system is also inefficient because it requires operation of a separate electric heater.
One unique and particularly efficient solution to the problem of defrosting is disclosed in U.S. Pat. No. 5,983,660 to Kiessel et al. The system of U.S. Pat. No. 5,983,660 provides a heat pump system having a geothermal subcircuit to provide geothermal heat for defrosting the outdoor air coil. The system also includes “pump down” circuitry that can be selectively engaged to draw refrigerant out of the geothermal heat exchanger when it is not in use. This addresses issues that may arise as a result of refrigerant imbalance during the various modes of operation. Although this system is a marked improvement over many pre-existing heating and cooling systems, there continues to be a need for a more efficient and more adaptive heating and cooling system.
The aforementioned problems are overcome by the present invention which provides a hybrid heating and cooling system having an indoor heat exchanger (such as an indoor air coil), an outdoor air coil and a geothermal heat exchanger. The geothermal heat exchanger can be buried in the ground or submerged in a natural water source, such as a lake, river or underground well. The circuit includes control components that permit the system to operate in a variety of different modes including: (a) air-to-air heating, (b) air-to-air air conditioning, (c) geothermal defrost and (d) geothermal heating. The system may optionally include an air-to-air defrost mode.
In one embodiment, the indoor air coil subcircuit, outdoor air coil subcircuit and geothermal subcircuit are connected in parallel with one another by control components capable of selectively routing refrigerant through any two of the subcircuits to provide the distinct modes of operation discussed above. In this embodiment, the circuit isolates one of the indoor air coil, outdoor air coil or geothermal heat exchanger as appropriate during each mode of operation. The circuit may be configured so that the isolated heat exchange device is connected to the low pressure side of the compressor in each mode of operation. As a result, the compressor automatically pumps down (i.e. draws refrigerant out of) the isolated heat exchange device.
In one embodiment, the indoor air coil subcircuit is connected with the outdoor air coil subcircuit by a gas refrigerant line and a liquid refrigerant line. The system also includes a compressor or other refrigerant pump for moving refrigerant through the system. In this embodiment, the geothermal subcircuit includes a first refrigerant line connected to the liquid refrigerant line and a second refrigerant line connected to the compressor.
In one embodiment, the system includes a collection of valves that are selectively adjustable to route refrigerant between any two of the heat exchangers (i.e., the indoor air coil, the outdoor air coil and the geothermal heat exchanger).
The present invention provides a hybrid geothermal/air coil heating and cooling system that provides a high level of adaptability and improved efficiency over convention systems. The control system permits selective operation of any two heat exchangers in combination, thereby providing a highly adaptable system that can be controlled to take advantage of the most efficient heating or cooling combinations for varying circumstances. In select modes of operation, the geothermal heat exchanger can be used alternatively to provide energy for indoor heating and outside air coil defrosting. Additionally, the unique circuit of the present invention provides automatic pump down of the isolated heat exchange device during each mode of operation to address potential issues associated with refrigerant imbalance. Further, when geothermal operation is not most efficient, the system is capable of operating in an air-to-air mode utilizing the outdoor air coil. The circuit of the present invention is easily implemented with a small number of relatively inexpensive components. Accordingly, the equipment and installation costs of the system are relatively low.
These and other objects, advantages, and features of the invention will be readily understood and appreciated by reference to the detailed description of the preferred embodiment and the drawings.
A heat and cooling system in accordance with an embodiment of the present invention is illustrated in
As noted above, the system 10 includes an outdoor air coil subcircuit 16 to permit exchange of heat with the outdoor air. The design and configuration of the outdoor air coil subcircuit 16 may vary from application to application, but a variety of conventional outdoor air coil subcircuits are suitable for use in connection with the present invention. As shown in
The indoor air coil unit 14 operates to exchange heat with the indoor air. The design and configuration of the indoor air coil subcircuit 14 may vary from application to application, but a variety of conventional indoor air coil subcircuits are suitable for use in connection with the present invention. The indoor air coil unit 14, such as Model No. ARPT032-00C-1A from Goodman Manufacturing Company, Houston, Tex., includes an indoor air coil 20 for exchanging heat with the indoor air, an expansion device 22 for creating a pressure differential in the circuit during the cooling mode, and a blower 24 for moving air across the coil 20. The expansion device 22 may include a bypass 23 which permits refrigerant to bypass 23 the expansion device 22 during the air-to-air heating mode and the geothermal heating mode. If desired, the expansion device 22 and associated bypass 23 may be incorporated into a single circuit component, such as a unidirectional flow restrictor, that meters the flow of refrigerant in one direction while permitting refrigerant to flow freely in the other. These components are typically contained within a single housing 26 that is integrated with or connected to the building's duct work in a conventional manner. The indoor air coil unit 14 is interconnected with the outdoor air coil unit by a gas refrigerant line 46 extending between the indoor air coil 20 and the reversing valve 32, and a liquid refrigerant line 48 extending between the outdoor air coil 28 and the indoor air coil 20. The refrigerant lines 46 and 48 are generally conventional and may be conventional copper tubing. The diameter of the refrigerant line will vary from application to application depending on the capacity and design of the heat pump circuit and the type of refrigerant used in the circuit. However, in this embodiment, the liquid refrigerant line 48 is three-eighths of an inch in diameter and the gas refrigerant line 46 is three-fourths of an inch in diameter. Although the indoor coil unit 14 is described in connection with an indoor air coil 16, the system 10 may include an indoor unit with other types of heat exchange devices. For example, the indoor unit may include a conventional refrigerant-to-water heat exchanger (not shown). In this example, the indoor heat exchanger (not shown) may transfer heat between the refrigerant and an indoor heat transfer medium (e.g. water) that is used to operate a generally conventional radiant heating and cooling system, such as a radiant floor heating system.
The geothermal subcircuit 12 is connected to the heat pump circuit 10 in parallel as shown in
The present invention is well suited for use with a wide variety of conventional geothermal heat exchangers. However, in the illustrated embodiment, the heat exchanger 50 is designed for use with the matched indoor air coil unit and outdoor air coil unit combination described above, which is a two and one-half ton unit providing approximately 30,000 BTUs. The heat exchanger 50 includes a plurality of loops 90a-e interconnected with a pair of conventional manifolds 92a-b. Each loop 90a-e includes a generally U-shaped section of conventional copper tubing having a diameter of three-eighths of an inch and a length of approximately 120 feet (overall loop length of approximately 60 feet). The number of loops and the diameter and length of each loop will vary from application to application depending on a variety of factors, including without limitation the volume of heat exchange desired, the type of refrigerant used in the circuit, the capacity of the system, the pressure differential in the circuit, the climate in which the system is installed, and the makeup of the geothermal heat source. As a general rule, the heat exchanger 50 will include three loops for each ton of capacity. This rule is not absolute and the ratio of loops to capacity may vary. The distribution manifold 92a interconnects the input end of each loop 90a-c with the refrigerant line 52. The output manifold 92b interconnects the output end of each loop 90a-e with the refrigerant line 54. This permits refrigerant to flow through the loops 90a-e in parallel. Although the geothermal subcircuit 12 is described in connection with a refrigerant-based heat exchanger 50, the geothermal subcircuit 12 may include other types of heat exchangers. For example, the geothermal subcircuit 12 may include a generally conventional refrigerant-to-water heat exchanger (not shown). With this type of alternative heat exchanger, the geothermal subcircuit 12 includes a separate circuit that circulates water (or other heat transfer fluid) through one or more loops (not shown) disposed in the geothermal heat source. Typically, the water is circulated by a conventional circulating pump (not shown) and the loops are manufactured from conventional polyethylene tubing (or other conventional tubing). Heat may be exchanged between the segregated water and refrigerant circuits using essentially any type of heat exchanger, including a generally conventional coaxial heat exchanger in which the water circuit extends coaxially through a portion of the refrigerant circuit.
The heat pump circuit 10 also includes a control mechanism 64 for controlling the operation of the solenoid valves 60, 62 and 63, and other elements of the circuit 10. The control mechanism 64 may be a conventional electromechanical control system that receives input from an indoor thermostat T (or the indoor controller 83), the outdoor controller 80, an outdoor thermostat T2, and, if desired, other inputs that might affect operation of the system 10.
The indoor air coil unit 14 and outdoor air coil unit 16 are installed in a conventional manner using conventional techniques and apparatus. The indoor and outdoor air coil units may be purchased as pre-assembled units from any of a variety of well known suppliers. Alternatively, the units can be assembled from the components described above. In either event, the indoor and outdoor units of the illustrated embodiment are interconnected by liquid refrigerant line 48 and gas refrigerant line 46 as described above, and the reversing valve 32 (or other refrigerant control valve) is operatively connected to the outdoor controller 80 (as described below) using conventional techniques and apparatus.
The geothermal subcircuit 12 can be installed during initial installation of the heat pump circuit or it can be retrofit to an existing heat pump circuit. In retrofit applications, the indoor air coil unit 14 and the outdoor air coil unit 16 may be specifically pre-configured to provide easy retrofit of the geothermal subcircuit 12, for example, by including the necessary fittings, valves, etc. In one embodiment, the outdoor air coil 16′ may include a geothermal upgrade port 100 to permit the geothermal subcircuit 12 to be easily connected to the outdoor air coil unit 16′ (See
The heat exchanger 50 may be buried in the ground or submerged in a river, lake, well or other body of water, and then interconnected with the heat pump circuit by refrigerant lines 52 and 54. Typically, the heat exchanger will be buried in the ground. In such cases, the loops 90a-c can be buried collectively in a single bore or individually buried in separate bores. In this embodiment, refrigerant line 52 is connected at one end to the distribution manifold 92a and at the other end to the liquid refrigerant line 48 by a conventional “T” joint 70. Similarly, refrigerant line 54 of this embodiment is connected at one end to the output manifold 92b and at the other end to the compressor 30 by a conventional “T” joint 72. In the illustrated embodiment, the refrigerant line 54 is connected to the compressor 30 upstream from the accumulator 38. The solenoid valve 60 and expansion device 56 are installed in refrigerant line 52 while the optional check valve 57 is installed in refrigerant line 54 (if included). The solenoid valve 62 is installed in the liquid refrigerant line 48 between the indoor air coil unit 14 and the “T” joint 70. The solenoid valve 63 is installed in the liquid refrigerant line 48 between the outdoor air coil unit 16 and the “T” joint 70. The solenoid valves 60, 62 and 63 are operatively connected to the control mechanism 64 using conventional techniques and apparatus.
The heat pump system 10 is capable of operation in five separate modes; namely cooling mode (see
In the air-to-air heating mode, the cycle is essentially reversed. The thermostat T sends a signal that places the reversing valve 32 in the air-to-air heating position so that refrigerant flows from the outdoor air coil 28 through the accumulator 38 and the compressor 30 to the gas refrigerant line 46. The control mechanism 64 opens solenoid valves 62 and 63, and closes solenoid valve 60 (if the valves are not already in those positions). The compressed hot gas refrigerant flows from the reversing valve 32 through the gas refrigerant line 46 to the indoor air coil 20. In the indoor air coil 20, the compressed hot gas refrigerant condenses into a high pressure liquid, thereby releasing heat energy into the indoor air. The transfer of heat is expedited by the indoor blower 24 which moves air over the indoor air coil 20. The liquid refrigerant flows from the indoor air coil 20 into the liquid refrigerant line 48. The liquid refrigerant flows through the bypass valve 23 of the expansion device 22. Because solenoid valve 60 is closed, refrigerant does not flow to geothermal heat exchanger 50. Instead, the refrigerant flows through the open solenoid valves 62 and 63, the expansion device 34, which meters the refrigerant to separate the high pressure side of the circuit from the lower pressure side of the circuit, and eventually to the outdoor air coil 28. In the outdoor air coil 28, the liquid refrigerant evaporates into a gas, thereby abstracting heat from the outdoor air. From the outdoor air coil 28, the low pressure gas (or vaporized) refrigerant flows back to the reversing valve 32 to repeat the cycle. The optional check valve 57 prevents gas refrigerant from flowing into refrigerant line 54.
In the geothermal heating mode, heat is abstracted from the geothermal heat source rather than the outdoor air. The thermostat T places the reversing valve 32 in the heating position so that refrigerant flows from the geothermal heat exchanger 50 through the accumulator 38 and the compressor 30 to the gas refrigerant line 46. The control mechanism 64 opens solenoid valves 60 and 62, and closes solenoid valve 63 (if the valves are not already in those positions). The compressed hot gas refrigerant flows from the reversing valve 32 through the gas refrigerant line 46 to the indoor air coil 20. In the indoor air coil 20, the compressed hot gas refrigerant condenses into a high pressure liquid, thereby releasing heat energy into the indoor air. The transfer of heat is expedited by the indoor blower 24 which moves air over the indoor air coil 20. The liquid refrigerant flows from the indoor air coil 20 into the liquid refrigerant line 48. The liquid refrigerant flows through the bypass of expansion device 22. Because solenoid valve 60 is open and solenoid valve 63 is closed, refrigerant does not flow to the outdoor air coil 28. Instead, the refrigerant flows through the open solenoid valves 62 and 60, the expansion device 56, which meters the refrigerant to separate the high pressure side of the circuit from the lower pressure side of the circuit, and eventually to the distribution manifold 92a of the heat exchanger 50. From the distribution manifold 92a, the refrigerant flows in parallel through the various loops 90a-e. In the loops 90a-e, the refrigerant evaporates into a gas, thereby abstracting heat from the geothermal heat source. The vaporized refrigerant flows from the loops 90a-e into the output manifold 92b and then into refrigerant line 54. From refrigerant line 54, the low pressure gas (or vaporized) refrigerant flows back to the accumulator 38, the compressor 30 and the reversing valve 32 to repeat the cycle.
As described in the Background, frost may accumulate on the outdoor air coil 28 when the system 10 is operating in the air-to-air heating mode and the exterior temperature is near freezing (e.g. between approximately 25 and 37 degrees Fahrenheit). The system 10 is designed to use heat energy from the indoor air or from a geothermal heat source to defrost the outdoor air coil 28. The system 10 may include a timing circuit that causes the system 10 to enter into the defrost mode approximately every 60 minutes when both the system 10 is in the heating mode and the outdoor temperature falls within the frost range (e.g. 25 degrees to 37 degrees Fahrenheit). Alternatively, other conventional methods can be used for determining when the system should enter into the defrost mode. In a typical outdoor air coil unit 16, there will be an outdoor controller 80 that determines, among other things, when to enter and leave the defrost mode. The outdoor controller 80 will typically have a defrost control line 82 for sending a signal to the indoor unit 14 to direct the indoor unit 14 to turn on the auxiliary heat source 84, which may, for example, be a gas furnace or electrical resistance heater. In one embodiment, the defrost control line 82 is routed through the control mechanism 64. When the control mechanism 64 recognizes a signal indicating that the outdoor air coil unit 16 is to enter the defrost mode, the control mechanism 64 can take appropriate action. In the geothermal defrost mode, the control mechanism 64 will use the geothermal subcircuit 12 as a heat source for defrosting the outdoor air coil unit 16. Accordingly, the control mechanism 64 will close solenoid valve 62 and opens solenoid valves 60 and 63. Also, the reversing valve 32 is moved into the cooling position by the outdoor controller 80. Accordingly, refrigerant flows from the gas refrigerant line 54 through the accumulator 38 and the compressor 30 to the outdoor air coil 28. In the outdoor air coil 28, the compressed hot gas refrigerant condenses into a high pressure liquid, thereby releasing heat energy into the outdoor air coil. This heat energy functions to melt away any frost collected on the outdoor air coil 28. The outdoor fan 36 is typically turned off by the outdoor controller 80 during the defrost mode. The liquid refrigerant flows from the outdoor air coil 28 into the liquid refrigerant line 48. The liquid refrigerant flows through the bypass valve 35 of the expansion device 34. Because solenoid valve 62 is closed, refrigerant does not flow to the indoor air coil 20. Instead, the refrigerant flows through refrigerant line 52, which includes opened solenoid valve 60 and expansion device 56. The expansion device 56 meters the refrigerant to separate the high pressure side of the circuit from the low pressure side of the circuit. The liquid refrigerant flows through the expansion device 56 into the distribution manifold 92a of the heat exchanger 50. From the distribution manifold 92a, the refrigerant flows in parallel through the various loops 90a-e. In the loops 90a-e, the refrigerant evaporates into a gas, thereby abstracting heat from the geothermal heat source. The vaporized refrigerant flows from the loops 90a-e into the output manifold 92b and then into refrigerant line 54. From refrigerant line 54, the refrigerant returns to the accumulator 38, the compressor 30 and then the reversing valve 32, after which it repeats the cycle.
In the air-to-air defrost mode, the system 10 is designed to use indoor air as the heat source for defrosting the outdoor air coil unit 16. In this mode, the defrost controller 80 sends a defrost signal on defrost control line 82 and moves the reversing valve 32 into the cooling position. The control mechanism 64 intercepts the signal. In response, the control mechanism 64 closes solenoid valve 60 and opens solenoid valves 62 and 63. Accordingly, refrigerant flows from the gas refrigerant line 46 through the reversing valve 32, the accumulator 38 and the compressor 30 to the outdoor air coil 28. In the outdoor air coil 28, the compressed hot gas refrigerant condenses into a high pressure liquid, thereby releasing heat energy into the outdoor air coil. This heat energy functions to melt away any frost collected on the outdoor air coil 28. The outdoor fan 36 is typically turned off by the outdoor controller 80 during the defrost mode. The liquid refrigerant flows from the outdoor air coil 28 into the liquid refrigerant line 48. The liquid refrigerant flows through the bypass valve 35 of the expansion device 34. Because solenoid valve 60 is closed, refrigerant does not flow to the geothermal heat exchanger 50. Instead, the refrigerant flows through expansion device 22, which meters the refrigerant to separate the high pressure side of the circuit from the low pressure side of the circuit, and into the indoor air coil 20. In the indoor air coil 20, the refrigerant evaporates into a gas, thereby abstracting heat from the indoor air. The vaporized refrigerant flows into gas refrigerant line 46. From refrigerant line 46, the refrigerant returns to the reversing valve 32, the accumulator 38, the compressor 30 and then back through the reversing valve 32, after which it repeats the cycle. The air-to-air defrost mode is very similar in operation to the air-to-air air conditioning mode and will result in heat being abstracted from the indoor air. To address the problems associated with cold indoor air, the control mechanism 64 may also forward the defrost control signal to the indoor air unit 12 so that the auxiliary hear source 84 may be engaged to counteract the cold air in a generally conventional manner.
The system 10 may remain in the defrost mode for a predetermined period of time, which will vary from application depending on the estimated amount of time needed to defrost the circuit. In the illustrated embodiment, the system 10 will remain in the defrost mode for approximately ten minutes. However, the length of the defrost cycle will vary from application to application.
As can been seen, the system 10 isolates one of the heat exchange devices (e.g. the outdoor air coil, indoor heat exchanger or geothermal heat exchanger) from the others in each mode of operation. Given that the various heat exchange devices have different refrigerant capacities, the isolation of a particular heat exchange device can result in refrigerant imbalance. To address this problem in the system 10, the circuit may be configured (as it is in the illustrated embodiment) so that the isolated heat exchange device is always operatively connected to the low pressure side of the compressor 30. As a result, the system 10 automatically “pumps down” or draws refrigerant out of the isolated heat exchange device. The system 10 may also include a receiver (not shown) or other conventional refrigerant storage device to further address issues of refrigerant imbalance.
The above description is that of a preferred embodiment of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents.
