Patent Publication Number: US-2013247558-A1

Title: Heat pump with turbine-driven energy recovery system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to heat pumps, and particularly to a heat pump with a turbine-driven energy recovery system to reduce power consumption. 
     2. Description of the Related Art 
     Heat pumps have the ability to move thermal energy from one environment to another, and in either direction. This allows the heat pump to effectively bring thermal energy into an occupied space, or to take it out. In practice, this is performed in the opposite direction of a temperature gradient. A heat pump works in the same manner as an ordinary air conditioner (A/C), which is also a type of heat pump. In the warming mode for a space, a heat pump effectively reverses a refrigeration unit so that the warm radiator is inside the space, rather than outside. 
     A heat pump uses an intermediate fluid, called a refrigerant, which absorbs heat as it vaporizes and releases the heat when it is condensed. It uses an evaporator to absorb heat from inside an occupied space and rejects this heat to the outside through the condenser. The refrigerant flows outside of the space to be heated or cooled, where the condenser and compressor are located, while the evaporator is inside. The key component that makes a heat pump different from an air conditioner is the reversing valve. The reversing valve allows for the flow direction of the refrigerant to be changed. This allows the heat to be pumped in either direction. 
     In the heating mode, the outdoor coil becomes the evaporator while the indoor coil becomes the condenser, which absorbs the heat from the refrigerant and dissipates to the air flowing through it. The air outside, even at 0° C. (or at any temperature above absolute zero), has heat energy in it. With the refrigerant flowing in the opposite direction, the evaporator (outdoor coil) is absorbing the heat from the air and moving it inside. Once it picks up heat, it is compressed and then sent to the condenser (indoor coil). The indoor coil then injects the heat into the air handler, which moves the heated air throughout the house. 
     In the cooling mode, the outdoor coil is now the condenser. The indoor coil is now the evaporator in the sense that it is going to be used to absorb the heat from inside the enclosed space. The evaporator absorbs the heat from the inside, and takes it to the condenser where it is rejected into the outside air. 
     Since the heat pump uses a certain amount of work to move the refrigerant, the amount of energy deposited on the hot side is greater than taken from the cold side. One common type of heat pump works by exploiting the physical properties of a volatile evaporating and condensing fluid. Such a volatile fluid is typically what is meant by the term “refrigerant”. 
     The working fluid, in its gaseous state, is pressurized and circulated through the system by a compressor. On the discharge side of the compressor, the now hot and highly pressurized vapor is cooled in a heat exchanger, called a condenser, until it condenses into a high pressure, moderate temperature liquid. The condensed refrigerant then passes through a pressure-lowering device, also called a metering device, such as an expansion valve, capillary tube, or possibly a work-extracting device, such as a turbine. 
     The low pressure, liquid refrigerant leaving the expansion device enters another heat exchanger, the evaporator, in which the fluid absorbs heat and boils. The refrigerant then returns to the compressor and the cycle is repeated. In such a system, it is essential that the refrigerant reaches a sufficiently high temperature when compressed, since the second law of thermodynamics prevents heat from flowing from a cold fluid to a hot heat sink. Practically, this means the refrigerant must reach a temperature greater than ambient around the high-temperature heat exchanger. Similarly, the fluid must reach a sufficiently low temperature when allowed to expand, or heat cannot flow from the cold region into the fluid; i.e., the fluid must be colder than ambient around the cold-temperature heat exchanger. In particular, the pressure difference must be great enough for the fluid to condense at the hot side and still evaporate in the lower pressure region at the cold side. 
     The greater the temperature difference, the greater the required pressure difference, and consequently the more energy needed to compress the fluid. Thus, as with all heat pumps, the coefficient of performance (i.e., the amount of heat moved per unit of input work required) decreases with increasing temperature difference. 
     When comparing the performance of heat pumps, it is best to avoid the word “efficiency”, which has a very specific thermodynamic definition. The term coefficient of performance (COP) is used to describe the ratio of useful heat movement to work input. Most vapor-compression heat pumps use electrically powered motors for their work input. However, in most vehicle applications, shaft work, via their internal combustion engines, provides the needed work. When used for heating a building on a mild day of, for example, 10° C., a typical air-source heat pump has a COP of 3 to 4, whereas a typical electric resistance heater has a COP of 1.0. In other words, one Joule of electrical energy will cause a resistance heater to produce one Joule of useful heat, while under ideal conditions, one Joule of electrical energy can cause a heat pump to move much more than one Joule of heat from a cooler place to a warmer place. 
     In order to improve the COP of a heat pump system, one ordinarily needs to reduce the temperature gap at which the system works. For a heating system, this would mean two things: First, one must reduce output temperature to around 30° C., which requires piped floor, wall or ceiling heating, or oversized water to air heaters. Second, one must also increase input temperature (typically by using an oversized ground source). For an air cooler, COP could be improved by using ground water as an input instead of air, and by reducing temperature drop on the output side through increasing air flow. For both systems, also increasing the size of pipes and air canals would help to reduce noise and the energy consumption of pumps (and ventilators). 
     Additionally, in order to improve COP, the heat pump unit itself may be modified by doubling the size of the internal heat exchangers relative to the power of the compressor, thus reducing the system&#39;s internal temperature gap over the compressor. This last measure, however, makes such heat pumps unsuitable to produce output above roughly 40° C., which means that a separate machine is needed for producing hot tap water. 
     It would be desirable to decrease the energy consumption of a heat pump with no reduction in the output of hot or cold air without making such modifications to the heat pump itself or to the surrounding ventilation or other structure. Thus, a heat pump with a turbine-driven energy recovery system solving the aforementioned problems is desired. 
     SUMMARY OF THE INVENTION 
     The heat pump with a turbine-driven energy recovery system is a heat pump for providing selectively cooled and/or heated air. The system recovers energy from refrigerant circulation. The heat pump with a turbine-driven energy recovery system includes a condenser for receiving refrigerant and condensing the refrigerant into a cooled liquid to release thermal energy therefrom. A first fan is provided for selectively blowing ambient air about the condenser to selectively produce heated air with the released thermal energy. An evaporator receives the cooled liquid refrigerant and boils the refrigerant, the evaporator absorbing thermal energy to boil the refrigerant. A second fan selectively blows ambient air about the evaporator to selectively produce cooled air due to the absorbed thermal energy. 
     A compressor circulates the refrigerant between the condenser and the evaporator, as is conventionally known. At least one turbine is positioned in a refrigerant flow path between the condenser and the evaporator, such that the at least one turbine is driven by the refrigerant circulating therebetween. At least one electrical generator is driven by the at least one turbine, the at least one generator being in electrical communication with the compressor for providing power thereto. 
     These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a heat pump with a turbine-driven energy recovery system according to the present invention. 
         FIG. 2  is a diagrammatic side view of a turbine unit and generator of the heat pump with a turbine-driven energy recovery system of  FIG. 1 . 
     
    
    
     Similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The heat pump with a turbine-driven energy recovery system  10  is a heat pump for providing selectively cooled and/or heated air. The heat pump and system  10  recovers energy from refrigerant circulation. As shown in  FIG. 1 , the heat pump  10  includes a condenser  12  for receiving refrigerant and condensing the refrigerant into a cooled liquid to release thermal energy therefrom. The condenser  12  may be any suitable type of condenser, as is well known in the field of heat pumps, heating and refrigeration. As shown by the directional arrows R in  FIG. 1 , the refrigerant flows through heat pump  10  in a clockwise direction (in the exemplary configuration of  FIG. 1 ) so that the refrigerant flows through the condenser  12 , starting in a heated vapor phase in the lower conduit  16  (in the exemplary configuration of  FIG. 1 ) and being output as a cooled liquid the into upper conduit  14 . 
     As is common in the field of heat pumps and the like, a first fan  34  is preferably provided for selectively drawing ambient air from about the condenser  12  to selectively produce a flow of heated air H from the thermal energy released by condensation of the heated, vaporized refrigerant into a cooled liquid phase. The cooled liquid refrigerant then circulates to an evaporator  22  via the upper conduit  14 . The evaporator  22  receives the cooled liquid refrigerant and boils the refrigerant to produce the heated vapor stage. Ambient thermal energy is absorbed to effect the boiling and vaporization. Similar to first fan  34 , a second fan  32  is also preferably provided for selectively drawing the ambient air from about the evaporator  22  to selectively produce a flow of cooled air C due to the thermal energy absorbed by the evaporator coil. The evaporator  22  may be any suitable type of evaporator, as is well known in the field of heat pumps, heating and refrigeration. 
     A compressor  24 , powered by an external power source V, circulates the refrigerant between the condenser  12  and the evaporator  22 , as is conventionally known. The compressor  24  may be any suitable type of condenser, as is well known in the field of heat pumps, heating and refrigeration. At least one turbine is positioned in the refrigerant flow paths between the condenser  12  and the evaporator  22 . In  FIG. 1 , a pair of twin turbine units  18 ,  20  are shown. It should be understood that any desired number of turbine units may be placed in the refrigerant flow paths between the condenser  12  and the evaporator  22 . Similarly, conventional turbines may be used, as well as the twin turbine units shown in  FIG. 1 . Each turbine is driven by the refrigerant flow. 
     Each turbine unit  18 ,  20  drives a respective electrical generator  26 ,  28 , and each generator is in electrical communication with the compressor  24  for providing power thereto, As shown, an electrical storage battery  30  is preferably connected to each generator  26 ,  28  and to the compressor  24 . In such an arrangement, the generators  26 ,  28  charge the storage battery  30 , which may be used either as a source of emergency power or to replace the external power source V when fully charged, thus allowing recovered energy to be used to power the compressor  24 . 
     As noted above, and as shown in  FIG. 1 , each turbine unit  18 ,  20  may be a twin turbine unit having first and second turbines mounted within a sealed housing  44 . The blades  40  of the first turbine and the blades  42  of the second turbine intermesh in a central region of the sealed housing  44 , and the refrigerant flow path passes through the central region.  FIG. 2  illustrates an exemplary arrangement for the turbine unit  18 . It should be understood that the second turbine unit  20  operates in a similar manner. Turbine blades  40  are mounted to a shaft  45 , the turbine blades  40  (and, similarly, blades  42  mounted on a similar shaft in the twin turbine configuration) rotating within a sealed housing  44 . Upper and lower bearings  46 ,  48  may be provided to effect free rotation of the shaft  45  with minimal frictional resistance. A gear  52  is mounted on the shaft  45  such that rotation of shaft  45  drives rotation of the gear  52 . The gear  52  may be mounted between the lower bearing  48  and a base bearing  50 , as shown. The gear  52  engages a gear  54  mounted on a drive shaft  56  of the generator  26  for driving the generator  26  to produce electrical energy. 
     As shown in  FIG. 1 , a pressure lowering device, such as expansion valve  16 , may also be placed in the refrigerant flow path between the condenser  12  and the evaporator  22 , as is conventionally known in the field of heat pumps and the like. In use, the user may operate the heat pump  10  to produce just hot air H (by selectively actuating the first fan  12 ), to produce just cool air C (by selectively actuating the second fan  32 ), or to simultaneously produce hot air H and cool air C. The two air streams H and C may be blended by venting, ducting or the like. The user may adjust the amount of blending between the hot air H and cool air C to adjust the overall resultant temperature. The refrigerant used in the heat pump  10  may be any suitable type of refrigerant. Preferably, the refrigerant is a multi-hydrocarbon blend, such as R443A. R443A consists essentially of about 40% propane, about 55% propylene, and about 5% isobutane by volume, as described in Applicant&#39;s co-pending U.S. patent application Ser. No. 13/106,701, filed May 12, 2011, which is herein incorporated by reference in its entirety. Another similar multi-hydrocarbon blend that may be used in the heat pump  10  is R441A, as taught by U.S. Pat. No. 8,097,182 B2, which is herein incorporated by reference in its entirety. It should, however, be understood that any suitable type of refrigerant may be utilized. 
     It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.