Abstract:
An improved CHP system combining a VCCHP system with an SOFC system for application as a combined CHP system wherein the compressor motor of a heat pump is powered by a portion of the electricity generated by the SOFC, and wherein the thermal output of the heat pump is increased by abstraction of heat from the SOFC exhaust. This integration allows for complementary operation of each type of system, with the benefits of improved overall fuel efficiency for the improved CHP system. The heat pump is further provided with a plurality of flow-reversing valves and an additional heat exchanger, allowing the heat pump system to be reversed and thus to operate as an air conditioning system.

Description:
RELATIONSHIP TO OTHER APPLICATIONS AND PATENTS 
     The present application is a Continuation-In-Part of a pending U.S. patent application Ser. No. 11/787,998, filed Apr. 18, 2007, now published as Published US Patent Application No. US 2008/0261093 A1, the relevant disclosure of which is incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with United States Government support under Government Contract/Purchase Order No. DE-FC36-04GO14319. The Government has certain rights in this invention. 
    
    
     TECHNICAL FIELD 
     The present invention relates to fuel cells; more particularly, to an Auxiliary Power Unit (APU) including a solid oxide fuel cell (SOFC) system; and most particularly, to a Combined Air Conditioning (A/C), Heat, and Power (CACHP) system for producing electric power, air conditioning, and heating through combination of an SOFC system and a reversible Vapor-Compression-Cycle Heat Pump (VCCHP). 
     BACKGROUND OF THE INVENTION 
     Solid Oxide Fuel Cell systems are high-efficiency generators of electric power from a variety of fuels including Natural Gas, Liquefied Petroleum Gas (LPG), Ethanol, and other hydrocarbon and non-hydrocarbon fuels. Due to the high operating temperature of an SOFC (700° C.-900° C.), the tail pipe exhaust is generally also at a high temperature. A known state-of-the-art integration of SOFC systems is as part of a Combined Heat and Power (CHP) system. Prior art CHP systems use the electrical output of the SOFC system directly, and also utilize the energy leaving the SOFC system in the form of hot exhaust for heating air or water for space heating or for heating water for domestic usage (showers, etc.). No fuel cell system is 100% efficient, so there will always be heat leaving in the SOFC exhaust. For a typical 1 kW electrical service demand (e.g., a small residence), the heating or thermal needs are typically in the range of 5-10 kW. If the SOFC system has a reasonably good electrical efficiency, for example 33%, the heat output for 1 kW net electric output is 2 kW. Since 2 kW is much less thermal energy than desired, auxiliary direct-fueled condensing or non-condensing burner-heat exchangers are commonly used to make up the difference. The best of these are 80-90% efficient in converting fuel to electric and thermal energy. In transportation (heavy-duty truck) applications, a direct fuel-fired heater is usually employed to provide heat to the sleeper cab. The fuel consumed for the fuel fired heater is used only for heating, and these units are typically 80-95% efficient. 
     Further, in many applications employing CHP systems for heating and power, it is desirable that air cooling (air conditioning) also be made available. 
     What is needed in the art is an improved CHP system with increased overall fuel efficiency that is capable of providing both heating and cooling. 
     It is a principal object of the present invention to increase the fuel efficiency of CHP systems while providing alternatively both heating and cooling of an effluent. 
     SUMMARY OF THE INVENTION 
     Briefly described, the invention seeks to improve the overall efficiency of a CHP system with respect to conversion of fuel energy to usable heating, cooling, and electrical energy. In addition, method and apparatus are presented to flexibly close the gap between thermal energy available vs. thermal energy demand without the need for an accessory burner-heat exchanger system. Still further, a method and apparatus are presented that allows for generation of chilled water or air conditioning. 
     The invention is directed to an improved CHP system which combines a VCCHP system with an SOFC system for application as a combined CHP system wherein the compressor motor of a heat pump is powered by a portion of the electricity generated by the SOFC, and wherein the thermal output of the heat pump is increased by abstraction of heat from the SOFC exhaust. This integration allows for novel and complementary operation of each type of system, with the benefits of improved overall fuel efficiency for the improved CHP system. The heat pump is further provided with flow-reversing valves, a refrigerant bypass valve, and an additional condenser, allowing the heat pump system to be reversed and thus to operate as an air conditioning system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic drawing of a CHP system substantially as disclosed in FIGS. 1-3 in Published US Patent Application No. US 2008/0261093 A1, wherein the evaporator section of a VCCHP is interfaced with SOFC exhaust which is tempered by mixing with intake system process air; 
         FIG. 2  is a schematic drawing of a CHP system in accordance with the present invention, similar to the prior art system shown in  FIG. 1  but with the addition of flow-reversing valves, a refrigerant bypass valve, and an additional condenser, allowing the heat pump system to be reversed and thus to operate as an air conditioning system, showing the heat pump system in heat pumping mode; 
         FIG. 3  is a schematic drawing like that shown in  FIG. 2 , showing the heat pump system in air conditioning mode; and 
         FIG. 4  is a top schematic view of an integrated CACHP system suitable for stationary or portable use as on a vehicle. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate currently preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. Temperatures referenced on the figures are for reference only and are subject to the specific design of system components and operating conditions. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a prior art CHP system  10 , as disclosed in Published US Patent Application No. US 2008/0261093 A1, is shown. A solid oxide fuel cell system  12  as is well known in the fuel cell arts is provided with a supply of fuel  14  and air  16 . Fuel  14  is typically a hydrogen-rich reformate formed conventionally by a catalytic reformer (not shown) from a liquid or gaseous supply of a hydrocarbon such as, for example, an alkane or alcohol. It is also known to fuel an SOFC directly with ammonia, obviating the need for a reformer. SOFC  12  provides electric power  18  and also emits a hot exhaust  20  comprising heated cathode air and anode tailgas, or a hot combustion product of the two, that is directed through one side of a heat exchanger such as evaporator  22 , creating a partially-cooled exhaust  24  that may be discharged to atmosphere  26 . 
     A VCCHP system  28  includes conventionally a compressor  30 ; a heat exchanger condenser  32 ; an expansion valve  34 ; the aforementioned heat exchanger evaporator  22 ; and a suitable first fluid working medium  36 . As used herein, a “working” medium is a fluid medium recirculated in a closed loop and present as either a gas or a liquid depending upon conditions of temperature and pressure. The working medium is pumped as a gas through a first side of heat exchanger condenser  32  wherein the medium is condensed to a heated liquid wherein the heat of vaporization is recovered. A second fluid medium  37 , also referred to herein as a thermal transfer medium, is pumped by a recirculation pump  35  through the second side of heat exchanger/condenser  32 , abstracting heat from the hot first fluid working medium  36 , and thence through a customer application  38  requiring heated fluid reservoir  39 , for example, hot air, hot water, or hot refrigerant. The second fluid medium  37  may be provided in a closed system wherein heat is extracted therefrom in customer application  38  and the medium is then returned through low temperature fluid reservoir  41  for reheating; or application  38  may consume the heated second working medium, in which case fresh cold medium is supplied to pump  35 . 
     For a heat pump system, a coefficient of performance (COP) is defined as the heat output to the high temperature reservoir divided by the heat, or work, driven into the refrigerant by the compressor. COPs for good heat pump systems are typically between 2 and 3. This means that 2 to 3 times the electric power (minus motor losses) driven to the compressor is driven to the high temperature reservoir (air, coolant, or water). This is a primary efficiency improvement for the utilization of fuel power to heat power. 
     Where constant massflow of coolant or air is desired at a prescribed temperature, the heat pump compressor may be driven at variable speed to adjust the heating load depending on demand or operating conditions. By this method, a simple control is obtained for either constant temperature or constant massflow heating needs under variable electric or thermal demand or environmental conditions. 
     A key feature is the integration of the heat exchanger for evaporator  22  with the process air inlet and exhaust streams  16 , 24 , respectively, of the device. Thus, heat from SOFC exhaust  20  is entered into the heat pump through extraction by evaporator  22 . 
     An SOFC system normally intakes both process air and auxiliary cooling air (cabinet, electronic, and space cooling) from an external source and vents the hot exhaust to a suitable outside air space. The evaporator also draws heat out of the process air  16  coming into the system via fan  60 . This low temperature air  16  is used for cooling and SOFC system operation. The lower temperature process air intake improves the efficiency of the SOFC air pumps and blowers as well as improving the cooling of onboard electronics and other devices. The heat entering evaporator  22  from this stream becomes available to the application at the condenser  32  through the heat pump system operation. The hot system exhaust stream  20  also travels through evaporator  22  giving additional heat input to the heat pump process. This integration allows for access to the low temperature heat source in the outside air without having to place an evaporator outside of the system or appliance boundary  62 , or directly outdoors. The mixture of outside air  16  via fan  60  and system exhaust  20  provides an intermediate temperature airstream through evaporator  22 . This provides for an increase in heat pump COP and better temperature compatibility in the evaporator using conventional refrigerants. This integration also improves system cooling and allows for efficient use of system exhaust heat. The specifics of the ducting and heat exchanger technology are not critical, but use of well-designed inlet and outlet ducts and multi-pass heat exchangers enhances the functionality and performance. 
     All of the foregoing prior art is disclosed in Published US Patent Application No. US 2008/0261093 A1. 
     Referring now to  FIGS. 2 and 3 , the improvement in accordance with the present invention in providing an improved CHP system  110  comprises a Reversing Vapor-Compression-Cycle Heat Pump  128  including an additional heat exchanger operating as a second condenser  112  disposed downstream of fan  60 , expansion valve  113 , and three-way valves  114 , 116 , 118  disposed in the flow path selectively connecting condenser  112 , evaporator  22 , and condenser  32 , allowing the heat-pump system to reverse and operate as an air conditioning system. The heat pump and air conditioning system in  128  is of a conventional vapor compression cycle type with a suitable refrigerant. Compressor  30  may be powered by SOFC system  12 . The heat pump system requires ambient air  16  to be mixed with the system exhaust  20  (driven with a fan) to improve heat pump operational efficiency and cool the SOFC exhaust to temperatures reasonable for most refrigerants. 
     Referring to  FIG. 2 , in Heating Mode, second condenser  112  is bypassed and, after working medium  36  passes through expansion valve  34 , heat pump system  128  drives evaporator  22  to a temperature below the temperature of the intake air (ambient air)  16  mixed with SOFC system exhaust  20 . This causes heat to flow from the mixture of ambient air and system exhaust to the refrigerant (first fluid working medium  36 ). The compression of working medium  36  by compressor  30  increases the temperature of the refrigerant to a temperature above the temperature of second fluid thermal transfer medium  37 , by utilizing some of the electric output of the SOFC system. The high temperature refrigerant then passes through first condenser  32  which transfers heat to second fluid thermal transfer medium  37  for heating, for example, space heating air, or coolant or water for circulation heating  38 . A separate water loop (not shown) may be channeled through the condenser to handle domestic water needs (showers, drinking, etc.). In this way, heat from incoming air  16 , compressor power and hot exhaust  20  are channeled to the high temperature reservoir  39  (coolant, water, or air). The amount of heat transferred from the low temperature reservoir  41  to the high temperature reservoir  39  is a function of the amount of compression power and system COP (assuming non-limiting cases in heat exchangers etc.). 
     The heat pump compressor may be driven at variable speed to adjust the heating load depending on demand, or operating conditions. By this method, high electrical demand or high thermal demands may be met by adjusting the power level to the electric compressor. Heating Mode operation shown in  FIG. 2 , wherein second condenser  112  is bypassed, is substantially the same as the heating mode shown in  FIG. 1 . 
     Referring to  FIG. 3 , a novel feature of the present invention is the addition of compressor flow-reversing valves  116 , 118 , refrigerant bypass valve  114 , and an additional heat exchanger—second condenser  112 , allowing system  110  to operate in Air Conditioner (A/C) Mode. Refrigerant flow through compressor  30  is reversed from that shown in  FIG. 2  and the condenser  32  used in the heat pump becomes an evaporator  132  and now operates with a cooling effect on second fluid thermal transfer medium  37  for use by application  38 . First evaporator  22  is bypassed, and heat is rejected from second condenser  112  to the ambient air  16  before mixing with the SOFC exhaust. This gives the most effective condenser heat rejection as it does not have SOFC hot exhaust mixed into the stream as in heat pump first evaporator  22 . 
     To serve the demands of power and climate control for transportation applications (heavy-duty truck, military), an exemplary arrangement  228  of a heating and air conditioning unit  210  is shown in  FIG. 4 . An SOFC system  212  is mounted on a support rail for a transportation application. This SOFC system has all provisions for operation on a vehicle  260  utilizing either liquid (diesel) or gaseous (natural gas, LPG, hydrogen) fuel. The air intake  262  and exhaust  264  of the SOFC system are along the rear face of unit  212 . An auxiliary enclosure  266  may be used to house electric compressor  268 , heat-pump evaporator  270 , and A/C condenser  272 , and refrigerant valves  274 . The refrigerant lines that serve the evaporator (HP)/condenser (A/C)  270 , 272  are routed outside of this system to an external heat exchanger (not shown) that can be used for application climate control (heating and cooling effect). This is equivalent to condenser/evaporator  32  in  FIGS. 2 and 3 . 
     In operation, external ambient air  16  is pushed into the system with a conventional fan  276  into enclosure  266 . A portion of this ambient air may be drawn into the SOFC system at this point. An additional feature that may be added to the embodiment is to allow the lines containing low pressure saturated-liquid/vapor phase refrigerant returning from the A/C condenser and expansion valve to exchange heat with the intake air of the SOFC system. This effectively cools the intake air of the SOFC system which improves system efficiency. The bulk of the airstream then passes through condenser  272  (active in A/C mode) where heat may be rejected from the air conditioning system to the air stream. After passing through the condenser, ambient air  16  is mixed with the SOFC system hot exhaust. This mixed stream  278  then passes through evaporator  270  (active in Heating Mode but deactive in Cooling Mode) wherein the heat in the ambient air and from the SOFC system is recovered for Heating Mode. 
     Note that the temperatures referred to in the figures are exemplary only and are subject to the specific design of system components and operating conditions. 
     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.