Patent Application
20130047616
The present disclosure relates to an electrical power cogeneration system, i.e., a system which uses different energy sources to electrically power multiple subsystems.
Cogeneration may be used to improve the efficiency of various electrical subsystems, such as the variety of electrically-powered devices used in a typical home or commercial building. Efficiency improvement is gained by capturing and using the waste heat from the generation of required electricity. That is, a portion of the energy in any fuel used to provide heat to a home or building is diverted by an engine and generator into the production of electricity. For example, one may use an internal combustion engine and an electric generator to generate a portion of the electrical energy required to power a building and use the heat produced by the engine to heat the building. The remainder of the required electrical energy can be provided by connecting to the electrical grid, or by other devices such as a windmill, solar voltaic panels, and so on. Likewise, the remainder of the required heating energy can be provided by other devices such as solar thermal panels.
Use of a cogeneration system allows a user to produce at least some of their own electrical energy on-site. This may be a particularly attractive option to electricity users residing or working in remote locations, or in geographic areas that are relatively susceptible to periodic blackouts or brownouts. Other electricity users may be apprehensive about relying on a single energy supplier for reasons of electricity cost. In areas that consume energy generated primarily via coal-burning power plants, the use of a cogeneration system can help to reduce the level of carbon dioxide emissions relative to exclusive use of electrical power supplied from the grid.
A cogeneration system is disclosed herein. In its various embodiments, the present system selectively diverts otherwise wasted fuel heat energy from a large gas-consuming engine, for instance an internal combustion engine or a fuel cell, to other beneficial uses. Such uses may include the charging of a battery module. In some embodiments, such a battery module may have a high-voltage energy storage system (ESS) of the type used to power an electric traction motor of an electric vehicle (EV). The charging function of an EV, an extended-range EV, or a plug-in hybrid electric vehicle (PHEV) battery is ordinarily accomplished by connection to the electrical grid when the vehicle is idle.
The power load of a typical EV battery exceeds by several times the output of a conventional cogeneration system. Such systems are ordinarily sized on the order of approximately 1 kW of electrical output to meet the heating needs and some of the total electrical needs for an ordinary house, but an EV battery may customarily be charged at power levels of between approximately 3 kW and 7 kW or more. The limited capacity and various other design limitations of conventional cogeneration systems can limit the types of functions that can be supported.
Other non-EV support scenarios can present power loads comparable to that of an EV battery. For instance, a household may simultaneously use multiple televisions, hair dryers, microwave ovens, and/or other high-wattage appliances at various times in a typical day. Central air conditioning is another relatively large electrical load. Homes relying on conventional cogeneration systems with a capacity of approximately 1 kW or less therefore must still rely heavily on grid energy during times of peak electrical use.
In the present system, a non-diverted energy stream is used for heating the air and/or water supply of a building. Instead of being consumed in a furnace burner, fuel is consumed by a heat engine. The heat engine converts some of the fuel into heat for heating for the building, but also diverts some of the fuel into producing mechanical power. In various example embodiments, and as noted above, the engine may be a large natural gas/propane gas internal combustion engine or a fuel cell. The engine delivers its waste heat to the building as needed to provide substantially all of the required space heating and water heating functions in the building.
In addition, the engine may be used to selectively charge an EV battery or for other purposes, such as for powering central air conditioning functions in the building. Only the amount of energy that is actually converted into useful work is diverted out of the overall energy stream. In other words, the amount of extra fuel that is fed into the engine above a threshold level required for climate control of the building equals the energy value of any useful work, thus providing a nearly 100% efficient process.
In particular, a cogeneration system as disclosed herein includes a gas engine, a motor/generator unit (MGU), and a compressor positioned in series with the MGU. The system also includes a coolant loop, a heat storage/hot water tank in communication with the engine via the coolant loop, and a vapor loop for heating or cooling air within the building. The latter function can provide central air conditioning and an optional heat pump function for a building as explained herein.
A controller is in electrical communication with the engine, the MGU, and the compressor. The controller is configured to control operating states of the engine, the MGU, the compressor, and one or more heat exchangers, pumps, clutches, and/or other components of the system, either alone or in combination, in order to heat or cool a supply of air in the building and/or the water contained in the hot water tank. The same controller can selectively charge an auxiliary device, e.g., a battery, via the MGU, which in turn may be selectively powered by the engine.
The central air conditioning function may be run directly via the engine using a natural gas or propane line, or it may be powered from the grid, whichever energy source is more efficient, more readily available, or less costly. For instance, the central air conditioning may be run by the engine during those times when demands on the electrical grid would otherwise exceed its capacity or when electricity prices are high. Relative efficiency or availability may be determined by the controller or signaled to the controller from an outside source of information. An optional geothermal heat sink/underground thermal well may be used as part of the vapor loop for optimized central air conditioning/heating functionality. For instance, waste heat can be stored underground to bring the average temperature below ground closer to the target temperature for the building in cold climates. Such an option may be beneficial when electrical power demands are low and therefore sufficient waste heat is not available.
The system and controller may be optionally configured to keep the building “grid-neutral” for as much of its total operating time as possible, i.e., using zero or near zero levels of electrical energy from the main electrical grid. In such an embodiment, the controller may use a current sensor to detect the incoming current from the grid to the building. The controller may thereafter control the various components of the system in a closed feedback loop in response to this detected/measured current to drive grid use by the building toward zero. Optionally, the controller may be configured to sense when control of the voltage in the building down to a minimum level cannot prevent power flow to the grid, which may be taken as a signal of grid power failure. In this instance, the controller can act to physically disconnect the building from the grid.
In various embodiments, the engine may be part of the power plant of the building, or it may be located in a vehicle or portable module. When used as part of the vehicle or module, a pair of conductive plates may be used to conduct waste heat to the building from the vehicle/module. One plate may be positioned at the underside of the vehicle and another plate positioned externally with respect to the vehicle, e.g., on or along the ground. When the vehicle is parked, heat may be transferred to the second plate from the first plate.
The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, a cogeneration system 10 is shown schematically in
The present cogeneration system 10 includes an engine 12, a motor/generator unit (MGU) 14, and a compressor 16. The compressor 16 is connected in series with the MGU 14 either selectively or continuously depending on the embodiment. In the particular embodiment shown in
That is, heat from circulating engine coolant in an engine coolant loop 18 and engine exhaust can be recovered to heat the water in the hot water tank 24. Heat from the engine 12 and/or from the hot water tank 24 can then be used as needed for any desired space heating, such as space heating of living or working space within the building 11. This particular configuration effectively replaces a conventional furnace and hot water heater of the type used in most modern homes and commercial buildings.
The engine 12 may be fed by a gas supply (arrow 44), e.g., natural gas from a main gas line, compressed natural gas (CNG) from a pressurized fuel tank (not shown), liquid propane gas (LPG) from a pressurized tank (not shown), etc. An intake silencer 17 may be positioned with respect to the engine 12 and configured to draw intake air (arrow 19) into the engine 12. A catalytic converter 20 and a heat exchanger 22 (exhaust condenser) may be used to purify the exhaust stream discharged from the engine 12, while the heat exchanger 22 also increases the amount of waste heat recovered from the exhaust 42.
Purified exhaust (arrow 42) can be allowed to escape from the building 11 to the outside of the building 11. The piping of purified exhaust (arrow 42) in the various Figures is simplified for illustrative clarity. In actual use, such purified exhaust (arrow 42) should be plumbed away from the building 11, e.g., via pipes or stacks oriented away from any possible entry points to the building 11 such as windows or doors. Water condensed from the exhaust stream can be discharged to a sump or waste water collector (not shown). Likewise, the various exhaust system elements shown in
In different embodiments, the engine 12 may be an internal combustion engine powered by the gas supply 44 in the form of natural gas, propane, or another suitable fuel, or the engine 12 may be a fuel cell, or a combination of fuel cell and fuel reformer. Non-limiting examples of fuel cells include a molten carbonate fuel cell and solid oxide fuel cell, both of which are capable of operating at high temperatures directly using natural gas as fuel. A fuel cell can operate well above the temperatures necessary for providing cost-efficient heat transfer for space and water heating of the building 11. A fuel cell produces electricity, but typically consumes mechanical power to operate some components of the engine 12. Thus, the MGU 14, when used in a system with a fuel cell engine 12, would need to function only as a motor and not as a generator.
The engine 12 is in communication with the hot water tank 24 via the engine coolant loop 18. A part of the engine coolant loop 18 may be embodied as a loop of pipe or tubing which conducts heated engine coolant from the engine 12 to/from the hot water tank 24 as needed, as indicated in
A thermostatic mixing valve 46 may be used to blend hot and cold water at the outlet of the hot water tank 24, and thus ensure delivery of hot water to various points of use within the building 11 within a regulated temperature range. This occurs even though the temperature of the water within the hot water tank 24 varies above the customary temperature for hot water along with the amount of heat energy stored within the tank 24. For example, the water in the hot water tank 24 may vary in temperature from 45° C., a minimum temperature for hot water, to 85° C., a normal operating temperature of the engine coolant loop 18, but the thermostatic mixing valve 46 may regulate its output to the building between 45° C. and 50° C. at all times by mixing cold water with water from the tank when the water in the tank exceeds 50° C.
Still referring to
The air handler unit 26 may include one or more heat exchangers therein so as to provide air flow across the vapor loop 25 and across the engine coolant loop 18. An additional heat exchanger is represented schematically in
Alternatively, a heat exchanger 122 as shown in phantom can be used between the loops 18 and 25 (arrow 247). In this instance, engine coolant can be excluded from the air handler unit 26. Air handler unit 126 is omitted in such an embodiment. Ideally, the number of heat exchangers used within the system 10 should be kept at a minimum, and this circulation and heat transfer within the air hander unit 26 is an alternative to providing a separate heat exchanger 122, an example of which is shown in phantom, between the engine coolant loop 18 and the vapor loop 25. This heat exchanger 122 can be positioned at one or more places along the vapor loop 25, for instance as shown, for the most efficient transfer of heat from the engine coolant loop 18 to the air in the building 11, or (not shown) between the compressor 16 and a heat exchanger outside the building 11, such as a heat sink or thermal well 28.
If the air handler unit 26 is used to provide an air stream from the building 11, through the vapor loop 25, and back to the building 11 and another air stream from the ambient outside of the building, through the engine coolant loop 18, and back to the ambient outside again, that option serves as a way to continue to run the engine 12 when the hot water tank 24 is fully charged with heat. This may be particularly advantageous on particularly hot, humid days when central air conditioning use is the dominant energy consumer in the building 11, in which case the engine 12 may be running to drive the compressor 16 so as to provide air conditioning using the vapor loop 25.
The compressor 16 of
The compressor 16 may be configured to reverse the direction of flow in the vapor loop 25, or the engine 12 may be configured to reverse flow in the engine coolant loop 18. The dual directions in vapor loop 25 are indicated via opposite arrows H (heating) and C (cooling). Reverse flow in either loop makes use of the separate heat exchanger 122 to convey heat from the engine coolant loop 18 to the vapor loop 25, and then, depending on the direction of flow in the vapor loop 25, either to the air handler unit 26 (heating) or the compressor 16 and then to the thermal well 28 (air conditioning).
The vapor loop 25 may include an expansion valve 38 or an optional electromechanical expander and/or pump 39 as shown in phantom, along with any required compressor and condenser coils. Some or all of these components may reside outside of the building 11, possibly in a separate enclosure (not shown) for noise and/or environmental reasons, although all are components shown inside of the building 11 in
Optionally, a portion of the vapor loop 25 may be routed under the surface of the ground 34 as shown. Such a routing can form the thermal well 28. Such an option may provide for geothermal heating and cooling of the building 11, as a preferred alternative to the conventional air conditioning condenser and fan now in use for many buildings. As understood in the art, the process of geothermal heating and cooling relies on an energy exchange between air within the building 11 and the ground, the latter having a relatively constant year-round temperature below approximately ten feet below grade.
Thus, when temperature of the building 11 exceeds a desired temperature, heat from the building 11 can be transferred to the ground via the thermal well 28. The process works in reverse when the ambient temperature of the building 11 is below a desired temperature, i.e., ground heat can be used to heat the air in the building 11. Typically, the temperature of the heat sink is closer to the desired temperature of the building than the ambient air outside the building. Thus, use of the thermal well 28 can help optimize overall performance of the system 10. The combination of cogeneration and geothermal heating and cooling is especially advantageous in those climates where the underground temperature is below that desired for the interior temperature of the building 11, so that waste heat from the engine 12 can make up the difference. In those climates, waste heat from operating the engine 12 to drive the compressor 16 for air conditioning of the building 11 can be transferred from the engine cooling loop 18 to the vapor loop 25, such as by heat exchanger 122, to the thermal well 28. At the thermal well 28, some of the heat will accumulate in the ground for use during later periods of heating, again using the vapor loop 25 and the compressor 16.
The vapor loop 25 of
Air can be blown through heat exchangers 22 used within the engine coolant loop 18 and the vapor loop 25. If dehumidification of the building 11 is desired, the compressor 16 could be operated to cool the air, and waste heat can be added from the engine coolant loop 18 to reheat air above its dew point. The engine coolant loop 18 and the pump 31 can therefore be used to provide space heating in a manner analogous to forced-air heating. Alternately, the engine 12 and the compressor 16 can be used to provide space heating analogous to an electric heat pump.
When space heating is to be provided via the engine 12, the engine coolant loop 18 extracts heat from the hot water tank 24 and carries this extracted heat to the air handler unit 26, whether by routing the engine coolant loop 18 through the air handler unit 26 as shown or using a separate loop to circulate heated water from the hot water tank 24 to the air handler unit 26. The former avoids the need for another pump, but the latter may be more efficient if it is desirable not to operate the engine during times when heating is required. An example of the latter is shown in
In order to fully coordinate the various components of the cogeneration system 10 shown in
Output electric power flow from the controller 50 may be provided to the building 11 as indicated by arrow 30, such as to power the various electrical outlets, appliances, and/or machines in the building 11, and to/from the EV 40 (arrow 36) for charging a battery thereof. Thus, the controller 50 is configured to control the components of system 10, alone or in combination as needed, to heat and/or cool a supply of air in the building 11, to heat the water contained within the hot water tank 24, to charge the EV 40 if so configured, and to provide energy to one or more power outlets in the building 11.
The controller 50 may operate the engine 12, e.g., by controlling fuel delivery and spark/compression, monitoring oxygen sensors (not shown) associated with the catalytic converter 20, control the MGU 14 using solid state switches, resolvers, encoders, etc. The controller 50 can also be configured or equipped with any required computer hardware, such as a high-speed clock, requisite Analog-to-Digital (A/D) and/or Digital-to-Analog (D/A) circuitry, any necessary input/output circuitry and devices (I/O), as well as appropriate signal conditioning and/or buffer circuitry. Any algorithms required by the controller 50 may be stored in memory and automatically executed to provide the required functionality.
In a particular embodiment, the cogeneration system 10 of
The controller 50 of
To implement these control modes, the controller 50 may be configured to measure net grid power into the building 11 as well a net power generation by the system 10. Building load may be measured or estimated by the difference in these two values. Instantaneous power measurements may be converted into a low frequency equivalent so multiple power cycles are considered when balancing power generation against loads. The controller 50 may also vary the generator power factor of the MGU 14 to modify the power factor of building 11. This can help reduce grid losses due to imaginary power drawn by the building 11. Where the controller 50 is commanded to target a power draw (or zero power draw), the measurements of power cab be used in a closed loop to regulate the power output.
Building management control algorithms may be used by the controller 50 to set the target power draw to minimize long term combination of fuel and electrical costs in a target ratio, including zero net cost for either. This can be accomplished by many methods. For instance, one may use finite horizon control and general predictive control, where fuel and electrical costs, along with stochatic models of heat demand, electrical demand, and weather forecasts are used to minimize the dynamic optimization problem. Furthermore, the stochastic models may be adaptive and learn from long term observations of household energy usage, conversion efficiency, and storage efficiency.
The cogeneration system 10 of
The controller 50 may be configured to selectively disengage the first clutch 13 and engage the second clutch 15 to power the compressor 16 via the MGU 14 using electrical energy from the grid, i.e., arrow 34. The controller 50 can also selectively engage the first and second clutches 13 and 15 so as to power the compressor 16 via the MGU 14. In this instance, mechanical power from the engine 12 is used when that configuration is determined by the controller 50 to be the optimal choice. Likewise, the controller 50 can selectively engage the first clutch 13 and disengage second clutch 15 to produce electricity with the MGU 14 and heat the water contained in the water tank 24 via the engine 12 without powering the compressor 16.
The controller 50 may be configured to selectively disengage the first clutch 13 and engage the second clutch 15 to power the compressor 16 via the MGU 14 using electrical energy from the grid, i.e., arrow 34. The controller 50 can also selectively engage the first and second clutches 13 and 15 so as to power the compressor 16 via the MGU 14. In this instance, mechanical power from the engine 12 is used when that configuration is determined by the controller 50 to be the optimal choice. Likewise, the controller 50 can selectively engage the first clutch 13 and disengage the second clutch 15 to produce electricity with the MGU 14 and heat the water contained in the water tank 24 via the engine 12 without powering the compressor 16.
Because an EV such as the EV 40 is typically charged at night when demand and electricity rates tend to be relatively low, charging of the EV 40 that is shown schematically in
Charging the EV 40 at night, especially during the summer, would give a more favorable choice of sources of electricity and would help to ensure that the engine capacity of the cogeneration system 10 remains available by day when its maximum output capacity may be needed the most, to provide air conditioning. The controller 50 can optimize efficiency using delayed/off-peak charging, or by charging the EV only when heating is required in the building 11. In this manner, the EV 40 and any air conditioning load within the building 11 can be effectively removed from the grid, especially during peak daytime hours, with an accompanying reduction of CO2 emissions relative to grid charging in the conventional manner.
Referring to
A generator 62 is aboard the EV 140, with the generator 62 sending power to a battery 56 in the form of a rechargeable energy storage system. The battery 56 may be selectively charged, for instance during regenerative braking, with power flow aboard the EV 140 controlled by a power controller 65. An electrical line 55 and a connector 54 can be used to enable supplemental electrical power delivery to the EV 140, e.g., connection to a charging station. Any required connections to the EV 140 can be provided via an umbilical cord-type unitary connection.
The engine 112 in this particular embodiment can be used to supply heat into the building 11. As with the cogeneration system 10 of
A second engine coolant loop 218, which is part of a second power plant, is in thermal communication with the first engine coolant loop 118. A pump 332 may be used to circulate coolant through the first engine coolant loop 118. A first conductive plate 70 of a suitable metal or other thermally conductive material may be connected to the EV 140 and positioned under the EV 40. A similar second conductive plate 72 may be positioned along/just under the ground 34, such that the EV 140, when parked adjacent the building 11, brings the first conductive plate 70 directly above the second conductive plate 72.
An interface 77 is thus between the conductive plates 70 and 72 with a minimal clearance as shown so as to optimize heat transfer to the second conductive plate 72 from the first conductive plate 70. The second engine coolant loop 218 in turn transfers heat to the hot water tank 24, with a pump 131 used in the second engine coolant loop 218 to help circulate coolant therein.
Within the building 11, a vapor loop 125 is in communication with the air handler unit 26 and the compressor 16 as described above, and also with the ambient to allow heat transfer (arrow 35) to occur with respect to the ambient. A dedicated hot water loop 27 may be used to communicate heat from the hot water tank 24 to the air handler unit 26 as an alternative to extending the engine coolant loop 218 into the air handler 26 as in the embodiment of
In this embodiment, the controller 50 within the building 11 can direct electrical energy to the building 11 (arrow 30), to the MGU 14 (arrow 32), and/or to an optional storage battery 61 (arrow 37). Power from or to the grid is indicated via arrow 134. The controller 50 may be in wired or wireless electrical communication with conductive plate 72 (arrow 136) so as to control the exchange of heat between the respective first and second conductive plates 70 and 72. The MGU 14 does not need to function as a generator in this example, but only as a motor, because it is connected to the compressor 16 but not to an engine.
Referring to
Connector 54, which may be electrically connected to the controller 50 via a control line 71, may be used to place the portable module 80 in electrical contact with the building 11, to provide electrical power from the power controller 65 to the controller 50 and thereby to MGU 14. The cogeneration system 210 can thereby provide substantially all of the same functions as the cogeneration system 10 shown in
While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.
