Patent Application
20140182319
Embodiments of the present invention relate to systems and methods for using on-board thermal energy storage to supply heated or refrigerated working fluid to the cabin and electrochemical battery compartment of an electric vehicle.
Driving range and upfront cost are considerations in a consumer's decision to purchase an electric vehicle (EV). Both are related to the on-board electrochemical battery: driving range is related to capacity and other performance characteristics of the battery, and the cost of the battery affects vehicle upfront cost.
In some EVs, the battery supplies energy to the vehicle's powertrain, heating, ventilation, and air-conditioning (HVAC) system, battery compartment, and other power systems (e.g., those responsible for steering, windows, locks, etc.). The HVAC system can require a significant amount of energy; in some cases, operating the powertrain and HVAC systems simultaneously can reduce driving range up to 35%. Furthermore, the cost of the battery required to supply energy to the HVAC system can account for up to 20% of vehicle upfront cost. The battery compartment requires energy to regulate battery temperature, which influences performance characteristics (as a general rule, temperatures that are too low decrease battery performance while temperatures that are too high destabilize battery chemistry). Therefore achieving and maintaining an appropriate battery temperature decreases the energy supplied by the battery to the powertrain and reduces driving range.
The powertrain requires electrical energy, but batteries are expensive for storing energy for the HVAC system and battery compartment. High-temperature thermal energy storage systems are less expensive than batteries and can provide thermal energy of sufficient quality for an HVAC system using direct heating and a thermally-powered refrigerator, and for a battery compartment to regulate battery temperature.
The following references are incorporated herein by reference in their entireties:
Deloitte LLP. “Unplugged: Electric vehicle realities versus consumer expectations.” 2011.
Barnitt, R., Brooker, A., Ramroth, L., Rugh, J., Smith, K. “Analysis of Off-Board Powered Thermal Preconditioning in Electric Drive Vehicles,” Presented at the 25th World Battery, Hybrid and Fuel Cell Electric Vehicle Symposium & Exhibition. Shenzhen, China November 5-9, 2010, NREL/CP-5400-49252, December 2010.
The Wall Street Journal. “Nissan Says Leaf Electric Will Be Profitable With U.S. Plant.” Published May 13, 2010; retrieved Oct. 25, 2012.
Birchenall, C. E., Reichman, A. F. “Heat Storage in Eutectic Alloys.” Metallurgical Transactions A, Volume 11A, August 1980-1415.
Embodiments of the system and method of the invention include a system and a method for using on-board thermal energy storage to supply heated or refrigerated working fluid to the cabin and battery compartment of an electric vehicle. The system comprises one or more of the following: a storage material to store thermal energy; an off-board energy source to provide thermal energy to the storage material during charging; a refrigerator powered by thermal energy stored by the storage material; piping and one or more working fluids to transfer thermal energy or refrigeration through the system; heat exchanger elements to enable thermal communication between the storage material, off-board energy source, refrigerator, battery compartment, and working fluids; and control elements to control the flow of the working fluids.
The invention is illustrated, by way of example and not by way of limitation, in the figures of the accompanying drawings in which like references indicate similar elements. References to embodiments in this disclosure are not necessarily to the same embodiment, and such references mean at least one. While specific implementations are discussed, it is understood that this is done for illustrative purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without departing from the scope and spirit of the invention.
In the following description, numerous specific details will be set forth to provide a thorough description of the invention. However, it will be apparent to those skilled in the art that the invention and embodiments thereof may be practiced without these specific details. In other instances, well-known features have not been described in detail so as not to obscure the invention.
Embodiments of the invention relate to the use of on-board thermal energy storage to supply heated or refrigerated working fluid to the cabin and battery compartment of an electric vehicle. In a preferred embodiment, a system in accordance with the present invention comprises: a storage material to store thermal energy; an off-board energy source to provide thermal energy to the storage material during charging; a refrigerator powered by thermal energy stored by the storage material; piping and one or more working fluids to transfer thermal energy or refrigeration through the system; heat exchanger elements to enable thermal communication between the storage material, off-board energy source, refrigerator, battery compartment, and working fluids; and control elements such as variable-speed fans/pumps and valves to control the flow of the working fluids. In the following figures, dotted pipes indicate no working fluid is flowing through them, and black heat exchanger elements, variable-speed fans/pumps, and valves indicate they are not active or closed.
Some embodiments, referred to as air embodiments, use air as the only working fluid. An air embodiment, shown in
Other embodiments, referred to as hybrid embodiments, use non-air working fluid (e.g., oil) in at least one pipe system. In a hybrid embodiment shown in
The requirements of an embodiment depend on EV considerations such as the temperature range of the environment around the EV (e.g., −80° C. to 60° C.), the heating and cooling loads of the EV (e.g., 10 kW), and the target upfront cost of the EV. The degree to which an embodiment meets these requirements in turn depends on the choice of working fluid(s), which can be influenced by many factors including, by way of example: the temperature range at which the working fluid is physically and chemically stable (i.e., it does not undergo phase change or chemical decomposition); the specific heat, thermal conductivity, and density of the working fluid; the chemical reactivity of the working fluid with the materials of the pipes, heat exchangers, variable-speed fans/pumps, valves; and the current and future prices, and availability, of the working fluid. Therefore an air embodiment may be best suited for one set of EV considerations, and a hybrid embodiment with at least one non-air working fluid may be best suited for another set of considerations.
In an embodiment, the off-board energy source 160 can be an electrical source, and can be the same electrical source used to charge the batteries that supply energy to the powertrain. In this case, the connector 170 establishes an electrical connection between the off-board electrical source 160 and the heat exchanger element 120a. The heat exchanger element 120a can be an electrical resistance heating wire that simultaneously converts electrical energy from the off-board electrical source 160 into thermal energy, and transfers thermal energy to the storage material 100.
In another embodiment, the off-board energy source 160 can be a high-temperature heat source such as a natural gas combustor. In this case, the connector 170 can establish a connection capable of transferring thermal energy in a working fluid between the off-board high-temperature heat source 160 and the heat exchanger element 120a, and the heat exchanger element 120a transfers thermal energy to the storage material 100.
The heated air is split at valve 140e, with the fraction used to heat the cabin directed to valve 140f through pipe 150n, and the other fraction used to heat the battery compartment directed to valve 140g through pipe 150o. At valve 140f, the heated air from pipe 150n mixes with ambient air from pipe 150p, and the heated air mixture flows to the cabin through 150r. The mass flow rate and temperature of the heated air mixture flowing to the cabin depends on the mass flow rates and temperatures of the heated air from pipe 150n and ambient air from pipe 150p. The mass flow rate of the heated air from pipe 150n can be specified by variable-speed fan/pump 130a and the fraction split at valve 140e; the mass flow rate of ambient air from pipe 150p can be specified by variable-speed fan/pump 130d; and the temperatures of the heated air from pipe 150n and ambient air from pipe 150p are measured by thermometers (not shown) located in pipe 150d and in the environment, respectively. Therefore the mass flow rate and temperature of the heated air mixture flowing to the cabin can be reasonably controlled by specifying the mass flow rates of the heated air and ambient air with variable-speed fans/pump 130a and 130d, and valve 140e.
At valve 140g, the heated air from pipe 150o mixes with ambient air from pipe 150q, and the heated air mixture flows to the battery compartment through 150s. Using the same logic as that in the above paragraph, the mass flow rate and temperature of the heated air mixture flowing to the battery compartment can be reasonably controlled by specifying the mass flow rates of the heated air and ambient air with variable-speed fans 130a and 130d, and valve 140e. Thermometers (not shown) located in pipes 150r and 150s can measure the temperatures of the heated air mixtures flowing to the cabin and battery compartment, respectively, and provide feedback to variable-speed fans/pumps 130a and 130d, and valve 140e.
Variable-speed fan 130c forces ambient air through heat exchanger element 120e to refrigerate the air. Using a similar analysis to that described above, the mass flow rate and temperature of the refrigerated air can be reasonably controlled by specifying the air mass flow rate with variable-speed fan/pump 130c. The refrigerated air is split at valve 140e, with the fraction used to refrigerate the cabin directed to valve 140i through pipe 150t, and the other fraction used to refrigerate the compartment directed to valve 140j through pipe 150u. At valve 140i, the refrigerated air from pipe 150t mixes with ambient air from pipe 150v, and the refrigerated air mixture flows to the cabin through 150x. At valve 140j, the refrigerated air from pipe 150u mixes with ambient air from pipe 150w, and the refrigerated air mixture flows to the battery compartment through 150y. Using a similar analysis to that described above, the mass flow rates and temperatures of the refrigerated air mixtures flowing to the cabin and battery compartment can be reasonably controlled by specifying the mass flow rates of the heated air and ambient air with variable-speed fans/pump 130a and 130d, and valve 140e.
There are a number of storage materials that store thermal energy, and a person of ordinary skill in the relevant art will recognize that any material that stores thermal energy may be used in an embodiment without departing from the scope and spirit of the invention. However, a storage material that at least partially melts to store thermal energy, and that at least partially solidifies to release thermal energy, is usable in an embodiment because it uses latent heat storage. The choice of a storage material in an embodiment can be influenced by many factors including, by way of example: the temperatures at which at least part of the storage material melts or solidifies; the latent heat associated with melting and solidification; the densities of the solid and liquid phases; the kinetics of melting and solidification; the thermal conductivities in the solid, solid-liquid, and liquid phases; the stability during cycling; the chemical reactivity with containment materials and heat exchanger elements; the effects of contaminants on the above factors; and the current and future prices, and availability, of the storage material. A preferred storage material has: a single temperature at which it melts and solidifies, to better predict the temperature difference between it and the working fluid; high latent heat and density so less mass and volume are required; comparable solid and liquid densities to reduce stresses associated with thermal expansion; fast kinetics and high thermal conductivities (in all phases) to decrease the duration of charging; a high degree of chemical stability; and low-priced and readily-available precursors.
Pure metals and eutectic metal alloys are useable in embodiments because they melt and solidify at a single temperature and have high latent heats and densities, fast kinetics, very high thermal conductivities, high chemical stability, and relatively cheap and available precursors. By way of example, aluminum-silicon alloy with 12 wt. % silicon melts and solidifies at a single temperature of approximately 577° C. and has a latent heat of fusion of approximately 515 kJ/kg, thermal conductivities in the solid and liquid phases of approximately 180 W/m-° C. and 70 W/m-° C. respectively, known and stable chemistry, and low historic precursor prices. Other examples of preferred pure metal and eutectic metal alloys include pure aluminum, pure magnesium, pure zinc, magnesium-silicon alloy with 56 wt. % silicon, and aluminum-magnesium alloy with 36 wt. % magnesium.
Hypoeutectic and hypereutectic metal alloys are also useable in embodiments. Hypoeutectic and hypereutectic metal alloys form a system with two distinct phase changes from solid to liquid. The first phase change from solid to mushy (i.e., partially solid, partially liquid) occurs at the solidus temperature, and the second phase change from mushy to liquid occurs at the liquidus temperature. Both phase changes depend on the relative fractions of elements, and type and quantity of trace elements present. When the liquidus temperature is equal to the solidus temperature, solid-to-mushy and mushy-to-liquid phase changes occur at a single temperature; the metal alloy with these relative fractions is termed the eutectic metal alloy. Metal alloys with a lower relative fraction of an element than the eutectic metal alloy are termed hypoeutectics, and those with a higher relative fraction are termed hypereutectics. For example, aluminum-silicon alloy with 12 wt. % silicon is the eutectic metal alloy of the aluminum-silicon system; any aluminum-silicon alloy with less than 12 wt. % silicon is a hypoeutectic of that system, while on with greater than 12 wt. % silicon is hypereutectic.
A person of ordinary skill in the art will recognize that any refrigerator that is powered by thermal energy may be used in an embodiment without departing from the scope and spirit of the invention. Two of the most common such refrigerators are absorption and adsorption refrigerators. Absorption and adsorption refrigerators both use thermal energy to drive a sorption/desorption chemical reaction in a generator, which compresses a working fluid and is analogous to the compressor in a compression refrigerator. Absorption refrigerators are based on liquid absorbent, with lithium bromide-water and water-ammonia the most common absorbent-working fluid pairs. Adsorption refrigerators, in contrast, are based on solid absorbent; there are many adsorbent-working fluid pairs, but zeolites, silicas, aluminas, active carbons, are graphites are common adsorbents for water working fluid. The compressed working fluid eventually evaporates in an evaporator, which absorbs thermal energy from its surroundings. In any of the above figures, the generator is in thermal communication with heat exchanger element 120d and the evaporator is in thermal communication with heat exchanger element 120e. In embodiments, the refrigerator is a water-ammonia absorption refrigerator, or an adsorption refrigerator that uses zeolites, silicas, aluminas, active carbons, and/or graphites as the adsorbent and water as the adsorbate.
The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the embodiments of the present invention. While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
This application claims priority to U.S. patent application Ser. No. 61/746,735, filed Dec. 28, 2012, entitled “THERMAL ENERGY STORAGE FOR TEMPERATURE REGULATION IN ELECTRIC VEHICLES” which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61746735 | Dec 2012 | US |
