Electric vehicles can already be fuel-efficient. The Tesla Roadster claims over 90% efficiency from batteries to wheels. However, in very cold or very hot weather, when air conditioning or heating requires the same energy used for driving the vehicle, range can suffer by as much as 40%. Along comes the Pacific Northwest National Laboratory (PNNL), which presented at the recent 2012 ARPA-E Energy Innovation Summit that ran from February 27 to 29 in National Harbor, MD, showcasing its molecular heat pump for electric vehicles. Its eventual plan? “A 5-pound EMOF-based heat pump [electrical metal-organic framework] the size of a 2-liter bottle could theoretically handle the heating and cooling needs of an electric vehicle.”
Heat pumps have been around for a long time. You might have one to heat and cool your home. They are related to air conditioners that operate with compressors and refrigerant to transfer heat from the evaporator coil to a condenser coil (the part that looks like a car radiator.) These are essentially heat exchangers between the working fluid (the refrigerant) and the air. Refrigeration and air conditioning work as the refrigerant is converted to a gas (evaporates) or a liquid (condenses) and a change of state has a cooling or heating effect respectively.
If you live in a relatively mild climate you may have a heat pump to air condition and heat your home. The heat pump is able to exchange the evaporator with the condenser so what gets hot and what is cooled is reversed. In the process, it can perform the seeming magic of taking heat from a cold environment and using it to heat a space like the interior of your car. The principal involved is enormously important for all sorts of alternative energy applications, like OTEC, ground-source heat pumps (aka geothermal heating), dry-well geothermal electric generation. And the physics involved is also found in updraft and downdraft solar towers. In addition, 15% of the US national electrical usage is for air conditioning.
Resistance heating (what you have in electric baseboard radiators and most portable electric heaters) is said to use its fuel with nearly 100% efficiency, but electricity doesn’t contain as much heat as fossil fuels, so we need lots of it. Heat pumps can give more heat using less electrical energy than resistance heating.
We also have thermoelectric devices that can perform a similar function. These solid-state devices will heat up on one side and cool on the other depending upon the direction of the applied DC current (see Peltier effect.) These can convert heat to electricity and electricity to heating or cooling with no moving parts. Devices that are both efficient and inexpensive have been difficult to achieve. They are often between 5 to 10% efficient.
The electrical metal organic framework (EMOF) is a nanotech construction that is engineered to bind with the refrigerants. This allows the MOF to replace the heat pump compressor and control the evaporation and condensation of the refrigerant electronically. The result is no moving parts and greater efficiency. Successful research will revolutionize not only EV cabin heaters, but potentially several other clean tech applications as well.
Photo Credit: EMOF Molecular Heat Pump by PNNL