BMW exploring heat pumps and infrared for BEV and PHEV cabin heating systems
18 September 2012
The BMW Group’s Efficient Dynamics strategy is targeting reductions in fuel consumption and CO2 emissions while at the same time increasing performance. In battery electric vehicles (BEVs) or automobiles using plug-in hybrid technology (PHEVs), the Efficient Dynamics strategy is aimed primarily at increasing the electric range.
One element of this comes under the general heading “Intelligent Energy Management”. BMW is working on a variety of individual solutions that help to reduce energy consumption by ancillary systems on board a BEV or PHEV; every kilowatt of stored energy that can be saved becomes available to the electric motor, enabling a greater operating range. Some of these new techniques could also be transferred to future vehicles with internal combustion engines.
In the area of passenger compartment heating, BMW is exploring the use of heat pumps as well as of infrared systems.
Efficiently delivering the required heating capacity to heat the passenger compartment at low outside temperatures is especially challenging when designing BEVs and PHEVs. Heat pumps, a technology well-known in the domestic housing sector, represent one approach. To really take advantage of the higher efficiency of the heat pump compared to pure battery-driven electric heating alone, the technology needs to work reliably under all driving conditions, BMW notes.
Like similar systems used for heating buildings, the heat pump in the vehicle uses ambient heat—in this case, the heat from the surrounding air. By means of an air conditioning compressor, the refrigerant is compressed and elevated to a higher temperature level. For use in vehicles, this technology needs to be able to heat, cool and also dehumidify the air in the passenger compartment.
The existing refrigerant circuit has been extended to include additional components and regulators. In addition to the heat present in the air outside, heat originating inside the vehicle can also be used as a source; this process is controlled by an intelligent thermal management system which monitors the entire vehicle.
The drivers of the BMW Group’s future BEVs will expect the comfort systems in their vehicles to deliver the same performance as those in conventionally powered automobiles. This includes the distribution of air of differing temperatures to a number of different interior zones. By using a heat pump, even this requirement can be realized. Through the use of heat pumps in BEVs and PHEVs, about 50% of the energy needed to heat the interior can be saved, BMW says.
Thanks to the “free” heat from the environment, the electric heater is required to contribute much less. The extension of range which is gained is between 10 and 30%, when the outside temperature is at freezing point, depending on the driving cycle. Use in conventionally powered vehicles is not currently under consideration.
Infrared heating surfaces. In the field of vehicle heating systems, modern infrared heating surfaces are a new solution that not only delivers low power consumption but can make a noticeable improvement in the passengers’ level of comfort, BMW suggests. Today, conventional vehicle heating or air conditioning systems heat the air inside the vehicle, which then transfers its heat to the driver and passengers. In contrast, in systems employing infrared heating surfaces, energy is converted into infrared radiation, which then warms the occupants’ bodies directly.
The thermal radiation generated by infrared heating surfaces provides a type of warmth comparable to the warmth of an infrared lamp. When used in vehicles, electrically-powered infrared heating surfaces provide even more benefits. The heating effect can be enjoyed just one minute after activation, an important plus point in the winter. In addition, the heat is distributed without any need for drafts of air and is completely silent. Moreover, the heat output can be focused locally and very accurately.
Theoretically, it is possible to focus the heating power solely on to the driver alone, in order to increase efficiency. From today’s perspective, infrared heating surfaces can be mounted in door panels, in the footwells and in certain areas of the dashboard.
Infrared heating surfaces could in particular conceivably be used to support conventional heating systems. Especially during the warm-up phase, the very rapid action of infrared would be advantageous. Separate regulated circuits, analogous to seat heating, with which the occupants can individually set their own degree of comfort are another possibility.
Particularly when used in battery electric vehicles (BEVs), infrared heating surfaces confer efficiency benefits, BMW says. Since no internal combustion engine is available to provide its waste heat, electrical energy has to be used in order to maintain the temperature of the interior of the vehicle at a comfortable level.
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