HVAC in Electric Cars

With a conventional fuel-powered car, interior heating comes from the engine coolant. Because the average gas or diesel engine is so inefficient, about 30 percent of the heat generated during combustion is transferred to the engine coolant, which in turn provides a ready source of heat

to warm the cabin. To keep the cabin cool on hot days, an air conditioning compressor is driven by the engine via a belt. Not having a hot inefficient engine powered by an energy rich fuel (running the AC in the summer only reduces mpg by 1 or 2) creates a challenge for electric vehicles. How to heat and cool the car without drastically reducing driving range? Nevertheless, it is nothing a little bit of engineering can’t handle.

Solving the heat issue is very straightforward. One simply replaces the heater core, which would have had engine coolant running through it, with an electric heater that has voltage running through it. The tricky part is to design it in such a way minimize drain on the vehicle’s battery pack since creating heat from electricity requires a lot of power. To do this, a Positive Temperature Coefficient (PTC) heater is used. It basically  consists of a resistor that increases its resistance as it heats up, thus limiting the current it can draw. That way it will never get too hot and waste battery power.

Solving the cooling issue is also straightforward. The compressor is simply driven by an electric motor which is powered by the car’s battery pack. The compressor is very similar to one found on a domestic refrigerator. It resides in the front just a like a conventional fuel powered car. The motor driving the compressor is very small (much smaller than the car’s motor) and creates little load on the battery.

Those two solutions allow electric vehicle drivers to turn on the climate controls like in a fuel-powered car and not worry about being stuck on the side of the road with a dead battery.