General Motors has made available the details of the Chevy Volt's cooling system. What needs to be cooled and at times heated, how it is accomplished and what "heat transfer medium" or fluid is used, has all been available for some time at the GM-Volt web-site. So at least for the Volt we have an answer to how the passenger compartment will be heated.
Most notable is the appearance of four radiators mounted at the usual spot in the front of the car. There's a sandwich effect as the radiators are standing in a series. Successively, they are assigned to the heat transfer and cooling responsibilities for the electronics and battery, air conditioning, transaxle, and 1.4 liter internal combustion extender engine (ICE).
Undercar air flow is directed to the radiator group by an air dam with an assist given by two variable speed electric cooling fans. One of the radiators features a partition that allows it to help manage the heat output of the power electronics in one half and the heating or cooling of the lithium ion high voltage battery in the other half. When the battery needs super cooling the coolant passes through a chiller on its way to thermal passages that are part of the battery's infrastructure.
Cooling Needed While Charging
Interesting to note is that within the power electronics loop is the capability to cool down the plug in charger assembly used to charge the Volt. This loop also manages the heat generated when DC current from the high voltage battery is converted into AC current for the 3 phase AC motor drive signals utilized by the motor generator units.
All of the radiators, except the one assigned to the trans axle use Dexcool as the coolant medium and the system comes with three different pressurized surge tanks that each carry warnings about the dangers of the sudden release of hot coolant under pressure.
Passenger Heat From Two Sources
Heat to the passengers' compartment is handled in different ways depending on whether the ICE extender engine is on. When the Volt is in EV operation the coolant is heated by a 360V heater on its way to the heater core. If the extender is in operation the coolant is heated internally and the 360V heater is either turned down or off by the car's Hybrid Powertrain Control Module.
Meanwhile the cooling of the extender is handled conventionally with a belt driven water pump and a thermostat that can be heated electrically to speed opening.
AC And Transaxle Cooling
The final two radiators are the AC condenser and the transaxle cooler. The ac condenser is cooled by ambient air funneled there by the air dam and fans. The cooler for the transaxle cools the electric drive units and uses pressurized Dexron VI automatic transmission fluid. Due to the power levels, the degree of heat generated is extensive, but the transmission fluid also serves to lubricate gears bushings and bearings and to activate the clutches.