By P Sanchez
We’ve talked in length about the A/C system in cars, a little history, how they work and some common troubles that could happen. Cooling the cabin is cool and all (pun intended) but it’s not quite useful if you’re living up the chilly north. So it’s time to touch on the “H” part of a car’s HVAC system: Heating.
As a first part, we’ll go a little bit in the interesting history and development of in-car heating. Later on, we’ll talk about its basic parts of modern heating systems and the possible troubles you should watch out for (and things you can do to fix them).
Turning Up The Heat
In the early days of the automobile, open cabin designs offer a limited reprieve from the sun and rain, and climate control meant wearing thick clothing if you wanted to drive out in cold weather. When automobile production methods improved and the popularity of automobiles grew, cabin designs became more enclosed, meaning you can now at least shut the doors and window glass if you need the elements kept at bay.
Riding in an enclosure meant that people can effectively use traditional heating methods long used in horsedrawn carriages such as heated soapstones, hot bricks, and lanterns The soapstone or flat bricks were heated in a fire beforehand and when they became sufficiently hot, were placed in flat metal containers which in turn were placed on the flooring of the automobile and covered with asbestos-lined non-flammable carpeting. This gave several hours of heating comfort for the foot and leg areas of passengers. More convenient gas lamps and coal burners became popular options later on.
Not long after, people easily realized that the internal combustion engine of their automobiles created a lot of excess heat that can be used to warm the passenger cabin. It was readily available heat that required less preparation and special attention and are far safer to use than gas lamps or hot bricks. The 1920s saw the creation of a new aftermarket industry of heating installations powered by the heat generated by the engine itself.
Note that nearly all automobile engines in those days were air-cooled and harnessing the excess heat generated meant either letting some heat from the engine compartment come through the cabin through vents, or a more popular method was redirecting some of the exhaust gases to tubes and pipings that fed some form of heat radiator. The radiator would have heated the cabin air directly, or heated the air coming from the outside as the air is brought in through pipes and venting.
There were a lot of challenges to using exhaust as an internal heating source. For one, regulating the heat from these systems was very difficult. The amount of heat generated varied depending on engine speed; heating of the interior was also not even, often the heat radiators located on the floor became scorching hot. Also, there were no standard designs so heating installations were complex and highly customized depending on the car make and model.
There were reliability issues as well. Often the tubes and pipings carrying the exhaust gas get corroded and damaged, leaking harmful fumes in the interior. And lastly, engines in those days created a lot of soot and as a result, the heating systems often get clogged and needed periodic cleaning. Maintenance required laborious disassembly and cleaning of the entire heating system.
The 1930s saw several designs that have engine exhaust heat the interior indirectly using water as an intermediate heat exchanging fluid. Basically, water is boiled to steam by the exhaust pipes then the steam is carried through tubes to a finned heat exchanger located in the cabin. Temperature control was a bit improved with designs using this system which uses a water valve and a means to open and close an external cowl that vented-in outside air to the heater. It was not until the 1940s that these hot water designs became factory-installed options and greater temperature control was possible through the use of thermostats.
The 1940s also saw the use of a separate gas-burning chamber to heat the water, instead of using the exhaust fumes. This offered faster heat-up times but also higher-cost of operation as they take fuel directly from the gas tank. As the 1950s saw the development of reliable A/C technology, heating systems were designed together with the A/C, offering a unified control system for both heating and cooling.
The 60s saw bigger and higher powered engines finding themselves in the mass market which meant air cooling the engine wasn’t enough anymore. Water-cooling the engine became the mainstream which also offered an important heating component that solved many of the problems of cabin heating: hot coolant. Engine coolant already circulated the cooling system via a water pump and it was just a matter of redirecting some of the coolant to the heater core in the cabin. Expensive gas-powered systems and the dodgy exhaust-heating soon fell out of favor for the simpler and more reliable coolant sharing design that’s still used to this day.
Source: The Evolution of Automotive Heating, by M.S. Bhatti PhD., for ASHRAE