How does car air-conditioning work?
Gone are the days of an open window being used to cool down your car’s cabin, now it’s all climate control and even individually adjustable zones. But, how does car air-conditioning work?
To be honest, air-conditioning ceased to be an automotive luxury a long time ago but not all systems are created equal. And there’s a lot more involved in the development of your vehicle’s air-con/climate control system than you might imagine. But let’s go back to the beginning.
The origin of vehicle air-conditioning
Back in the 1930s it was Packard that became the first car maker to install an air-conditioning unit which was called a Weather Conditioner. It was a retro-fit option that was performed by a parts supplier once the vehicle rolled off the factory line. That said, it wasn’t particularly effective; the condenser unit used to fill half the boot space, there was no thermostat, and it was pricey launching just after the Great Depression.
At the same time, Chrysler had been busy developing and refining its own system which it launched in 1953, like the early Packard unit, the Chrysler system also used a boot-mounted system. It was the Nash Ambassador in 1954 that launched with a fully integrated front-end mounted HVAC system. Nash was a joint-venture with Kelvinator and its refrigeration experience allowed it to produce a better and cheaper system than any other car maker. This system quickly became the what you could call the father/mother of the modern HVAC system.
What about now?
Climate control systems have come a long way from the early days with computers, simulations, bench tests and field tests used to tailor a ventilation system to the car. That means that while the components of the ventilation system might be the same from model to model, the ventilation software will be unique, some will need to run single-, dual- and even tri-zone systems with filters and so on.
To that end, more than just the shape and size of the vehicle, car makers need to consider occupants and the range of climates the vehicle will be sold and used in. the modern ventilation system requires just as much thought, development and testing as, say, the way a vehicle rides and handles.
How does it actually work? In exactly the same way that your reverse cycle system does at home. In a nut shell, you have a compressor, condensor, expansion valve, receiver and evaporator. Car air-conditioning systems have a refrigerant that via the compressor is changed from a gas to a liquid, then as it passes through the condensor fresh air flows through the condensor (think small radiator) removing the heat created as a result of the change from the high-pressure change from a gas to a liquid, it then moves through an expansion valve where it returns to a gas and then as it enters the evaporator, fresh air blowing through the evaporator removes the heat (generated as the liquid becomes a gas again) and cool air is blown into the cabin…this process continues as required by the vehicle.
Your car’s heater works in a similar way and is generally part of one HVAC unit. Essentially, to warm the cabin, the vehicle makes use of heat generated by the engine via a radiator that acts as a heat exchange; hot coolant flows through the ‘radiator’ with a restricter for warmer or hotter air and a blower blows air through the radiator and into the cabin. Yes, it’s more involved and complicated than that, but this is a nutshell explanation.
In the same way, car makers design their vehicles to be as slippery through the air as possible, the same goes for the interior of the car. Although, it’s not for fuel efficiency, rather it’s for how the air moves through the cabin, the temperature changes in different parts of the cabin, the noise of the ventilation system and more.
“Proper airflow ensures good visibility from the car, defrosts the windows in winter and prevents fogging throughout the year,” said Skoda’s internal aerodynamics coordinator David Svítil.
“When a new car is being designed, we work with the design department on the distribution of the ventilation system’s various component.” For instance, Skoda said that with the design of both the new Scala and Kamiq, the blowers in the middle of the dashboard had to be lowered because of the high-mounted infotainment screen. “Using computer simulations, we could instantly shape and design them to make the airflow in the cabin as comfortable as possible,” said Svítil.
From the lab to the real world
Car makers make use of climate chambers to test the general performance of the ventilation system. These chambers can be used to adjust the temperature from -40 degrees C to +60 degrees C. “For our purposes, we usually set the temperature inside the chamber to 40 degrees Celsius,” said air-conditioning development coordinator Jan Hrnčíř.
“Air-conditioning efficiency is verified using standardised pull-down testing. We can set up the fluorescent lamps to simulate a burning sun at 1000W per m2, which is consistent with conditions you might find in the Arizona desert. We monitor passenger comfort with the aim of reaching a temperature of around 25°C at passenger head level within 20 minutes.
“We distinguish between countries with mild climates and those with tropical climates, such as India and China. Here, the fan start-up curves are higher in order to generate more intensive air exchange. Cars in Europe respond more slowly.
“The chamber will show us the overall performance and efficiency of the ventilation system, but it can’t simulate the software set-up conditions. This is something we have to examine over thousands of kilometres on cold mornings, hot days and in alternating and rainy weather,” said Jan Hrnčíř.
Once the ventilation system has passed the lab testing phase, it’s then tested in the real-world along with all the other vehicle components.
“We drive in polar regions and in the desert. Obviously, these are extremes,” said Jan Hrnčíř. “Spring and autumn alpine environments are ideal testing grounds for the automatic mode. You may be in a situation where it’s frosty outside, but the harsh rays of the sun are warming the interior. That’s the most complicated situation for the control system to handle. Using a range of sensors, the ventilation system must correctly adjust the flow rate and temperature for both the feet and the head so that the car’s occupants feel comfortable and don’t need to adjust the settings.”
Climate control is smarter than you think
Of course, not all climate control systems are the same, some are able to switch on and off internal recirculation if, say, air pollutants are detected. And some systems have a second filter that’s used when the air is on re-circulate. Then there are humidity sensors which stop sudden misting of the glass and if you’ve driven a vehicle with a humidity sensor you’ll know how impressive that feature can be when you drive into an underground carpark on a wet day. And most more-advanced systems can ventilate with fresh air when needed to avoid occupants from travelling in a stuffy environment. There are sensors to monitor outside and inside temperature and humidity, system pressure, and the compressor settings. And those systems with a sunlight sensor can tell the direction and intensity of the sun and adjust the climate control accordingly.