From Concept to Car: Keeping cool
A new car needs to stand up to the elements. Not just rain, snow, and wind, but harsh cold and blazing sunshine too. With drivers all over the world looking to Polestar for their next EV, each and every car with the star on its nose needs to perform flawlessly no matter what the elements throw at them. Performance can’t be left down to sheer luck. Testing — and more testing — is the only way to make sure a car performs the way Polestar wants it to every time.
You probably don't think about how your car's air conditioning works very often. On the list of things to worry about, 'heat machine' may not be high up, and that's fine. It's one of the things in cars we simply assume works and sort of forget about. The thing is, an enormous amount of work goes into making sure your car keeps the air around you at the perfect temperature (and that you don't notice it doing so).
This is where Matt Clowes, Principal Engineer for Climate and Thermal Attributes at Polestar, and his team come into play. His job is to make sure you're comfortable no matter what's going on outside the car — rain, shine, shadow, wind, snow, you name it. Listening to customer feedback is key, and some markets come with more demanding conditions when it comes to cooling than others, which is how Clowes and his team found themselves in Dubai. "In the summer months, they have temperatures up to the 50-degree mark with very high humidity," explains Clowes, "In North America, you might get similar temperatures, but in Dubai, you get that and 40-50% humidity. It's a really, really challenging environment."
For most people, you get in a car, set the a/c, wait for it to cool and go about your day without thinking how the car deals with it. There's a huge difference between how a car deals with a drizzly March morning in the middle of Germany to a cloudless July day in Dubai. The car has to work so much harder to keep you cool when the asphalt outside could do a decent job of frying an egg. In fact, Dubai and warmer climates present the team with a dilemma. "There was some really fundamental tuning needed at the start. We need to find the right balance between how much fresh air you use versus recirculated air." Clowes explains that recirculated air uses less energy to cool, as it's already cooler than air outside the cabin. Using less energy is a good thing, but you can't ignore the fresh stuff for a very good reason. "You can't use recirculated air exclusively because you don't want CO2 to build up and make everyone pass out."
Measure everything, everywhere
To make sure the car is the temperature it says it is, Clowes and his team measure everything, everywhere. While the idea of a thermometer in the cup holder and a tiny windmill by a vent is cute, it's far more complicated than that. "There are at least 40 temperature sensors dotted around the car. We've buried them in the HVAC system, in the cabin—they are everywhere," adds Clowes. What there isn't, he comments, is a way to measure airflow. Why? Because that's already been accounted for. "We don't need to measure that when we're in the car because we've done rig work in the build-up to this testing. We tested the rig in maybe 200 or 300 different variations of different fan speeds and different settings. We know how much air comes out of which vent in any given condition." For a normal driver, an airflow setting is measured by how big the 'blobs' are on the setting, but it's actually a measurement of how many kilograms per hour of air are fired through a vent.
A temperature readout is one thing, but how else does the team measure comfort in the car? Some good old-fashioned subjectivity. "We do subjective evaluations with a really commonly used scale: seven points, from minus three to plus three. Zero is entirely neutral, minus three is very cold, and plus three is very hot," Clowes elaborates. It's used to measure how quickly and efficiently the car goes from uncomfortable to… not that. "If you're getting in the car in Dubai, you'll probably start at a plus three—very hot—and you want to bring yourself down to that zero point as quickly as possible."
Subjectivity isn't the only way to measure a car's ability to do its job—benchmarking works, too. Clowes explains. "We objectively test our direct competitors. We'll have benchmarked them and measured how quickly they bring temperature down in hot temperatures. If you can match them, that's half the job done."
Clowes likens the subjectivity of the testing to the processes you'd find in vehicle dynamics. There's the "fixed-number" side of things (time to cool, time to warm, etc.), but then there's the "feel" of the system. Is it too intense, too weak? The only way to find the right balance is to spend time with the car and tweak settings.
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Finding the magic number
Testing takes place in a number of environments in Dubai—the system reacts differently depending on the outside environment. It’s cooler in the shade, warmer in direct sunlight, and that puts different strains on the car’s inner workings. As the outside world changes, the car’s software needs to keep up with demands from both the car, and its occupants. “We try to drive as a customer would. There will be occasions where we want to do a test which is perhaps a little bit abnormal and stresses the system a bit more than you might normally expect,” adds Clowes, “But generally we want to try and simulate a customer parking the car at the office or whatever, and then coming back to the car an hour or so later, finding it really hot, and then having to drive the first few kilometres in very slow moving traffic through the city. The very low vehicle speed means you're relying on the fans to move the air over the cooling pack. On the highway at 100kph the air does that for you.”
Polestar aims to have a neutral temperature of 22 degrees centigrade, blowing at you with whichever ferocity you choose. Except all may not be as it seems. 22 degrees can mean many things. “Yeah, 22 degrees probably won't be 22 degrees,” says Clowes, “We're tuning the car to feel comfortable based on our subjective evaluation. The temperature in the car when it's set to 22 could be 24 or 25 and that subjective feeling could change depending on what the conditions are outside. If it's minus 18 outside, that 22 degrees you need to feel comfortable will actually be higher.” The car knows what’s going on around it and will adjust itself to make sure you’re not uncomfortable.
When testing is complete, and the team is happy with its various settings, its work is presented to the wider business for sign-off — the team’s subjectivity might not line up with everyone’s, and it’s important to make sure everything’s in good order. Polestar tests its vehicles in all sorts of extreme environments all over the world, not just to make sure the things you can see and touch work but even the things you might not even notice. Next time you’re feeling a little stuffy on the commute home, remember that a team of people went to very warm, very cold, and very far-flung places to make sure your comfort is within easy reach.
