While clearing the cars of frost Thursday morning, I was reminded of a difference of opinion Kate and I have about the best approach to a cold car. I tend to start the car up, and immediately turn the defrost on full blast; she prefers to let the car warm up for a while first, because it just blows cold air for a while. My feeling is that while the air from the defrost is not warm in an absolute sense, it’s still passed over the engine on the way in, and thus is warmer than the outside air. Which means that it’s going to increase the temperature inside the car somewhat, and thus will heat the interior to an acceptable temperature faster than waiting until the car is fully warm and just blowing in hot air.
Of course, this ought to be experimentally testable, but it would be a gigantic hassle. My car is much larger than Kate’s (2007 Ford Freestyle vs. 2003 Toyota Prius), so a direct comparison would be meaningless. And while I do have a colleague with a nearly identical car that we used for a previous experiment, he doesn’t live anywhere near me, and getting his car over here would necessarily warm it up, ruining the experiment (I guess we could try to coordinate our schedules to do a test after work some day, but I’m not sure I’d want to ask anybody else to stand out in the cold for SCIENCE!). And the morning temperatures vary widely from day to day making it difficult to do an extended series of tests.
I toyed with the idea of simulating this mathematically, but a few minutes’ thought show that it’s a horrible problem. I don’t know how the temperature of the defrost air increases over time, or how to model the mixing with the air that’s already in the car (which presumably exits in some manner, because running the defrost on full doesn’t overpressure the car to any significant degree. And I’m really not willing to spend a lot of mornings standing out in the cold long enough to collect data for this.
I suppose what I need is a USB temperature sensor that I could put inside the car, and use to log data from inside where it’s warm. Hmmm…