We all know that you should not leave, inside a car on a hot summer day, living things that are unable to get out by themselves (e.g. infants, pets.)
Even opening the windows a crack to allow air to enter the car is not sufficient.
My question is:
What happens if you open all four windows all the way?
For the sake of argument, assume that the car is a typical four-door sedan with four windows, e.g. Honda Accord (honda.com).
If the person sitting in the car is in the shade, and all the windows are open, would the temperature in the car be much more than the temperature outside the car?
P.S. Now that I think about it, I could just try the experiment myself, using a thermometer, but maybe someone already knows the answer to this.
If the car is truly shaded, then it will be fairly close to the ambient air temperature, even with the windows up. A person sitting inside is going to heat the car up though. A human body at rest puts out roughly the same amount of heat as a 100 watt light bulb (the old fashioned kind, not a fluorescent). So, in the shade, with the windows down, a person would be comfortable.
If the car isn’t in the shade, then a lot depends on the wind speed. If you’ve got a good wind then the car could be reasonably close to the ambient air temperature inside. If the air is pretty stagnant then the car will get much hotter. A typical summer breeze would probably put it somewhere about in the middle between the two extremes.
There is no shade in our work parking lot. There is usually enough wind around here that just cracking the window usually makes a significant difference in my car. YWMV (your wind may vary).
What I meant to say is that the car itself is in the sun, but because of the roof of the car, the person sitting inside the car is in the shade.
The situation that prompted the question: I saw a dog in a sedan with all four windows open. The car was in a parking lot (in front of a store). The car was in direct sunlight, but the dog was in the shade (because of the roof of the car). The people I was with said that you should never leave a dog in the car. I thought that since all four windows were fully open, the dog would be OK in the car.
It is probably going to get pretty warm in the car, not as hot as if the windows were closed, but it still might be dangerous for the dog. The roof doesn’t really shade the car. The roof absorbs the sunlight and gets hot, and much of that heat gets transferred by conduction into the car. You’ve also got sunlight going through the window and heating everything inside the car (air, seats, dash, etc). You’d need to move a fair amount of air through the car to get rid of all of that heat.
With no breeze I would guess the interior of the car could get 10 to 15 degrees hoter than outside standing in the sun.
I’ll have to try it myself. I was assuming that if the air in the car was that much hotter than the air outside, then the open windows would be enough for the hot air to mix with the cooler outside air. A 10 to 15 degree difference seems like a lot to me.
The sunlight wouldn’t be heating the seats if there was no direct sunlight on the seats due to the roof of the car being in the way. The dog I saw was sitting in a car seat that was not exposed to direct sunlight.
You should note that the colour of the car make a big difference.
A black car can be murder when you get into it if it’s been left in direct sunlight. A white one less so.