Hot breezes

Okay, wind - generally speaking - feels cool because the increased air movement increases the heat loss from your body to the surrounding air. But this would go both ways - a particularly hot wind will feel hotter than stagnant hot air, because the moving air will add heat to your body faster than the stagnant air.

So I ask: at what temperature does a breeze go from making you cooler to making you hotter? The obvious answer would be your body temperature. However, it seems that even when the temperature is 100, wind will still feel cool. Of course, I’ve felt wind when the temperature is 115, and it most definitely makes me feel hotter, so my theory must be at least partially valid. Anybody here wanna clue me in? If I’m unfortunate enough to be driving in Sacramento during the summer without an A/C, at what temperature should I roll up the windows to keep from getting hotter? And why isn’t it at 99 degrees?

Even hot air evaporates your sweat, cooling you a little. Besides, if you roll up the windows to be cooler, the solar gain will make the still air inside evenhotter. Instead of a 115 degree convection oven, you’ll be in a 180 degree conventional oven. When your roasted carcass is discovered, they’ll put your mommy in the slammer for leaving you in there even though it wasn’t her fault.

Fair enough, AskNott, but assume that I’m standing in a big open field, instead of inside a car. At what temperature should I be hoping for wind, and what temperature should I the wind goes away?

It would depend on the humidity as well. If humidity is 100% there is no evaporative cooling and the problem is simple - the cutoff temperature is the body temperature. At lower humidity the cutoff temperature will be higher; air flow will bring hotter air to your skin but also remove the moisture around your skin and improve evaporative cooling.

Sorry, I’m not sure about the exact temperature.

You won’t find a specific temperature for a feeling. You may find one that will actually cool or heat the body, but whether you feel it to be such depends. It’s not so much the absolute temperature that makes you feel cold or hot, but more a change in temperature.

I’m from Canada, and this past winter has a lot of days in the -15C range. When it went up suddenly to -5 or 0 because of a chinook, that wind definately felt warm… even though it would have killed me through hypothermia had I ran naked in it for a few hours. When I was in Thailand at 30C, and the temperature cooled down to 20C with a breeze, it felt freezing. Both those temperatures were below my body temp, but had opposite effects depending on the direction of change.

I’m not sure, but the hot winds here can be unbearable. The air is so hot that it is worse having it rush into your car window than having the windows closed and the car baking.

I would guess somewhere over 100F, but I haven’t measured it.

Ah, yes, istara… I would wager the summers over there make Sacramento seem balmy. :slight_smile: In my experience, the switch-over temperature is definitely somewhere north of 100 around here. Thanks, scr4, for bringing up humidity - I should’ve figured that on my own (and the whole explanation for the higher-than-body temp switchover point, for that matter). Guess it’s time to drag out the ol’ heat transfer text books and figure it out myself. Thanks, guys.