Saturday, September 26, 2015

Insulation, thermal mass and acclimatization

It was somewhere in the mid-50 when I walked to the campground toilet shortly after sunrise. I was wearing shorts and a t-shirt. The air felt fresh and clean, not cold. Along the way I talked with a couple who were all bundled up in down jackets and wool caps. They said they were going to head south before it got any colder. I shrugged, having just come from considerably cooler places.

Part of the story must be what one is used to. But another is what one sleeps in. They were in a tent. They depended upon their clothing and sleeping bags for warmth. I depend upon the Rolling Steel Tent.

Daytime highs here in Green River, Utah, have been in the low 90s with humidity in the teens. So I keep the doors and windows open for ventilation. The insulation reduces the transfer of radiated heat through the roof and walls. According to my thermometer, it's about ten degrees cooler in the van. It's like a very comfortable place in the shade.

The air cools quickly when the sun disappears behind the mountains, but the mass of the Rolling Steel Tent (and everything in) it is still warm, giving off some of the heat it absorbed during the day. I can keep the doors and windows open past midnight, sleeping without covers, in just a t-shirt and shorts. (Well, maybe socks to keep my feet from being chilled.)  Then, sometime in the middle of the night, I close the doors, keep a window partly open and let my body heat warm the air inside the van. Exhaled breath raises the humidity a little, so I'm happy to step out into the fresh, clean morning air.

The game changes, of course, when the day and night temperatures are fifteen to twenty degrees lower. I dress warmer and the windows and doors spend more time closed. However, being a full-time camper rather than a vacationer, I've become less sensitive to temperature flutuations, even though I occasionally whine about the cold. At least when I do I'm probably less bundled than those around me. (I'm certain my layer of insulating fat has nothing to do with it. Right?)

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