Hot Tin Roof

My responsibility here being to show you how to beat the heat in Bangkok, and having displayed a bit of information on the annual weather cycle, I plan now to talk a bit about how the buildings we live in repsond to the weather, particularly how they respond the dreaded sun.

I claim that of the principal elements of foreigner felicity in Thailand is the achievment of thermal comfort. One of the principal enemies of thermal comfort is a hot roof.

Why?


Because our comfort in what Jack calls the sub sweat stage is sometimes determined more by the radiant temperature around us than by the temperature of the air. Thus, if the air temperature is a pleasant 27 C (80 F) and the wall or roof temperature is 39 C (ie 102 F) which it often is in these parts, we are going to "feel" as if the temperature is in the nineties (ie aboout 33 C) Since this is virtually the same as our skin temperature, we cannot dump any of our body heat into our surroundings, and that is not pleasant and we will soon enter the sweating stage, which is our body response to inadequate cooling by convection*.

If the underside of our thin metal or cement tile corrugated roof is say 43 C (110 F), which is typical midday, we are going to miserable no matter how cool the air is.


The reason the underside of the roof gets hot is that the outside of the roof on a sunny or partly cloudy day in bangkok is typically 45 C, and that heat is easily transmitted through the thin conductive material (R is only say .05, vs the 10 or more that is desirable for a roof). Because the layer of air against the bottom of the roof is a fair insulator, say R= 2 to 5, most of the temperature drop is going to be in the air, not the thin roof, so the radiant temperature of the underside is going to be almost as high as the outside temperature. A temperature of 45 degrees, by the way, is enough to cause medical-class burns to the skin.

And this, remarkably, is the usual state of Thai buildings, especially in the countryside. And if you ask the Thai about this, they will act as if the problem never occurred to them, they don't pay any notice to it, or who knows what they think or feel, I have been unable to get a clear answer to that question. It must be like asking an Eskimo whether he objects to the color white, it's so ordinary it's just a little outside the range of notice, maybe like asking a person how they feel about nitrogen.

But we, as rational heat-sensitive westerners, feel compelled to take action to increase our thermal happiness. So what can we do about this problem?

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*Convective heat loss (body to air) for typical conditions is about 8 watts per square meter per degree difference temperature (Centigrade). Hence, a half naked fellow, with an exposed skin area of about one square meter and a skin temperature of 34 deg, will convect about 32 watts of heat into surroundings that have a warmish 30 degree temperature (8*(34-30)=32). This is not enough because his body is producing about 50 watts of heat even when he is quietly gazing at his Thai girlfriend. (We are assuming here that radiant surroundings, walls and ceiling and suchlike, are at body temp, so there is no loss by radiation. If he were say praying in a Mexican cathedral with cool walls at say 25 degrees, he would lose an additional 40 or so watts by radiation.) So a bit of what my mother used to call "stickiness" will develop, maybe even a bead or two of perspiration. Perspiration will supercharge the heat loss, depending on how hot and humid it is, and whter a breeze blows. More on this advanced but very important topic of evaporative heat loss later.)

But the Thai lady will almost always have a lower body weight to skin area ratio, less heat-producing kilos of meat per square meter of skinny arms and legs, therefore she doesn't need to dump 50 watts of heat per square meter, maybe only 25 or so, so she will not be sweating but thinking "fahlang get too hot here in Thailand."


Commetrs
Timothy Pellissier 25/04/2007 09:59 IP: 58.9.39.243

Hey all you comedians... Cut the crap and add some usefull information on creating sustainable comfort in the Thai home: like materials, methods, sources of materials, costs, and results. I'm on my way to HomePro to see what I can find for myself.
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Ian 08/03/2007 10:33 IP: 124.121.71.46

Ggrass, thanks for the info, who sells it? Do you think it might be an idea to start a blog just to exchange info like this, where things can be bought which are not normal to Thailand? I am sure many newcomers struggle to find the things they need to make life here more comfortable. A simple example is it took me 3 months to track down an importer of my favourite cigar:-) Incidentally "staycool" and other loft/roof type insulation is on sale at Homepro, which is also where I managed to buy a RCCB (residual current circuit breaker), ELCBs which are the norm here are actually illegal in the UK:-)
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GGrass 08/03/2007 10:10 IP: 203.113.15.234

bagger (it's pronounced baYer) cool paint <-- the new innovative paint that's currently on advertisements. it's supposed to contain some ceramic stuff, that reflects sun's heat upto 90% or something like that. they say it's the technology used in space-shuttles. ________________________________________

Ian 07/03/2007 19:01 IP: 124.121.72.124 Ron, my neighbours complained of dazzle when I painted th e walls white, however they shut up when I pointed out they never ventured outside until after sunset. The white paint you mention is I suspect the same or similar to the paint used for reflective street signs and marking, it contains microspheres of glass. Regarding your Thai lady and sweating, apart from when in the shade her brown skin is a better radiator, if you examine her skin carefully you will find she has less sweat glands per square cm than you do:-) ________________________________________

Ron Swelters 07/03/2007 18:23 IP: 58.8.69.43 In regard to the white paint, there is a special heat reflective kind that is even better than normal white (your eyes can't tell the difference.) The Australians promote this solution, reflects maybe 25 percent more of the sun's heat. But your neighbors might not like it, if that matters to you. We will compare some other solutions son. Thanks for the other excellent ideas. ________________________________________

Ian 07/03/2007 16:51 IP: 124.121.74.247 energy watch, 15% of body heat is lost through the head, yet your genitals which are much smaller lose 10% of body heat, this is why you should wear very loose briefs or better none when at home. If you are outside and want to cool fast wet your wrists as the blood vessels are closest to the surface here. Diet is another factor in keeping cool, have a word with a local Chinese about "heating and cooling" foods. ________________________________________

EnergyWatch 07/03/2007 16:29 IP: 58.136.227.174 Ron Swelters>>>> Your body is like 4000 cc jaguar but your wife is 1300 cc corollar. When you both sit in the tin-roofed room (idle condition) your jaguar engine consume more gasoline to keep it idle than her idle condition. Heat has speed. If the gap between your body and room temperature is more, your body lose more heat at more speed. In this theory, I may advise you, that, take a bath to make your body wet, then lie on the tile floor with fan, your body heat runs out quickly. The tile is a secret how Thais cool their body. Tile conduct heat very fast, here from your boiling body to tile floor. Baked Tile is good conductor of heat. >>>> If you can 'hole' in the roof, the air is afloat and leak over as hot air always flows up. I put roof 'natural fan' that pump out the 'under roof hot air insulation, and keep the room in natural ventilation, of course wet my body and lie on clean tile floor in only brief, under standing fan (absolutely not ceiling fan !) and tease my wife,,, Cool !,,,,HaHaHa !
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n 07/03/2007 15:04 IP: 124.121.71.98

I yesterday asked one of my local builders to paint my roof white, he was horrified:-) He produced many reasons against this, the paint would only last a year, the accepted colours are red, blue, green or cement, paint is expensive and would not survive the rain. I pointed out that my walls were white using an exterior grade cement paint, he said that ok as they vertical so not get wet! I said I want the same paint on my roof, he said no way much too expensive. I said 700 Baht for 10 litres not expensive. He said have to paint every year, I said if so it will be worth it. I think I will have to paint it myself, you cannot alter the way a Thai thinks.
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Ron Swelters 07/03/2007 14:30 IP: 61.90.146.66

Why sure, steal whatever you want. Is being under your ass better than being under the dust that is under your shoes? I'm new to Thailand.
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EnergyWatch 07/03/2007 14:13 IP: 58.136.227.249

Ronswelters !

Can I steal your 'scatch under tin'. I am your neighbor. You are under my ass.
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