Cold exceptions prove the hot rule

Now considering solar declination alone the 29th of April should be the hottest day of the year in Bangkok, latitude 13.9, for that is the day when the sun passes directly overhead and there is no shadow at noon. But saturday there were no shadows at noon, and in fact the past few days have been downright cold. When I stopped by Jack and Dah's place after a thunderstorm several of the tall willowy trees that have sprung up in their garden had bent all the way over so the crowns of the trees were splayed out in the garden. Evidently the wind had got the water-soaked tree swinging back and forth until it reached a point of instability and collapsed, though Jack told me later that he was able to put them right again without permanent damage.

Young willowy trees, as unstable as young men.

Now when I first came to Thailand I thought the hot season was going to be a relentlessly increasing tide of heat peaking in April and agian in September. But this is not how things have behaved at all the past few weeks, and if you look at the march of temperature and wind as we do here you get a picture that looks a little like those trees in Jack's yard. "Normal" hot weather (orange zones) with steady breeze from the south, punctuated by unstable wind directions accompanied by storms and cool weather.

Cold strokes in the hot season or the other way around?

I don't know anything about meteorology, low pressures and the South China Sea, but the behavior of the wind and the level of comfort looks more like the stock market or my girlfriend's moods than some orderly sun-driven cosine thing.

I guess I'm going to have to start reading a little Mandelbrot if I'm ever going to survive in this place.

My fan's fan

I am ashamed to admit this, but one time when my girlfriend fell asleep I crept into her room and took a picture of her fan. I was really impressed with its clean design and checked out the price at Lotus, only 750 baht. It comes in a little box and you can pretty much put it up by yourself. It's a Thai product, a good one.

Overhead fans are great, even when you have aircon.

Anyway, who wouldn't want an overhead fan? Romance, Humphrey Bogart, plot your own revolution. And they work, too, the one above provides a nice efficient and smooth flow of air.

Brother Jack decided he had to have a fan under his mosquito net, and he loved to talk about this Honeywell model, which I admit seems to work pretty well, though it's airstream is choppy, narrow, and turbulent. Dah says it doesn't keep her cool. Maybe because jack points it at himself.

Dah sleeps on a wood bed when it gets hot (more on that tommorrow) and she put up this large overhead model which she says cost 3000 baht. I'll admit it looks pretty nice in her and Jack's place, but it is also very quiet and seems to provide the largest and least turbulent flow of the three models. I know that "turbulence" isn't on the list of things people usually consider in buying overhead fans, but I've come to the conclusion that it is important.

Regional heat agony today

This dreadful day I made the mistake of getting my girlfriend to accompany me to Klongtoei, where I wanted to idle away the afternoon browsing machine shops.

My idea of a date.

After almost fainting in the heat (both of us) they we took refuge in the huge Lotus, collapsing on a wood bench from which we could listen to American country music and watch a Charlie Chaplin VCD and eat a McDonalds ice cream cone. My numb mind filled with happiness at the cold air.

Is there any hiding from it? See for yourself, here are the 1 pm temps all over SE Asia on what must be the hottest day yet this year. The folks in Udorn have my heartfelt sympathy.

How cold that night sky

People who write learned papers and books about tropical architecture and comfort --Floridians, Singaporeans, Australians, and, God knows why, even some Norwegians -- talk of "dumping" building heat, ie trying to find places where the enthalpy is low to which unwanted building heat can be efficiently transferred.

Alas, this is not easily done in Thailand because there aren't any cool places to be found. With a mean temp over the year of nearly 28 degrees, the earth itself is warm -- about 28 degrees, which does not provide much of a "sink" for heat. (One night I walked into a bar in Pnom Penh and started taking the radiant temperature of the palms of all the girls in the bar. I told them that I was measuring what kind of a wife they would be. I leave what one girl did it to the reader's imagination )

The sky, which cools the overheated brow and roof in the night desert (or in places like Hollywood, where I lived a rather disappointing life, but for other reasons than heat, until recently) is fairly warm, and efforts to radiate heat into the sky from buildings are not usually considered to yield much benefit, especially in the hot season.

But since we have recently seen that we are not asking for much cooling, just a few degrees, I've been taking some night sky temperature measurements* with my little radio Shack radiant thermometer. Here are the results on the left. Evidently the night sky temperature is a function of sky moisture, or dew point. And in the hot season, when there is a lot of moisture in the air, the night sky becomes less effective as a heat sink.

But still. How much can we get from a night sky of 15 degrees?

According to radiant heat theory, we should be able to transfer about

k*(Troof^4-Tsky^4) watts/m2

where k= 5.6697xlO-8 w/m2-°K. T

which comes to about 50 to 80 watts per square meter of roof. This is enough to lower the roof temperture, suppress it as we say, by two or three degrees.

Can we use this natural cooling to some good end?

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* I know that this instrument is not really measuring the temperature of anything in the sense of say a thermometer, rather it is feeling how much radiation is being emitted by whatever you point it at. Or whatever you point it's 30 degree "eye" at. It thinks that the emittance of everything is the same, maybe 0.9, which is not true or things like aluminum and skies. But since radiation is what we are talking about here, I'm just going to go ahead and figure the heat transfer as if the "temperature" of the sky was what the radiant thermometer says it is.