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.

Local wisdom, upstairs/downstairs

There's a lot to be learned from the natives.

Here I am going on about how terrible hot tin roofs are, and then I discover, from reading my own blog, that if it's a good sleep you're wanting, you might be best off under a hot tin roof.

Here's the idea: even though the night sky in the tropics is fairly "warm", that is, its temperature as measured by a radiant themometer is not close to freezing as it would be in the desert (so don't try to build a heavy masonry building in Thailand and expect it to be cool like a Mexican church), but rather closer to 12 deg C, owing to the high moisture content of the air. But the sky still does does manage to pull off some heat by radiation, so that the temperature of, say, a roof surface will be suppressed by perhaps 2 degrees. With the outside night air in the hot season remaining at a sweaty 30 degrees, the roof temp might fall to say 28 degrees. In the case of a roof with no insulation, say a metal roof or cement tile roof, this cooling would carry through to the underside of the roof--where it might be a big help to sleepers below, happy to be able to radiate from their hot 35 degree brows to a 28 deg surface above, maybe pick up some convective air cooling as well.

Result: the Thai family that avoids the upper floor during the day, but sleeps there at night, would do best without any roof insulation!

So what does this family do in the day?

Everyone knows that they spend their time under the house. Because it's cooler there.

How much cooler?

Here are the measurements above for three hottish days in early march 2007. And we can see that Jack and Dah's house is about 4 degrees cooler downstairs during the day.

Note that the upstairs remains a little warmer throughout the night as well. The moderate insulation of the roof (R=4) doesn not encourage the sky radiant temperature suppression we discussed above.

Worst night yet

Yes, last night was serious challenge.

After several days of cooler disturbed weather that seemed to bring the hot season to a close, the heat came back yesterday, with daytime temps around 38, temperature in Jack and Dah's bedroom (where I am temporarily staying to hide from my girlfriend) still at 33 in the evening, slowly declining over the night to 30. Since the maximum sweat free sleeping temperature under the best of conditions (good overhead fan and nude sleeping) is 29 as shown above, it was a sweaty night without aircon, only barely comfortable even at dawn. Looks like more punishment may be on the way, with the solar intensity not peaking for another 11 days.

The dawn air temperature in Bangkok according to Weather Underground was 29 degrees this morning, a high for this year. Dew point was only a little less, 26 degrees. Even though the (apparent, measured by radiation thermometer) dawn sky temperature was 12.5 degrees allowing for a slight suppression of the surface roof temperature to about 26.5 degrees, a couple of degrees below air temperature. Little of this carried through to the underside of the roof. The wee hours of the morning are a time when a roof minimum R-value would actually be a benefit, allowing more of the radiative heat loss to carry through to the rooms beneath. As it is, the room temperature even in this light house stubbornly remains about 2 degrees above the air temperature throughout the night. This is a two degrees that could make a difference in comfort.

A two-hundred foot tree

After lving in the house and accruing a few days of hobo measurements I had a pretty good record of how the house behaved during a typical day in the hot season, April 3-5 in this instance. April 3 turns out to be the second hottest day of the year so far, with temperature on the house deck and bedroom peaking in the afternoon at close to the Don Muang maximum of 37 degrees. Note the circled part of the record, where the bedroom temperature seems to have a little "kick" starting at about 3 or 4 pm. This is caused by the sun striking the dark wood wall panels in the late afternoon, when the sun angle is low enough to slip beneath he roof overhang.

From this and other data we derive the following basic principle: Shade from the fahlang's ancient enemy, the sun, is the first defence against heat in Bangkok.

Though Jack might have done better, in theory, by orienting the house so the long axis was east-west, thereby reducing the exposure to the direct sun, especially in the afternoon (hottest time of day is about 3 pm), other siting conditions governed (as they usually do) so that the roof and wall of the house, the bedroom wall, were exposed to late afternoon sun. Fortunately the light construction of the house does not allow for much storage of heat, so that the roof and wall would cool soon after sunset (not like concrete walls and roofs, which stay warm well into the evening). Note however that the bedroom temperature persists at about 2 degrees higher than the outside air. This may seem like a small amount but it is important when we consider that the threshold of sweaty discomfortfor a well-fanned sleeper is around 28 to 30 degrees.

But Jack and Dah have enjoyed a stroke of luck.

A tall apartment building stood to the west of the house, so that during the hottest part of the year, mid-April to September, the building throws a shadow that arrived at just abouot 4:30 pm! (Yep, when you are site planning you can check all this out yourself on Google)

Two hundred foot tree

An escape from romance

"The mosquitoes are eating us up, my pillow is soaked with sweat, and Dah, last night she was up and down all night, this morning she is in a terrible mood. I see by your blog that it's just going to get worse for the next month, I can't stand it, I'm taking her to Singapore for a couple of days." Jack called me and suggested I might like to stay at his place for a bit, maybe come up with some practical solutions. "Practical" is the word he used, meaning that my research on tropical comfort was somehow lacking in that regard.

"I'm thinking of changing the blog to "Tropical Comfort Hacks", what do you think?"

"I don't care what you call your blog, Ron, just try to help me out on this, would you please?"

My girlfriend had started to talk about a "salary" which was a new and unwelcome idea to me, so maybe it might be a good idea to take a little vacation from our relationship.

Jack and Dah's place wasn't bad, in an old fashioned sort of way. Dah fixed up the guest bedroom pretty nice and Jack slipped me 5000 baht on his way out. I was a little tired. I walked around the corner to a little shop and bought two bottles of Singh, a plastic bag of what looked like little sugar-coated donuts, and two plastic bags of ice, then I went back to the house and sat in the room and smoked a nice cigar that I had found on Sukhumvit, 400 baht for a box of ten, and settled in for some pleasant reading. It was still a little warm inside the room at 8 o'clock, 31 degrees and the ceiling about 33. Outside the world was 28 and the sky about 11. I couldn't figure why the roof wasn't losing more heat to the sky but I was too lazy to climb up on something to check the roof temperature. I fell asleep reading about the origins of the Stefan Boltzmann radiation constant, it was another one of those scientific ties, like Newton and that german guy with the calculus.

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The next morning I woke up early and made some coffee in this cool little french coffee machine that they had and then offloaded data from the two Hobos that I had given Jack, one to put in the bedroom and the other out on the deck. During the night it had been on the warm side under the mosquito net and I was sweating even with no clothes. But it cooled down and by the next morning it seemed just about right, you didn't wish you had aircon at all.

First thing I wanted was to compare the temp at the house with the Wundergound temps at Don Muang and Asoke. After and hour or so I had the little comparative graph you see here. This confirmed my sense that you couldn't say what the "real" temperature was at Bangkok, it wasn't something you could find like that gold meter bar with two little scratches on it that the french said they had in a museum in Paris. They said that it was the "real" meter. I remembered reading that in a book in a course called "scientific french", that's how old I was getting to be these days to remember ancient history like that.

So temperature in Thailand is a little like morality nowadays. It depends on your local situation. After all, the sun can't heat the air, you can't do anything to air with radiation (almost true, anyway) you had to heat it by convective transfer from local things. Don Muang was pretty hot maybe because of all those asphalt taxiways soaking up the sun. Jack's deck was better, it was partly shaded by a nice big mango tree, though the other part was shaded by the roof overhang, which most likely a warm underside. Asoke I couldn't figure, maybe it was on the cool side of a building. Who knows, it might give readings that were tow high in one season, two low in another. My bedroom wasn't too bad, it lagged the deck by a couple of hours, but at night as I had discovered it stayed two or three degrees warmer than most earthly things in the neighborhood outside. So here was a good problem: could I figure a way to drop the bedroom temp a little. so it was more like the outside? Or maybe was I myself helping to raise the bedroom temp, the observer interfering with the observed?

When will the heat break?

The chart below shows the 2007 season data, increasing heat and dew point, through March. It conforms to our recent experience of increasing discomfort as the hot season approaches. It follows the pattern you can see in the background of the major El Nino year of 1983. (However the 2007 data are from a new weather station downtown Bangkok, at Asoke, while the 1983 data (white points) are for Don Muang which for various reasons is consistently warmer than downtown.) The intensity of solar radiation for cleart weather is shown as a yellow line, you can see that the heat pattern so far follows solar intensity.

It is evident that we are on the same track as in the past, and that we can expect a "break" in the heat during the next month or two. The Thai say that Songran is the hottest day of the year and there appears to be good reason for this. If Bangkok were located at latitude 8 instead of latitude 15, April 15, Songran, would also be the longest day, the day of no noon shadow as well. Latitude 8 conforms to the location of southern Thailand, perhaps the early calendars were devised there.

Other years, not major El Nino years, show a break in heat earlier than 1983, which is extreme. Since 2007 is not a major El Nino year, we may expect an earlier break as in the the years 1984 and 1985, shown below.

A hat for her apartment

After a few weeks in Bangkok I met a nice lady. I told her I'd like to cook a meal and she invited me to her apartment. I stopped at Villa supermarket and bought too much capelloni and fifteem tasty looking Australian scallops for 150 baht and some buttterhead lettuce and a bottle of Shiraz, a little expensive but not too bad at 550 baht. Excellent bread, too.

I arrived at the lady's apartment at about seven o'clock and it was like an oven. The place was on the top floor and there was a 4 inch concrete slab between her and the sun, the slab was still glowering away in the night, about 40 degrees sti;; even after sundown. "This will never do," I said.

The next week I made a model of the daily heat budget of the roof and room, you can see a two day run in the illustration. The top of the roof gets up to about 60 degrees but the underside gets pretty warm too, a little later in the afternoon.

I figured a nice black net would prevent that big heat buildup during the day.

My lady friend had a contractor who owed her a favor and I showed him how to build a tent on top of the roof, using that net-like stuff that they put over plant nurseries and fish markets. I got the idea from watching fisherfolk on the Mekong River near Vientiane.

I took temperature measurements later, of course. The bedroom was much more comfortable with the net.

Here I am standing on the roof next to the net.

Funny thing is, turned the contractor owed here a favor but not that big a favor, so I loaned here the money to make up the diffrence, a couple of thousand baht. Funny thing is, she hasn't given me the money yet, but I'm very proud of the accomplishment.