Coldest day in bangkok, 2007?

Up this morning at dawn, one of the coldest days of the year here in Bangkok, no fan last night and a quilty cover needed for warmth. How luxurious to be cold! At 5:48 it's two minutes before nautical twilight and the first prayer cries form the mosque half a mile away float scratchily through the dawn air and are picked up by a not unpleasing wave of dog howlings. One of these mornings I must make a catalog of "dawn sounds from Bangkok", add them to this blog. I make a few myself, throwing latches and carefully working my way out on to the deck so I don't stumble on the many levels we've built into this house, then climbing shakily up on a chair to measure the roof temperature.

One of the first steps in engineering a solution to Bangkok's heat problem is to make an inventory of possible heat sinks, cool places to which unwanted heat might be transferred. For example: practitioners of alternative thermal climate control in temperate regions of the world usually think of a presumably cooler underground where the temperature is likely to hover at somewhere near the mean annual temperature in that region. For example, a considerable quantity of 98 degree air can be cooled to a pleasant 75 degrees if a source of 60 degree heat sink is conveniently available. A cubic meter of earth at a depth of three meters , where the ground temperature will be, in say northern Europe, about 15C (60F), will pull the required 22 degrees of summer heat from a houseful of august air. Alas at the latitude of Bangkok, with a mean annual temperature of about 28, relatively cold earth is not found at any depth; in fact, the earth begins to warm to about 30 degrees fifty meters down. (In fact a recent analysis of subsurface temperatures beneath BKK indicate a 1.7 C increase in earth temperatures during the past fifty years in the inner city due apparently to urban heat island effects, over and above global warming effects). Annual variation in subsurface temperature at a depth of 3 meters is only one degree or so.

So we can forget about earth cooling, we've got to find some other cool place.













Here is my measuring instrument, about fifty bucks form Radio Shack.

You can see here that the roof temperature which I took yesterday in a test run is 20 degrees, the sky temperature -2 degrees.






But this morning I measure as follows:


Roof temperature: 16 degrees C
Air temperature: 20 degrees C

But how can this be? This is the same question I used to ask myself about the frost on the pumpkin. How can the frosty pumpkin be colder than the air, which is above freezing temperature?

Here is he answer: when I turn the thermometer upward to the sky the temperature reads -7 degrees.

Sky temperature: -7 deg C!!!

In other words, here at latitude 13 the sky is seven degrees below zero, more or less the same temperature of the air today in Wisconsin where

The bitter frostes, with the sleet and reyn,
Destroyed hath the grene in every yerd;

So the sky is very cold, even here in tropical Bangkok, and this -- in spite of the warmth of the air-- is sucking heat out of the roof to the extent that the temperature is supressed 4 degrees below air temperature. Can I use this to my advantage when the dreaded hot season arrives three months from now?