Condo facing: key to sustainable tropical cooling?

Studies today indicate big impact of building azimuth on aircon costs. Short book useful to guide tropical condo buyers?

Morning heat in new condo

East-facing new Bangkok condos, 9 am October 1, 2015. Direct sun at an altitude of 40 degrees delivering about 400 watts per square meter net to interiors, or about 3 kw to room interior, say 10 kw-hrs cooling every non-cloudy morning. Curtains are deceptive from a thermal point of view: they keep out the light, but not the heat.

This is equivalent to four floor radiant room heaters blazing away in the room. Cooling power requirement for air conditioners to offset this solar gain will be about 3 kw-hrs electric, or 15 baht ($0.50) daily and the room interior comfort will be further diminished by radiant warm curtains and a need to keep windows shut without benefit of mildly refreshing morning air. ("I feel suffocate", my Thai wife says.)

But what is the fashion in condos these days? Glass, glass, more glass.....!

I talked to the salesman in this place. "Thai people do not like the west facing, too hot in the afternoon," he said. But what about the morning? Do you want a hot bedroom at 8 am?

Inside and outside temps in a Bangkok condo: a family history

This chart represents an elementary study of urban tropical temperatures in the rainy season using Netatmo data. It compares the daily cycle of temperatures inside and outside a condo bedroom, in the city of Bangkok. The condo is empty for the first three days of the study and occupied in the last two days.

One would expect the inside temperature to be damped and lagged version of the outside temperature during the first three days with no occupancy. However this is not exactly the case. The inside morning temperature rises quite quickly, parallel with the outside temperature rather than being delayed as one might expect. After a couple of hours it stops tracking the outside temperature and then seems uninfluenced thereafter by outside temperature. What is happening here is that the morning sun enters the condo through the large sliding glass doors, heating the curtains. As soon as the window is shaded later in the morning this heat source disappears and the outside air temperature influence is not strong enough to cause it rise further. We see that direct sun through windows is the enemy of comfort, not outside air temps. Curtains keep out the light do little to help with heat gain when the room has large sliding glass doors.

Another surprising thing about the first three days is the average temperature of the condo seems to be steadily below the outside temperature average. How can this be if there is no apparent cooling source inside the condo when it is unoccupied? the answer is that the interior of the condo likely borrows cooling transmitted through the walls from the adjoining unit. In fact the radiant temperatures of those walls are typically about 2° below the floor and ceiling temps; the adjoining neighbor likes to use air-conditioning during the day.

On the second day a welcome thunderstorm breaks the heat mid-afternoon.

Returning to the condo Saturday mid day after a long drive from our farm, we take a bit of a midafternoon nap. With the bedroom temp at 30 (86 F), we turn on the aircon with a set temp of 24 (75 F). Later I am early to bed without aircon, but my Thai wife, oddly less tolerant of heat than I am, turns on the aircon sneakily a little after midnight (T=29) when she retires. I turn it off again in the predawn while up doing my old man things. Thus the story of all marriages of long term?

Lessons learned:

1. Interior curtains block light but not heat. Small windows better?

2. Nothing wrong with benefitting a bit from your neighbor's aircon!

Major breakthrough indoor thermal studies

This remarkable and inexpensive instrument fills the difficult data gaps in room air exchange and metabolic heat contributions (via precision CO2 tracking). A major breakthrough indoor thermal studies. I plan to use it to study issues in building air leakage in the tropics, which effects I have long believed to be widely exaggerated in connection with cooling needs for tropical climates.

Rain: I feel so good

Tonight my wife Nim tells me about her memory of rain as the thunder crackles sharply outside our condo in west Bangkok, Sukhumvit. Tonight we can forget the air conditioning. We don't pay much, but today I paid the electric bill, 3600 baht, $100, for last month. Normally half or less in the cool season. Our use of air con is sparse, nights only.

"I always think how good I feel when it rain."

"Why?"

"Because privacy. In my life, my home town, even outside one hundred people talking all the time, in the rain they go home and I can go to my room alone and not worry about anyone. I feel wonderful."

My wife is now fifty years old. Lately she praises anonymity, How she loves living in Bangkok because "I don' have to go anyone funeral".

What is it about tropical thunderstorms that spurs remembrance of things past?

Here in Thailand, we await the rains.....

That angry rising sun

Absent rain, the hot season deepens, even dangerously. Here I am driven to indulge in what was once a serious sin in English prose composition, the pathetic fallacy, attributing human feelings to the sun itself. Why should the sun be angry? Because we have messed up its little sister, the earth?

Anyway there are some serious points to be made here.

First, note that the sun is rising not directly to the east, but slightly -- five degrees -- to the north of east. This means that the twin condo tower on the right is not going to protect my bedroom from ascending sun over the next few hours, the way I imagined it might back ten years ago when I bought this place. It will become hot to the point where I will either get up and head out for coffee, or hit the aircon button and flop back into bed. A dollar or two of electricity for the latter course.