Good and bad shading in Bangkok fashion area

These two examples of east-facing condos in one of Bangkok's most fashionable districts show different attention to thermal detail that has great impact on interior comfort.

The first building is an older expensive building with an impressive street level facade but little upper floor protection against strong morning sun. As you can see many of the rooms have no provision for shading. Interior curtains will rapidly rise to 40 degrees or more soon after sunrise, subsequently transferring by convection alone 100 watts or more per square meter of window into the interior air. If as it appears the entire wall or most of it is glass, it will take all the cooling an air conditioner can provide to offset morning warming. This makes for highly uncomfortable conditions especially if the room is a bedroom.

People who buy units like this are impressed by views. But in truth once they occupy the place they realize that they actually don't care for the glare and lack of privacy so they leave the curtains closed all or much of the time, leaving the room with no natural light. This irrational consumer behavior is exemplified by the old American advertising saying, "they buy the sizzle, not the steak."

The second building is a more utilitarian modern design with smaller east-facing windows. The building long axis is roughly east-west so the views from the units are north and south, and the sun strikes the living space windows at a sharp angle -- less exposed area and higher reflection coefficients (for glass). Note however that some of the northerly windows have no shading from decks. With the early sun now at this time of year (August) well to the north of the long axis of the building (the building axis is 102 deg east, not 90 deg) significant heating will occur in the early morning hours in those rooms or spaces. Other windows, probably the living areas, are well shaded by being recessed. I will show this in another entry, using my own building as an example backed up by Netatmo weather station data.

The showroom near street level strikes me as a solar oven. Sometimes tinted glass is used to attempt to mitigate this solar heating but it should be remembered that dark glass absorbs solar heat. The glass itself gets hot, and this heat, or a significant amount of it, is convected into the interior.

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.....