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!