The hot season broken by moisture

Mid-May dawn: with the coming of rainy and cloudy weather, the back of the hot season seems to be broken, with dawn temperatures below 30 degC (86F) in my downtown neighborhood. At the peak of the hot weather a couple of weeks back they were consistently over 30. 

Notice the 28-30 temps downtown and the 27 or so further out including the Don Muang airport area where our long-term records are. This agrees with my previous study indicating a 2-3 deg "heat island effect" in the Sukhumvit area.

Afternoon Bangkok sun blasts glassy condos

In an earlier post we showed how anyone seeking a "view condo" pays the penalty of terrible heat either in the morning (east facing) or afternoon (west facing). Curtains, blinds, or dark glass don't help much, they just heat up to 50 deg C (130F) and act like ski-cabin radiators. Ugh! Few of us think of this when we buy a condo, we are charmed by views which become minor considerations after we occupy a condo for a few weeks.

Be warned! Air conditioning does not alleviate this radiant heat problem!

Netatmo shows local heat island effect in Bangkok

This is a mix of select data showing you local differences in dawn temperature. On the recent right side you can see several sources superimposed. My condo Netatmo outside temp (brown) is the highest, probably because of all the walls and concrete that surround the sensor. The yellow points from the Planetorium are very similar, suggesting that the Sukhumvit area overall has a generally elevated temperature probably from urban heat island effects, about +3 C degrees heating.

Red points are Don Muang data, for which I have long term data, and green points from Korat, higher elevation and upcountry, generally 2-3 deg lower than Bangkok. The new airport at Souvanaphoum is also a little lower than Don Muang; it's further out of town.

Notice how last year the morning low at Don Muang was over 30 for several days. No such days this year at Don Muang, so last year's peak was a little worse, because the rains came a little later. (Sukhumvit area is this year is over 30, only because of +3 deg heat island effect). I had earlier expected this year to be worse by comparison, but that was before I realized that my Netatmo local readings were boosted by urban heat island warming.

If I want to estimate Don Muang dawn temperature from my Netatmo data I should subtract 3 deg. These corrected values are also plotted here shown as blue points.

So we have just now this week hit the probable high point in discomfort for 2017. To me it was suffocating. I found myself turning on the aircon all the time. My pub mate Al, exactly my age: "I never complained about the heatt here before, but this year it really hit me." We both thank clouds and rain that are now pulling the dawn temperature down into the mid 20s.

But even now today I am turning on aircon on arriving home at the end of the day, after 6 pm.

Glass condos: good way to throw away money and suffer at the same time

So when you buy a west or worse east facing condo with those big glass walls that are fashionable now in Bangkok (Wow! Look at that view!) you don't think of the expense and years of misery you are taking on. But let's start with my glass door to a small veranda exposed this month to morning sun from about 8 to 11 am. Here are the calcs for refrigeration capacity and expense. A sunny morning heats the curtains to about 50 C, which then serve the same function as hot water radiators. To offset this added heat I need a dedicated 26000 BTU split air conditioner unit, it barely provides the needed 10 kw of cooling power (2.6 kw electric power). So maybe you need two such units for this small room?

But you have plenty of money, so problem solved!

No, not at all. When you look at that curtain on waking up, you are looking not at a 25 degree cooled wall, but at a 50C heating panel, and though the room air may be 25 C, you are feeling that blast of radiant heat, as unwelcome on your face and body as it might be welcome in a northern ski lodge.

I will claim that it is not possible to live comfortably in such an environment, being driven from bed every morning because of solar heating via windows, regardless of air conditioning and curtains, blinds, etc which do little to prevent heating in the room, especially radiant heating from interior window coverings (or tinted windows). But anyone who has ever parked a closed car in the sun knows this already! 

A fiery April ascendancy of the sun

A noon without shadows, April 26

Now at the end of April last week the sun reached its noon zenith over the city of Bangkok. The morning 6 am temperature never dropped below 30 C -- possibly a record high in an era of ascending thermal discomfort. The temperature on my bedroom air conditioning thermostat, hardly ever different than the 29 C that drives me to flip the switch on at night, actually now tends to read 30 C, a level I never remember seeing before. My neighbor's walls are slightly cool to the touch, about 27, indicating that they, to my benefit, are using their air conditioning, holding room temperatures to about 25 which is the usual here in Thailand (though the government is trying to get people to raise their set temperatures to 26.)

Creeping heat shown by Netatmo module station 17th floor condo.

6 am temperatures on Sukhumvit,
Bangkok over the past 10 days

Based on a 50-year stay in Thailand and study of long-term records I have concluded that the dawn (6 am) temperature is the best indicator of hot season discomfort for the coming day. This just broke through the 30 degree C level this Sunday morning, a rare event, for the first time this year, portending some major hot weather during the peak of the hot season over the coming three weeks. (Maximum sun exposure will be this coming Friday but the greatest discomfort arrives a couple of weeks later, unless we have a strong and early onset of rains). Over the past few decades there has been a very fast rise in hot season dawn temperature, 2 degrees since the late 1970s, reflecting both urban heat island effect from pavements etc but also probably an ominous long term land warming throughout Thailand. The consequences of a continuing trend at this rate over the next 20 years are almost unthinkable —  the doom temperature is said to be about 35.

Meanwhile those of us living in our Bangkok condos and apartments must cope with this difficulty. Even now for some, this means full air conditioning 24/7, typically two to four split unit compressors whirring away, 12 hours a day, as much as 50,000 baht a month. For many systems this produces an unpleasant clammy coolness because the on-again, off-again operation of the typically oversized condo units set to temperatures of 25 or less accumulates interior humidity reaching as much as 80 percent or more. Not comfortable!

A moderate amount of adaptation by owners and smart use and scheduling of the machinery can cut this power use and cost by as much as three quarters or more. My own bill for a typical month is less than 1500 baht and our condo is just as comfortable as our neighbors' who have the big bills of 15k baht or more.

Given the current rate of increased warming in the city, this is an excellent time to experiment a bit, both to economize and to set better standard practices for the coming generation who are expanding the use of air conditioning. I will follow up later this week with another post setting forth specific steps aimed at improved comfort at much reduced cost — with continuing use of air conditioning when it is really needed.

Netatmo map this morning predicts daily discomfort

We approach (in 7 days) the maximum direct solar heating of the year at latitude 13.75 (BKK) with the prospect of encountering this year the "most sweltering year in Bangkok ever", which case I will argue later. But for now, notice today that the dawn temperature, which I claim is the singlemost important indicator of perceived heat for the day, is about 29-30C( 84F) according to the excellent Netatmo weather map, which includes my own dawn reading of 29C (84F). Today is likely to be "the worst heat" for a long time from the human point of view. Although it has been claimed in the scientific literature that the hot season daily minimum temperature is higher in the big city than in rural areas, this fresh data from this morning suggest otherwise.

If you dread tropical discomfort, look only at the 6 am temperature. More than 29C (84F) and you are not going to be happy unless you can find either aircon or more wisely local spots of radiant cooling at say T=25 (79F) or less.

Only when we go far afield and higher elevation do we get the reduced early am temperature, as at Nakhorn Ratchasima, where I have my farm. The data suggest (to my surprise) that heat island effects may not be as important as often believed.