Enter humidity

My mother called it "sticky", and it's a subject that we've been avoiding here, hoping that the weather would just stay cool enough. But when the Don Muang temp hits 29.5 as it did the last couple of nights we just can't seem to convect and radiate that heat away, and the dreaded sweat begins to bubble from our pores and we have to get our hard little pillow, however full of mold it may be (according to our faithful correspondent wch). The other day I took a wet washcloth out on the deck in the shade with a nice breeze and let it dry a bit. It was ten inches square and after an hour it had lost 8 grams of moisture, that's about 5 watts of cooling power, equivalent to 80 watts per square meter.

Depends on wind and humidity, you're thinking, so here's a formula to figure it for whatever you like:

Evaporation in tropics, grams
E=(25+19*V)*(30*(1-RH)/3.6/1000)*A*T
E=evaporation, grams
V=wind, m/s
RH=relative humidity
A=area, sm
T=time, sec

And here is a handy little graph of that formula:

Now you might have the same problem that I do here, because when I try to find a rate of 80 watts per square meter on this grpah, I don't. So maybe I'm a lousy experimentalist, or the formula, which is supposed to be for open pan evaporation, doesn't work for wet washcloths. I'll have to look into it. But what you can see in general here is what you know already, that is, when you begin to sweat to the point where half of your boys is soaked, and you're in a good breeze on a hot dryish day, you get a lot of cooling power, enough to take care of the 200 watts or so that you generate when excercising.

Are the Thai really different?

For some years academics have been debating whether thermal comfort varies among different enthnicities, with the balance of opinion seeming to shift in these days of multicultural pride toward discoveries of ethnic difference. A recent study by a Thai professor at the excellent Silpakorn University follows thsi view by concluding, based on a field survey of many Thai people in their own settings, that Thai prefer much warmer and more humid environments than fahlang. Based on my experience giving bedtime thermal comfort questionnaires to my girlfriend (is that why she is mad at me?), I half believe this, and when I read the paper by the professor I knew that I was supposed to believe it without question.

You saw the Olgyay chart in the last posting here, and now you can see the results of the survey here.

Do you believe it?

I've superimposed the zone of favored conditions for Thai people on top of the Olgyay bioclimatic zone diagram shown last post. Do you think the Thai are most comfortable in their ordinary lives and activities at a temperature of 30 and RH of 80 percent? The warmer days and nights of last month (April 2007)? This is certainly enough to make me miserable.

I wonder. I have some methodological issues with the research, but I'm going to give you the link to the paper below so you can make up your own mind. We'll talk more about his later, meanwhile I look forward to your views.

http://www.unige.ch/cuepe/html/plea2006/Vol2/PLEA2006_PAPER842.pdf

Hungarian attack on US hegemony

The reader has been introduced to the famous Carrier psychrometric chart which will be easly recognized as an attempt to confuse and perplex ordinary people with the goal of herding them like sheep into the corrals of air conditioning salesmen. Air conditioning engineers, whomever they may be, love this Carrier chart with its arcane title, its Cal Tech terminology ("enthalpy", etc). Internationals hate it because it is just one more attempt to foist American hegemony on the world. Architects despair at knowing which is up and which is down and which is sideways on the chart, the French hate it because it spelled the death of Scientific French as surely as McDonalds has proven to be Vichy regime of French cuisine, and Freudians consider "psychrometric" an invasion of their stranglehold on epistemology.

Along comes this Hungarian, Victor Olgyay, and saves us by making another kind of thermal comfort chart, as shown above. Notice that it is written in Spanish, so it will not be understand by Americans. I've plotted a couple months of Bangkok weather on it, so you can see how justified you are in just turning on the fan and relaxing, because you are at the limite de trabajo while still safe from a golpe de color.

Banish unsightly necksweat!

One of the thermal challenges in hot-season Bangkok is sleeping comfortably without air conditioning between bedtime and about 2 am, when things finally begin to cool off. With temperatures remaining in the low 30s, the body cannot pass off its 100 watts of heat to the environment by convection, especially if one is sleeping on a fahlang-style mattress and using a fahlang-style pillow. So sweat begins, and soon enough you are lying on a disgusting wet pillow that is hard to dry. Your head, with its ample blood supply, becomes especially sweaty.

It never would have occurred to me, even after watching the natives, but a guy on Soi Cowboy told me that fahlangs are overly attached to their sleeping apparatus, fluffy pillows and soft mattresses, but the fact was that in a few nights they could get used to the local way, hard pillows and sleeping on concrete was no serious inconveneince once you got used to it.

So I replaced the fahlang pillow for a few nights with this smaller hard thing. He was right, I was more comfortable the first night, with air circulating nicely around my neck. Assuming that I am evaporating half a can of Singh every hour, 90 grams at 2500 joules per gram heat of vaporization, I'm picking up 60 watts of cooling. Good for my blood pressure, too!

Next challenge: go all the way, sleep on a wooden pallet which is the Thai tradition.