Fans and turbines for a hot afternoon

Now children, if you are going to learn science, sometimes you just have to do some things that might seem a little boring, we can't be making gunpowder and coating your coins with mercury and dripping acid on your friends homework every day!

So today we practically fell asleep looking up the capacities of wind turbines and fans on the web. It wasn't easy, and then we converted them all into the same units! Then we climbed all the way up to the Asoke BTS and took this picture of all those turbines whizzing away in the stiff afternoon breeze! Then we went to get a beer in the pub!

Here they are, diameter in inches and manufacturers rated capacity (cubic meter per second) for various wind velocities.

Performance Data
	diam inch	wind vel, km/hr	cm/sec
axial fan	9		0.15
axial fan	16		0.90
axial fan	14		0.63
turbine	32	6	0.58
turbine	18	6	0.23
turbine	12	8	0.16
turbine	32	16	1.29
turbine	6	6	0.05
turbine	18	16	0.47
turbine	24	10	0.94
turbine	20	6.4	0.80
turbine	20	15	1.25
turbine	6	16	0.13

Now here is your homework:

What would you rather have if the wind velocity is 1 meter per second: a one square meter open window on each side of the room (assuming it has two sides) or eight 12 inch turbines as shown?

Big open windows

We talked last time about the need for major ventilation. If we hope to cool spaces under roofs that a lightly insulated with "passive" openings, say windows or grill vents we will need very large openings to keep the temperature rise less than about one degree C. when the roof gets hot. Here you can see an example, a high roof vent that provides about a square meter of open ventitlation at the peak of both ends of a traditional Thai house.The house is oriented N-S, so it presumably does well at catching the southerly breezes characteristic to the hot season.

In addition in this view you can see that the open windows with curtain billowing into the bedroom provides cross ventilation in the other direction as well.

The result in this case is a room that does not become much hotter than the outside air (maybe a degree or two at most) even though the roof, which is only lightly insulated, gets up to about 70 degrees on the outside in mid afternoon, late march.

In this case, there is no dropped ceiling or loft/attic space. but the same principle jolds if you have such space in your house and don't want a 40-degree dropped ceiling over your head when you nap, or (if your roof is concete and retains the heat) when you sleep at night. If you are goinng to cool space by ventilateing poorly insulated areas, you've got to have strong ventilation through big openings.

You probably don't vent enough

We come now to a problem that is in my experience the most misunderstood thermal building issue in the tropics, the source of more than half of the discomfort in non-air conditioned buildings, that being the lack of understanding of cooling ventilation. By cooling ventilation I mean ventilation that aims to reduce the temperature of the air of building materials within the building or within any space (such a an attic) that is subject to heating from an overlying roof.

When I was a kid growing up in Boston, Massachusetts during the "dog days of August" when the heat and humidity would sometimes reach the levels of Bangkok in March, my mother would leave the shades dawn and windows closed in the morning, then in the late afternoon when the inside of the house would get too warm, she would open everything and then in the evening turn on a big attic fan, that would roar away all night supposedly pulling cool outside air through the house.* The afternoon-evening ventilation was meant to cool the house -- which was probably 30-35 degrees, with outside air that by late afternoon might be cooler than the interior temperature.

Now times have changed and in the US people are trying to build airtight houses with central air conditioning which is considered a sort of basic right similar to the right to own a big gas guzzling SUV, with much the same wasteful effect, in my humble opinion. As a result the defintion of ventilation has undergone a drastic change, it now being something like "providing just enough replacement air to prevent the house from stinking of cabbage or cigarette smoke or poisonous off-gassing of all the crappy modern furniture and devices people put in their houses these days." This means only a tiny amount of air, not enough to cool anything. Anything more than this minimum to prevent you from getting nauseous is considered wasting energy and bringing in outside pollution (presumably from the SUVs).

Yes, the modern world and it's lobbyists have really created some big unsolvable problems that they then propose to tackle with even more ridiculous ideas like wind farms. Fortunately Thailand has not yet copied these bad ideas and is still pursuing old-fashioned bad ideas by burning cubic miles of coal (with associated planetary detriment) in order to cool leaky concrete structures.

But let's say you want to go back to the real old days, like my brother Jack and his partner Dah, and live in country-style house with low thermal mass (e.g. wood) and a lotta ventilation, enough to keep the house from getting too hot. Then you 've got the same problem, providing enough ventilation to exhaust any heat buildup either in the house or in the "attic" espcially in the mid-late afternoon when you want to realx with a big bottle of Singh beer and a ciager. The real problem where almost everyone goes wrong is getting sufficient ventilation, which is a lot of ventilation, not the amount of ventilation you'd find recommended in any fahlang websites or literature, since this is all aimed at the new paradigm of sealed houses.

We touched on this topic earlier when we noted the oven effect that you usually find with a dropped ceiling, as shown on the sketch and previously discussed:

Now what a lot of people do is put in some kind of a dropped ceiling, which of course intercepts the radiant heat from the underside of the roof. But even though you can turn off the radiant heat, but the convective transfer will soon enough heat up the air in the "attic", maybe all the way up to the high 40s. Then the gypsum ceiling will heat up, then....you are right back where you started, a hot gypsum ceiling instead of a roof. Sure, there is a little time factor here, each square meter of hot roof has to heat up a couple of cubic meters of air and a little bit of gypsum, but that may be as little as a few minutes, since the hot roof with an R value of less than 1 will deliver about 100 watts per square meter of heat.

But how much in the way of openings for ventilation is enough?

To find the answer in a proper engineering way you've got to know the R value for the roof, from which you can determine how much heat is going to flow through the roof into the space below. Given the rate of air heating, you then need to reckon the air replacement rate necessary to prevent the temperature from rising more than a nominal amount, say 1 degree C. Then you've got to figure the sizes of openings (we'll save fans and turbines until next time) necessary to deliver this amount of air to the space under normal conditions -- let's say a breeze of 1 meter per second, typical for hot weather in Bangkok.

Now I have done this for you generically (and will post the derivation here some time for your criticism) but am going to summarize my results below to save you the pain (while meanwhile adding to your suffering when you realize that your vent area probably doesn't meet the standard).

Standard for wall openings to prevent interior heating significantly above outside air temperature**

1. No roof insulation, eg metal or thin tile roofs only: Not recommended because underside of roof will get very hot and radiate onto your head, and wall openings will have to be 20 percent or more of the wall area. Better just lie under a grass rood with no walls.

2. "The usual" roof insulation -- a layer or two of air, maybe a sheet of aluminum, plus a wood or gypsum dropped ceiling. R value on the order of 5: vent must be 10 percent of wall area. For example for a 4 m high by 5 m long bedroom wall, you will need 2 square meters of open windows on opposing walls (ie full cross ventilation) to maintain temp at 1 degree above outside air temperature.

3. Good roof insulation, eg at least 3 inches of fiberglass or equivalent foam material, R value of 15: Same as 2 above, except area can be reduced to 2 percent of wall area, eg a grill with about 0.5 square meter opening area.

------------------------------------

* In retrospect I remember the fan as being about 15 inches diameter, which would move about one-half cubic meter a second -- not enough to cool several rooms very quickly. But the R value of the roof was probably pretty good, there was about 6 inches of fluffy stuff -probably asbestos, now that I think of it, over the ceiling.

** Don't ever forget, you're not going to "cool by ventilation" anything to below outside air temperature, which may be pretty unbearable on April afternoons. (Then it's time to go under the house...you do have an underhouse, don't you?) True, as we shall see, you can cool surfaces like nightime roof surfaces, to below air temperature, more on this disappointing topic later.

Bangkok 's lovely breezes

Preparing now to take on the grim subject that in my experience leads to the greatest thermal suffering and disappointment, namely the lack of ventilation/insulation of enclosed subroof spaces (ie "attic" spaces), we need to tarry a bit blathering on some about the happy existence of tropical breezes here in Thailand.

First, some data:

Bangkok is fortunate in this regard, enjoying a hot season breeze that typically ranges from 1 to 2 meters per second (4 to 8 km/hr), as you can see from both the annual history for 2005-2006 at Don Muang, and also from the history of the last few days. (Both of these graphs are readily available from Weather Underground)

I include the temperature history on both graphs because it is quite lovely if you are a scientifically oriented person to sit and look at the season pass in this little data-world, the moment of pneumatic confusion followed by the decisive reassertion of the wind from south to north at the end of the rainy season, etcetera. Christians will rejoice at the miraculous plunge of the dew point to create, as best as Thailand can do, a starry windless Christmas eve, others will doubtless enjoy finding their own divine interventions, Tuesday's predawn tussle between Boreas and Notus, and so on.

But let's stop fooling around here, what we want is comfort, and we rejoice that Bangkok fairly consistently delivers a breeze of about 8 km/hr, which is about 2 meters per second, which you can compare with the general standards used as follows:

0.5 m/s: pleasant breeze. Lowers apparent temperature by about 3 degrees C (mainly by improving convective transfer from body to air)

1.0 m/s: desirable indoor upper limit in USA, according to various authorities in that country. Enough to feel on face, move hair and papers slightly.

2.0 m/s: further cooling effect, but felt as unpleasant or gusty by fussy people. Recommended as permissive upper limit for indoor by tropophiles.

It would appear, then, that if a substantial portion of wind can be brought into the indoors, our thermal felicity will be well served. So our general aim here is to put this windy energy to work in improving our indoor environment, which we propose to do in the next chapter.

Why so hot at Don Muang?

For years climate control specialists have relied on weather data from the Don Muang airport about 20 minutes drive north of downtown. But now new weather stations have been established in various parts of the city, and indicate significantly cooler temperatures and dew points downtown as indicated on the graph for this summer. My local readings in the Sukhumvit area closely match the red data, not the Don Muang data.

Blue, Don Muang. Red, downtown

As I will try to prove elsewhere, "dew point" is probably a better measure of comfort that temperature. You can see that by that measure Don Muang should be significantly less comfortable than the Sukhumvit area.

How can this be? At this point I offer no more than speculation. Maybe more heat-absorbing concrete, hence higher enthalpy. Maybe the sensor at Don Muang is defective.

Strange too, that Bangkok is said to be an urban "heat island", with temperatures about 5 degrees C higher than the adjoining countryside.

One of these days I am just going to have to take one of my "Hobo" recorders on a taxi ride to the airport and leave its brother at my brother's house downtown.

Anyone have any theories?

Adventure tour the world's most uncomfortable cities!

Why go along with the crowd in a vain, un-Buddhist quest to find luxury and comfort? Wouldn't you like to spend a month touring unforgettable places like the diamond mines from Blood Diamond, evenings visiting local villages with the boy soldiers? Or spend an idyllic week at the site of the Reverend Jim Jones massacre? Or join a session of aerobics followed by a fun run through the stalls at Jatujak market, Sunday at 3 pm in mid April?

To aid you in planning your trip I have brought you yesterday's global dew point map from weather underground (showing a possible itinerary), along with the latest surface sea temperature record from satellites. Note that these valuable maps will not, like inferior imitations, just show you places with sauna-like heat -- those are a dime a dozen -- but allow you to select locales where you can be assured that you will be immediately soaked in healthy sweat even before you finish dealing with the scowling customs agent with the automatic weapon.

(Whoops, what's that missing square in he middle of Africa? Maybe the boy soldiers just paid a visit to the weather station!)

And remember, you can find a few places in the world (at least this week) where the comfort level is even less than Bangkok!

Any suggestions from Ian out there for special events?

Happy travels!

Foiled by the foil

Now I'm not supposed to show you this, but my brother Jack is building this house, he's very proud of it, but he's made a couple of mistakes and this is one of them. It's a common enough mistake in Thailand, you might say that the Thai building industry is commited to making it, because you see it everywhere. Aware of all the problems we've been discussing here in regard to tin, tile, and concrete roofs, the futility of dropped ceilings as insulators, and so on, they have turned to the use of insulation, which is all to the good. Unortunately they've all been conned into one of the great snake-oil building techniques of the 20the century, aluminum foil insulation.

The type of roof my brother Jack had in mind was cement tile underlain with teak planking ceiling, with a little space in between. Anyone who has observed Thai construction practices knows that the usual heat protection with this arrangement is the addition of a sheet of reflective foil insulation between the two materials (the space is about two inches.) The purveyors of the foil will tell you, while catching their breathe in the course of praising their product, that you only have to leave a little space between the foil and the next layer in the sandwich, then you will be rewarded with a reduction in heat of more than 50%, etc etc

Jack succumbed aboriginally to the magical promises of aluminum, and decided to use foil insulation.

This was a mistake.

We see above the guys putting on the roof panels, over the foil which (shiny side down) is in turn over the teak panels. And you can see from the picture that there is not going to be much space, maybe very little space at all, between the bottom of the foil and the teak ceiling. And very thin or irregular spaces are not very effective at interrupting the flow of heat from the roof tile, which as we've seen may reach 60 degrees on a sunny day.

So Jack thought to himself (after I toldf him about the importnace of the space) , should I start shouting at those guys not to walk on that foil when they are putting on those roof panels? What do you think? Jack thought not.

Let's see what theory tells us about the effectiveness of foil like this, whether applied correctly or not.

The first little sketch below shows the R value for the roof "sandwich" without any foil at all. We assume the roof temp is 50 C, the room temp is 36 C in each case. The foil-less sandwich delivers an R value of 2.7 altogether, and the estimated temp of the underside of the teak roof is 40 C--much too warm. Moreover, the heat transfer into the room is 28 watts per square meter, or in excess of 500 watts for a room. Not as bad as a simple tin roof, but not what we'd like.

Now suppose wwe add foil. First, we do it badly, the way Jack did it, so the foil is mostly resting its shiny side on the top of the teak. No surprise here, the foil is not very effective, as shown on the third of the little sketches.

Now suppose we do it right, we leave a space of an inch or more beneath the foil. That's the middle sketch. This time the R value is 3.85, a littlle improvment over the no-foil case(R=2.8), bringing down the underside of the roof to 38.5 C. The heat flow drops from 28 watts to about 20 watts -- hardly the "more than 50 percent" claimed by the aluminum salesmen.

What you get from the theory is that the correct spacing would improve things a little, but not much.

One other conclusion here: whether we use foil or not, the fact that we've got a roof "sandwich" has reduced our heat flow from more than 100 watts per square meter (the hot tin or tile roof) by about 75 percent. This eases our ventilation problem a bit, we don't need a howling wind blowing through the room to blow away the heat seepage like we did with the tin roof. As to how much ventilation, we'll develop some guidelines in a future posting.

Conclusion: foil may have it's uses (more on that later) but the way it's used in Thailand does not do very much to improve either ceiling temperatures or heat flow through a roof.

But let's ask this: what constitutes "improvement" anyway?

The simple answer is: "a cooler room below". But what is cool? The answer is "not just air temperature", but also a cooler underside to the roof, because the heat you feel in a room is about fifty percent air temperature and fifty percent radiant temperature, ie the temperature of surrounding surfaces. And as long as you leave the windows open so the place doesn't heat up like an oven, the air temperature will not rise much. But if the ceiling is say 37 or 40 degrees, you are going to wish you were back in misty England or foggy San Francisco, that ceiling will deliver maybe 35 unwanted watts per square meter to your suffering fahlang head.

So how did Jack's roof turn out?

Pretty much as predicted by theory. With outside temps about 32, the interior surfaces got up to a somewhat uncomfortable high 30s, but as long as the windows were open and the breeze was good, the place was bearable, even in the afternoon, or at least not much worse than a shady spot outside where you would have to live with a slightly sweat-inducing 32 C.




Warm but bearable all around. The temperatures shown around the room are temperatures of the wood interior surfaces, which radiate heat
to all objects of lower temperature within the room. Such as Jacks's 34 degree bald head.This accounts for about half of the perceived heat, the rest being related to air temperature, which with good ventilation would reach 32-33 C, as you can see from the floor and shady wall temps.

But here is the big question: what would have been better than foil?

Carrier's Magic Chart

Air Conditioning engineers trace the decline of US-French relations to the popularity of the chart which was invented by the American patron saint of aircon, Willis H. Carrier. Carrier's so-called psychrometric chart replaced the beloved French Mollier diagram, marking the end of French superiority in science. Sigmund Freud was fascinated by the chart, which he mistakenly thought quantified the human psyche (misreading psychrometrics as psychometrics). However, after discovering his mistake he thought it soounded like a good idea anyway, and went on to develop his concepts wherein he substituted libidinous pressures (The "Id") for vapor pressures.

For those readers who are seeking a little more rigorous discussion of Bangkok weather, I am taking a break from roofs and such to put the recent weather, which we see here as red and green points, in the context of the Carrier chart (basics of which you can look up in Wikipedia if you are really curious).

What I do here is trace the natural history of a cubic meter of Bangkok air which you might find around, say, Benjasiri Park at 6 am when folks are out there doing Tai-Chi and aerobics. The moisture, temperature, dew point, and enthalpy of the air at 6 am is shown as the starting point of the day's oddyssey. The wet bulb temp, ie the temperature of all those dewy flowers across the street at Villa supermarket, is about 24 C, and the enthalpy (ie energy) is a little over 70 KJ per cubic meter. With a relative humidity of about 80 percent, those joggers are going to start to sweat pretty quickly.

It always struck me as curious that the Bangkok air does not change its energy content much over the day, by afternoon it's a lot hotter but a little drier so energy is much the same. But look what happens to that air if it is lucky enough to get sucked up in the Emporium air con engines which blast off at about 10 am. This air will be cooled down to its saturation point (ie the dew point) and then with further cooling dump about half of it's moisture, so that the nice icy feeling you get when you go into the mall is your own dear sweat getting sucked up by this dry hungry air. It's not the air that's so cold, it's your own vaporizing sweat!

We can look ahead with delicious dread at the daily cycle at the peak of the hot season in early May, shown in red away up on the diagram. For all those Buddhists out there, lots more suffering to come!

The colored zones on the chart are so-called comfort zones, green where everyone is happy, yellow where some fahlng experts say folks in "undeveloped" tropical countries should be happy (so they don't use so much of that fuel meant to fire up big SUVs). Everyone is unhappy in the red zone.

Nice going, Emporium, I think we'll all go shopping!

Solar-heated concrete roofs

Now we noted and you might recall that those big churches in Spain or Mexico are pretty cool inside and imagine that thick masonry walls or roof would do the trick of keeping you cool in your house. So let's exchange the thin hot roof (metal or cement tile) which we discussed last time for a nice typical 4 inch concrete roof slab. What happens?

Not only does the 4 inch concrete not slow the heat penetration down much (R= about 0.5 which is still a long way from the 10 or so we would like*) but the heavy concrete stores much of the afternoon heat about (10 kilowatt hours for a 25 square meter room), then releases it back into your room in the evening until 9 or 10 o'clock. This is not the time when you want a lot of heat!




And if you deal with this by turning on an overhead fan, you just accelerate the rate of heat transfer from the warm underside of the roof to the lower part of the room--and yourself. Sure, you can turn on an air conditioner, but what kind of "green" living is that? First you go and use solar heating to store unwanted heat in your concrete roof, now you use fossil fuel to suck it into the room, pump it back out in the form of vaporized refrigerant gas, then blow it on your neighbors, just like that hi-so Italian restaurant does on Soi 23, blowing hot air from its battleship array of compressors on lowly pedestrians.

Increase global warming! What a waste!

But wait. Why do thick walls work for those cool churches?

First, the walls are truly massive, maybe several of feet thick, so the heat takes a long time to penetrate (just as the ground deeper than a few feet is not heated much by the day's sun). Second, the dry desert regions have night sky radiant temperatures that are very low, maybe even below freezing, and whatever heat collects in the masonry bleeds back out to the outside sky at night, not into the church. Solar heating is offset by effective nocturnal cooling. But in the humid tropics the night sky temperature drops to only only 15-20 degrees. So there may be a little bit of night cooling (maybe 50 watts per square meter), but not enough to offset the effect of strong daytime heating (which is closer to 500 watts per square meter).

So if you are unforunate enough to be living in the top floor of a house or an apartment I have a two ideas that I think are better than blowing your budget on ai rconditoners that (like most in Bangkok) mainly cool solar-heated concrete.

First, you can create what I call an "artificial tree," which is almost as good as a real shade tree over the roof ( which would be the best of all solutions to the problem). I first noticed this technique at fish markets on the Mekong River in Laos, where the market folk created shade nets made from the plastic netting sold for use to cover plant nurseries. The netting, usually either green or black-- both seem work as well-- is suspended like a Berber tent a meter ot two above the roof, absorbs most of the solar heat and allows it to dissipate away into the air, so that the netting material itself (amazingly) doesn't get very warm. Two layers work better than one, but you don't want to use an unperforated fabric or plastic or canvas cover, because this will immediately heat up to 50 C or more and radiate this too the roof, just as bad as the dreaded tin roof we discussed yesterday. This all requires some effort because suspending a net big enough to cover several rooms requires some support structure. I did it at both his top floor apartment and a top floor office, each 150 square meters area, at a cost of about 6000 baht each for installation. The comfort level was immediately improved, and much cooling money saved (though some air conditioning was still necessary to reduce humidity). In both cases the results were worth the effort.



Second, you can paint the surface of the roof bright white to reflect half or more of the solar radiation back into the sky. This is what governement energy folks in both Australia and Florida have been recommending for years, and several readers brought up this idea in my last entry. I have not tried this but it makes sense and the improvements are well documented. There are special paints for this, they appear to be more effective than ordinary white paint.

But what about a new house that aims to have a bit of architectural style? Nets and white paint?

Neither of these approaches may be acceptable on esthetic grounds. A white roof would look wrong, and be an annoyance to neighbors as well--they don't want our glare and heat. And a traditionalThai house covered by a black net?

I don't think Jim Thompson's ghost would stand for it.

So another approach is required here: insulation . We'll get into that, and all the ways you go wrong with it too, next time.

----------------------------

Just for handy reference, here are the R values, English units (Btu/hr/sq ft/deg F) for the common building materials in roofs and walls:

concrete 0.1 (per inch thickess)

wood 1 (per inch thickess)

foam 7 (per inch thickess)

material/air interface 0.6 (still air)

material/air interface 0.2 (15 mph breeze)

to figure heat transmission you can use the following:

Watts/square meter=5.6*(temp difference C) /R

So a 4 inch concrete slab is

R=4*.1+0.2=0.6,

and heat transmission for say a temp drop across the slab of 50 to 30 deg is

Watts/square meter=5.6*(50-30)/0.6=200 watts.

Which is A LOT!

Tropical Cool: Hot roof unmitigated

Yesterday we looked at hot tin roofs, today we will see some ways folks try to reduce the heat from same.

First, just to show that I'm not joking about hot roofs, I just took the temp of a piece of roofing which has been sitting in the mild morning sun with a nice cooling breeze for a while. Almost 50 C, as you can see. And guess what, when I check the temperature under the tile, it is within a tenth of a degree of the top temperature. This afternoon the reading will be more than 60 C. (Night time is a different story, and an improtant one from the standpoint of human comfort, but more on that subject later.)

If you were sitting under this roof, and had no hair, you would be suffering, even if the air in the room were cooled, as by an air conditioner or by strong ventilation. This is because the 50 degree underside of the roof radiates about 100 watts per square meter on objects below, regardleess of the air temperature in the room. If the iar temp is say 30, you will feel 40 on your head.

If there is not strong ventilation the air will quickly heat, as much as 5 degrees in a few minutes, and you will suffer from high air temperature as well. With no ventilation you could easily die. (Remember the sorry case of the prisoners loaded into hot trucks?)

Now what a lot of people do is put in some kind of a dropped ceiling, which of course intercepts the radiant heat from the underside of the roof. But even though you can turn off the radiant heat, but the convective transfer will soon enough heat up the air in the "attic", maybe all the way up to the high 40s. Then the gypsum ceiling will heat up, then....you are right back where you started, a hot gypsum ceiling instead of a roof. Sure, there is a little time factor here, each square meter of hot roof has to heat up a couple of cubic meters of air and a little bit of gypsum, but that may be as little as a few minutes, since the hot roof with an R value of less than 1 will deliver about 100 watts per square meter of heat.

But what you can do, is try to get rid of that heat -- 100 watts per square meter over a 5 meter square room is 2500 watts -- but to do this by ventilation you will need about 60 air changes per hour in the room, a change every minute. The requires a pretty good wind moving through the room (or attic). And if there is no wind outside, or you don't have huge openings, and if you don't dela with the radiant heat as well, you are still mighty uncomfortable. (I know, everyone raises their hand and wants to talk wind turbines and fans, but that's for next time.)

Ah, but hasn't the building industry come up with a magic solution, aluminum foil?

More on that, too, next time.

Comments
Ian 12/03/2007 16:47 IP: 124.121.71.249 sgh, my electricity costs are around 1500 baht per month, again like you my Thai friends are horrified, but then I pay 80 pounds per month in the UK on a budget account. My aim is to get it down to 500 baht, not to save money but rather as a technical challenge:-) Sounds like you could easily do a loft conversion, this would also help to keep the groundfloor cooler.	Delete
sgh 12/03/2007 14:07 IP: 124.157.240.105 Ian, thank you for your input it will be helpful. My roof is large and tall ,about 5mtr from top to ceiling of suspended gypsum board, with a pitch of i think 45deg ,with a Lanna style to the front . The tials are a cement pantial and in all a weight of 10 tonnes. This roof sits on a bungalow of 16mtr by 14 mtrs, with AC but no insulation some heat loss from the Lanna part of the roof this has a grill to the front. So you see i have to be environmentally friendly and insulate , my costs are bht 1300to bht 1800 a month and have been acceptable to a farange but the Thais have a fit when they see my bill. Every ones posts have been interesting reading thank you.	Delete
Ian 11/03/2007 13:57 IP: 124.121.71.184 sgh, I have a fan in my loft in England, basically because my internet router lives there and it was overheating and dying:-) At the moment it is on a manual switch, will fit a thermostat soon. Polyurethane foam will certainly work but is expensive, why not glue sheets of expanded polystrene foam to the underside, much cheaper. The main advantage of the polyurethane foam is it is fire resistant, but both foams give off heavy highly toxic fumes when heated so pushing the urethane is a sales gimmick rather than a safety one. But it is still better to reflect the heat away rather than block its conduction. If your roof overheats it may expand enough to create cracks and stop being waterproof.	Delete
sgh 11/03/2007 13:10 IP: 124.157.240.210 i have seen in American movies ,an electric fan built in to the gable end of the roof this may have a stat on it . A practice i have not seen in England but with us getting hotter may happen.	Delete
sgh 11/03/2007 13:03 IP: 124.157.240.210 should be polyurethane sorry	Delete
sgh Phetchaburi. 11/03/2007 13:00 IP: 124.157.240.210 Does anyone know if polyuethane rigid foam sprayed on to the underside of a roof is good or not, LOHR TRADE & CONSULTING PTS,LTD http://www.1stplanet.com/lohr-trade advert in paper ,seems a good way ,i would do it if it worked.	Delete
Ron Swelters 09/03/2007 17:17 IP: 124.120.225.72 Some more interesting ideas I hadn't thought of, I'll be discussing these again when we get to preventive measures.	Delete
Ian 09/03/2007 10:04 IP: 124.121.72.45 Ron, if you buy a small pump and spray "atomised" water on your roof, the evaporative cooling obtained is very good. A small pump and a few litres per hour of water is much cheaper than the equivalent aircon unit. ........Energy watch, these high efficiency bulbs are miniature fluorescent lights, basically a Ultra-Violet discharge exciting a phosphor coating, there is almost zero Infra-Red radiation from them, and the visible light is at the high end of the spectrum. As to other lights, I decorated my main room with lots of twinkling coloured lights for Christmas, my partner liked this so much I cannot take them down now:-)	Delete
EnergyWatch 09/03/2007 08:23 IP: 58.136.225.121 Ron,,, I suggest an idea how to cool your burning tin roof.>>> You can find around you, the weaved long grass that is used to rice pad cottage usually. A piece costs 10-15 baht. You can lay them over the tin root. Also you can spray the water over the grass at sizzling sun light. It will not only cool the tin but also absorbs heat around by the water vapours.	Delete
EnergyWatch 09/03/2007 06:06 IP: 58.136.227.253 Ian, from the departure of Plank's, I try to imagine if your 15w light bulb could send unpleasant frequency (of the light) to your Thai partner. I also brought why candle light makes most of women feel romantic, apart from your knowledge of chicken. This is my method to find new intelligence, HaHaHa >>> Well, why dont you change the bulb, the one immitating candle flame. I have one, a string for christmas tree and I found my daughter likes it more than other brightly flinkering ones. Ian 08/03/2007 20:12 IP: 124.121.73.153 Energy watch, I think I understand what you mean, even though your physics is very strange:-) I think you are quoting Plank's constant E=hν, where E is energy, h is Planck's constant, and ν (Greek letter nu) is frequency. Yes artificial light will stimulate a chicken to lay eggs, so it probable has a greater effect on a woman than a man:-) In effect you are saying that artificial light increases a woman's resting state metabolism, an interesting suggestion. Delete EnergyWatch 08/03/2007 17:59 IP: 58.136.227.134 Ian,,,Energy of photon is measured by its frequency, not density (here, like Lux) but certainly the energy may afflict her bio-rhythme assuming photom provokes electrons on her nerve and her body engine burns more glucose as if phonton excites electrons in photovoltaic semiconductor (Quantum theory). So not all for her psychology. >>> Most of women want to turn off light or reduce into wax candle size in night time. I suspect her reproduction system relates !. Delete Ian 08/03/2007 13:23 IP: 124.121.73.151 energy watch, now I know where my Thai companion gets her strange ideas, that a 15w high efficiency light bulb makes her feel hot, it is part of her cultural psychology:-) Remove the sun's radiation by being in a dark room, turning on a 15w bulb will make no difference to the heating, the output of the bulb is primarily in the visible part of the spectrum not the infra red. ............with ceiling height there is a conflict, a high ceiling will allow the hotter air to rise, but a low ceiling reduces room volume and makes life easier for the aircon. EnergyWatch 08/03/2007 12:46 IP: 58.136.227.210 In Attic, I installed two fans, suction and exhaustion to keep gymsum board cooled when no proper wind moves the hot chamber airholding.>>> Solar Light is made of photon, the elementary particles of having frequency and wavelength. This particles bombards other materials (like air, oxygen and nitrogen) to generate heat. From this theory, If you keep your room in dark, it will be cooler. The solar light does not carry heat but when it bombards your skin, the skin generates heat to warm your body.>>> In daytime, I come down to ground floor room that has good granite floor, darkened by thick branches of kapoke tree, facing my fish pond that disperse sun light away from my room and keep fine humidity around, all hot air is guided to flow up through the stairway corridor upto attic exhausting fan or naturally, It is cool to work on this computer. At two - three PM the hottest time zone, I showered at attached bathroom and lie down on granite floor and take a nap.>>> If one tries, there are good construction materials, such as heat preventing hollow brisk, double brick with inner foam filler or roof padding insulation foam or fabrics. In design, there are many wisdom to prevent sunlight and warm air invasions. One of them is concrete wings that is found in many college or business buildings. This wing-like fin prevents sunlight invasion as well as expelling the heat of building structure. The structure by itself is designed for natural ventilation, generally vertical corridor through which all interior warmed air is expelled and refill !!!. Such house has generally lofty roofing structure like Temple. Go and sit in large mass hall in a temple, It is cool because of lofty ceiling and wise ventilation arrangement.	Delete

Hot Tin Roof

My responsibility here being to show you how to beat the heat in Bangkok, and having displayed a bit of information on the annual weather cycle, I plan now to talk a bit about how the buildings we live in repsond to the weather, particularly how they respond the dreaded sun.

I claim that of the principal elements of foreigner felicity in Thailand is the achievment of thermal comfort. One of the principal enemies of thermal comfort is a hot roof.

Why?


Because our comfort in what Jack calls the sub sweat stage is sometimes determined more by the radiant temperature around us than by the temperature of the air. Thus, if the air temperature is a pleasant 27 C (80 F) and the wall or roof temperature is 39 C (ie 102 F) which it often is in these parts, we are going to "feel" as if the temperature is in the nineties (ie aboout 33 C) Since this is virtually the same as our skin temperature, we cannot dump any of our body heat into our surroundings, and that is not pleasant and we will soon enter the sweating stage, which is our body response to inadequate cooling by convection*.

If the underside of our thin metal or cement tile corrugated roof is say 43 C (110 F), which is typical midday, we are going to miserable no matter how cool the air is.


The reason the underside of the roof gets hot is that the outside of the roof on a sunny or partly cloudy day in bangkok is typically 45 C, and that heat is easily transmitted through the thin conductive material (R is only say .05, vs the 10 or more that is desirable for a roof). Because the layer of air against the bottom of the roof is a fair insulator, say R= 2 to 5, most of the temperature drop is going to be in the air, not the thin roof, so the radiant temperature of the underside is going to be almost as high as the outside temperature. A temperature of 45 degrees, by the way, is enough to cause medical-class burns to the skin.

And this, remarkably, is the usual state of Thai buildings, especially in the countryside. And if you ask the Thai about this, they will act as if the problem never occurred to them, they don't pay any notice to it, or who knows what they think or feel, I have been unable to get a clear answer to that question. It must be like asking an Eskimo whether he objects to the color white, it's so ordinary it's just a little outside the range of notice, maybe like asking a person how they feel about nitrogen.

But we, as rational heat-sensitive westerners, feel compelled to take action to increase our thermal happiness. So what can we do about this problem?

--------------------
*Convective heat loss (body to air) for typical conditions is about 8 watts per square meter per degree difference temperature (Centigrade). Hence, a half naked fellow, with an exposed skin area of about one square meter and a skin temperature of 34 deg, will convect about 32 watts of heat into surroundings that have a warmish 30 degree temperature (8*(34-30)=32). This is not enough because his body is producing about 50 watts of heat even when he is quietly gazing at his Thai girlfriend. (We are assuming here that radiant surroundings, walls and ceiling and suchlike, are at body temp, so there is no loss by radiation. If he were say praying in a Mexican cathedral with cool walls at say 25 degrees, he would lose an additional 40 or so watts by radiation.) So a bit of what my mother used to call "stickiness" will develop, maybe even a bead or two of perspiration. Perspiration will supercharge the heat loss, depending on how hot and humid it is, and whter a breeze blows. More on this advanced but very important topic of evaporative heat loss later.)

But the Thai lady will almost always have a lower body weight to skin area ratio, less heat-producing kilos of meat per square meter of skinny arms and legs, therefore she doesn't need to dump 50 watts of heat per square meter, maybe only 25 or so, so she will not be sweating but thinking "fahlang get too hot here in Thailand."


Commetrs
Timothy Pellissier 25/04/2007 09:59 IP: 58.9.39.243

Hey all you comedians... Cut the crap and add some usefull information on creating sustainable comfort in the Thai home: like materials, methods, sources of materials, costs, and results. I'm on my way to HomePro to see what I can find for myself.
________________________________________

Ian 08/03/2007 10:33 IP: 124.121.71.46

Ggrass, thanks for the info, who sells it? Do you think it might be an idea to start a blog just to exchange info like this, where things can be bought which are not normal to Thailand? I am sure many newcomers struggle to find the things they need to make life here more comfortable. A simple example is it took me 3 months to track down an importer of my favourite cigar:-) Incidentally "staycool" and other loft/roof type insulation is on sale at Homepro, which is also where I managed to buy a RCCB (residual current circuit breaker), ELCBs which are the norm here are actually illegal in the UK:-)
________________________________________

GGrass 08/03/2007 10:10 IP: 203.113.15.234

bagger (it's pronounced baYer) cool paint <-- the new innovative paint that's currently on advertisements. it's supposed to contain some ceramic stuff, that reflects sun's heat upto 90% or something like that. they say it's the technology used in space-shuttles. ________________________________________

Ian 07/03/2007 19:01 IP: 124.121.72.124 Ron, my neighbours complained of dazzle when I painted th e walls white, however they shut up when I pointed out they never ventured outside until after sunset. The white paint you mention is I suspect the same or similar to the paint used for reflective street signs and marking, it contains microspheres of glass. Regarding your Thai lady and sweating, apart from when in the shade her brown skin is a better radiator, if you examine her skin carefully you will find she has less sweat glands per square cm than you do:-) ________________________________________

Ron Swelters 07/03/2007 18:23 IP: 58.8.69.43 In regard to the white paint, there is a special heat reflective kind that is even better than normal white (your eyes can't tell the difference.) The Australians promote this solution, reflects maybe 25 percent more of the sun's heat. But your neighbors might not like it, if that matters to you. We will compare some other solutions son. Thanks for the other excellent ideas. ________________________________________

Ian 07/03/2007 16:51 IP: 124.121.74.247 energy watch, 15% of body heat is lost through the head, yet your genitals which are much smaller lose 10% of body heat, this is why you should wear very loose briefs or better none when at home. If you are outside and want to cool fast wet your wrists as the blood vessels are closest to the surface here. Diet is another factor in keeping cool, have a word with a local Chinese about "heating and cooling" foods. ________________________________________

EnergyWatch 07/03/2007 16:29 IP: 58.136.227.174 Ron Swelters>>>> Your body is like 4000 cc jaguar but your wife is 1300 cc corollar. When you both sit in the tin-roofed room (idle condition) your jaguar engine consume more gasoline to keep it idle than her idle condition. Heat has speed. If the gap between your body and room temperature is more, your body lose more heat at more speed. In this theory, I may advise you, that, take a bath to make your body wet, then lie on the tile floor with fan, your body heat runs out quickly. The tile is a secret how Thais cool their body. Tile conduct heat very fast, here from your boiling body to tile floor. Baked Tile is good conductor of heat. >>>> If you can 'hole' in the roof, the air is afloat and leak over as hot air always flows up. I put roof 'natural fan' that pump out the 'under roof hot air insulation, and keep the room in natural ventilation, of course wet my body and lie on clean tile floor in only brief, under standing fan (absolutely not ceiling fan !) and tease my wife,,, Cool !,,,,HaHaHa !
________________________________________

n 07/03/2007 15:04 IP: 124.121.71.98

I yesterday asked one of my local builders to paint my roof white, he was horrified:-) He produced many reasons against this, the paint would only last a year, the accepted colours are red, blue, green or cement, paint is expensive and would not survive the rain. I pointed out that my walls were white using an exterior grade cement paint, he said that ok as they vertical so not get wet! I said I want the same paint on my roof, he said no way much too expensive. I said 700 Baht for 10 litres not expensive. He said have to paint every year, I said if so it will be worth it. I think I will have to paint it myself, you cannot alter the way a Thai thinks.
________________________________________

Ron Swelters 07/03/2007 14:30 IP: 61.90.146.66

Why sure, steal whatever you want. Is being under your ass better than being under the dust that is under your shoes? I'm new to Thailand.
________________________________________

EnergyWatch 07/03/2007 14:13 IP: 58.136.227.249

Ronswelters !

Can I steal your 'scatch under tin'. I am your neighbor. You are under my ass.
________________________________________

Tropical Cool: How was it for you?

Well for me it wasn't too bad, , the first part of the year, I think I'm getting used to the heat and humidity a little. But they say that this year is going to be a bad one. The question is, how much worse is it going to get?

I took the worst year I could find, the big El Nino year of 1983, when the Pacific practically started boiling. (You saw that sequence of years in my last posting, years 1982-1985). Then I superimposed the daily high temperature and dew point for the Asoke station* right down the road from where I am now writing this. The 83 data are in white, the 2007 data, right up to this morning, are in red and green.

What you can see here is how it began to warm up in January, then took a refreshing little dive in the beginning of February, now it's back on track again, with even the Thai beginning to comment a little on how hot it is, and now it's heading for the big peak usually around mid to late April or even May. The graph suggests it may be a little cooler than 1983, but the 83 data are from Don Muang, not downtown, it may be a little hotter up there with all those hot (but uncracked) taxiways. But the dew point -- I will argue later that dew point is probably a better all-round indicator of thermal discomfort -- looks about the same this year as 83.

AND, by the way, the weather the last few days has been almost exactly the same as the weather in Boston, last year in July, (2006), the dreaded heat wave of '06 (see my first posting), when the streets were deserted and water was being passed out and they made one hundered fifty thousand phone calls to warn people that it was hot!

Stay tuned!