Insulating film on windows?

[gejohesch]

I'm not usually in Thailand around April, but this year it turned out I could not avoid it, and I'm shocked with he heat levels. It's around 40 Celsius every single day, temperature does not drop below 28 Celsius in the early morning, and no rain in sight to cool the climate down for weeks, where I am in Isan!

 

I've done some work in my wife's village house over the years, but not enough, obviously. I noticed that the walls and especially the windows radiate heat inside like mad. It's like we had radiators all around us, not a good idea... 

 

One wall is tiled up half way up on the outside and the sections that are tiled up feel a bit cooler on the inside than the untiled sections. So maybe tiling up more is a good idea?

 

But more importantly, the window panes are damn hot. Replacing them with double glazing windows would be expensive and there would be the added problem that probably no one around would ever have installed such things. So I come to the idea of placing insulating films on the windows: does anyone have any experience with that in Thailand?

 

Obviously, one solution would be to install AC units. We already have one in the bedroom and it's great! For the rest of the house, I will consider 2 or 3 AC units at some stage but not in the immediate. And btw, the AC in the bedroom has to fight its way against 2 of those heat radiating windows anyway, so back to the question : what can I do with those windows?

[nigelforbes]

Presumably you mean reflective film? We installed reflective film on three sets of patio doors in our living room, it doesn't do hardly any good whatsoever but it's great for privacy!

 

What has worked is the installation of wooden or bamboo slat blinds on the outside of the house, that prevents the sun from hitting the glass or the walls in the first place. Planting trees to shield the house is also good but that obviously takes time.

 

The problem with film is that the unless you have wooden window frames and thermal break, the heat hits the walls and then transmits laterally to the frame and the glass. There are plenty of double glazing guys out there, Thai Asahi is the leader in the glass business here and they will supply details of locals who can make up the units. But see the problem above about window frames and thermal breaks, unless you solve that problem, double glazing wont work.

[sometimewoodworker]

43 minutes ago, gejohesch said:

what can I do with those windows?

Not just the windows you need to either build a second wall outside the hot ones or add insulation on them. Then for the windows use shutters outside or the bamboo blinds, again outside.

[gejohesch]

4 minutes ago, sometimewoodworker said:

Not just the windows you need to either build a second wall outside the hot ones or add insulation on them. Then for the windows use shutters outside or the bamboo blinds, again outside.

To you and nigelforbes just above.

 

Thanks, what I take from you is the idea of installing bamboo slats on the outside. Btw, it's not just about blocking out direct sunlight and heat, it's also about insulating against the outside temperature even if there is no direct sunlight! It's a matter of heat radiation!

 

I have done everything I could so far with planting trees around etc, reshaping the roof completely (adding space between the roof and the hanging ceiling for better ventilation + replacing the roof sheets with sheets + 5cm insulation), and putting insulation rolls (5 cm) on the hanging ceiling before closing up again.

 

What remains, mainly, is the heat radiating from outside to the inside.

[sometimewoodworker]

The idea about thermal breaks being required in hot countries is tosh. Thermal breaks are designed to stop the problems of condensation when you have a cold outside and warm humid inside.

Yes the thermal breaks will reduce heat transfer but the idea that without them your windows are going to be radiating much heat is so much ball cocks

Quote

Glass is a very poor heat conductor. It has one of the lowest possible heat conduction a solid (without air trapped in it)

 This suggestion is an example of someone being totally lazy and misunderstanding basic physics.

[sometimewoodworker]

Just now, gejohesch said:

To you and nigelforbes just above.

 

Thanks, what I take from you is the idea of installing bamboo slats on the outside. Btw, it's not just about blocking out direct sunlight and heat, it's also about insulating against the outside temperature even if there is no direct sunlight! It's a matter of heat radiation!

 

I have done everything I could so far with planting trees around etc, reshaping the roof completely (adding space between the roof and the hanging ceiling for better ventilation + replacing the roof sheets with sheets + 5cm insulation), and putting insulation rolls (5 cm) on the hanging ceiling before closing up again.

 

What remains, mainly, is the heat radiating from outside to the inside.

You need to use heat reflecting paint to stop the walls heating up as much

[gejohesch]

1 minute ago, sometimewoodworker said:

The idea about thermal breaks being required in hot countries is tosh. Thermal breaks are designed to stop the problems of condensation when you have a cold outside and warm humid inside.

Yes the thermal breaks will reduce heat transfer but the idea that without them your windows are going to be radiating much heat is so much ball cocks

 This suggestion is an example of someone being totally lazy and misunderstanding basic physics.

Allow me to disagree with some here. When I touch the walls, especially at the end of the day, they feel warm. When I touch the window panes (glass), they feel very warm. That's exactly as radiators feel (the type used in cold countries). And heat radiates, that's simple physics, is it not?

[sometimewoodworker]

2 minutes ago, gejohesch said:

Allow me to disagree with some here. When I touch the walls, especially at the end of the day, they feel warm. When I touch the window panes (glass), they feel very warm. That's exactly as radiators feel (the type used in cold countries). And heat radiates, that's simple physics, is it not?

Your empirical observation is absolutely correct. However you are missing some rather important facts of physics. And that it was the total rubbish being spouted about thermal breaks that I was addressing.

Yes glass will heat up by radiation, yes there will be some heating by convection, nut NO there will be little heating of the glass by conduction from the hot frames

 

the Physics of heat transfer is somewhat complex and it isn’t easy to determine, without instrumentation, the path of heat transfer 

[tomazbodner]

Had 3M film installed by the company "goodfilm" a good month ago. They have between 10 and 80%. I've chosen 60% light blocking, which lowers IR light that causes heat significantly. Now the windows are still hot, but 10cm from them it's cool. Before heat came a meter+ into the room.

 

Basically, at 30+ floor looking directly west with windows top to bottom over entire walls, in the past I had to have UV curtains closed all the time. Now I keep them open and the temperature inside is about the same or lower. Only downside I see is that it always looks like it's cloudy outside even it's sunny. Unfortunately it doesn't make the smog disappear.

 

Top one on below image is 3M, bottom one is Nanotech, starting at 80%, then 60%, 50%, 40% and 30%.

 

The lady that was selling it also had Nanotech, which was clearer (looking through 3M film looked like a tiny bit blur, while Nanotech was just perfect, only darker), but I'm told that despite longer warranty by Nanotech, 3M has better glue. Overall, Nanotech is about 20% cheaper.

 

 

 

The website of the shop for 3M is www.goodfilmshop.com. For Nanotech I don't remember, but you could reach out to sales lady Nathita at 094-545-3000 or add her on Line with ID @goodfilm.

 

Hope this helps.

[nigelforbes]

The problem you're trying to overcome is similar to the problem everyone has here. Virtually all houses are made from concrete and steel which acts the same way a storage heater does, load it up with enough heat and it will continue to release it into the living space for hours after the sun goes down. The trick is to prevent direct sunlight from hitting as much of the building as possible, shielding the glass windows on the outside with bamboo blinds is effective but that doesn't address the heat hitting the rest of the building, especially the roof. Heat hits roof tiles, transfers to steel and concrete and eventually your inside walls get hot. Painting the outside of the building white helps, as does using paint that reflects heat. But ultimately you're left with the same problem, only the scale of it and time of day overload changes.

 

We found that by trial and error we addressed different parts of the problem in different ways over time. Ventilating the roof space/void using vents on the gable ends and installing vented soffit boards at the eaves helps create air flow and keep attic temperatures lower than they would otherwise be, that in turn helps delay heat transfer from the roof tiles and steel, into the walls. Our biggest success with the roof was when we painted it light grey, which results in the house being cold at certain times of the year and negates the need to use air con even during the hottest months - needless to say the walls remain quite cool.

 

We've already discussed the external bamboo blinds, they work extremely well and our current set are in their eighth year....we have a one meter overhang which helps.

 

The film? Well, as said it's great for privacy but when that was our only heat avoidance/reduction measure, it wasn't satisfactory, for us....others mileage may vary. We have four sets of sliding patio doors in our living room on two adjacent walls, the metal frames get very hot unless the bamboo blinds are pulled down. I won't say more about that un case our physics teacher throws a tantrum but I think you get the picture.

 

 

 

 

 

[Denim]

When its this hot the only real solution for most people is air con.

 

I have tried every passive method to keep the house cooler and they work. Outside on the balcony in the shade ,40 degrees. In living room 32.

 

BUT .....32 although cooler is , in my opinion not cool enough. To feel comfortable i need a temperature of no more than 28 , and for that I need the air conditioning on most of the day.

[gejohesch]

11 hours ago, Denim said:

When its this hot the only real solution for most people is air con.

 

I have tried every passive method to keep the house cooler and they work. Outside on the balcony in the shade ,40 degrees. In living room 32.

 

BUT .....32 although cooler is , in my opinion not cool enough. To feel comfortable i need a temperature of no more than 28 , and for that I need the air conditioning on most of the day.

I very much agree with you. In fact, 28 Celsius only feels good to me when I come in from a warmer place, but it quickly feels not so comfortable after all. My "sweet spot", if I may say, is around 25-26 or even a bit lower (23-24 about) if working (like being in an office space). It's actually amazing how sensitive one can be to a single degree difference!

 

At the moment, I keep all windows open at night in our daily living space, to capture the relative coolness of the early morning (28 degrees) - with screens on to keep the bugs away, of course!

 

In my view, (1) = keeping a house cool in a hot climate has much in common with (2) = keeping a house warm in a cool/cold climate. It's just that the heat transfer one tries to reduce is in the opposite direction (from outside to the inside or the reverse). Therefore, one of the first things I think should be done is to reduce to the maximum all possible gaps, like around the window and door frames, to avoid cold air to getting out or coming in (depending whether (1) or (2) situation). 

 

Then comes the question of all materials around the inside-outside interface that could be considered as good conductors, and that will effectively transfer heat across the interface. Sure, metal is an issue then; the aluminum window frames feel down hot at the end of the afternoon! Sure, glass is a relatively poor conductor, but then : relatively to what? If it was such a poor conductor that I would not have to worry about it, then why can I not hold a glass of hot water in my hands? Or why do we need double (if not triple) glazing to keep houses warm (or cool)? The fact is that in double (triple) glazing, the space between the glass panes is filled with argon, a gas which is considerably less conductive than glass. Also, if you consider an insulating flask made of glass (Thermos), the real insulator is not the glass but the vacuum between the two walls of the flask.

 

Once a given material (metal or glass) gets warm, it starts radiating out energy, hence heat transfer to the inside (situation (1) = our problem here in Thailand).

 

So, yes I agree with the AC's, but before I install the AC units, and to make their work easier (and less costly), I would like to explore ways of:

- a) reducing the "gaps";

- b) reducing how warm surfaces such as window frames and glass panes, but also walls actually get warm;

- c) reducing the extent to which those surfaces will be radiating heat to the inside of the house.

 

a) is easy (plug the gaps);

b) I have done everything possible around the house to provide as much shading as possible (trees, plants, roof). So there is not much direct sunlight hitting the house. The surfaces in question nevertheless get warm because of the ambient temperatures. As someone said above, the walls in Thailand are not very helpful (concrete blocks + a bit of cement + metal). Is there a way to paint or coat the window frames that would reduce their heat absorption? Would cladding the exterior with ceramic tiles provide some degree of insulation? I'm thinking of why house are tiled up and down in Portugal - there should be a reason other than purely decorative!

c) Inside of the house then, same question about painting / coating the window frames. I'm not interested in putting films on the glass panes, since there is no direct sunlight anywhere anymore.

 

Ouf! I know this is rather long, and I apologize for not having addressed all the points made above. It's a complex matter and it takes time to discuss!

 

[Denim]

1 hour ago, gejohesch said:

c) Inside of the house then, same question about painting / coating the window frames. I'm not interested in putting films on the glass panes, since there is no direct sunlight anywhere anymore.

I recently put up some fake brick panels on one wall ( warmest ) inside the bedroom to try and help keep the cool air from the conditioner in !! The self adhesive panels are foam backed and about an eighth of an inch thick. 80 baht each panel from Mr DIY.  That's how desperate I am to be as pro active as possible along the lines of every little helps ( maybe ).

Cant do every wall , but I might do another small wall in the kitchen in the same stuff.

 

 

[gejohesch]

26 minutes ago, Denim said:

I recently put up some fake brick panels on one wall ( warmest ) inside the bedroom to try and help keep the cool air from the conditioner in !! The self adhesive panels are foam backed and about an eighth of an inch thick. 80 baht each panel from Mr DIY.  That's how desperate I am to be as pro active as possible along the lines of every little helps ( maybe ).

Cant do every wall , but I might do another small wall in the kitchen in the same stuff.

 

 

That's also where I'm coming from : every little help helps!

 

I guess the foam improves the wall insulation. At least, the wall looks good from an aesthetic point of view ! It ends up being cheap too, I guess, maybe a couple of 1,000 THB for an entire wall, and rather easy to put in place. So, that's an idea I will keep in mind.

[nigelforbes]

For sure there is no one single thing that will do it all, you have to do a myriad of things to attack the problem from a variety of angles.

[Denim]

4 minutes ago, nigelforbes said:

For sure there is no one single thing that will do it all, you have to do a myriad of things to attack the problem from a variety of angles.

Absolutely. Our house is raised up from the ground by 80cm rather than being on the ground. This to allow for airflow under the floors. As an experiment I crawled under there last year and painted the underside of our living room floor ( under house ) white to see if it reflected heat better than grey unpainted cement. No perceivable difference topside between living room and other rooms. At least I tried.

 

This is the first year that in the late afternoon , the floor tiles actually feel warm as opposed to a bit cooler ! Lying down on the floor is no longer a cool option !

[nigelforbes]

13 minutes ago, Denim said:

Absolutely. Our house is raised up from the ground by 80cm rather than being on the ground. This to allow for airflow under the floors. As an experiment I crawled under there last year and painted the underside of our living room floor ( under house ) white to see if it reflected heat better than grey unpainted cement. No perceivable difference topside between living room and other rooms. At least I tried.

 

This is the first year that in the late afternoon , the floor tiles actually feel warm as opposed to a bit cooler ! Lying down on the floor is no longer a cool option !

I imagine that's the effect of heat transfer via the concrete and steel in the upper part of the house, you should patent it and sell it to the UK, you'll make a fortune.

[indyo]

those films help if you already have a well insulated home and the windows are the only way for the heat to go inside, if you install them in a non insulated home is likely to install a gate in the middle of desert 

[sometimewoodworker]

4 hours ago, gejohesch said:

I very much agree with you. In fact, 28 Celsius only feels good to me when I come in from a warmer place, but it quickly feels not so comfortable after all. My "sweet spot", if I may say, is around 25-26 or even a bit lower (23-24 about) if working (like being in an office space). It's actually amazing how sensitive one can be to a single degree difference!

 

At the moment, I keep all windows open at night in our daily living space, to capture the relative coolness of the early morning (28 degrees) - with screens on to keep the bugs away, of course!

 

In my view, (1) = keeping a house cool in a hot climate has much in common with (2) = keeping a house warm in a cool/cold climate. It's just that the heat transfer one tries to reduce is in the opposite direction (from outside to the inside or the reverse). Therefore, one of the first things I think should be done is to reduce to the maximum all possible gaps, like around the window and door frames, to avoid cold air to getting out or coming in (depending whether (1) or (2) situation). 

 

Then comes the question of all materials around the inside-outside interface that could be considered as good conductors, and that will effectively transfer heat across the interface. Sure, metal is an issue then; the aluminum window frames feel down hot at the end of the afternoon! Sure, glass is a relatively poor conductor, but then : relatively to what? If it was such a poor conductor that I would not have to worry about it, then why can I not hold a glass of hot water in my hands? Or why do we need double (if not triple) glazing to keep houses warm (or cool)? The fact is that in double (triple) glazing, the space between the glass panes is filled with argon, a gas which is considerably less conductive than glass. Also, if you consider an insulating flask made of glass (Thermos), the real insulator is not the glass but the vacuum between the two walls of the flask.

 

Once a given material (metal or glass) gets warm, it starts radiating out energy, hence heat transfer to the inside (situation (1) = our problem here in Thailand).

 

So, yes I agree with the AC's, but before I install the AC units, and to make their work easier (and less costly), I would like to explore ways of:

- a) reducing the "gaps";

- b) reducing how warm surfaces such as window frames and glass panes, but also walls actually get warm;

- c) reducing the extent to which those surfaces will be radiating heat to the inside of the house.

 

a) is easy (plug the gaps);

b) I have done everything possible around the house to provide as much shading as possible (trees, plants, roof). So there is not much direct sunlight hitting the house. The surfaces in question nevertheless get warm because of the ambient temperatures. As someone said above, the walls in Thailand are not very helpful (concrete blocks + a bit of cement + metal). Is there a way to paint or coat the window frames that would reduce their heat absorption? Would cladding the exterior with ceramic tiles provide some degree of insulation? I'm thinking of why house are tiled up and down in Portugal - there should be a reason other than purely decorative!

c) Inside of the house then, same question about painting / coating the window frames. I'm not interested in putting films on the glass panes, since there is no direct sunlight anywhere anymore.

 

Ouf! I know this is rather long, and I apologize for not having addressed all the points made above. It's a complex matter and it takes time to discuss!

 

The majority of your post is excellent, though plugging up the gaps is usually far from as easy as you suggest.

 

However I saw an interesting experiment that took 3 panels of aluminium one untreated one with a commercial IR reflecting paint and the last coated with barium sulphate nano particles of 3 differing sizes. In full sun. The results were plain aluminium 20C above ambient air temperature, IR reflective paint 10C above ambient air temperature and the barium sulphate nano particle paint 3C under ambient air temperature 

 

So it is possible to make an inexpensive paint of barium sulphate and reduce the heat gain by a very substantial amount. you can have any colour you like as long as it’s white.

 

Though the painting process is rather arduous as you need extremely thin coats of paint that (on a small surface) take about 20 minutes to get to the repaint stage and probably 30+ coats

[gejohesch]

18 minutes ago, sometimewoodworker said:

The majority of your post is excellent, though plugging up the gaps is usually far from as easy as you suggest.

 

However I saw an interesting experiment that took 3 panels of aluminium one untreated one with a commercial IR reflecting paint and the last coated with barium sulphate nano particles of 3 differing sizes. In full sun. The results were plain aluminium 20C above ambient air temperature, IR reflective paint 10C above ambient air temperature and the barium sulphate nano particle paint 3C under ambient air temperature 

 

So it is possible to make an inexpensive paint of barium sulphate and reduce the heat gain by a very substantial amount. you can have any colour you like as long as it’s white.

 

Though the painting process is rather arduous as you need extremely thin coats of paint that (on a small surface) take about 20 minutes to get to the repaint stage and probably 30+ coats

Thanks! I tried my best to navigate this issue and, frankly, it's not straightforward!

 

I like your line "So it is possible to make an inexpensive paint of barium sulphate and reduce the heat gain by a very substantial amount. you can have any colour you like as long as it’s white."

 

So, yes, white paint (and the barium sulphate nano particle type you mention). I guess it's the outside that should be painted, rather than the inside of the house? Sorry for asking, but I'm not an expert and I would prefer to avoid assuming too quickly, and then wasting my time (especially if 30 coats are required!).

 

What do you think of tiling the exterior of the walls? I guess that would add to the thermal mass and possibly be useful somehow?

[sometimewoodworker]

1 hour ago, gejohesch said:

Thanks! I tried my best to navigate this issue and, frankly, it's not straightforward!

 

I like your line "So it is possible to make an inexpensive paint of barium sulphate and reduce the heat gain by a very substantial amount. you can have any colour you like as long as it’s white."

 

So, yes, white paint (and the barium sulphate nano particle type you mention). I guess it's the outside that should be painted, rather than the inside of the house? Sorry for asking, but I'm not an expert and I would prefer to avoid assuming too quickly, and then wasting my time (especially if 30 coats are required!).

 

What do you think of tiling the exterior of the walls? I guess that would add to the thermal mass and possibly be useful somehow?

Yes the paint is external for best results. I doubt that there is a commercial version that you can buy, but making it isn’t a significant challenge. The proof of concept is here 

 

my opinion on adding mass with tiles is that it’s likely to be a waste of money as you really don’t want more mass, unless of course you like to be kept toasty warm after the sun goes down.

 

This is a reason why concrete walkways around a house are only good to keep mud down.

Night storage heaters use concrete as a heat storage method.

[unheard]

22 hours ago, sometimewoodworker said:

the barium sulphate nano particle paint 3C under ambient air temperature

 Surely 3C above ambient?

[unheard]

Take it back.

"the paint can keep surfaces 19 degrees Fahrenheit cooler than their ambient surroundings at night."

https://www.purdue.edu/newsroom/releases/2021/Q2/the-whitest-paint-is-here-and-its-the-coolest.-literally..html

[Denim]

22 hours ago, gejohesch said:

What do you think of tiling the exterior of the walls? I guess that would add to the thermal mass and possibly be useful somehow?

There is another fairly cheap possibility .......................water.  You could try rigging up blue piping along the top outside edge of the wall , then spraying the wall with water for about 30 seconds , three times an hour during the hottest part of the day to cool the walls down. I have seen several people in the village have rigged up water sprinklers on their roofs with the same thing in mind. Might help but don't know as haven't tried it .

 

 

[sometimewoodworker]

42 minutes ago, unheard said:

Take it back.

"the paint can keep surfaces 19 degrees Fahrenheit cooler than their ambient surroundings at night."

https://www.purdue.edu/newsroom/releases/2021/Q2/the-whitest-paint-is-here-and-its-the-coolest.-literally..html

The actual quote is

Quote

The paint’s whiteness also means that the paint is the coolest on record. Using high-accuracy temperature reading equipment called thermocouples, the researchers demonstrated outdoors that the paint can keep surfaces 19 degrees Fahrenheit cooler than their ambient surroundings at night. It can also cool surfaces 8 degrees Fahrenheit below their surroundings under strong sunlight during noon hours.

Or in real money 5 degrees under ambient air temperature, so even better that my example above.

[sometimewoodworker]

13 minutes ago, Denim said:

There is another fairly cheap possibility .......................water.  You could try rigging up blue piping along the top outside edge of the wall , then spraying the wall with water for about 30 seconds , three times an hour during the hottest part of the day to cool the walls down. I have seen several people in the village have rigged up water sprinklers on their roofs with the same thing in mind. Might help but don't know as haven't tried it .

I have seen this system used in some places in Thailand though with continuous flow and on the roof. The disadvantage is that there is a need for maintenance, this is something that is often not done here.

[gejohesch]

1 hour ago, Denim said:

There is another fairly cheap possibility .......................water.  You could try rigging up blue piping along the top outside edge of the wall , then spraying the wall with water for about 30 seconds , three times an hour during the hottest part of the day to cool the walls down. I have seen several people in the village have rigged up water sprinklers on their roofs with the same thing in mind. Might help but don't know as haven't tried it .

 

 

That's an interesting idea. Water is known as a great help against the heat. It's an excellent conductor, so absorbs energy (heat) very quickly away from the surfaces it comes in touch with. I don't know how easy it is to install such a thing however. Some studying ahead for me, I guess!

[sometimewoodworker]

57 minutes ago, gejohesch said:

That's an interesting idea. Water is known as a great help against the heat. It's an excellent conductor, so absorbs energy (heat) very quickly away from the surfaces it comes in touch with. I don't know how easy it is to install such a thing however. Some studying ahead for me, I guess!

Your physics knowledge seems a little restricted. It’s the amount of heat needed to cause a phase change between liquid and gas. Yes water can transfer heat quite well as a liquid, but that is much less than the phase change heat transfer, something in the region of 1,500kJ/kg this number is not exact as the temperature at which vaporisation occurs is not at 100C

[gejohesch]

1 hour ago, sometimewoodworker said:

Your physics knowledge seems a little restricted. It’s the amount of heat needed to cause a phase change between liquid and gas. Yes water can transfer heat quite well as a liquid, but that is much less than the phase change heat transfer, something in the region of 1,500kJ/kg this number is not exact as the temperature at which vaporisation occurs is not at 100C

Hmmmm, I studied physics to quite a high level when I was younger - actually coming from a rather good background in maths. Various types of mechanics (celestial, thermo, acoustics, wave propagation, even quantum, applications to civil engineering etc), also chemistry (organic and mineral) plus a bit of chemical engineering and elements of metallurgy. Obviously, I have forgotten a lot over the decades since my studies, but nevertheless it is quite funny to read your comment.

 

Please don't jump on me for writing a bit too fast and forgetting to mention that the most important cooling factor is the evaporation process. Such as we all experience through sweating, for example.

[Denim]

2 hours ago, gejohesch said:

I don't know how easy it is to install such a thing however. Some studying ahead for me, I guess!

Pretty easy. Just buy some lengths of blue tubing and join to required length. Drill lots of tiny holes in the pipe, mount on brackets and connect to a standpipe. Make sure to plug the end first so pressure builds up and water doesn't flow straight through. Turn on 3 times an hour should be enough. Less than 500 baht.

 

Not going to make a huge difference but just another little push in the right direction. What I have been doing lately is just plain hosing down the walls. Bit of a hassle as needs to be done a few times an hour for a minute or two but does keep wall cooler.