i was taught at school that HEAT/warm air always RISES !!!!

so how does your heat come DOWN???

A friend of mine made a different attempt. He bought a house, maybe 10 years old, being covered with very, very dark brown clay bricks. He recently painted the whole roof with white roofing paint and says inside the house it is now 4 to 5 deg C cooler. Not sure you can do that with any other tiles.

6 minutes ago, essox essox said:

i was taught at school that HEAT/warm air always RISES !!!!

so how does your heat come DOWN???

R-A-D-I-A-T-I-O-N

1 hour ago, AAArdvark said:

No idea where to find one of these in LOS.

[email protected]

 

[email protected]

4 minutes ago, paddyfield7 said:

A friend of mine made a different attempt. He bought a house, maybe 10 years old, being covered with very, very dark brown clay bricks. He recently painted the whole roof with white roofing paint and says inside the house it is now 4 to 5 deg C cooler. Not sure you can do that with any other tiles.

makes quite a difference but 4-5ºC is a gross exaggeration.

17 hours ago, zeekgarcia said:

are these attic vents with fans in them, what you are talking about?

Does anyone know of anywhere that sells anything like these here in Thailand?

And could you use them with the standard cement roof panels like the red one below

 

Thanks

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5 minutes ago, paddyfield7 said:

A friend of mine made a different attempt. He bought a house, maybe 10 years old, being covered with very, very dark brown clay bricks. He recently painted the whole roof with white roofing paint and says inside the house it is now 4 to 5 deg C cooler. Not sure you can do that with any other tiles.

I have a flat roof in one area of the house and used white roof paint, the roof is ~7 deg cooler in the heat of the sun, room below is cooler for sure though it is also well insulated.

3 minutes ago, Naam said:

makes quite a difference but 4-5ºC is a gross exaggeration.

Maybe he put in some attic fans as well?  ????

5 minutes ago, wgdanson said:

are these attic vents with fans in them, what you are talking about?

Those look like furnace and sewage vents to me.  IE: no fans.

7 minutes ago, Naam said:

makes quite a difference but 4-5ºC is a gross exaggeration.

I would say, perfectly possible. An unpainted grey wall is about 10~15 degrees hotter than the same wall with white paint.

if you use AC insulate (minimum 4 inches) the attic floor (interior ceiling), put a thermostatically controlled fan at one end and an intake (non powered) at the other.   Size the fan based on the volume of the attic to give 6-8 air changes per hour.

 

If you do not use AC put a large ceiling fan discharging into the attic and make sure there are vents in the roof or gable to let the air out.  If you do this you have to have screens on windows.  Be aware that with this your house will be about the same temperature as the outside air and or rainy days the inside humidity will be high.

32 minutes ago, Naam said:

makes quite a difference but 4-5ºC is a gross exaggeration.

I think the engineer living in there can read a thermometer.....

20 minutes ago, sometimewoodworker said:

I would say, perfectly possible. An unpainted grey wall is about 10~15 degrees hotter than the same wall with white paint.

I was sceptical of this so just been out and checked my wall (same colours) which has been in the sun all morning there is a ~5°c difference.

1 hour ago, essox essox said:

i was taught at school that HEAT/warm air always RISES !!!!

so how does your heat come DOWN???

There are three modes of heat transfer: conduction, convection, and radiation. Heat rises due to convection, but radiant heat transfer is from a warm body to a cold body.  At some point with a hot attic, you get the conductive effect of hot air warming the ceiling surface (or insulation), and eventually increase that temperature. 

 

So for (active) cooling, you need to stop the radiant heat transfer with the foil, and slow the conductive heat transfer with as much insulation as possible, as well as exhausting the attic air (which is hotter than outside air). 

 

For passive cooling, shading, light colored roofing, high ceilings that allow hot air to stratify (like Subarnabuhmi), thermal mass that slows temperature rise, and natural breezes keep a place cool. 

13 hours ago, Naam said:

"no breeze = insufficient air flow"

That's why you can now buy solar powered whirlybirds.  Saw some at a trade show ten years ago. 

19 hours ago, wgdanson said:

Would the whirly-gig things work, either powered or not please?

Whirly gigs are great for getting heat out of the attic, I've two with a small electric fan on one to force the air flow...on a still day you can feel the air flow through the nearest window!

2 hours ago, essox essox said:

i was taught at school that HEAT/warm air always RISES !!!!

so how does your heat come DOWN???

radiation

2 hours ago, CGW said:

I was sceptical of this so just been out and checked my wall (same colours) which has been in the sun all morning there is a ~5°c difference.

Maybe we have different sunshine up in Udon in the hot season or my white paint is more reflective. ???? But the difference was around the numbers i posted.

 

FWIW these measurements were from the surface that the sun was shining on, it was rendered 75mm AAC block. The inside temperature difference was much smaller.

26 minutes ago, sometimewoodworker said:

Maybe we have different sunshine up in Udon in the hot season or my white paint is more reflective. ???? But the difference was around the numbers i posted.

 

FWIW these measurements were from the surface that the sun was shining on, it was rendered 75mm AAC block.

Same sun, I am outside Udon, lot of variables for sure, I have measured 10°c difference on the white painted flat roof and non painted area adjacent, that's in direct sun which would be more reflective, the white paint has actually rendered the roof area unusable when the sun is out, roof is cool but with the reflection its bloody hot!

3 hours ago, Artben said:

Size the fan based on the volume of the attic to give 6-8 air changes per hour.

I just got a quote from sunyintlpowerltd.com in China, who sell solar powered roof fans. They also suggest 8 changes of air per hour for my 112 sq metre roof. They suggest 4 x 50 watt jobbies @ $180 plus $88 shipping EACH. Over the top or what do you think?

22 hours ago, wgdanson said:

Would the whirly-gig things work, either powered or not please?

Works well in my place, I have two (non Powered).

6 hours ago, sometimewoodworker said:

6 hours ago, Naam said:

makes quite a difference but 4-5ºC is a gross exaggeration.

I would say, perfectly possible. An unpainted grey wall is about 10~15 degrees hotter than the same wall with white paint.

yawwnnnn... measuring the difference of wall temperature inside/outside is as irrelevant as are the reproductive organs of a nun who vowed eternal chastity. relevant is the difference of room temperature and outside temperature. if somebody claims this difference to be 4-5ºC at or after 12.00 noon then...

I retrofit one of these a few years back on my roof (non powered). Doesn't stop the need for fans but definitely reduced the temp inside the house. When the guy cut the hole in the roof, the heat coming out nearly burnt his eyebrows. You also need to fit vents in the soffits to replace the air escaping.

 

Just took this video of it whirling around nicely and there is hardly a breeze here at the moment.

 

On 8/15/2019 at 10:47 AM, Naam said:

R-A-D-I-A-T-I-O-N

 

But I was taught by many action movies that's dangerous!

5 hours ago, mrbojangles said:

I retrofit one of these a few years back on my roof (non powered). Doesn't stop the need for fans but definitely reduced the temp inside the house. When the guy cut the hole in the roof, the heat coming out nearly burnt his eyebrows. You also need to fit vents in the soffits to replace the air escaping.

 

Just took this video of it whirling around nicely and there is hardly a breeze here at the moment.

 

The point I raised in 19#, the air escaping thru' the whirly will cause it to  rotate -  provided there somewhere for fresh air to enter the roof space, however the rudimentary "fan" within the whirly will add bugger-all to the outflow taking place as hot air rises. 

10 hours ago, mrbojangles said:

I retrofit one of these a few years back on my roof (non powered). Doesn't stop the need for fans but definitely reduced the temp inside the house. When the guy cut the hole in the roof, the heat coming out nearly burnt his eyebrows. You also need to fit vents in the soffits to replace the air escaping.

 

Just took this video of it whirling around nicely and there is hardly a breeze here at the moment.

 

 

10 hours ago, mrbojangles said:

I retrofit one of these a few years back on my roof (non powered). Doesn't stop the need for fans but definitely reduced the temp inside the house. When the guy cut the hole in the roof, the heat coming out nearly burnt his eyebrows. You also need to fit vents in the soffits to replace the air escaping.

 

Just took this video of it whirling around nicely and there is hardly a breeze here at the moment.

 

If I may ask: Where in Thailand did you let install the whirly on this corrugated iron roof and could you tell us the name of the performing builder/company? Thank you!

Has anyone tried that heat-reflecting paint? A fag packet calculation shows that an investment in the paint could mean I won't need to use the air con so much, potentially saving me several hundred Baht per month.

Just now, SteveK said:

Has anyone tried that heat-reflecting paint? A fag packet calculation shows that an investment in the paint could mean I won't need to use the air con so much, potentially saving me several hundred Baht per month.

Yes, it works.

15 hours ago, ThiAmo said:

 

If I may ask: Where in Thailand did you let install the whirly on this corrugated iron roof and could you tell us the name of the performing builder/company? Thank you!

I'm in the Chaiyaphum area. I think most roofing suppliers will have them or know somewhere that will. Just show them the picture. It's not really a specialized job, so any local roofer should easily be able to do it.

Went out to Global House, bought 60 packages of R22 insulation at 200 baht a pack, hired a handyman, and he installed it in the attic. Took him a day. He laid all of the cables and wires on top of the insulation for easy access, and simply cut the sheets where needed, to accommodate the suspension wires as it is a typical suspended ceiling. House is now cooler, and far more comfortable. After I turn the AC off in the bedroom in the morning, that room stays cool for many hours. Used to be an oven within two or three hours. House overall is at least 2-3 degrees (C) cooler. Made a big difference, at a cost of only 13,000 baht. Could not install exhaust fans, as it is a rental house, and there is absolutely no place to vent the attic, without substantial work. It has made the house alot more pleasant to live in. Really worth it.