White Roof Tiles - Passive Solar Cooling

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White Roof Tiles - Passive Solar Cooling

Postby arranp » Sun Jan 11, 2015 7:37 pm

Please note no hypothesis on my part, just publishing what I have found on the internet via google with various search keywords, topics may also be coolthai house however have not ranked on the first page or 2 of google result, I take no responsibility for this.

Quick Summary of Results from FSEC Study on the Effect of Roof Construction on Attic Temperatures: http://www.builditsolar.com/Projects/Cooling/FSECRoofPaperSummary.htm
results:
Typical mid June attic temperatures with various roof constructions

Attic
Temp Roof Material + Ventilation Area
134.9 Black shingles, no radiant barrier, ventilation area 1 in 300
128.1 Black shingles, radiant barrier, ventilation area 1 in 300
116.1 Black shingles, radiant barrier, ventilation arae 1 in 150
115.7 Red tile
102.2 White metal (68% reflectance)
091.5 White tile (72% reflectance)

For this typical day, peak ambient temperature was 92F.

Conclusions:
The radiant barrier alone results in a modest improvement

The radiant barrier plus more ventilation area results in somewhat more improvement

A dark colored tile roof is about as good as radiant barrier plus more ventilation

White tile or white metal roofs result in a marked improvement over all the above.


David's White Roof Experiment: http://www.builditsolar.com/Projects/Cooling/WhiteRoofExperiment/WhiteRoof.htm
results:
House temperatures with regular roof and AC OFF......... 87-92F.
WHITE ROOF (and ac OFF)........ 79-82F.

ATTIC temperatures with regular roof.................... 120 - 140F
WHITE roof ................... 90 - 97F
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Re: White Roof Tiles - Passive Solar Cooling

Postby Andyfteeze » Mon Jan 12, 2015 4:47 am

This white roof ref you posted is full of holes. Its full of contradictions and very shallow analysis of whats going on.
Eg, white roof keeps house cooler than styrofoam in ceiling. Then he mentions venting along the ridge.

Everyone knows a white or bright objects reflect heat and dark surfaces not so much. BUT it is not the only factor at play.
What are the thermal properties of hydrated lime in this scenario? What are the shingles made of?
Is hydrated lime acidic or alkaline? How many hrs of sunshine per day? The list goes on.

Use good practice and materials in the roof design AND then paint the roof white or buy white materials.
Just painting a roof white is of some minimal benefit only. Do somemore reading Arranp. The space shuttle had both black and white tiles. But then 10% of 1500c is different to 10% of 60c
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Re: White Roof Tiles - Passive Solar Cooling

Postby arranp » Mon Jan 12, 2015 9:02 am

is it agreed a white roof is an efficient if not the efficient way to cool the attic ?

the same afternoon, I read Fredlk thread about his house in Sattahip, he used a colourbond white roof.

My time is taken up by taking care of my 2 children (6 years and 3 years) single father, no nanny, and running a 130 room accommodation in the UK from my home in thailand.
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Re: White Roof Tiles - Passive Solar Cooling

Postby fredlk » Mon Jan 12, 2015 9:13 am

arranp wrote:is it agreed a white roof is an efficient if not the efficient way to cool the attic ?

You're turning things around. The white roof does not cool the attic, BUT stops it from heating up.

My research told me that metal roofs were less of a heat-sink than tiles or concrete.
Further research told me that a metal roof, colour white would reflect 92% of the sun's heat which was the highest number I could find.
Add to that the PU-foam insulation which maybe accounts for a 50% heat reduction, I find that my rooms - I have no attic - do not heat up at all in the sun.
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Re: White Roof Tiles - Passive Solar Cooling

Postby arranp » Mon Jan 12, 2015 9:22 am

Thanks Fredlk,

I looked at yours and that confirmed what I read on the net.

what do you do to achieve ventilation ?

I understand you used 2 courses of superblock with insulation in the cavity, you windows are 260 high, did you use any film on the windows or special glass to keep the heat out?
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Re: White Roof Tiles - Passive Solar Cooling

Postby fredlk » Mon Jan 12, 2015 9:41 am

arranp wrote:what do you do to achieve ventilation ?

The whole house is only one room deep meaning that every room and bathroom has airflow from a minimum of 2 sides while most have it from 3 sides.
arranp wrote:I understand you used 2 courses of superblock with insulation in the cavity

I used a single course of 20 centimetre superblock which will achieve the same result I guess.
arranp wrote:you windows are 260 high, did you use any film on the windows or special glass to keep the heat out?

The roof overhangs are mostly a minimum of 2 metres which keeps the sun off the windows and a couple are even 3 metres. I have no film or special glass.
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Re: White Roof Tiles - Passive Solar Cooling

Postby arranp » Mon Jan 12, 2015 12:16 pm

fredlk wrote:
arranp wrote:I understand you used 2 courses of superblock with insulation in the cavity

I used a single course of 20 centimetre superblock which will achieve the same result I guess.


did the 20cm hide the columns, I would imagine the columns are wider than 20cm ?
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Re: White Roof Tiles - Passive Solar Cooling

Postby arranp » Mon Jan 12, 2015 12:30 pm

arranp wrote:
fredlk wrote:
arranp wrote:I understand you used 2 courses of superblock with insulation in the cavity

I used a single course of 20 centimetre superblock which will achieve the same result I guess.


did the 20cm hide the columns, I would imagine the columns are wider than 20cm ?


columns in the bungalow I'm renting are 24cm, so I guess with the render, columns are 20cm.
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Re: White Roof Tiles - Passive Solar Cooling

Postby fredlk » Mon Jan 12, 2015 1:22 pm

arranp wrote:did the 20cm hide the columns, I would imagine the columns are wider than 20cm ?

If you'd look at some of my photos you would see that they did. The whole idea of 20 centimetre superblock was to hide the columns.
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Re: White Roof Tiles - Passive Solar Cooling

Postby arranp » Mon Jan 12, 2015 1:43 pm

fredlk wrote:
arranp wrote:did the 20cm hide the columns, I would imagine the columns are wider than 20cm ?

If you'd look at some of my photos you would see that they did. The whole idea of 20 centimetre superblock was to hide the columns.


I'm sat here generating weekly statements for 130 tenants and updating the business account, now I have to go collect the kids from school, forgive me for not have the time to look through your material.
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Re: White Roof Tiles - Passive Solar Cooling

Postby fredlk » Mon Jan 12, 2015 1:52 pm

arranp wrote:I'm sat here generating weekly statements for 130 tenants and updating the business account, now I have to go collect the kids from school, forgive me for not have the time to look through your material.

Then I suggest you wait till you have some downtime and read through some of the building stories for the wealth of information in them.
You will learn a lot and at the same time see that many of the questions you pose have been answered a number of times.
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Re: White Roof Tiles - Passive Solar Cooling

Postby arranp » Mon Jan 12, 2015 2:14 pm

yed, but the children want my attention. im a single father with a 3 year old and a 6 year old
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Re: White Roof Tiles - Passive Solar Cooling

Postby schuimpge » Mon Jan 12, 2015 10:18 pm

Andyfteeze wrote:This white roof ref you posted is full of holes. Its full of contradictions and very shallow analysis of whats going on.
Eg, white roof keeps house cooler than styrofoam in ceiling. Then he mentions venting along the ridge.

Everyone knows a white or bright objects reflect heat and dark surfaces not so much. BUT it is not the only factor at play.
What are the thermal properties of hydrated lime in this scenario? What are the shingles made of?
Is hydrated lime acidic or alkaline? How many hrs of sunshine per day? The list goes on.

Use good practice and materials in the roof design AND then paint the roof white or buy white materials.
Just painting a roof white is of some minimal benefit only. Do somemore reading Arranp. The space shuttle had both black and white tiles. But then 10% of 1500c is different to 10% of 60c


Not very scientific, given how one month in TH doffers from the next, but after painting my roof white (concrete tiles, old, dirty dark greyish color before paint), my electricity bill dropped 500 baht.
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Re: White Roof Tiles - Passive Solar Cooling

Postby Andyfteeze » Wed Jan 14, 2015 5:01 pm

Is that the same as 20% reduced fat? :D
you saved 500b, but from what ?
Keep a track of the next few months and then we can see a trend. But dont forget to tell us the plasma died and you got an LED tv. :D
There are many factors at play and infrared reflection is but one. What are the thermal properties of the paint you used? Is the roof space ventilated?
what was the temperature during that month? Did you turn the aircon up from 18c to 25c? did you go on any holidays? Did you take less hot showers? Did you have more people living with you previously? Did the hot water unit run for shorter periods? did you do less washing? was the electricity tarrif correct? Did they read the meter correctly? we have had many variations over the last 12 months. i can go on, but you get the picture.........fair comment demands you cover every base. :D
But hey, if you discover a 20% reduction in your bill, we DO want to hear about it. just need to fill us in on any variables that influenced the result.
" they say you want a revolution, yeh air air
we'd love to see the plans" CHL
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Re: White Roof Tiles - Passive Solar Cooling

Postby fredlk » Wed Jan 14, 2015 5:07 pm

Andyfteeze wrote:........fair comment demands you cover every base.

Which he did extensively in his building story. Get reading!
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