Increasing air flow rate in a ventilated roof
Increasing air flow rate in a ventilated roof
(OP)
Hello!
I had an idea to increase the air flow rate under a metal roof by painting the back layer of the metal roof sheets that are at the upper part of the roof in black (see pic). Therefore the upper part should be slightly hotter than the lower part (since I'm guessing radiation passes through to the back of the metal roof) therefore creating a higher buoyancy. Sorry if this is a stupid idea, I'm not that good at h&m transfer that's why I'm asking here
. Any cheap ideas on how to increase the air flow are welcomed :). Thanks!

I had an idea to increase the air flow rate under a metal roof by painting the back layer of the metal roof sheets that are at the upper part of the roof in black (see pic). Therefore the upper part should be slightly hotter than the lower part (since I'm guessing radiation passes through to the back of the metal roof) therefore creating a higher buoyancy. Sorry if this is a stupid idea, I'm not that good at h&m transfer that's why I'm asking here
. Any cheap ideas on how to increase the air flow are welcomed :). Thanks!





RE: Increasing air flow rate in a ventilated roof
RE: Increasing air flow rate in a ventilated roof
RE: Increasing air flow rate in a ventilated roof
RE: Increasing air flow rate in a ventilated roof
I know but wouldn't airflow be increased if the upper part would be hotter than the bottom part as opposed to constant temperature over the entire roof?
You're right! To increase the temperature difference even more I can paint 6/7 in white (bottom) and 1/7 or less in black (upper part) and also decrease the heat transmission as you said on 85% of the roof.
So maybe I can get thicker or just put two vertical wooden battens on which the horizontal battens sit, therefore increasing the air gap.
Another thing, since I need to put anti-condensation sheet all over the roof I was also thinking of putting 1/7 aluminum foil(AF) at the upper part as-well. I wanted to put AF all over the roof but the roof producers told me that the wood has to "breathe" through the anti-condensation sheet, so therefore I cannot block it with aluminum sheet all over due to mold formation. But I'm guessing that narrow and long parallel rectangles of aluminum sheets with space between them should let the wood underneath release it's moisture through there and still reflect most radiation in the back of the black paint part of the metal roof.
RE: Increasing air flow rate in a ventilated roof
Even if the gravity ventilation works, it is totally solar dependent and will vary during the day and almost stop at night or on cloudy days. It will also vary with local winds.
How would you even test it to see how much air flow you get?
RE: Increasing air flow rate in a ventilated roof
RE: Increasing air flow rate in a ventilated roof
Furthermore, do the math. For such a restricted air flow channel, you'd be lucky to get 50W/m^2 of cooling, as contrasted with a possible maximum heat load of 800W/^2.
TTFN

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