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Forum Index : Solar : Ceiling Heat Recovery.
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| Phil23 Guru  Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Posted my project in the Micro forum, as it was a bit more related to the micro. Still, it is definitely a form of solar energy, so I'll mention it in here as well. Cheers Phil. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Thanks Phil, Some time ago I spotted a similar idea however there was an extra twist. the roof had that reflective sheeting on the underside of the timbers so there was a 75 mm gap between that and the corrugated iron. the air was drawn from this space. I have tried to find a link or photo and I have found nothing. I do remember that the sheeting started on the first timber in from the edge of the house and stretched to the last timber before the ridge then straight across and down the other side leaving a large triangle space in the centre. the ridge was sealed so outside air could not enter from there and the back was closed in. the air inside the roof was drawn through the holes between the timbers and the iron and heated as it made its way to the centre pitch. I would have tried it myself but my roof is tiled. I'm confused, no wait... maybe I'm not... |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
I don't think the tiles should present an issue. The roof space alone contains a lot of energy. In line fan I used was $150.00, 200mm & 800m³ per hour; the motorised dampers $35 each. It's produced very good results on the right days; Considering my roof space has a problem, the eves being very ventilated in places; you can fell the wind when from the appropriate direction. Average still winter day I can see 27°C in the roof space, at an outside ambient of 19°C. Still very useful energy. Cheers Phil. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Well Spring is almost here & it's been doing fine. Really reduced firewood consumption during both day & night periods, Probably due to retaining a bit more thermal inertia by not letting the daytime temp drop inside. Just been thrown off base for Summer by an old engineer client/friend. I was intending to divert the Summer heat out of the ceiling space with another damper on the fan; had previously used fan assisted Whirly Birds. 40 watts each, but don't move anywhere near the volume of the 100w inline fan. His comment was what I really should be doing is moving the cold air from under the house into the ceiling space to displace the hot air...... Can't argue with the logic & there's not a lot of damp in our climate, but he's thrown out a challenge that's a bit difficult to ignore. Where to plumb it is the main question. Up a wall cavity is the first idea that comes to mind. Any thoughts on the whole idea? Haven't compared temperatures yet, but I know it's always much cooler under there even on 35°C plus Summer days. Phil. |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Ultimately what you are trying to do is cool the inside of the house. Why not draw the cool air from under the house into the house through floor grills or through the bottom of the walls. Then through ceiling vents into the roof cavity. Inside the house will be cooler than putting that cool air directly into the roof. Plus the warmest air inside will be drawn up into the ceiling. What I have decided to do is install air conditioning to run off my off grid solar as I have excess power when there is plenty of sun. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9306 |
Madness - please empty your PM box, so I can reply to your PM to me.  Smoke makes things work. When the smoke gets out, it stops! |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
I often thought of doing that. This would make it possible to just reverse the air flow (if fans do the air pushing) in Winter to heat the house a little during the day. Klaus |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Yes I've had a read about that. Have 2/4 here. A single 8kW in the main living area, And an 8kW Multi-head feeding 3 other rooms. Cheers Phil. PS, waiting impatiently to debate the Hot Air thing, Lol. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Hi Tinker, Did you check my other post? (See above link to the Micro forum). Pushing hot air into the house is exactly what I've been doing for the past 6 months. It's been very effective & efficient. Probably just a 5-6 week frame mid winter where the ceiling heat was insufficient to use. Cheers. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Try telling that to people in a hot air balloon 
Do you have any references to back up your theory? Your ceiling is getting hot due to the air heating in the ceiling and/or possibly infra red heat radiating directly off the roofing material. If you don't have any insulation/foil that is going to cause problems for you. If the air in the roof is getting removed and replaced with cooler air then it can't get so hot. Painting the roof a lighter cooler or even silver will help, I know someone who painted the roof a dark green after being a light cream, the difference was very noticeable. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
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| greybeard Senior Member  Joined: 04/01/2010 Location: AustraliaPosts: 161 |
Same theory I was given by a Physics lecturer back in the olden days. The dense drop to the bottom and the less dense get pushed up. 
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Absolutely correct too. Changes the entire dynamics of things when you look at it that way. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Those that can do, those that can't do teach, those that can't teach, teach those that teach! Cold air displaces hot air, so the hot air still rises, it does not fall or stay still when mixed with colder air. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| greybeard Senior Member Joined: 04/01/2010 Location: AustraliaPosts: 161 |
Partially correct, the colder (more dense) air does displace the hot air by virtue of the colder air moving in the direction of the force of gravity. Putting substances with differing densities into a centrifuge and turning it on will displace the substance with the lighter density away from the outside of the centrifuge. Whilst it appears as though the lighter density has moved towards the center, it is a secondary effect to being displaced by the substance with a greater density. Once you've got your mix of hot and colder air there is no longer any hot or cold air. it's all the same temperature. If you had a sealed container and some method of removing the cold air the 'hot air' would spread out (reduce in pressure) to fill the void. If it wasn't in a sealed container then adjacent air would fill the void depending upon the relative densities of the air. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Particularly if you are maintaining good thermal mass in walls, floor & furniture. Drafts coming in then make a huge difference. Ensuring that I'm maintaining the thermal mass has probably lead to the biggest area of my energy savings. Phil. |
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