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M Del Senior Member Joined: 09/04/2012 Location: AustraliaPosts: 155
Posted: 02:35am 03 Dec 2018
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"I know that aircon is supposed to be most efficient with a sealed house, but in practice, those extractor fans seem to make a big difference"
Hi Boppa, that little bit of 20-25-30c "ish" room air you are losing to the roof space is taking the place of 50-60c plus air that was sitting on your ceiling insulation. This reduces the heat load transfer through the insulation a huge amount.
In effect, a little like the false roof idea Yahoo2 was talking about except a powered version, not passive. Mark
Jarbar Senior Member Joined: 03/02/2008 Location: AustraliaPosts: 224
Posted: 01:32pm 07 Dec 2018
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I originally experimented with a ceiling fan located in the roof space. This moved stratified air around. I also fitted a large manhole in verandah area which when left open on a hot day significantly reduced temperature in roof, and heat transfer through insulation.
At my mothers house one day the manhole which is in the garage under the same roof-line as house, it was noticed that cover had been lifted off by the wind pressure. This led me to investigate placing a 650 cubic meter/ hour exhaust fan in the cover and a thermostat.In the first instance a Heatermate and subsequently a preset 35 deg button type.
Pumping ambient air into roof-space sees a temperature reduction approaching 10 degs reducing heat load on ceiling and reducing AC cycling times. What seems to be happening is the cooler fan forced air is settling onto ceiling forming a blanket of cooler air.Whats above doesn't really matter unless you have ducting in this space. And it also raises its efficiency.
Was looking to commercialize this by placing a fan in the eaves or verandah but health precluded that happening. I also now open the window and turn on 350 cubic meter/hour exhaust fan in bathroom, then close the door. This draws cooler air into the roof-space at the opposite end of house. Both fans consume about 50 watts each.
House stays noticeably cooler by 2 to 3 degs which equates to a 20 to 30 percent reduction in cooling costs.I should install 650 cubic meter fan in bathroom for greater effect.
Houses with evaporative cooling would do better if some of exiting airflow went via the ceiling as opposed to a window giving the same effect. Both houses had tiled roofs. I also installed one in my sisters corrugated roof home with similar effects.
Whirly birds only move about 100 cubic meters an hour if that.Edited by Jarbar 2018-12-08"Creativity is detirmined by the way you hold your tounge".My Father
"Your generation will have to correct the problems made by mine".My Grandfather.
yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166
Posted: 03:27am 08 Dec 2018
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I called through to see the modified house yesterday. I can give you guys a report.
outside temperature 42 C when I arrived 31 C as I left
weather report bloody hot Hot intermittent cloud then thunderstorms later. no wind, very calm.
The house is open-plan kitchen/dining/lounge plus 4 bedrooms and a poorly insulated attached bathroom that cops afternoon sun on the wall.
There are two of these Akai aircon units in the house, only one was switched on.
the specs say this is what it can cool
The house is actually 210 square meters two bedrooms had the doors shut so one A/C was cooling 160 square meters.
Set at 24 degrees it was running 30% of the time when the outside temperature was around 40 degrees and it settled down to between 15-20% run time when the outside temp dropped below 34 degrees.
100% ontime while cooling is rated 1300 watts
so my best guess is it was using between 240 watts and 400 watts per hour
Temp drop of 17 degrees (41 to 24)is removing 4000BTU (1kw) of energy from the 160 m2 space using 400 watts of electricity.
Temp drop of 11 degrees is removing 2200BTU (600 watts) of energy from the space using 240 watts of electricity per hour.
the only thing I would add is there is a cement floor in half the house that is used as a thermal mass and that was helping a small amount on this particular day, if it was even mildly windy the combination of rapid air changes from the still leaky walls and the shocking heatsoak from the bathroom would have cancelled any effect from the floor.
I have to admit while I can pick faults in what we have done so far, I am hugely impressed with the progress, twelve months ago the same house could not reduce the temperature by 5 degrees with both A/C units running at 100%
It was removing 24,000 BTU's (6.4 kw) per hour and not keeping up. that is a big difference from yesterday. My rough calculations is that we have reduced the heat transfer into the house (on a calm day) by 90-94%.Edited by yahoo2 2018-12-09 I'm confused, no wait... maybe I'm not...
M Del Senior Member Joined: 09/04/2012 Location: AustraliaPosts: 155
Posted: 02:59am 09 Dec 2018
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I was going to start another thread but this is related.
I lost another bathroom extractor fan today, they last 18-36 months (cheap/expensive no difference), but the radiator fan under my wirlybird was 12 years old before I got it and has done 3 years solid work in my roof.
I can get a new 10 inch radiator fan cheap enough or 2nd hand to use in the bathroom but am unsure/don't know what type of power supply to use to give it reliable 12v DC from 240v AC.
Any ideas
Roof space is heating up above normal today. Mark
isochronic Guru Joined: 21/01/2012 Location: AustraliaPosts: 689
Posted: 09:38am 12 Dec 2018
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Is it worth using an evaporative cooler to cool the water (eg outdoors), then piping the cooled water to a heat exchanger (ie car radiator) inside ? At a guess many evaporative coolers could be modified fairly easily, and it would still be cheap to run
Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664
Posted: 10:58pm 15 Dec 2018
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Hi Glenn,
I curious about what could be achieved if you could use the radiator as an evaporator & the 80W to run some sort of compressor.
Condenser end being a copper element in a nearby water tank maybe.
The whole lot charged with; what's it called? R290???.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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