Using sub floor air for cooling?

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Using sub floor air for cooling?

Postby moemoke » Wed Jan 13, 2010 11:42 am

As the title says I'm thinking of using the sub floor air to help cool my house down, either this or the wife wants to buy a power hungry air cond :cry: .
We have central heating which draws through a return air grill fitted in the lower section of a wall and exits through ceiling registers in each room,
so I was thinking if I cut some holes in the floor inside the return air duct and suck air from the sub floor, I can turn off the heating and just use the fan to circulate the air, the cool air will be pump out through the ceiling registers. I would put flywire over the holes to keep out any bugs etc and I'd block it off during winter
to reduce the work required for the cental heating

Are there any health risks with using sub floor air?
The area below the floor is about 800 off the ground and the subfloor area is clean, well vented and dry.


Any thoughts?
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Re: Using sub floor air for cooling?

Postby Tracker » Wed Jan 13, 2010 12:17 pm

I could not see that there would be a health issue , provided that there was no mold from consistent dampness..

The only thing that I am unsure of, is just how useful it will be.
The coolness under the house is because of the isolation/insulation (walls etc.) and the cool ground.
I would think that once you start drawing cold air from under the floor, then it must be replaced by hot outside air. I would presume that you would get a benefit for a time, and then nothing, as the air was effectively sucked from outside and there was no thermal mass left to cool the air.

I would like to hear from someone who has tried it to confirm my scepticism..


There is only so much Cold-Heat in the ground, so without burying pipes under the ground it's a short term value to you. You could (depending on space) install a RAC (ReverseCycleAirConditioner) unit under there and at least take some advantage of the cooler air.. ( even if you dug a pit to give more space)

I saw on the tube, a project where a small room was sealed off and fitted with clothes lines, and a fan used to suck hot roof air from the ceiling. A second fan in the wall, sucked the warm air thru the room and outside. The constant cross-flow of warm air, quickly and cheaply dried clothes.
In winter they shut off the exhaust fan, allowing the warm air to flow into the house to supplement heating
That is a practical use of the ceiling energy, as it is continuously replaced by the sun.
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Re: Using sub floor air for cooling?

Postby moemoke » Wed Jan 13, 2010 12:39 pm

Good point Tracker, Our house takes about 4-5 days to get warm / hot inside, the wife says she wants the air con for the 5th day but I know she would have it on most of the time.

Maybe what I need to do is calculate how much cool air is under the house and how much the central heating fan would draw through the hole in the floor, how do I do that?

The drying room is something I would like to try, just need a bigger house
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Re: Using sub floor air for cooling?

Postby Tracker » Wed Jan 13, 2010 2:59 pm

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The space under is 800mm..
The ceiling height is near 3 mtrs..
The house sits on the underfloor..
The underfloor will cool 1/3 of the house for a few minutes !!

A pretty dumb explanation, I know.. but , unless the in-rushing air can loose it's heat to something, fast, then that's it.

In a perfect world, you would install an RAC and run it for half an hour and the house would be cold all day.
Life was not meant to be easy !

Don't get me wrong - it would be better to suck air from under the floor , but it is not going to provide a viable solution (I think) -- Otherwise, many would have done it B4.
The analogy of the Drying room was intended to point to the heat continuously coming from the tiles during sunlight... Under the house, there is little to provide a constant supply of cold.
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Re: Using sub floor air for cooling?

Postby Gordon-Loomberah » Wed Jan 13, 2010 4:44 pm

Tracker wrote:.
.. Under the house, there is little to provide a constant supply of cold.


True, unless you can tap into the ground with a big heat exchanger.

The ground under the house is shaded all the time if it is enclosed, so a metre and a bit down it will be close to your annual average temperature. Transferring your internal house heat into the ground without pre-dug trenches for pipes could be a bit tricky with only 800mm clearance.

A giant bladder full of water sitting on the ground under the floor, and circulating that water into heat exchangers in the house would probably remove a fair bit of heat from the house though.

Gordon
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Re: Using sub floor air for cooling?

Postby Tracker » Wed Jan 13, 2010 5:18 pm

Thanks Gordon..

and -- please, the purist out there, we do know that there is no such thing as COLD..
It's LOW heat, or as I saw a US expert calling it -- Cold-Heat

Dig a pit between the piers -- Line it suitably - Install a trap door in the floor and let the bride sit under the floor when she's hot..

See - I do have some good ideas !
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Re: Using sub floor air for cooling?

Postby KarenS » Wed Jan 13, 2010 10:22 pm

How's the humidity down there? Do you get a lot from the power stations and cooling ponds etc etc?

If not, you could investigate evaporative cooling - much less expensive than Reverse-cycle A/C. Although it does need water, but not a great deal. Less exxy to purchase, and much less exxy to run. It won't turn the house into a fridge, but it should get around 10 degrees cooler than outside, more or less.

I have one, and I'm in Melb, eastern suburbs. Mine was struggling the other day, when it was 43, but I have a 50 y-o weatherboard house with some but not enough insulation, and a hideously exposed west wall, so anything would have been struggling on Monday, or else using hideous amounts of power for a couple of degrees. I just wrapped myself in a damp trowel in front of the fan, and waited for it to all go away!!

If you put the evap cooler on auto, it turns itself on and off, and if your house takes a few days to heat up, you'll find that even if Madam turns the cooling on, she'll have to keep fiddling with it to keep it going if the internal temp is less than about 24 or 25. And unless there are people in the house with some unpleasant illnesses, 24 or 25 isn't really too hot inside for a day or so in our summer.

Also, you can run the evap cooler with just the fan, no water, so when the change finally arrives, you can turn the fan on (like a cyclone if you want, but we prefer a gentle breeze, LOL) and get the cool air outside into the house even when it goes still in the evenings.

Worth investigating - ask around your friends / colleagues etc to see if anyone has one, or go looking for them on rooves, and see if you can ask the occupants!

Evap coolers don't work fabulously in humid weather/climates, so if you get a lot from the local industry, it might not be an option.
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Re: Using sub floor air for cooling?

Postby Tracker » Thu Jan 14, 2010 8:26 am

KarenS wrote:If not, you could investigate evaporative cooling - much less expensive than Reverse-cycle A/C.


Karen - I suppose the energy plate is unreachable - is it? I wondered what power the cooler motor draws.
My first cooler was one of them - a portable one but built into a window in Melbourne.
Useless - Usually when you needed it most, the humidity was high and it just made it far worse.

I have 5 small AirConds, in critical places.. Gradually added them over time. We only turn on the one's that we need at the time.. only cool the room that is needed.. No "wasted Energy"

I saw a great system being built in the US. Mentioned it elsewhere..
It used a combination of evaporative and refrigerated cooling.. Very efficient.. and low humidity, 'cause the refrigeration removed the added moisture, which was recycled to the cooler.

Depending upon needs, I would still go for a small refrigerated unit.. Installed in a critical "Survival Area" , like the lounge room.. Somewhere to go or even sleep, or to help the distressed kids. We HATE humidity!
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Re: Using sub floor air for cooling?

Postby mikepotts64 » Tue Jan 19, 2010 8:00 am

Passive cooling using underfloor air as a cooling source is one of the oldest cooling technologies in hot area building design in Australia and internationally. This method of cooling is particularly effective in combination with ducting through a maze of unglazed ceramic pipes that are drip hydrated to improve evapourative cooling of incoming air. The latter modification can also be deployed if there is no under floor space such as a slab floor. As the cooler under floor air is drawn into the house living space the warmer replacement air is cooled proportionally to the temperature variation from 'outside' to 'underneath' and air flow, ie, the slower the flow (damped inlet or outlet) and greater the temp differential, the greater the cooling effect.

You may also consider cooling a specific area of the house instead of the whole house to reduce the demand on the cooling mechanism.

Passive venting at lowest floor and highest ceiling points that can be 'dampened' by a closing mechanism works best. Ceiling vents in combination with 'wirlybirds' evacuating the roof space are effective. An exhaust fan strategically placed can be used if passive air flow is not viable.

This underfloor venting mechanism enhances the drying of underfloor but I would not recommend this as a solution if a 'wet' underfloor is a problem due to the mould health risks. IN this case the underfloor should be vented to the exterior of the house, passively (opening underfloor vents on prevailing wind side of hourse) or even actively (electric fans).
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Re: Using sub floor air for cooling?

Postby Tracker » Tue Jan 19, 2010 9:17 am

mikepotts64 wrote:Passive cooling using underfloor air as a cooling source is one of the oldest cooling technologies in hot area building design in Australia


Mike - I have not attempted to utilise the sub-floor as a source of "Cold", but are you saying that you will get a long term benefit, without additional measures, like wet pipes etc.
I would have thought that the benefit would be relatively short lived as the warm-outside-air, warms and dries things up under the floor.
For someone who really wanted to try it, and not risk problems with moulds etc. you can get great filter materials that would remove any possible mould spores.
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