Using sub floor air for cooling?

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Re: Using sub floor air for cooling?

Postby mikepotts64 » Tue Jan 19, 2010 10:17 am

The temperature impact is relative, and I'm generalizing, but you can achieve a 5-10 degree shift in internal temperature during the hotest part of the day (highest internal temp),this is when a convective cooling mechanism is at its best. This contrasts to the practice of creating a sub climate in air conditioned areas of a home down to a predefined temp provided the aircon is capable reaching the preset temp.

Regarding water assisted cooling, I have run a 30 metre 100mm teracotta pipe laid 600mm deep in a natural sepage with the intake open to outside air. Soil was a shale so ther was no pooling of water around or in the pipe. I could wet the area with grey water if there was a prolonged dry period in hot conditions. This ducted cooled air into my house by between 5-10 degrees. Flow rate was controlled by a damper on a ceiling vent and on the outlet from the teracotta pipe into the house. All windows were closed to maximise the cooling effect.
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Re: Using sub floor air for cooling?

Postby GreenhouseGlenn » Tue Jan 19, 2010 10:34 am

Years ago my father did as the original post proposed - but more simply by just removing the side panel on the heater that exposed the fan and ensured that the fan sucked in mostly under-house air.

For the minimal effort it certainly helped - for more than a day is my recollection.

The benefit is greater than just the volume of cool air under the house - as the replacement warm air drawn under the house from outside was also cooled appreciably by first passing over the cooler under-house soil/house structure and other junk before reaching the fan. Having the fan in the centre of the house helped here.
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Re: Using sub floor air for cooling?

Postby solar4phil » Tue Jan 19, 2010 12:03 pm

You should take a look at a company called 'HRV" they are a Kiwi and Aussie company that has such a product. It is called a "Summer Kit" it is in addition to their ventilation system that uses filtered, warm thermostatically controlled air from the ceiling cavity to heat a home
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Re: Using sub floor air for cooling?

Postby 470rigby » Tue Jan 19, 2010 3:04 pm

you could investigate evaporative cooling - much less expensive than Reverse-cycle A/C. Although it does need water, but not a great deal
.

I think that you would be surprised to know just how much water Evaporative Coolers use. 30 LPH is not unusual, and more if poor water quality (Suspended Solids, Dissolved Salts etc) means that the bleed off rate has to be increased to prevent deposition. Because they only work at low humidities...usually in inland locations where water is scarcest.... they are not a good option IMO.

Electricity consumption can be considerable too unless a more expensive system with an inverter fan motor drive is used.

Unfortunately we seem to have a shotgun approach to building construction in this country....build energy inefficient houses..and then throw dollars and resources at heating and cooling them :( .
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Re: Using sub floor air for cooling?

Postby greg cooper » Tue Jan 19, 2010 3:05 pm

I recently saw an article on a system titled sub floor pipes or tubes, its a much larger scale than what you require, but provides a concept of an idea that you could use. The key design criteria is identifying how much air you require to provide a certain termperature drop into your space. This will then be a basis for designing how long and how large a diameter your tubes need to be to provide the necessary energy transfer from the ground to the air as it moves through the pipes.

To get an accurate answer you may need to engage an air conditioning designer capable of assessing the energy transfer needs and associated pipe diameter.

The main problem though is that you need to bury the pipe, a challenge I suspect as you only have a low underfloor space to work in.

Anyway the link for an example of a sub floor pipe system is;

http://www.aldoleopold.org/legacycenter ... es.html#ET

Best of luck.
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Re: Using sub floor air for cooling?

Postby Deep Down » Sat Feb 06, 2010 9:26 pm

I have been thinking of using something similar to cool my house. My idea is to bury an earthenware pipe about one metre underground and have a run of about 200m from the inlet to the outlet. One end of the pipe where air is drawn in, the inlet, would be meshed to stop insects etc from getting into the pipe and the other end that comes up under the house, the outlet, would also be meshed. I don't know whether to rely on natural convection to draw the cool air up from the pipe into the house :?: whilst discharging the hot air through the roof or to use a fan. My question concerns the feasibility or otherwise of my plan. Any ideas?

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Re: Using sub floor air for cooling?

Postby KarenS » Sun Feb 07, 2010 12:29 am

470rigby wrote:
you could investigate evaporative cooling - much less expensive than Reverse-cycle A/C. Although it does need water, but not a great deal
.

I think that you would be surprised to know just how much water Evaporative Coolers use. 30 LPH is not unusual, and more if poor water quality (Suspended Solids, Dissolved Salts etc) means that the bleed off rate has to be increased to prevent deposition. Because they only work at low humidities...usually in inland locations where water is scarcest.... they are not a good option IMO .


Mine is not one of those with a continuous water flow. According to our water bill, our daily usage for the quarter ending in mid to late February is about 20 to 30 litres per DAY more than the July quarter, and in any case we are way below the recommended 155 litres/person/day for Melbourne. And I water the lemon tree and the strawberries in the summer too. Melbourne has good water quality. Our electricity consumption goes down in the Jan and April quarters, a lot!

Electricity consumption can be considerable too unless a more expensive system with an inverter fan motor drive is used.
Unfortunately we seem to have a shotgun approach to building construction in this country....build energy inefficient houses..and then throw dollars and resources at heating and cooling them


Yes, I agree about energy inefficient houses - 1960 weatherboards aren't too flash - If I'd known when we bought this hovel what I know now, I'd probably never have bought it, but at the moment I'm stuck with it, and on a pension, so I have an interest in NOT throwing either dollars or resources at it. Yes, an air-con would probably cool bits of it better, but I can't afford to buy one, let alone run it! I have got our electricity usage down to around 9kWh/day in the summer and 12 in the winter, and am using my Green Loan to get a new smaller fridge, some sun blinds, pelmets, heavier curtains, and a major fix of the unshelterable west-facing window. I would extend my PV system if I had more north-facing roof, and if next door's would chop down the *&^%$ tree which shades my panels for about 2 hours in the mornings (they SAID it was going 2 years ago - it's still there, and I offered to go halves with them!). I have an ancient heat pump HWS, and it eats electricity, but I don't get ANY RECS, rebates or anything to replace it, as it is a heat pump.

So for now, the evap cooler is a great deal better than nothing, and from what I can gather from friends who have RACs, the water and electricity consumption is much less.
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Re: Using sub floor air for cooling?

Postby Gordon-Loomberah » Sun Feb 07, 2010 8:27 am

Deep Down wrote: My idea is to bury an earthenware pipe about one metre underground and have a run of about 200m from the inlet to the outlet.... I don't know whether to rely on natural convection to draw the cool air up from the pipe into the house :?: whilst discharging the hot air through the roof or to use a fan. My question concerns the feasibility or otherwise of my plan. Any ideas?


See my previous postings about this system...

Your propsed 100mm X 200m pipe will need a good size fan to get much air through it, convection alone wont draw much at all through it, due to too much friction.
http://gunagulla.com Loomberah weather and astronomy including live solar radiation intensity and UV + Gunagulla aquaponics, organic eggs and cherries
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Re: Using sub floor air for cooling?

Postby 470rigby » Mon Feb 08, 2010 5:32 pm

KarenS wrote:our daily usage for the quarter ending in mid to late February is about 20 to 30 litres per DAY


Evaporative Coolers (let's call them what they are..and not Air Conditioners!) work on the basis of absorbing the Latent Heat of Evaporation from the water that is blown through the filter medium by the fan...therefore..the less water used..the less is the cooling effect. The efficiency of this is due to the Temperature and Humidity of the Air being "sucked" in the Building Interior. My small Bonaire Window Mount unit which does one small 2 room Bungalow consumes a measured 12 LPH on average (I have fitted a dedicated Water Meter)and that is with the Bleed Off inactive (I use rainwater) . Bonaire suggest that the bleed water should be running at 6-12 LPH, and more if the Total Dissolved Solid (TDS) is over 300 ppm.

So, even this small unit with the Bleed Off operating is capable of consuming more than a Melbournites daily water allocation!
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Re: Using sub floor air for cooling?

Postby KarenS » Tue Feb 09, 2010 10:32 am

470rigby wrote:
KarenS wrote:our daily usage for the quarter ending in mid to late February is about 20 to 30 litres per DAY


Evaporative Coolers (let's call them what they are..and not Air Conditioners!) work on the basis of absorbing the Latent Heat of Evaporation from the water that is blown through the filter medium by the fan...therefore..the less water used..the less is the cooling effect. The efficiency of this is due to the Temperature and Humidity of the Air being "sucked" in the Building Interior. My small Bonaire Window Mount unit which does one small 2 room Bungalow consumes a measured 12 LPH on average (I have fitted a dedicated Water Meter)and that is with the Bleed Off inactive (I use rainwater) . Bonaire suggest that the bleed water should be running at 6-12 LPH, and more if the Total Dissolved Solid (TDS) is over 300 ppm.

So, even this small unit with the Bleed Off operating is capable of consuming more than a Melbournites daily water allocation!


Sorry, we're way OT for this thread here, but 470rigby, please note I have only ever referred to what I have as an evap cooler. While I failed Matric Physics in 1964, I do understand how they work. I said we use 20-30 litres per day MORE than in the winter, but that includes a small amount of garden watering. I base my reports of my usage on the information provided by my water bills. As a pensioner with a severely limited income, even if I do get a Green Loan, I cannot afford to either purchase and install, nor run any sort of RAC until I do a number of other things to my house to make such a course of action even vaguely efficient.
I put a Powermate on the Evap cooler the other day (I've borrowed one from the ATA), and it pulled 550watts when cooling on the setting we use 95%+ of the time, and the fan alone (no water) pulled around 420-440 watts. This cools most of the house reasonably most of the time. The A/C people have quoted me a 2.5-3.5 kWh RAC to cool 1 or 2 rooms, and that would not include bedrooms.
Yes, RAC is 'better' in many ways than evap cooling, but it depends on your location, your climate and weather, your house, and your available money, and for the next few years, an evap cooler is going to have to suffice for me, till I move into the retirement village!
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