Thread: Semi Passive Cooling. Ingenious or Insane?

Background
My intended build area is lower Nakhon Sawan where it is, quite frankly, bloody hot all year round (3 days below 30 degrees in the last year).
The house will be a low stilt house with a high roof and plenty of both natural and mechanical ventilation and shade. Only the bedroom will be wall insulated and airconned. The roof will be white or silver and will have an internal radiant barrier on top of the ceiling.
The objective is to add cheap green cooling.

Please note I have little idea of the mechanics of heat interchange and air, nor materials science.

The Idea.
Reading up on passive cooling systems, I have started to think about the adjoining fish pond which at 3 meters or so is pretty cool down the bottom.
How to leaverage this naturally cooling source?

The Plan.
Build an array of pipes with several inlets and outlets and sink it to the bottom of the fishpond. Use solar powered fans to draw air through this array, where it is hopefully cooled by the surrounding water and expell it into the house through several vents.

The bits I have no idea about.

Pipe material.
The standard blue plastic plumbing pipe, will this allow sufficent heat exchange between the water and air? Is there something better?

The length of Run. How long will the air need to be in this pipe under water to cool it to the maximum?

How to stop Condensation from filing up the pipes and keep them clean. Will these pipes just turn into a giant germ factory pumping poison into the house?
Could some sort of wick system extract unwanted water buildup?

Net Result. Could this process inject enough cool air into the building to noticably cool it.

Costs. Somes hundred (?) meteres of blue pipe.
Some glue.
One or 2 solar fans
Some Somchai time.

It is worth the effort or am I a clueless loon with too much time on his hands?

You want to add fins to that pipe to maximize heat transfer. I'm not a materials expert, but I don't think plastic blue pipe will suffice. You want something with a good heat transfer. You'll also have to insulate the pipes carrying the air to the house or it will heat up before you get to the house. You'll also have to have large enough fans to push/pull the air down into pond and then be able to get that air back over to the house. A filter system will be needed so you don't suck all the little things flying around in the air.

But the biggest problem is the fish pond. You're going to heat it up. It doesn't matter that it's 3 m deep. It depends on the area of the pond and amount of water (heat sink) available. You have to get the heat that you just dumped in the fish pond out of the pond or it will heat up, which your fish won't like that much. I don't think it will be viable.

Originally Posted by stevefarang

You want to add fins to that pipe to maximize heat transfer. I'm not a materials expert, but I don't think plastic blue pipe will suffice. You want something with a good heat transfer. You'll also have to insulate the pipes carrying the air to the house or it will heat up before you get to the house. You'll also have to have large enough fans to push/pull the air down into pond and then be able to get that air back over to the house. A filter system will be needed so you don't suck all the little things flying around in the air.

But the biggest problem is the fish pond. You're going to heat it up. It doesn't matter that it's 3 m deep. It depends on the area of the pond and amount of water (heat sink) available. You have to get the heat that you just dumped in the fish pond out of the pond or it will heat up, which your fish won't like that much. I don't think it will be viable.

Good point, didn't think of the fish. Though they are tropical....
Could bury the pipes under the pond.

aircon seems to work OK

Originally Posted by DrAndy

aircon seems to work OK

Not when the power is off.

Check this site out:

GeoComfort Geothermal Systems | The geothermal process

It's a pity that the evaporative cooling systems you see in Australia don't work in the tropics, they are relatively cheap and work great.

Evaporative coolers work well in desert heat but here you will still have the humidity to deal with. Good luck though hope it works.

Originally Posted by Necron99

Originally Posted by DrAndy

aircon seems to work OK

Not when the power is off.

Once our house is finished, over in Nakhom Pathom, I intend to work with my son (graduating Electrical Engineer this year) to design a solar/wind system to run at least one a/c unit and hopefully the rest of the house load. If I can generate enough juice to run more than one a/c unit, great !!

We are fortunate in that we have 3 large lots, 1 for the house and 2 spare. We have room for solar cells and we do tend to get a good breeze there.

I don't know if you can find anyone who can competently build a geothermal system in Thailand and I'm not even sure how huge the grid (heat sink) would be to provide adequate cooling for a house. If you're able, please keep us updated.

Originally Posted by stevefarang

Originally Posted by Necron99

Originally Posted by DrAndy

aircon seems to work OK

Not when the power is off.

Once our house is finished, over in Nakhom Pathom, I intend to work with my son (graduating Electrical Engineer this year) to design a solar/wind system to run at least one a/c unit and hopefully the rest of the house load. If I can generate enough juice to run more than one a/c unit, great !!

We are fortunate in that we have 3 large lots, 1 for the house and 2 spare. We have room for solar cells and we do tend to get a good breeze there.

I don't know if you can find anyone who can competently build a geothermal system in Thailand and I'm not even sure how huge the grid (heat sink) would be to provide adequate cooling for a house. If you're able, please keep us updated.

At it's heart it's just some pipe with air blowing through it. Wouldn't need any skill to construct. Heres a one page review of the process as applied to earth buried pipes. Mine being in water would be easier and cheaper. What's 4 inch blue pipe going for right now?

Design notes on earth tube cooling

Originally Posted by Necron99

Originally Posted by DrAndy

aircon seems to work OK

Not when the power is off.

It would be cheaper to buy a generator if you have power problems.
Or you could build a house into a side of a hill as the under ground is
cooler about 20 deg C

Is guess its an idea worth piloting, but I would thought that even at the bottom of the pond the water temperature is not going to be comfortably cool.

There are systems that use hot water to drive an air-conditioning cycle, but the systems I have seen have been more of a commercial building scale.

Originally Posted by stevefarang

Originally Posted by Necron99

Originally Posted by DrAndy

aircon seems to work OK

Not when the power is off.

Once our house is finished, over in Nakhom Pathom, I intend to work with my son (graduating Electrical Engineer this year) to design a solar/wind system to run at least one a/c unit and hopefully the rest of the house load. If I can generate enough juice to run more than one a/c unit, great !!

We are fortunate in that we have 3 large lots, 1 for the house and 2 spare. We have room for solar cells and we do tend to get a good breeze there.

I don't know if you can find anyone who can competently build a geothermal system in Thailand and I'm not even sure how huge the grid (heat sink) would be to provide adequate cooling for a house. If you're able, please keep us updated.

You can forget doing it with solar in Thailand. To generate enough electricity via solar to power one 18,000 BTU home air-con will cost around 800,000 thb for the solar system. The return on investment is 20+ years.

During the flood I bought a 25 amp output gas generator. The cost was 22,000 thb. Probably the smartest thing I ever did. I spent about another 1,000 baht and bought some heavy duty wheels so the generator can roll around quite easy. Really a godsend when the power goes out, or when we want to travel somewhere and need electricity. Key start, just turn the key and you are ready with instant electricity.

^^I suspect that very few installations use solar cells to drive air conditioners, when its far more effectent to use systems based on hot water.

Originally Posted by liveinlos

Originally Posted by stevefarang

Originally Posted by Necron99

Originally Posted by DrAndy

aircon seems to work OK

Not when the power is off.

Once our house is finished, over in Nakhom Pathom, I intend to work with my son (graduating Electrical Engineer this year) to design a solar/wind system to run at least one a/c unit and hopefully the rest of the house load. If I can generate enough juice to run more than one a/c unit, great !!

We are fortunate in that we have 3 large lots, 1 for the house and 2 spare. We have room for solar cells and we do tend to get a good breeze there.

I don't know if you can find anyone who can competently build a geothermal system in Thailand and I'm not even sure how huge the grid (heat sink) would be to provide adequate cooling for a house. If you're able, please keep us updated.

You can forget doing it with solar in Thailand. To generate enough electricity via solar to power one 18,000 BTU home air-con will cost around 800,000 thb for the solar system. The return on investment is 20+ years.

Thank liveinlos,
I know the return will be a while, but it will be a mix of solar and wind. The set-up I envision will be modular and quite simple. It will take up some space, but we have plenty of land to do it in.

Originally Posted by hazz

^^I suspect that very few installations use solar cells to drive air conditioners, when its far more effectent to use systems based on hot water.

I am familiar with steam powered a/c systems, but they would be impractical for a house, they require a vacuum pump, the fluid inside is extremely corrosive & can crystallize if you're not careful, and you have to have a reliable source of steam.

Do you have any details on this hot water version? Obviously, there will be a need to generate hot water. So I wonder how efficient it really is.

Thanks!

^the solar hot water air cons use water with a min temperature of 80c so you have to use the evacuated tube solar systems. I belive the heat pump units use a ammonia as the refrgerent which is used to chill glycol. I have details which i will try to dig up of a demonstration of the techology at a university installed about 6 years ago. If. Rember the efficeny is not hat great. To create 1000 btu of cooling, you need 1000 btu heat in the water and you have to dispose of 2000 btu of heat into the air outside.

The alternative, is to use a desicant disk, it drys the inbound are, which is then cooled by evaporating water into it, the desicant is then recharged using hot solar heated air to drive off the water. But this would only work with cental ar conditioning.

Only to your idea to blow air through pipes in the pond. If at all the other way around would be efficient. Pump water through pipes in the house and do the heat exchange there. You cannot move enough air with small energy use. To avoid clogging of the pipes you would probably need a pool filter too for that water.

I also have no idea what it will do to the ecology of the pond if you heat up the bottom. Probably best to take out the cool water near the bottom and let it reenter the pool near the top. But with the small difference in temperature you will need fairly large exchange surfaces. If I would try anything like this I would probably put the pipes in a concrete floor for exchange and insulate from below. So the floor would remain cooler and produce a sensation of coolness in the room.

The most effective part of a natural cooling system might be clinging plants growing up the sun exposed walls. But my wife would not approve because it might be a habitat for snakes.

A picture of a floor heating system. To give you an idea on how much piping would be needed. The heating would have a greater temperature difference to work with but it aims for a bigger temperature difference to achieve as well. So a similar density for your application might be appropriate for a little cooling.

If the pool is big enough to provide enough of that cooler water.

insane

Originally Posted by hazz

I suspect that very few installations use solar cells to drive air conditioners, when its far more effectent to use systems based on hot water.

Tesco do.

Originally Posted by Necron99

It is worth the effort or am I a clueless loon with too much time on his hands?

Sorry, but I have to side with the latter
Invest in a generator or hook a fan up to a pushbike and kill 2 birds with one stone by excercising the wife