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Heating hoop house/ polytunnel with air or water?

 
sam na
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Hi my new polytunnel will be 20 meters from our house/ woodburner. I'd like to use some of it's heat to warm the tunnel.

The obvious one would be to put a spur off the radiator system and put a radiator in the IBC i'm using as a heatstore. However this has the potential to freeze/ crack.

So I was wondering about a 12cm diameter Insulated pipe  dug into the ground with a computer fan at both ends (one sucking, one blowing)

Do you think the heat would stay in the pipe well enough to be worth doing? Or should I think about water some more?
 
Gilbert Fritz
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Location: Denver, CO
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Does your polytunnel have any way to store its own surplus heat during hot days? Many such structures overheat during the winter, and the valuable heat is vented to the sky. If you set up your pipes and fans to blow air into a rock bed, or set up a radiator with water circulated from some 55 gallon drums in your polytunnel, this might work better.

http://permaculturenews.org/2010/08/16/clever-rocky-mountain-greenhouses-give-major-season-extension/

Like that.

Or:

http://northernhomestead.com/car-radiator-for-heating-and-cooling-a-greenhouse/


That would be a long way for computer fans to blow.

Also, pressurized hot water is tricky; you might know this, I thought I would mention it.
 
sam na
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Thanks Gilbert.

In my smaller polytunnel I made such a heat store, it's a copper pipe 60cm deep run along the bedrock, with around 1000litres of water in bottles above it. The air is circulated through the pipe using a 7w solar panel and computer fan.

This certainly helps mediate the temp and keeps it a degree or so warmer than it would be otherwise. I think in the larger new system I'd like some actual heat input.

Maybe it's three or four fans at intervals along the pipe? I'd really like to avoid water if at all possible.
 
Gilbert Fritz
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Location: Denver, CO
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Hi Sam,

Where in the world are you located? How much heat input would you need to keep your polytunnel at your desired temperature?

I'm wondering if the computer fan would burn out pushing against a 20 meter pipe.

Did you look into the climate battery? Jerome is in Aspen, Colorado, which is very cold. And he is growing bananas in a greenhouse without much supplemental heat.

What are you growing in the tunnel? I assume not bananas.

I tend to have a prejudice against heating and moving air; I much prefer heating mass. But if you give your hot air pipe a try, let me know how it goes. It would certainly be easier, if it works, then either of the two systems I linked to.
 
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