geothermal heat pump in greenhouse

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Old 01-28-09, 08:29 AM
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geothermal heat pump in greenhouse

This one MUST be interesting -- it's the old question of how to best heat a greenhouse BUT I'm investigating using excess heat from my de-superheater (DSH). I'm cross posting to the Heat Pump forum because I have two concerns that I need an expert opinion on: 1) will it hurt the HVAC equipment (Heat Pump forum)? and 2) is it healthy for the plants (greenhouse / shed forum)? Read on...

I have a geothermal heat pump (external split which means the pumps for the ground loops are outdoors). Also outdoors is my de-superheater (DSH) which reclaims heat from the main heat pump and converts it for use by my hot water heater. I was going to just insulate the DSH because it is all copper and throws off a lot of heat... it needs to keep circulating water the colder it gets to keep from freezing up. ANYWAY... I eventually thought "why not just build a greenhouse around it and use the DSH heat? I can isolate and vent it in the summer".

Make sense? Any problems with the equipment as long as it is well vented when it is hot? Humitidy issues? I thought, if the plants stay healthy then surely some equipment must stay healthy... T/F?
 
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Old 01-28-09, 07:39 PM
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What is he up to now????

knot completely understanding how a system works and trying to re engineer it is is knot a good idea.

The beauty of a Geo system is that the earth temp is a pretty constant (say) 50 degrees. The comp in heat or cool gives up or picks up heat at a constant rate versus the extreme fluctuations on the ambient air.

At some point in Geo development someong thought "Hey, before we dump this heat into our loop water and then into the earth, lets put some in the water heater 2 or 3 feet away". I call a desuperheater a heat recovery because that is what it does. It recovers heat that will be injected into the earth and sticks it in the water heater.

Your heat recovery should be insulated. There is a temp switch (should be) to start the circ pump around 120 and stop it around 140. Not going to freeze because of circulation and radiant heat from other components.

The heat recovery is designed to inject heat to the hotwater tank, not heat a green house. BTU's at work here.
 
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Old 01-29-09, 03:23 AM
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geothermal heat pump in greenhouse

Maybe knot such a great idea but, wit all due respect (and I mean that sincerely!), I dont know if I was clear before. I understand the basic mechanics (pumps, ground loops, heat recovery (HRU) and house conditioning requirement). There is a circ pump on the HRU BTW.

But was I clear that the HRU is outdoors? The pump / condenser is outdoors too. It gets as low as 0 - 10 F here in N. Virginia where I am.

I fully accept that I need to insulate the HRU and thats what started me on this. My idea to build a greenhouse around it stems from another project I was working on. It seems heating a greenhouse is always one of the little challenges but folks talk about using as little as 2 x 100 W light bulbs. The HRU is scalding hot to the touch when it is running (about as hot as a hot light bulb - maybe more) so I would think it throws off enough. Right now those BTUs are just going out into the night air.

I think VERY few people will even have this type of arangement (outdoor geo compresor AND outdoor HRU) so wont understand what the opportunity is. I'm not a huge fan of nutty ideas but this just seems possible. A bit like reclaiming excess heat from the heat recover unit (if that makes any sense!).

Thank you ALWAYS for the great steer on different issues - this site has always sent me the right direction so I am a big fan. Given all of that, is it a dumb idea to enclose your outdoor geo pump and HRU in an outdoor greenhouse or have I just done one to many DIYs? Will it hurt the kit?
 
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Old 01-29-09, 11:10 AM
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I think I would just insulate it. I don't see this as excess heat. I see this as lost heat since your in the heating mode. Greenhouse cooling is also a problem in the summer. If you system has enough spare capacity you can find a better way of heating your greenhouse.

If your designing a new greenhouse, I would incorporate a system that uses the ground as a large heatsink. Essentially, they duct warm summer air through underground pipes and heat the hundreds of tons of earth and are able to extend the growing season 6-8 weeks, a primative geosystem. There are plans available online. Then you can always supplement with addditional heat if desired.
 
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Old 01-29-09, 04:17 PM
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Well, first of all, in my experience you generally have come up with some very good ideas.

But, with due respect, the good idea comes at the top of the hill and getting down the other side isn't mentioned.

Many people in Hampton Roads have Geo's outside in little shed type things. I've seen some with elec baseboards in them.

Making a green house would trap the radiant heat and make a greenhouse. One could also re pipe and heat the greenhouse area when the hot water tank is satisfied.

Chris brings up good points with respect to cooling. You do not always heat a greenhouse, heat has to be removed at some point.

Again my friend you have a very good idea. Heat a greenhouse with excess heat. What about removing excess heat from the same greenhouse?

Basic HVAC, not only do we have to put heat in efficiently, we also need to take it out.
 
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Old 01-29-09, 04:50 PM
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Thanks gents. Quite a bit of engineering to do on this one -- as you point out. If I cant crack how to properly vent the excess heat in the summer then it will get filed in the "one minor little issue" drawer ). Will let you know if it ever takes off and thanks for your inputs!
 
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Old 01-29-09, 05:48 PM
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I will add one more point with regard to heat rejection.

You already have water.

But code and common sense precludes mixing drinking and process water.

I've a feeling there will be good news at the end of this tunnel.
 
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