# geothermal; convert forced air to radiant floor?



## barnartist (Jan 5, 2011)

Hope im in the right place...

My Dad has a geothermal system in his home. I have a wood boiler and installed radiant floors and love it. When I visit his home it is not comfortable and the floors are cold. I would like to learn about what it would take to run a radiant system on a geo unit. While I dont know allot about geo, I realize the idea is behind a constant temperature of water coming from the ground (52 or so?). 

First of all I still dont understand how this kind of system helps with winter heating, but there must be a plus or they would not be installed. Anyway what would need to be done-get that 50f water up to 120f or so? This is where I lose focus because I am aware that even the coldest water returning from a radiant run would be way warmer than any ground water.

Any help or direction on this matter would be great!


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## semipro (Jan 5, 2011)

I maintain and operate a geothermal system at my house but I don't consider myself an expert.

One way to think of a heat pump, any heat pump, is like a fridge running backwards.  The compressor, evaporator, condenser, etc. operating on the Rankin cycle "concentrate" the heat and move it from one place to another.  

In a geothermal system the heat source/sink (the ground or groundwater) contains a lot of heat even if the temperature is low.  Basically any substance with a temperature above absolute zero contains heat.  That heat is transferred to the house by piping where it flows through a heat exchanger to transfer the heat to freon and then energy is added via a compressor etc. to concentrate the heat at a point where air can blow through it and be circulated to the house (air coil).  That same heat can instead be concentrated in a liquid flowing through radiant in-floor heating.  You just need a different heat exchanger instead of the air coil.  

The answer to your question is yes, it can be done.  There are some pretty good sources on the web.  

http://www.greenbuildingtalk.com is a pretty good resource for this.  

Good luck.


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## CALJREICH (Jan 5, 2011)

Yes, but at some cost and losses.
It CAN be done but at some cost, both in terms of money and efficiency.

If you go geothermal you need a heat pump, and what a heat pump basically does is concentrate heat, from your pickup which has loads of volume but a low concentration and into your heating system which has less volume but needs more concentration. 

The trouble with using geothermal to feed baseboard heaters is that the baseboard heaters needs to be fed with a rather high temperature to work properly, which means that the heat pump must work hard and well to be able to concentrate that kind of temperatures out of the pickup loop.

It's easier to use geothermal to power a water-carried floor heating system. The bigger area of the floor heating system as compared to the baseboard heaters enables the heated floor to be able to work properly at a much lower temperaure of the input water. 

If I remember correctly a heated floor will operate from as low feed temperatures as 45 deg C, while baseboard radiator requires around 20-30 deg C higher feed temperatures.


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## btuser (Jan 5, 2011)

My advice would be to learn to love the geothermal and then get a wood stove for the cozy corner.  Even a pellet or gas stove for local heat. If he can't handle the stress or real wood then get biobricks or something.  Adding floor radiant after the fact is hard.  Really hard.  You would have to run tubing all over the place. Not a big problem if its a ranch with an unfinished basement but what about the 2nd floor?


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## barnartist (Jan 5, 2011)

Much of my dads living area upstairs has unfinished basement below, and exposed floor joists. A small part of the house would continue to run on the forced air. 

In running my system I am familiar with the temps needed for certain types of heat. I am slowly converting all of my forced air to floor radiant because I am able to heat on such lower temps. My air exchanger works best at 180f, while my floor heats great even down to 100-130f.

I certainly dont want to run less efficient if geo runs best exchanging water to air.


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## spacecowboyIV (Jan 5, 2011)

It is possible for a geo unit to heat up the water in a radiant system.  My dad used to heat his barn with an outdoor wood boiler with in floor radiant heating, when he decided he didn't want to do that anymore he had a geo unit installed that heats the holding tank and then pumps through the concrete slab piping to heat the area.  I am constantly surprised at how such a small unit can heat such a large area.


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## hemlock (Jan 5, 2011)

One thing to consider is capacity.  Would you have to increase the overall "tonnage" of the current system to accomodate radiant?  Radiant requires lower temps, but a bit more capacity.  If you had to drill another well, or lay antoher loop, it could get costly.


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## pybyr (Jan 5, 2011)

I've got no direct experience, but I'd think that an existing geo. heat pump that was set up to provide warm air heat would have even more capacity for in-floor radiant, being that the required temperature differential (between source and load) is actually lower.  

What I do wonder is whether you'd be getting into complex/ expensive parts and labor to change the HP's output heat exchanger from air to water (especially if you still wanted the air HX in place to use for A/C in warm months).  That'd depend very much on the particulars of the unit that is there, and an evaluation by someone who really knows that unit and is knowledgeable/ open about whether it is compatible with adaptations.


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