In-ground concrete tank as Geo-exchange source

by **wmkemper** » Mon Oct 12, 2009 12:48 pm

I have plans for a 180,000 gallon in-ground tank (needed for fire protection). Can I use this tank for geo exchange? Will the concrete provide adequate conductivity to the earth to make this concept work?

by **jrh** » Mon Oct 12, 2009 7:02 pm

what kind of heating/cooling load are trying to meet?

by **urthbuoy** » Mon Oct 12, 2009 8:25 pm

Your loads will dictate that - you've basically created a very small pond, so I'll say it's unlikely. If you have matching heating/cooling loads taking place on opposite days, yes. If you are planning on pulling heat out all winter, you are unlikely coupled with enough ground to make it work.

That being said, this may be a good opportunity to couple your water bunker with solar hot water.

by **spence57** » Mon Oct 12, 2009 10:07 pm

180 thousand gallons? Are you sure about that number? That's 24,000 square feet of water. You could put water 6' deep into a 4,000 square foot home. If that's correct and you're not heating the Taj Mahal then I think the location of the tank would have a larger influence on it's temperature. As in how much dirt/insulation was on the top of the tank and what type of soil was underneath it. I see a lot of potential.

by **engineer** » Mon Oct 12, 2009 10:44 pm

That's a big tank.

What are the heating and cooling loads of the associated structure?

180,000 gallons of water can store / buffer 1.5 Million Btu per deg F. That's a large and potentially useful thermal storage facility. Whether it can be effectively applied to a geo system is another matter entirely.

by **wmkemper** » Tue Oct 13, 2009 8:45 am

Thanks for the input.
Details:
Heating load: 142,000 btu
Cooling load: 102,000 btu
6" concrete
about 5560 squre feet of contact with earth.

by **Mark Custis** » Thu Oct 15, 2009 6:10 pm

for a spring to tank geo system. I will let you know what I find. My system will get 35 gpm from a spring that never freezes.

Engineer: Help.

by **engineer** » Fri Oct 16, 2009 5:52 am

Mark,

Whatcha got?

35 GPM of eternally liquid water sounds promising, but we both know that won't be the whole story

by **Mark Custis** » Fri Oct 16, 2009 6:11 am

Run the spring water in and out of the tank, as the owner needs the water for his farming activity. I am working on how many BTUH the geo heat pump will need so we can size the tank and the loops contained within. The spring water is very aggressive and will eat 1/4" hardware cloth in a single growing season.

I am starting with a 750 gallon poly tank and then trying to steal the BTUH at design day amounts.

by **engineer** » Fri Oct 16, 2009 6:39 am

Ah - I think I get it - a very small pond with really high flow through it.

If the 35 GPM is truly continuous how about using a stainless steel flat plate heat exchanger? They are used in brewing and other food industry uses so are widely available - I think I've seen them on Ebay. They are small and accommodate high flows with low Delta-P.

Would stainless steel beat back the tough water? It comes in different grades - I believe 316 is tougher than 18-8 / 304. 316 is easily distinguishable from lower grades by it not sticking to a magnet.