Geothermal loop field under basement cistern?

[dcb1101]

Hello all,
I have a 3500sqft house that is 2 story's plus a unfinished basement. I have already done a large amount of air sealing and insulating. The next thing I want to do is switch both of my AC units to geothermal. I will be needing a 1.5ton upstairs and a 3ton downstairs.

I am thinking about building a large cistern in my basement that my gutters will fed into for potable water. I am wondering if I can bury my geothermal loop field under the cistern and use this thermal mass without having to dig through the yard.

Thank you for your help!

[S-F]

You might freeze your slab. There are a lot of people here in the "happy Valley" where I live who are fly by night geothermal installers. I've heard more than one story of disapointed customers with $400 electric bills and frozen foundations.

[AC_Hacker]

So, your plan is to use the cistern as a heat sink, not as a heat source, right?

S-F's comment is based on the practice of using the ground as a heat source and drawing out so much heat that it freezes (in his example) the foundation... If the installers knew their stuff, they would have put in a much bigger loop field, and located that loop field a safe distance from the foundation.

In your case, you are going to dump your house's heat to the ground (and cistern).

So, the cistern will get warmer, because the ground it sits on will get warmer... An you will be trying to cool a house that has a continuously-heated cistern in the basement.

Maybe not such a good arrangement.

You might want to think about this one a bit longer...

-AC

[S-F]

Originally Posted by AC_Hacker

If the installers knew their stuff, they would have put in a much bigger loop field, and located that loop field a safe distance from the foundation.


-AC

Very well put. Unfortunately installing geothermal systems seems to have a bit of the flavor of art to accompany it's engineering. Or at least many of the people doing it out here lack the proper engineering. But there are most certainly some experts who have been doing it for decades and know exactly what they are about. The point is that it can be pretty complicated and there are very real concerns which must be respected if there is to be success.

[AC_Hacker]

Originally Posted by S-F

...Unfortunately installing geothermal systems seems to have a bit of the flavor of art to accompany it's engineering. Or at least many of the people doing it out here lack the proper engineering.

There's really not so much art to GSHP installations, the unknowns are now very well known and good, durable procedures have been worked out.

The center for this work is Oklahoma State University, where the International Ground Source Heat Pump Assocoation is located.

They have professional-level trainings on a regular basis, and they have a thorough collection of manuals and software that contain all of the science & lore that has been collected on the subject, to date.

So no, it is not at all a black art... it is a science and a craft with best practices completely spelled out. Now, whether the installers you are referring to in your area have availed themselves to these well-respected resources and practices is another matter altogether.

If their work has resulted in frozen foundations, it says a very great deal about just how little they know, since this kind of hazard is very well understood.

Originally Posted by S-F

But there are most certainly some experts who have been doing it for decades and know exactly what they are about. The point is that it can be pretty complicated and there are very real concerns which must be respected if there is to be success.

Quite so... but it doesn't take decades to come up to speed on best practices, the information is easily accessible.

In the Manifesto thread, I purposely downplayed my technical background so as to not discourage people from trying it out, because I realized I was having successes that did not require any advanced training or degree, and I wanted to enable others to have similar successes.

-AC

[pinhead]

Originally Posted by AC_Hacker

So, the cistern will get warmer, because the ground it sits on will get warmer... An you will be trying to cool a house that has a continuously-heated cistern in the basement.

Don't forget to preheat your domestic hot water in that concentration of heat.