Geothermal control

Brett Hall

http://www.honeyrunapiaries.com/store/ranco-etc111000000-digital-temperature-controller-p-86.html

Here's the unit, this place is calling it the Goldline SP-30 alternative. From the datasheet of the SP-30 I didn't think that unit would have done what I needed, but maybe it would have.

For info, I bought one of these on eBay for under $50 shipped. Certainly worth the money considering how long it would have taken me to design and build my own. The electronics aren't terribly complicated, but building one-off electronics isn't fast.

-B

Brett Hall

Supplemental geothermal heat pump control

I've got a geothermal/radiant setup that requires some fine tuning. The rundown is that I've got 3 zones, 3-loop (500 ft. ea.) basement in 8" concrete, 4-loop 1st floor (hung under subfloor), 3-loop 2nd floor (hung under subfloor). Unless my basement loops are running the system doesn't dissipate enough heat fast enough for my 5-ton geothermal unit. After probably 45-minutes of 7-loops running the return water temp has crept up enough to trip the geothermal unit off. The radiant is directly fed from the geothermal btw.

What I'd like to do is limit my loop temperature to 90 or 100 degrees max. So, what I'd like is a product with a single temperature sensor and a relay. Optimally, it would open the relay if the temperature sensor (on the return water) reached 85 degrees and then close when it got down to 70. It would also be nice if it would keep from turning back on until at least 10 minutes had passed, but that's not as critical. This way my radiant system would continue to circulate hot water. If the radiant system stopped calling for heat while the geothermal was off, then no big deal because the control line going through the relay would now be off anyway.

Does anybody know of a product that does this or a way to accomplish it?

Just for info, with 7 loops on (I don't allow my 2nd floor to run by itself) it takes approximately 45 minutes to reach 90 degrees on the return side, and it takes about 15-20 minutes to get back to 70 degrees so short-cycling is not a huge worry.

Thanks,
Brett Hall

GW

GEO

so, maybe you need a buffer tank? You may also need some smarter controls calling the shots like Tekmar. Do you have a local geothermal contractor?

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Brett Hall

Option found

I purposely didn't design in a buffer tank as directly run off of the HP is the most efficient. There are a couple of geothermal contractors around, but I installed this setup myself.

What I did is I just bought a Ranco Electronic Temperature controller. This will do exactly what I had explained using a single temperature probe and a relay. It uses 1 or 2 temperature setpoints and temperature differential settings to accomplish what I'm looking for.

The difference between this and normal aquastats is that this will work for temperatures down to -20 (for chilling applications) whereas many of the aquastats I looked at couldn't be set for anything under 120 degrees.

Thanks for the reply,
Brett

GW

great

do you have a link to that beast?

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