Re-thinking geothermal

[Rob-D]

Hi gang,
Well as some of you know I've been working up the numbers to do a geothermal at my place.
I figure doing it myself will save me about 15 to 18k. The price for my 3 ton system is ~25k and I can do it under 10k.
I dug a 6' deep hole yesterday and ran some sensors down to see what the temp is at different depths.
The temp at 6' is 42.26F and at 5' it's about 1.35F different (probably warmer in the summer and colder in the winter)

Here's the problem. If I use a heat pump I'm converting 42F to 115F to my radiant tubes. Right now I'm converting my basement temp (~58-65) to 115F.
The spectrum is much greater to convert the 42F to 115 than it is to convert 55 to 115. And the spectrum equates directly to energy use.
Granted I'll be off oil but in this climate I'm not sure it's a good idea.
Living in the south is different story. You guys have 8 or 9 months of heat and that 42F works in your favor because most of you HVAC is in cooling, not mine.

So what's your input on this? I know some of the northern climate people have geo in.

Thanks,
Rob

 

[tractordog]

Can you do a open loop system?

 

[amaxwell]

I don't understand your thinking on the temp. diffrence.The heat pump will be using the ground temp.in winter instead of the outside air temp., which would be much lower up north.

 

[TheGoose]

Our groundwater temperature here is more like 72-74*F.

 

[flyingcow]

There have been a few people not happy with the geo therm systems. At least not impressed with the $$$'s spent and performance. If you got time go to Hearth.com - Information on Gas Fireplaces, Wood Stoves, Gas Logs, Pellet Stoves, Fireplaces, Chimneys and Hearth Products and go to the BB's. Some pretty good experienced guys there. post first under the boiler room section. Quite a few heating pro's on that site. One in particular is "Heaterman". look him up .

 

[Rob-D]

I don't understand your thinking on the temp. diffrence.The heat pump will be using the ground temp.in winter instead of the outside air temp., which would be much lower up north.

I understand what you're saying which is that I have to draw outside air in to replace the heat going up the stack. But here's the problem. This system is costing me ~25k and I have to do the trenching. Even with my BH I still have to call an excavator in to do the 75 foot 6 foot deep long trenches. Now we're talking 28k to get off oil.

I have a grant to put in 6.8Kw of PV that won't cost me anything and I want to put an electric element after my oil fired boiler that uses electricity which I have now and will have in spades after the summer when my windmills and hydro go in. I expect to have close to 9Kwh of juice that won't cost me more than a couple of grand to implement. It will keep the heating element going and if I ever need oil the boiler will kick on but I doubt it will happen.

What you're saying, and rightly so, is that the air I suck into my house in the winter will be outside temp BUT not the water that I heat from an electric element in my closed loop radiant heating system. That element doesn't need any outside air to work. It's only converting the return water from my floor back up to the 115F going back into the floor. I haven't done the math yet but I imagine heating 10F of water with a 4.5Kw electric element won't be a problem.
Roughly, let's say that I'm heating my floor 15 minutes on the hour during the winter. OK that's 6 hours a day at 4.5Kw. that = 810KWh a month. Worse case scenario, double it to 1600KWh a month. I'm still way ahead.

Rob

 

[Rob-D]

Our groundwater temperature here is more like 72-74*F.

It's not ground water it's geothermal, that's the temp of the ground down about 6 feet.

Rob

 

[Rob-D]

Can you do a open loop system?

I can but it's too wasteful. My well is 20gpm+ so the 3 ton system which uses 3 gpm per ton or 9 gpm will work but I still have the compressor costs, etc. to contend with. That comes in about 5 to 7 grand.

Rob

 

[Rob-D]

There have been a few people not happy with the geo therm systems. At least not impressed with the $$$'s spent and performance. If you got time go to Hearth.com - Information on Gas Fireplaces, Wood Stoves, Gas Logs, Pellet Stoves, Fireplaces, Chimneys and Hearth Products and go to the BB's. Some pretty good experienced guys there. post first under the boiler room section. Quite a few heating pro's on that site. One in particular is "Heaterman". look him up .

Thanks, I'll check it out.
Rob

 

[fowllife]

I have a geothermal ground loop system, and I love it. The ground temp here is closer to 56* which makes it a more appealing system. Your cost seem really high for what they are in my area. I had less them $15k for the entire forced air system, pump, loop, duct work, ect.

For what your talking for an installation cost, I would think you may be better off with just a closed loop radient system. It seems like it would be less effecient to run a ground loop, at least in the winter. In the summer the ground loop would help a lot in terms of cooling though. For that high of an installation cost, you may be better with a closed loop in your house and the PV.