Is Anyone Here Using A Ground Source Heat Pump?

[goldbrick]

Does anyone know how deep older wells typically are? We live right on the banks of the Hudson river. The well was abandoned either because there was a lot of sulphur in the water, or (less likely) because it was polluted. If we could have a single well system using that, it might be unusually inexpensive...

Probably about as deep as the water table which could be pretty shallow if you're that close to the river. If any of your neighbors still use their wells you could ask them how deep they are as they are probably a similar depth. Here in semi-arid CO, all wells need permits and those records are kept at the county courthouse. You might ask there if they have any records for your well.

 

[LeftieBiker]

Given the lack of care that generally went into this house, I'd guess that they only went down as far as the water table required, and that probably is shallow - the river is about 30' from the well, although with a drop of about 10'. So maybe 25-30'?

 

[SageBrush]

Lefty, you are at best partially informed and obviously want to stay that way so I'll wish you good luck and not waste any more time.

 

[LeftieBiker]

That's the spirit! I'm sure we'll all miss your wisdom.

For those who would like to help me get what I want, rather than have me chase modest efficiency gains by reconstructing my house, here are the remaining questions:

* What is the price difference between the AS systems that will extract heat down to the lowest temps possible, vs those that give up a little below freezing?

* What kind of current draw will a resistance backup require to provide, say, 40-50,000 BTUs of heat? (we don't fully heat every room).

* We have an existing high efficiency central air unit with a coil in the plenum over the furnace. How much modification would this require to replace the central A/C unit with an AS heat pump unit? It's a 30amp circuit, IIRC, so new cable and a 50 amp breaker at least...plus new working fluid lines...and I guess a new heat exchanger?

 

[GerryAZ]

If you put in a duct heater,, you will need about 15 kW to be equal to 50,000 BTU. You would likely need to split the total capacity into at least 2 segments so you would need two 40-ampere, 240-volt circuits (32 amperes actual draw on each circuit).

 

[BrockWI]

The first two I don't know, you would have to check with a contractor. I would agree your looking at dual 7.5 kw or three 5kw resistant elements.

I would guess you would simply swap out your existing outside AC for ASHP and I would be willing to be it would be noticeably more efficient as an AC unit alone. Our 2 ton unit is on a 20 a 240vac breaker so I think that would be close to what you have now. I am guessing they would pull the AC coil out and replace it with the coil to match the new ASHP, space wise it would likely be close.

Every time I know of anyone wanting to replace their home AC I always strongly encourage them to go to an ASHP, it adds a bit of cost but so much more flexibility as a unit. They are essentially the same thing, just run backwards but usually more efficient.

 

[LeftieBiker]

I understand about heat pumps - I learned a lot of it here, but knew about them long before. IIRC, I mentioned them when we had our current system installed, but my housemate wasn't interested. Our current A/C unit was a super-high efficiency unit when new: 13.0 EER. Now I'm guessing it's just "efficient," but I wouldn't expect a huge savings in A/C. As for heat, I didn't know that the backup heat units are completely separate from the heatpump unit. That gives a bit more flexibility in that area, anyway. I think I can get 2 40amp circuits into the main panel, with a couple of half-sized breakers for existing small circuits.

It looks like I'll be asking for a quote on a GS system, but if it involves multiple wells in the yard, that isn't likely. (One in the yard and the existing one in the cellar might be worth it, if feasible.) I really don't love the idea of spending a bundle on a heating system that bows out at 25F, though. It's a shame we have a slate roof that no one will use for a leased solar PV array, to help defray the cost of electric heat...

 

[wwhitney]

1 kW = 3412 BTUs/hr

Fixed electric space heating is considered a continuous load, so it requires a circuit rated at 125% of nominal current. If you have a 60A circuit available, you can use up to 48A. At 240V, that would be 11.5 kW, or 39,300 BTUs/hr.

Cheers, Wayne

 

[LeftieBiker]

Thanks, Wayne. I could probably find room for all that, but with electric range, water heater, furnace & blower, I'd be pretty close to full load adding 50A for electric heat.

Going back to GS systems: If one well equals one "ton" of cooling (and I assume heating?) and one ton equals 12,000 BTUs, then I'd need 4 wells total. If I had two wells, though, that would cover half of our heating needs in frigid weather, leaving half the electric heat requirement (or running the oil furnace, or both). I'd be much happier with a system that provided at least 50% of our heating needs 24/7/365...

 

[BillHolz]

You are correct about the 1 ton of cooling/heating per vertical well being the basic standard in the industry. What these vertical wells are is nothing more than a loop of pipe stuck deep in the ground. They do not draw any water from the surrounding water table, so the existing well in your cellar is not part of the system. After they are drilled and the pipe put in them, they are filled back in and the landscaping replaced over them. I know someone that has a GSHP and he loves it. It works all winter without needing to use the backup heating system at all.

 

[LeftieBiker]

It seems that typical water wells have a degrading effect on the working fluid lines, though...? If I could just use the cellar well for one ton, and have one or two wells drilled in the yard, that would persuade me, I think. Speaking of which, how much disruption is involved in drilling the vertical wells? We had a septic system installed in the 1990s, after discovering that the sellers had lied to us about there being one. It was horrible, and we would never tear the yard up like that again. Can someone estimate for me the 'radius of disruption' for a vertical well? 10'? 20'? More? And also the trenches needed to connect them.

 

[BillHolz]

If I remember correctly, that GSHP that I mentioned in the previous post uses 5 vertical wells that are somewhere in the lawn areas of the property. Without knowing where they are, you can't tell that they are there. Yes, it will tear up the lawn, but less than a year later, nobody but you will know where they are.

 

[goldbrick]

The actual drilling rig doesn't look like it would cause a lot of disruption so the trenching to bring the lines into the house would probably be the biggest impact. This CO company shows some pictures of an install.... http://www.cogeothermal.com