Is Anyone Here Using A Ground Source Heat Pump?

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LeftieBiker

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Upstate New York, US
We have hydroelectric power, and I'd like to switch from our mix of dirty fuel oil and clean electric heaters (and one large solar thermal panel) to a ground source heat pump. I looked into them over a decade ago, but they weren't exactly problem-free then, and with my housemate being terrified of gas heat I had little choice but to go to a high efficiency oil furnace. With the worst climate change predictions coming true - and fast - I believe I can get her to abandon oil as our primary heat source. I think, though, that unless I can show her convincing date on how reliable ground-loop heatpump systems are now, she'll want a cheaper air source unit, with electric and oil heat as backups. Our Winters are too cold to use just an air source unit, even one with electric backup heat.

Is anyone here using a late model ground loop system? If not, can you point me to real world reviews of such systems?
 
Ground-source heat pumps are unpopular for a lot of good reasons except for isolated cases.

* Expensive to install
* Difficult to install
* Inefficient due to resistance losses along the tubing

In your shoes I would be considering PV, AS heat pump, and conservation measures like a better home envelope and DHW heat exchange. A mixture of things tends to be much cheaper for the same improvement. Start with improving your home envelope, both in terms of insulation *and* leakiness.

A new generation of AS heat pump with CO2 as the refrigerant have a COP of ~ 2 at 0F
 
We have a 4 ton horizontal ground source heat pump. We also have a 2 ton air source heat pump. I can say that the ground source is more efficient the majority of the time, but cost quite a bit more to install. Ours is now 10 years old and the only maintenance we have ever done is replace a starter capacitor on the motor, our system has 26,033 hours on it. Our ground return is about 40F or 4C in winter to about 60F or 15C in summer. In summer I can circulate the field water through the coil in the furnace and cool the house that way as well consuming only 100 watts for the furnace fan and 70 watts for a circulation pump, which is how it warms the field up to 60F by the fall.

We got the Air Source for two main reasons, mostly becasue we can't really run the geo on on our solar PV system, but I can easily run the air source and secondly becasue we use "time of use" electrical rates we wanted 6 tons of cooling in summer. We use the air source mostly in the summer for added cooling, running the air source from PV during on peak or demand rates and some in the spring and fall when the outside temps are more mild. Once it gets colder than the incoming field I switch over to primarily the ground source.

I would agree that geothermal systems are a lot more expensive, more difficult to install, but not on the Inefficient due to resistance losses along the tubing. Our system has two 70 watt pumps (mostly for redundancy sake, usually only have one on) to circulate. I am quite sure our air source looses a LOT more in the fan moving all the air than the pump circulating water.

But I do agree that it would take a LOT longer to get ahead cost wise with a geothermal system compared to a modern air source. I might save 20% by running the geothermal compared to air source but it would take 15 years for that to pay off, which it likely will in our case.

Having said all that unless you like to mess with system to get the most out of them I would suggest an air source. For instance in summer we can cool the house and that excess heat is put in to our pre hot water tank instead of dumping it outside, I can even circulate it between our two hot water tanks and get 130 gallons of hot water heated up to 140F before switch back to the field to dump heat, but usually at that point I switch over to the air source. Again that involves me switch valves and tinkering with things to make it more efficient.

Since we are on the Leaf forums I can compare it from moving from a car that gets 15-20 mpg to one that gets 40 mpg (air source) or 50 mpg (ground source), but going from 40 mpg to 50 mpg triples the cost.
 
I'm also interested in ground source heat pumps and would enjoy any reliable links that can be provided. In the meantime, what is the major expense/difficulty inherent in them? Is it the cost to bury the 'coolant' lines? Does it matter if large amounts of land are available?

I'm considering adding something like this to my parents' house which is situated on 60+ acres with a 1/2 mile driveway. I've always thought just trenching a line on either side of the driveway would be cheap (ish) and would be enough for the heat pump. Is this not the case?
 
Yes the real expense is the pipe, trenching, burying and returning to inside the space with the lines. Our field is a minimum of 8 feet below ground, you for sure have to be below frost and try to avoid places you might dig up :) We also buried 5000 feet of pipe, in a trench 12 feet wide and 2500 feet long with a turn around at the end. Then the pipes were about a foot apart out and back, then in to a header turning it in to a 2 inch in and out. Then everything was buried. There are issues, like you have to be pretty level and need a large pump to prime the system to make sure all the air is out.
 
I do know about the expense. About $25k, but NYSERDA offers a rebate that should return about $7500 of that. The big problem with using an air source unit is that it WILL require that we keep burning oil. Solar is out of the question, both because we have a slate roof with a modest yard, and because it doesn't heat at night. I'd also want to use a vertical well instead of horizontal; does that add to expense or just reduce available heat?
 
Why can't you use electric heat as your backup to the heat pump? Cost? Or a technical restriction I'm not aware of?

I looked at an ASHP last year with the goal of turning off my natural gas connection. They were proposing electric backup. And my climate is more or less identical to yours.
 
Vertical systems (wells) are usually more efficient, they maintain temp more consistently, but usually cost more to install. I wanted to go vertical for the efficiency, but we are in an area where they have city water and sewer. So becasue of that the town will not let anyone drill wells, which is essentially what your doing. Our geothermal guy and I tried explaining it to the board but they didn't care, didn't listen, they said a well is a well and they will no longer issue any permits for them, some of them even thought I using that as an excuse to get around the ordinance just to get a well.

Luckily we have 1.5 acres on this property and a horizontal fit. It was about $4000 less expensive to go horizontal rather than the 3 vertical's he had initially planned so at least I had that. The installer we had was good and he sized our field for 6 tons, mainly for future expansion, but also to make it a bit more efficient.

We have natural gas backup for ours, it came with the system, but I could have chosen electric. I try to use the gas furnace once in a while to make sure everything works or if I want to heat up the house more quickly.

We also have radiant that is heated by the geothermal off our first hot water tank as another option.
 
It is my understanding that the electric backup option for AS systems isn't very effective at really frigid temps - the same temps at which our electric space heaters don't cut it except in one or two rooms. If this isn't true, and an AS unit with electric backup can actually keep the house warm enough at -15F, that's probably what I'll suggest. This is an old house, and even with blown in insulation added it isn't super airtight or warm.

I'm fairly sure that we could drill a well here, as this is an exo-urban area with little oversight, even though we have city water and sewer. Actually, we have an old (shallow, I suspect) well right under the basement, with a giant old well pump sitting over it. Given the need for 2 or 3 deep (?) wells, though, I suspect we'd still have trouble. Do they make ground source units that use just one well and have electric backup...? Ah, well, this is why we still have an oil furnace...
 
Talk to a couple of geothermal contractors in your area. One of them should know what the best way to go is. I believe if I had chosen the electric back-up option it had quad 5 kw resistance heaters (approx 65,000 BTU) and they came on in succession as needed.

You could go with a single well and say 1 ton unit and let it do 90% of the work. Most HVAC contractors will want to really oversize it to cover any conditions, but if you have a working backup, you could get a smaller system.
 
We have a vertical system.
14 “wells” 100 ft deep, for a total of 2800 linear feet.

This provides our 2400 sq. ft house with 100% of its heating needs (radiant floors), 100% domestic hot water needs and our cooling (forced air) in the summer.

As others have said, it is expensive, especially vertical wells. Horizontal will be cheaper.
It is vastly more efficient than any other active heating method. However, it is important to get some guys that know what they are doing, so the system is sized properly for your needs. If you get ‘Joe’s Furnace’ who buys GSHPs in back alleys and just connects the tubes, don’t expect good results (don’t ask me how I know).

Before you put in any system, check for insulation improvements first. These will be cheaper and may drastically lower the cost of a higher priced system.
 
Since all of the GS options seem to require tearing our yard up, it will be air source. We'll get one with electric backup, but leave the oil furnace in place. (Yuck.)
 
Nothing wrong with a good ASHP, if it can cover most of your needs that is WAY better than burning oil for all of them :) If your going to leave the oil in place you might not need electric backup, although electric backup it the least expensive to install.

Our ASHP has a smart box and is set to switch over to natural gas if the HP runs more than 120 (user adjustable between 30 and 120) minutes or if the outside temp is below 10F (adjustable 10 to 40). It does have a duct temp sensor as well so that if it isn't outputting 85F air (adjustable between 85 and 105) it switch over to gas. I did run it at 10F to see how it worked and it was putting out 85F air and worked fine, but at about 20F is when the unit goes into defrost mode every so often which uses more power. I was amazed how well it worked even at low temps.
 
Nothing wrong with a good ASHP, if it can cover most of your needs that is WAY better than burning oil for all of them :)

We don't use oil for all of our heating, or for any of it until temps drop below freezing. We use electric heaters "burning" hydroelectric power from a hydro plant 3/4 of a mile away.

Let me change the question, now that I've eliminated the kind of system I want. ;-( How well does the electric backup heat for a good AS system work in single digit and subzero temps? Keep in mind that our house isn't airtight, and isn't going to become airtight anytime soon. (The issue isn't so much cost as the level of disruption caused by replacing numerous windows and doors.) It doesn't leak like a sieve, either.
 
The backup electric part can be adjusted according to need. Do you know how many BTU you oil is now? If it is say 60,000, then you can just get 60,000 BTU of electric. The catch with that is if the house is older you might have a smaller service coming in, maybe 100 amp? The ones that would have been in our system were four 40 amp 240 vac breakers for the electric backup. But even if you only had two of them becasue that is what your current electrical service could handle and those were running flat out you still would have oil as a backup to that.
 
LeftieBiker said:
This is an old house, and even with blown in insulation added it isn't super airtight or warm.
Insulation and air-tightness are very different things. If you improve the envelope then an AS heat pump will work well.
 
SageBrush said:
LeftieBiker said:
This is an old house, and even with blown in insulation added it isn't super airtight or warm.
Insulation and air-tightness are very different things. If you improve the envelope then an AS heat pump will work well.

Yes, I know that. That's why I wrote that we won't be replacing a bunch on windows and doors. The house isn't drafty, either. It just isn't airtight or super-insulated. As for the ASHP working well in a better insulated and draft-proofed house, it won't matter at all if the temp is 10F, because the heat pump won't be doing the heating. The issue is that I don't particularly want a system that's a 'fair weather friend', shutting down and switching to massive electric resistance heat while it's still just normally cold outside. We have a 200 amp service, BTW, which I helped install after we moved in. I can find room in it for another 50-75 amps, tops.

The single well system sounds interesting, but might be hard for me to sell to my housemate. 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...
 
I can't answer most of that, but I do wonder how many days (hours) in a year do you really have below 10F temps outside. I am guessing there are a few days, and probably triple that at night, but again if the majority can be done with the ASHP that is a good thing. I would compare this to a plug in hybrid where 90% can be done on battery but you still need that 10% of burned oil or when the electric resistance kicks in, when it's really cold out.

In the end it's hard to say if it is worth it to you to move to an ASHP and factor in the avoidance of using heating oil also plays in to the decision, but only you can answer that part.
 
BrockWI said:
I can't answer most of that, but I do wonder how many days (hours) in a year do you really have below 10F temps outside. I am guessing there are a few days, and probably triple that at night, but again if the majority can be done with the ASHP that is a good thing. I would compare this to a plug in hybrid where 90% can be done on battery but you still need that 10% of burned oil or when the electric resistance kicks in, when it's really cold out.

In the end it's hard to say if it is worth it to you to move to an ASHP and factor in the avoidance of using heating oil also plays in to the decision, but only you can answer that part.


You're about right in your estimate, but the nights are long. It depends on what kind of Winter we're having, too, but there can be a whole month in which it drops below 25F (that's the important number) every single night, with maybe a third of the days not rising above that.
 
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