We looking at installing geothermal in our new build in Canada, North of Toronto. We have the option to install a horizontal loop system, but I question whether it would be effective during the winter where it can get to -4 F to -22 F? The frost goes down to 5ft in our area, so if they did horizontal trenching and laid the pipes at 6ft, what is the likelihood that layer is going to stay warm in the middle of winter? If the soil cools down to under 40 F, would that not render the heat pump unit not useful? Any thoughts?

Yes they work during very cold winters.. Loops should probably be more then 1 foot below frost line.

With antifreeze/glycol/methanol protecting the loops to 15*F there is still useful heat in loops that are in the mid to high 20's.

Chris

Thanks Chris, I was not aware that there is still enough heat at 20 to 30 F. What does the COP drop to at that temperature?

It seems to me that we would have to pump a lot of liquid at 25F to get the room temperature to 70 F. How much electricity would I still expect to save vs. straight electric resistance heat? Also, how deep below the frost should the pipes be laid?

The hit in COP with outdoor temperature is system- specific- there is no generic answer. With any GSHP system the actual efficiency depends a on the system design, and thus the system designer, as well as how close to the margins you design the system. Most are not designed to 100% of the load at the 99% outside design temperature, since that adds quite a bit to the up-front cost to handle the last 5% of load. Some amount of resistance heating (at a COP of 1) is usually designed in to cover that last few percent fraction, which adds only modestly to the operating cost due to the very low number of hours it gets used.

In the real world the all-in COP of a "typical" GSHP system isn't as-advertised, due to compromises (or in some cases incompetence) in the system design. If you take this road, vet your system designers & installers very carefully- having to fix a "cheap" GSHP system design can be pretty expensive.

In most Ontario locations the ground heat exchangers are more likely to be drilled wells rather than trenched-in, since the frost depths will be pretty deep.

I had temps that were below zero for about 8 days this winter. The worst night was -26 and my system kept up. The loop temps got down to 22 out going and 26 incoming. The systems work well but shop around and talk to many installers.

I have electric resistance as my third stage.

Thanks Johnny, that's amazing that the system can still extract heat from 26 F and keep up. So it seems as long as the ground loops don't freeze over and stay above mid 20, it could still heat the house.
I definitely realize the importance of having a properly sized and installed system. Would you be able to tell me if your system was sized for 100% of your heat loss? My contractor is recommending sizing to 70% partly because my heat loss is so high. A 6 ton geothermal furnace would meet only 70% the 75,000 BTU heat loss, so I'm worried about that system might not keep up. (Of course, I'm also looking to improve insulation to bring down that number)

"In most Ontario locations the ground heat exchangers are more likely to be drilled wells rather than trenched-in, since the frost depths will be pretty deep."

There are horizontal installations. Remember frozen earth often moves heat better than drysoil for instance. I don't think we can generalize. Local experience always trumps us remote design guys.

Mickey, shop for the best installer in your area and all else will take care of itself. I will dispel you of a couple of misnomers however.
1) the likely hood the earth around your loops will stay warm or 40F in the winter is nil. You will be removing heat from that soil. Most loop designs are for a minimum EWT (entering water temperature) of 30F. Sometimes during extreme conditions you can dip below that as Johnny pointed out. As Chris points out we freeze protect to 15F so you can get EWT's in the teens and still extract heat.
2) Most system designs are for an average of 3.5-4 COP in spite of 30F EWT.
3) A 6 ton for a 75MBH load provides 99.55% of your heat as Toronto has 6263 heating hours based on a 20 year weather average and you would need 270 hours of additional heat. The 6ton in this model btw offers an average COP of 3.43. Whats better is the 5 ton (TE64) offers 99% of the heat with 600 hours of aux annually at a 3.8 average COP so it costs less to run. The 6 ton BTW only offers about 5kbtu (again in this model).
Percent of heating is not the heat pump capacity from the heat loss, it is the percent of heat provided by the heat pump versus supplemental.
BTW I used a hot water generator in the model to save you money on that as well.

Now I'm not familiar with local conditions and can only select Toronto on my calculator so I will yield to the local guys opinion as long as he is properly vetted.

Joe, thanks for running this model. Is there a version of the model online somewhere that I can look at? I am about 1 hour north of Toronto so it is a bit colder. But based on your calculations I'd be running the equivalent of ~11 days on auxiliary heat? Other than that the system should fine to supply my heating needs?

And the reason (I guess) is because the heat loss is modeled at -6 F, but usually it does not get this cold, and there probably will be only ~270 hours where average temperatures fall into this range?

I am about 100 miles south of you, in Buffalo NY. Check out some of the systems streaming online data. We measure seasonal COP over 4.0 in heating mode on most of the systems.

Most of our loops are horizontal, not drilled.

I agree with Joe, if your heat loss is 75 KBTU at -6F, a 5 ton might run more economical over the season. It depends actually on the brand.

Yes, please add insulation.



http://buffalogeothermalheating.com/sample_diagram.html

"Joe, thanks for running this model. Is there a version of the model online somewhere that I can look at?"

If you go to the Climatemaster website go to the contractor section and then tools, the model software is a free download.

"I am about 1 hour north of Toronto so it is a bit colder. But based on your calculations I'd be running the equivalent of ~11 days on auxiliary heat?"

That's KW hours so if you have a 10 K auxiliary heater it will run for just over a day. Remember though, your heat pump still runs when the auxiliary is on so what you'll have is 5 minutes here, 10 minutes there of auxiliary use.

"Other than that the system should fine to supply my heating needs?"

I grit my teeth at the question. Designed in auxiliary is proper and the most cost effective design. If you wanted to avoid auxiliary use you'd have to jump to 8 tons. So it is not "fine" it is best. By the way that 8 ton unit would run for about $45/yr less (at .15/kwh).

"And the reason (I guess) is because the heat loss is modeled at -6 F, but usually it does not get this cold, and there probably will be only ~270 hours where average temperatures fall into this range?"

Yes. Like any renewable, the sweet spot is not to design for 100% but to try to get most of the demand. Can you imagine the cost of a solar system if you wanted to go off grid? You'd need a lot and then storage for cloudy days. So much more bang for your buck to stay on grid.

There is a lot to this you are starting to understand, but the thing we need to emphasize most is carefully vette and check references for installers. Once you find the best one in your area everything else will take care of itself.

Posted By docjenser on 06 May 2014 07:34 PM
http://buffalogeothermalheating.com/sample_diagram.html

Docjenser, thanks for providing those live stream links for the systems you've installed. I found them very helpful. Would you happen to have a screen shot/historical chart of the system running in February? I noticed that some of your horizontal trenches were at 8' and some at 6'. What determines that? I'm worried that I might have a high water table, would that mean the trench depth might be limited? Too bad you don't install up here, otherwise I would be interested in getting a quote.

Posted By joe.ami on 07 May 2014 09:30 AM
If you go to the Climatemaster website go to the contractor section and then tools, the model software is a free download.

Joe.ami, will check this out. Thanks for taking the time to explain everything to me. It's definitely giving me confidence with proceeding with geothermal.

MM, you've got your investigations backward. It always amazes me to read of someone about to build a new house in a very cold climate, the house is "ordinary" construction, and the owner is looking for a cheap way to provide the terribly high heat load it will need. Your 75,000 BTU/hr need strikes me as triple what it ought to be for an ordinary single family residence, unless you are talking something like a 12,000 sq.ft mansion. The very first thing you should be doing your homework on is what goes into a superinsulated house. There is plenty of information on that subject at: www.buildingscience.com and at www.greenbuildingadvisor.com. A good read is the blog on the latter site (GBA) on the "Pretty Good House," the efforts of a group of builders in the Portland ME area.

Put your first money into a superinsulated shell. The house will be far more comfortable, the heating load will be far smaller, and how you heat the house will matter a lot less. If you still want to do a GSHP for the heat, the system will be much smaller and thus less expensive. If your builder won't or doesn't know how to build a superinsulated shell, find one who does. It's your house, not his.

My own house, in central NH, is superinsulated, about 4,00 sq.ft. of conditioned space (less walls and whatever isn't included in "sq.ft."), and is heat quite nicely with a two-ton heat pump. Even in the cold winter we just had, the unit never had to go to second stage. The savings in drilling cost for the well and minimal GSHP size vs what would have been needed for "ordinary" (just meeting code) construction easily paid for the extra cost of the superinsulated shell. For new construction, it's a no-brainer.

" I'm worried that I might have a high water table, would that mean the trench depth might be limited?"
Wet soil conveys heat better. Things that determine loop capacity are depth, length, moisture content of soil. If you have a lot of one, you can have less of another.

Dick Russell's advice is sound.

Thanks DickRussell, I've started a new trend on reducing heat loss. Let me know if you have any suggestions. http://www.greenbuildingtalk.com/tabid/53/afv/topic/aff/21/aft/82418/Default.aspx

Posted By MickeyM on 07 May 2014 11:07 AM

Posted By docjenser on 06 May 2014 07:34 PM
http://buffalogeothermalheating.com/sample_diagram.html

Docjenser, thanks for providing those live stream links for the systems you've installed. I found them very helpful. Would you happen to have a screen shot/historical chart of the system running in February? I noticed that some of your horizontal trenches were at 8' and some at 6'. What determines that? I'm worried that I might have a high water table, would that mean the trench depth might be limited? Too bad you don't install up here, otherwise I would be interested in getting a quote.

As Joe said, sometimes we have a lot of water, and then I only go down to 6'. What are you looking for in terms of February chart? Loop performances should reflect the last 12 months, so you should look back a couple of months and look at the loop temps.

Thanks Doc, it's great to see your loop temps say above 30F the whole winter.

We're putting in the foundation soon, but have not picked a geothermal installer yet. How big should the two holes in the foundation be for the incoming and outgoing pipes?

Posted By MickeyM on 09 May 2014 03:05 PM
Thanks Doc, it's great to see your loop temps say above 30F the whole winter.

We're putting in the foundation soon, but have not picked a geothermal installer yet. How big should the two holes in the foundation be for the incoming and outgoing pipes?

We like to put the pipes under the foundation if we can. Second best thing are 3" PVC sleeves for 1.25" header pipes. Then using metraflex seals.

Posted By MickeyM on 09 May 2014 03:05 PM

it's great to see your loop temps stay above 30F the whole winter

Mickey:
I am reading this thread and I wonder whether you have system design information that the loops will surely be above 30f ? Or are you counting on someone elses empirical data logs?

Posted By nooboo on 10 May 2014 12:14 AM

Posted By MickeyM on 09 May 2014 03:05 PM

it's great to see your loop temps stay above 30F the whole winter

Mickey:
I am reading this thread and I wonder whether you have system design information that the loops will surely be above 30f ? Or are you counting on someone elses empirical data logs?

It was meant as examples that 100 miles further south one can indeed achieve 30f or above with horizontal slinky loop fields. There is no reason why this could not happen 100 miles further north, especially to counter the notion expressed here that horizontal in cold climates would not work. It depends on the specific design, not one the loop field configuration (vertical versus horizontal for example). Plus what would be the downside of the EWT dropping down to lets say 28F? Less efficient, some would say. Probably $50/year, I would argue. Not worth to get too excited about it in the big picture. One has to really screw up the design if it drops significantly below that.