Inefficient home or inefficient GSHP?

[Mikesolar]

OK., assuming Randon has 3/4" tubing, he has a heat exchange surface area of 706 ft2. He will have to say what the spacing and ground cover area is being used.

Yours is 1256 ft2 of surface area but there is not a direct correlation between the surface area of two different tube sizes and their heat transfer. The majority of the fluid just flows through the centre and it takes a lot longer to exchange the heat. On top of this is the problem of low turbulence in a big pipe, further reducing heat transfer.

My rough guess is that you have perhaps the same heat transfer as Randen does, all other things being equal so i expect 6 tons is difficult to achieve. This is just a rough thought tho...

[SDMCF]

It doesn't seem particularly low to me. I see similar temperatures from our ground loop, and ours also goes below 0 at times. In our climate we have similar low temperatures to you so maybe it is a valid comparison.

I think you would have been better to have dug longer trenches but not so deep. I have read claims that putting the ground loop too deep reduces performance year-on-year because the ground at that depth doesn't get re-heated so much during summer. I can't say if that is correct or not but it seems sort of logical. Still, I wouldn't be too concerned at the temperatures you report. I would look more to the house or the heat pump rather than the ground loop.

[stevehull]

Mechanic,

I agree with AC. Check air infiltration with blower door test and replace bathroom vents with small ERVs.

Something is not right.


Steve

[Mikesolar]

It is almost never good to oversize a HP unless you are able to store the extra heat in a big buffer tank. First, the compressor should be limited to 4-5 starts per hour for longevity and 6 tons is a lot for a house like yours. That is one reason why I think it would be useful to limit it to stage one if possible and see what transpires. It may be a better balance for the loop size.

With an ICF basement (and I assume at least 2" of foam underslab) there should be minimal heat loss there. I'm not too familiar with RTM construction but a typical 2x6 wall with glass insulation and without 2" of foam on the outside may barely meet code. I would get that blower door test done. There was a report recently that showed OSB to be quite porous to moisture so should not be considered as a moisture barrier by itself.

What is the exterior finish of the house and do you think 2-3" of EPS foam could go on there? It would do wonders for the heat load.

[mechanic]

It's 2x6 with typar wrap on the outside then vinyl siding. I ordered one of those flir iPhone cameras for our business, at that price it should be a pretty useful tool. I'll maybe price out that blower test, were 65km out of the city so mileage is a killer... I blocked out stage 2 for now. Hp manual says that limits it to 67%.

[mechanic]

Originally Posted by SDMCF

It doesn't seem particularly low to me. I see similar temperatures from our ground loop, and ours also goes below 0 at times. In our climate we have similar low temperatures to you so maybe it is a valid comparison.

I think you would have been better to have dug longer trenches but not so deep. I have read claims that putting the ground loop too deep reduces performance year-on-year because the ground at that depth doesn't get re-heated so much during summer. I can't say if that is correct or not but it seems sort of logical. Still, I wouldn't be too concerned at the temperatures you report. I would look more to the house or the heat pump rather than the ground loop.

Our frost line is at least 6', can they be run that much closer?

[mechanic]

As far as the extra insulation I guess a guy could pull all the siding down and add it in, would be a fairly big job though...

[randen]

Mechanic

Man now your talking. Putting a big overcoat on your home. HUGE. You would eliminate the bridging with the 2 x 6.

I have an acquaintance he install two layers of foam on the exterior. I believe first a shiplap blue SM with taped joints and then he followed with another layer of foam for the stucco. In the end I think he was using recessed plastic plugs with 3 1/2" screws. a good 3" of foam on a 2 x 6 wall.

Randen

[SDMCF]

Originally Posted by mechanic

Our frost line is at least 6', can they be run that much closer?

I really don't know, and the claims I have seen about problems running the loop too near the surface are not something I have seen proven anyway. Perhaps someone else has better knowledge, but even if true I don't think that is your real/main problem.

[Mikesolar]

There are a few important things here. First, the heat load is LARGE for todays houses. Is there foam under the basement floor? If not, take up the wood and put some down, minimum of 3" for your area. The walls need to have the foam. It doesn't need to be SM, it can be higher density EPS like the stucco guys use....and a minimum of 3" thick. Then Typar, then vertical slats about 8" apart made of 1/2" plywood (not OSB). This allows a rainscreen so that any moisture that does get behind the siding (and it will do so) can run down to the foundation and out, without being held against the typar (which is what you have now). This will keep the Typar dry and extend it's life. I have seen wet Typar after 4-5 years and it is not good. Then put the siding onto the slats.