Good result Solar recharge of shallow field

[buffalobillpatrick]

Blue Bomber, did U read post #9?

A/C 8,800' altitude.

Many differences vs. England. Does this change the question?

Closer to the Alaska climate than to England, but not as severe & with better solar.

8" snow yesterday.

[jeff5may]

That's the two things I don't miss most about Colorado: the snows in May and the thin air. I can run a few miles here and still have energy for the rest of the day. I still get heckled for carrying a coat with me year-round, though. I don't know if I'll ever shake that habit.

[AC_Hacker]

Originally Posted by buffalobillpatrick

...A/C 8,800' altitude... Many differences vs. England. Does this change the question?

Since you're building your house and building your solar/heat pump/radiant system, you might want to check the HDDs and solar gain potentials of the places you're trying to compare.

It might be in your interest to do so before you build.

BTW, did you ever post your building drawings on the forum?

Somehow, I must have missed that part.

-AC

[MN Renovator]

Originally Posted by AC_Hacker

Do you actually think that a traditional hydronic heating setup (which is designed for 140F - 160F feed temps) will provide the required heat transfer?

This is exactly the place where traditional thinking fails in low temperature heating installations like solar, geothermal, etc.

Very few hydronic installations (Daox excepted) have built-in efficiency to take advantage of feed temps on the 110 range (and lower).

Vlad's house works with 12" spacing & aluminum heat spreaders because he heats all the floor area, has rigorously reduced infiltration, and put in very good insulation from the start. With three floor levels, his floor area/house volume ratio is fairly high, which favors radiation. Also because his house is large and vaguely tends toward a cubic form, his external area/house volume ratio is relatively low so his house favors lower skin losses.

Did I mention his floor is topped with porcelain tiles, which has a very high U-value?

Lastly, he lives in the Vancouver Canada area and the HDD are not as high as they are in a place like Minneapolis, MN.

Vlad reported feed temps in the 112 range when the weather got really awful.

Of course, awful in Vancouver could be a relief in a Minneapolis winter, or a Colorado winter at high elevation.

-AC

When I was talking traditional, I was actually thinking of in-floor as opposed to radiator against the wall. Traditional being hydronic as opposed to a heat pump setup. Even Daox has loop overkill for his serious window and high levels of insulation with 110f input temps. A hydronic in-floor loop, air sealing of 3ACH or less, insulation better than code(I prefer double of the older R20/R13+5 code and a step better than the 2012 IECC 20+5 or 13+10 values for climate 6+), and double pane or better windows with good seals should be fine with 110f input temps and a reasonable water flow rate.

"Lastly, he lives in the Vancouver Canada area and the HDD are not as high as they are in a place like Minneapolis, MN."

Values are in SI (C, not F).
Minneapolis, MN
http://cms.ashrae.biz/weatherdata/STATIONS/726580_s.pdf
Vancouver, BC
http://cms.ashrae.biz/weatherdata/STATIONS/718920_s.pdf

You weren't kidding, Vancouver seems nice.

[buffalobillpatrick]

What I wanted was discussion on solar recharge of shallow loop field.
Then I asked about insulation over loop field.

I expect to have excess solar heated water most of the weeks per year.
360ft2 panels mounted close to vertical.

For $800 I could buy a 2nd 1000 gallon fiberglass tank.

House is 48' x 36' rectangle ICF, main level is a walkout basement.

About 40% of walls will be below grade. Simple 2 plane roof, ridge running East & West.
Front faces East, high ceiling greatroom/kitchen, 2 bedrooms with 2 bathrooms in rear 1/2 (West end) Rear 1/2 will have upstairs 3rd bedroom & bathroom.
R23 walls R51 vented steel roof.

[AC_Hacker]

Originally Posted by MN Renovator

...Even Daox has loop overkill for his serious window and high levels of insulation with 110f input temps...

I haven't actually talked this issue over with Daox, but it seems pretty clear that he is working on the principle that a highly efficient house, coupled with a highly efficient floor, means that sufficient heating can be achieved at very low feed temperatures.

That is at the core of 'low temperature heating'.

With fossil fuel, the difference in lowering feed temperatures a degree or two is pretty small.

With a heat pump, lowering the feed temp a few degrees makes a big change in efficiency.

With solar, it means that you can heat directly with solar heated water down to a lower temperature before you need to either extract more heat with a heat pump or else rely on a back-up heat source.

-AC

[buffalobillpatrick]

http://www.byfy.lth.se/fileadmin/byf...-1018EKweb.pdf

Solar + heat pump Combisystem, Sweden study.

System 5 pg82 gave best performance.

[jeff5may]

Originally Posted by AC_Hacker

I haven't actually talked this issue over with Daox, but it seems pretty clear that he is working on the principle that a highly efficient house, coupled with a highly efficient floor, means that sufficient heating can be achieved at very low feed temperatures.

That is at the core of 'low temperature heating'.

With fossil fuel, the difference in lowering feed temperatures a degree or two is pretty small.

With a heat pump, lowering the feed temp a few degrees makes a big change in efficiency.

With solar, it means that you can heat directly with solar heated water down to a lower temperature before you need to either extract more heat with a heat pump or else rely on a back-up heat source.

-AC

This statement fits perfectly in BBP's other thread, concerning the operation and design of his combo system. Just as with very low (outdoor/source) temperatures, the efficiency of the heat pump suffers when you demand high heating temperatures out of it. He was concerned on how to efficiently source 130+ degree domestic water from the heat pump. When I suggested running a gas boiler when the sun source ran out, the wolves jumped on me.

At a certain point, the gas boiler would do a better job than the heat pump at providing hot water. Especially when the hot water tap is running, the heat pump may just not keep up with demand. It is better doing the recovery of the hot water tank after the demand has stopped. In any case, the heat pump would just rob more solar energy from the solar heat store, where the boiler would not.

[NiHaoMike]

The heat pump, being a pretty big unit at 2 tons or so, will have no problems keeping up with DHW demand. (My little 1/2 ton unit easily keeps up with demand running only 3-4 hours per day on average.) So the only remaining reasons to switch to the boiler are if the heat pump breaks down, if the heat pump can't keep up with home heating demand (at which point you switch into hybrid mode if it's still above the balance point), if the incoming water gets too close to the freezing point, or if it becomes more efficient to use the boiler.

The only demand for 130F water (dishwasher) only needs a few gallons per use. As such, just warming up the boiler will significantly cut into the efficiency. The heat pump condenser has much less thermal mass (especially for a plate exchanger) so the heat pump will still be more efficient than using the heater built into the dishwasher. (Of course, it would help a lot to have the dishwasher as close to the heat pump as possible. Like put the heat pump in the basement directly below the kitchen.)

[jeff5may]

The topic was what happens when I fill up my hot tub.