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Old 03-07-14, 11:12 AM   #11
stevehull
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dhaslam,

Tell us more - this is fascinating. I have long thought about this but until now I have not yet known anyone that did this. What are the dimensions of your "above ground" heat storage.

Fascinating that you can get up to 50 C by the end of summer. What is the temperature of the bed at the end of the winter?

180,000 liters is about 45,000 gallons (US) or about 6,500 ft3 or about 240 cubic yards (meters). How thick is the storage bed and did you use slinky HDPE or a series of linear tubes.

VERY interesting! Pictures of the bed won't show much, but a diagram of the dimensions, solar collectors and tubing would sure be interesting.

Steve

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Old 03-07-14, 11:38 AM   #12
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Hello, thanks thus far.

No cooling required, house will be at 8,800' altitude, in a Zone 5 county right next to Park county which is Zone 6. Average year temperature is 40* acording to Teller Co.

I agree 100% that the most important factors to address are insulation & infiltration.

It's biggest heat loss is the large East facing windows on the great room / kitchen. I want alot of morning sun in there + it faces Pikes Peak, but lots of trees on neighbors property block most of view.

Roof will be about R51, vented 9:12 pitch, 3" polyiso + 11.5" dense packed cellulose, Roofing is already bought Decra steel shake dark green.
1/2 will face South, but I am reluctant to put holes in it to mount PV panels.

Walls will be 8" ICF about r23, gable ends above ICF about r40. 3" polyiso on exterior + synthetic stucco with drainage plane. Stud wall: 2x6, 24" OC filled with dense packed cellulose.

Under radiant slab will be 8" of type 2 EPS. FPSF (frost protected shallow footers) insulated on exterior with 8" type 2 EPS. AFI = 2,500

I'm limited to R28 below slab, as not enough heat would be released to keep shallow footers 16" from freezing below, acording to building code.

Heat loss at design temperature of 2* is about 6 btu/ft2 depending on wind.
Which is pretty good. Many believe that Passive House standards are overkill.

Solar storage will be VERY well insulated with 12" EPS + pearlite at corners inside foam cube between round tank & foam.

Useful stored heat between 80* - 35*
45* x 1000 gal. x 8.3# / gal = 373,500 btus.
I think this is worth using with heat pump.
Also the panels will gain more heat in this range than when they get hot.

BBP
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Old 03-07-14, 12:25 PM   #13
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The mound is round and about eight metres across. Originally the heating source was to be hot air supplied by home made coroplast collectors so there were large land drainage pipes for heating. There are two 1.5" pipes for heat extraction. I had to abandon the hot air idea because there was too much heat loss in transmission of heat even before reaching the store. Now the inner hotter water pipe is used to heat and the mainly the cooler outer one for heat extraction. This year the two had to be used at the end of the winter because the temperature dropped to about 8C and the combined flow reduced the temperature drop. I hope to be able to keep the temperature above 15C in future. The heating rate is fairly predictable and so is heat extraction but the heat loss from the store is hard to predict. Over the first winter there was minimal heat loss because the store temperature wasn't much higher than ambient temperature.

In Ireland other system are being built with the seasonal heat store under the house but I think that there could be problems of excessive summer temperatures in a hotter climate. The advantage of the heat pump rather than direct heat transfer is the temperature range can be much wider and using lower temperatures reduces storage losses.

One modification I am making shortly is to put a VAWT on top of the mound. This is mostly for decoration but in windy weather it will put a little heat into the store.
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Old 03-07-14, 12:35 PM   #14
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Then your setup is going to be easy. For the main, build a water to water heat pump plus a few valves to bypass it. For hot water, first stage would be a heat exchanger to preheat it using the heating water. Second stage would be a separate small heat pump (a hacked window A/C would work nicely) that is either air source (if dehumidification might be needed) or water source off the solar tank. Run R22 or an equivalent in a R410a compressor so it will handle high evaporating and condensing temperatures with ease.
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Old 03-07-14, 05:17 PM   #15
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Mikesolar,

I think my Burnham CI NG RV-3 88% Eff. is a pretty darn good choice.
Should last 25 yrs + low maintenance.

I have had much trouble with mod-cons at high altitude. Never-again!

1. I have installed 3 top name brands and they all had problems fireing off, and yes, I have a nice combustion analyzer and they were setup correctly.

2. I don't think that they are designed or tested for high altitude.

3. Mod-cons don't condense very much up here so anything over 90% Eff. is fantasy.

4. Mod-cons seem to break too often.

NiHaoMike:

It's very low humidity here so no dehumidifier needed.

Would R410a or R22 scroll compressor work best with Propane R290 ?

I don't get: "high evaporating and condensing temperatures" why would I have this?

It looks like the TXV needs to be adjusted for 20-35K Superheat ?

what type of HX for IHX or what ever its called ?

I copied this somewhere:
"In other words: R290
profits in capacity and efficiency from useful superheat, the
use of a heat exchanger between the suction and liquid lines
is therefore an advantage."

BBP
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Old 03-07-14, 05:57 PM   #16
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dhaslam, My family has quite a bit of Irish heritage.
My daughter is Michelle Kathleen, son is Sean Patrick, his new son is Liam Patrick.

I hope to someday visit your lovely country.

The house I live in now has a mass storage under the 24' x 46' basement slab. 2' of earth on top of 6" XPS with a loop of 1,000' 1" poly pipe. + a 1200 gallon burried insulated tank, solar heated.

Sounded good at the time but was a waste of money.
When I found that it was uncontrollable, I stopped using it & took apart the solar array. When the basement got hot for weeks at a time, the only relief was opening all the windows.

On the new house, I may use solar heat of the earth over the pipe field?
I would cover the flat ground with dark gravel or coke oven cinders.
I have 30 or so 3' x 7' double glass sliding door units. Place the glass on pressure treated 2x4 rack secured in place just above the dark surface.
I worry about Deer & Elk walking on it.

BBP

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Old 03-07-14, 06:56 PM   #17
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Quote:
Originally Posted by buffalobillpatrick View Post
It's very low humidity here so no dehumidifier needed.

Would R410a or R22 scroll compressor work best with Propane R290 ?

I don't get: "high evaporating and condensing temperatures" why would I have this?

It looks like the TXV needs to be adjusted for 20-35K Superheat ?

what type of HX for IHX or what ever its called ?

I copied this somewhere:
"In other words: R290
profits in capacity and efficiency from useful superheat, the
use of a heat exchanger between the suction and liquid lines
is therefore an advantage."

BBP
Then stick to a water source unit for the hot water. It's more efficient. You can either use two water/refrigerant heat exchangers or just put some coiled up tubing inside the DHW (Domestic Hot Water) tank as some others have done. The latter saves the cost of a pump, but requires the heat pump to be attached to the hot water tank. That's probably not an issue for your case.

Use a R410a compressor for the DHW heat pump and a R22 compressor for the main heat pump. The reason you use a R410a compressor for the DHW is because it might need to operate with high evaporating and condensing temperatures. Such as the solar tank being at 90F and the DHW at 140F (for washing dishes). A R22 compressor running on R290 would overload under those conditions, but a R410a compressor would run quite well. I named that the "Davuluri Treatment" after a model who recently lost a lot of weight.
http://ecorenovator.org/forum/geothe...ssor-r290.html
The reason the suction pressure matters and not just the pressure difference is because the refrigerant gas becomes more dense at higher pressures, putting more load on the compressor. For the main heat pump, since you put the maximum solar temperature at 80F (above which you bypass the heat pump altogether), a R22 compressor would likely stay well in spec. You might still want to put in a current sensor and dial back the evaporator water flow if it starts going over spec.

The TXV is generally set for 8-15F of superheat. Try to go as low in that range as you can without the valve hunting.

The heat exchangers commonly used are tube in tube ("snake" or "coax coil") and plate. The former is somewhat more resistant to freezing, has a high thermal mass (easier to design the control system), and more internal volume (easier to get the charge correct), while the latter is more compact. Efficiency of the two are similar and the surplus store has deals on the coax coils, so that's what I recommend.

The benefit of a SLHX is much less than you think, especially with low delta T between the condenser and evaporator. Certainly not worth the cost of another heat exchanger assembly. Soldering the liquid line to the suction line is a cheap way to do it.
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Old 03-07-14, 07:05 PM   #18
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Quote:
Originally Posted by buffalobillpatrick View Post
Mikesolar,

I think my Burnham CI NG RV-3 88% Eff. is a pretty darn good choice.
Should last 25 yrs + low maintenance.

I have had much trouble with mod-cons at high altitude. Never-again!

1. I have installed 3 top name brands and they all had problems fireing off, and yes, I have a nice combustion analyzer and they were setup correctly.

2. I don't think that they are designed or tested for high altitude.

(haha, I just read Mikes post above so you may take my thought about the pot with a grain of salt)

3. Mod-cons don't condense very much up here so anything over 90% Eff. is fantasy.

4. Mod-cons seem to break too often.

NiHaoMike:

Would R410a or R22 scroll compressor work best with Propane R290 ?


I copied this somewhere:
"In other words: R290
profits in capacity and efficiency from useful superheat, the
use of a heat exchanger between the suction and liquid lines
is therefore an advantage."

BBP
I'm a bit taken with Viessmann (probably it's why I continue to put them in) and I know they have 1000's of boilers in the Alps doing well. That said, the Burnham will serve you well.

Last edited by Mikesolar; 03-07-14 at 07:08 PM..
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Old 03-07-14, 07:14 PM   #19
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Yes I understand about the problem of overheating the soil underneath the house. Overheating isn't so much of an issue here because we are about 15 degrees farther north so the sun isn't so hot in summer and because of the gulf stream it isn't very cold in winter, just 5C average in January.

There is a company, in the same county as me, called Viking House who are experimenting with seasonal stores and solar heating and currently they seem to favour large areas of variable output, drain back, solar panels combined with more limited underfloor heat storage.
In the UK there are big subsidies for PV so the development there is tending towards PV powered ASHPs. The end result is to save money and scarce fossil fuels.
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Old 03-07-14, 07:31 PM   #20
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Quote:
Originally Posted by buffalobillpatrick View Post
...Roofing is already bought Decra steel shake dark green. 1/2 will face South, but I am reluctant to put holes in it to mount PV panels.
I share your concern with drilling holes in a Decra roof. When I installed my 4400W PV system on my Decra Tile roof, I drilled only one hole in it, at the peak, for the weatherhead. My 6 PV mounting rails and 20 PV panels are mounted on 102 Creotecc (Unirac) tile hooks. I couldn't get enough engineering data on the Aussie Tile Hook for my structural engineer to determine if a system designed using aussie tile hooks would survive a 3-second gust of 170mph (South Florida residential design criteria). Creotecc (Unirac) tile hooks came with uplift and down force engineering load ratings my structural engineer could work with. I can offer more details if you need them.

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