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paulstef

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Reply with quote  #1 
It sounds silly, but I'm still dreaming about heating my house ONLY by the sun, nothing else.

I think I have about the same amount of heating degree days like Gary from builtitsolar, meaning January and February it gets  quite cold, like -20F.

I guesstimate I would need to store about 8000kWh during the summer months, June, July, August.

Where would I store that amount of heat, how many cubicmeters of what material (water, Rocks)

I'm a little lost, I'm not asking for someone doing the calculations for me, but maybe there is some reference project somewhere you could point me to?

I think I have about 500 sqmeters I could use as collector area.

Thanks

solardan1959

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Reply with quote  #2 
a bit overkill but... http://inhabitat.com/a-unique-solar-powered-community-in-canada/

The simplest answer is as large a body of water as possible and very heavily insulated.  But your 500 square meters is going to have to be able to heat it up.  Probably is good enough to heat a small underground lake to 110 degrees during the summer but not be able to sustain, or build up enough to keep it warm throughout the winter.
Realistically a 500-1000 gallon would probably meet your needs.

did you really mean 500 square meters? I get 1600 square feet out of that or 8X200 feet of collector.  maybe I calculated wrong but that is an awful lot of collector for one or two houses.  one half of that should provide all the heat needed for most average houses.

Dan
paulstef

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I'm aware of that project. Indeed a "bit" overkill. ;-) I wonder if anyone ever managed to do it in our climat. And I mean retrofitting, not for a new house.
solardan1959

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Paul,
   Sorry was typing while you answered and added more food for thought.
Dan
paulstef

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Reply with quote  #5 
Quote:
Originally Posted by solardan1959
a bit overkill but... http://inhabitat.com/a-unique-solar-powered-community-in-canada/

The simplest answer is as large a body of water as possible and very heavily insulated.  But your 500 square meters is going to have to be able to heat it up.  Probably is good enough to heat a small underground lake to 110 degrees during the summer but not be able to sustain, or build up enough to keep it warm throughout the winter.
Realistically a 500-1000 gallon would probably meet your needs.

did you really mean 500 square meters? I get 1600 square feet out of that or 8X200 feet of collector.  maybe I calculated wrong but that is an awful lot of collector for one or two houses.  one half of that should provide all the heat needed for most average houses.

Dan


Yes I meant 500m2 collector area. That would be the maximum area I could use for that purpose. Preferably less. ;-) Actually I'm already stuck at how big of a tank I would need for 8000kWh. I've seen I would need 26000 gals for that many Btus.
paulstef

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Also, people are talking about installing a heat storage tank into their home. I wonder if nobody is concerned with the additional weight of such large tanks. It's like parking several cars in a basement that was never built to support such weight.

EDIT: ok following the calculations on this site: http://www.engineeringtoolbox.com/energy-storage-water-d_1463.html I would need about 2000 Gallons for 176F heated water to store 3000000Btus.
solardan1959

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2000 is a whole lot easier to accomplish than 26000.  did it say how much collector you might need to meet that goal, (though 176 is rather hot).  I'm still thinking about 1/2 that or 800 square feet would more than meet your goal.

Dan
paulstef

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Reply with quote  #8 
Quote:
Originally Posted by solardan1959
2000 is a whole lot easier to accomplish than 26000.  did it say how much collector you might need to meet that goal, (though 176 is rather hot).  I'm still thinking about 1/2 that or 800 square feet would more than meet your goal.

Dan


From another site I got 1.2kWh/m2/day solar insolation end of december. Useful would be half of it from 10am to 14pm, i.e. 0.6kWh/m2/day or 190Btu/ft2/day.

According to my utility bill I guess I need about 60kWh (200000btu) per day in winter which means I'd need 100m2 (1070ft2) of a collector that works at 100% efficiency with sun shining every day. Let's say the collector works @30% efficiency I'd need 3000ft2 of collector area just to heat my home, not being able to store heat. This is why I think heat should be stored in summer... Unless I mixed something up on these calculations this seems a little bit discouraging. On the other hand I always hated math maybe I have to go through this again. :-)
kcl1s

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Reply with quote  #9 
Summer heat storage was discussed a couple of years ago on the old Yahoo SS group. As attractive as it seems to utilize all that summer warmth it just is not cost effective.

I did some quick calcs on your 26000 gal storage using these parameters

26000 gal would need a tank 15x15x15 ft (1350 sq ft surface)
storage water 180 F
ground or air outside 60 F
insulation R30 (6" blue board)
Results
Tank heat loss 5400 btu/hr or 130,000 btu/day or almost 4 million btu / month
So your first 250 sq ft or so of collector is used to just mitigate tank loss.

All that construction expense BEFORE you start to add heat to your house!

My suggestion is go back to basics and start with the most cost effective projects. Add insulation to your home and seal cracks to cut down on heat loss. Build some air or water collectors with the aim of cutting the heating bill by 50% in winter and 75-90% spring/fall. Your pay back time on this would typically be 2-3 years. To take your system close to 100% of your heating bill you will raise the pay back time dramatically.

Gather the low hanging fruit first.

Hope this helps
Keith

kcl1s

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Reply with quote  #10 
Quote:
Originally Posted by paulstef

EDIT: ok following the calculations on this site: http://www.engineeringtoolbox.com/energy-storage-water-d_1463.html I would need about 2000 Gallons for 176F heated water to store 3000000Btus.


Paul,
That page is a little misleading. Useable storage is different than gross storage. It is hard to heat a home with water that is less than 120 deg. You can only draw the temp down 60 deg on a tank that starts at 180 deg.  Therefore the usable storage capacity of one gallon of 180 deg water is 180-120=60 deg useable. 60 deg x8.3 lb/gal=498 btu/gal. So your 2000 gallon tank can only store about 1,000,000 btu's of useable heat.

Keith
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