Tuesday, July 11, 2006

Solar Thermal Seasonal Storage for Space Heating

Solar seasonal thermal storage is in the news thanks to the very cool Drake Land project in Canada. Where the cover garages of about 60 homes with solar thermal panels and dump the heat into one large well field.

picture from the website below

See http://www.dlsc.ca/ and http://www.sterlinghomesgroup.com/drake/northamerica.html

Solar experts in Wisconsin are thinking once again about seasonal thermal storage for homes in Wisconsin.

Mark Klein of Gimme Shelter is thinking about setting aside a "room" in the basement that would hold a several thousand gallons of water in a very well insulated tank. The water would be heated during the summer and used for space heating during the winter.

Alex DePillis of Seventh Generation Energy Systems did these calculations.

Residential customers in Wisconsin use ~ 1000 therms each, annually. The room would need to hold ~ 40,000 cubic feet of water; about 5400 gallons. A cistern of size 8' x 20' x 200'+

Here are the calculations (corrections please!)
1 Btu per # per degree F.
Raise the water from 60 to 100 F (delta T = 40)
8.3 pounds per gallon water
So raising the temperature of one gallon of water by 40 degrees stores 333 Btu, or 0.0033 therm

(one gallon per 0.0033 therm) x (1000 therms per customer) = 1000/0.0033 = 303,030 gallons
(7.5 cubic feet per gallon) x (303,030 gallons) = 40,404 cubic feet

If this is a cistern in the basement of a house, limited at 8' height...
8 high by 20 wide by... 252 feet long. Or pick your tank/cistern dimensions.

Now my 1100 square foot home, with about R-4 (concrete) walls uses about 600 therms per year (for hot water, cooking and space heating). So lets say it uses 500 therms per year for space heating. (Yes I am working on insulating those walls from the inside - which means studding up new walls and making my home even smaller.)

If the thermal envelop of the home is improved, have the house solar tempered, and
assume some solar thermal heating during the winter season (as there is sun
in the winter)... and maybe that tank can be reduced to: 8' by 20' by 100'

Humm, that is more square feet than my entire home.

Niels, 5400 gallons would only require a tank 8x10x9 (720 sq ft)
I mean 720 cubic feet
I mean 720 cubic ft
I think your calculations are way too high!
You certainly would not just collect during the summer. You would be collecting all year, right? So, even in the dead of winter you are still collecting heat.
You only have to have enough of a reserve at the beginning of the year to get you through what you cant collect on a daily basis.

I think this is not likely to be more than 1/3 of your calcualtion and maybe less.
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