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Posted by on January 4, 2008, 8:00 am
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> ... I'm in the middle of building mine in Scotland.
Where, exactly? Got weather data? You might need some seasonal heat storage
for 100%-solar heat. I worked on an Irish house design that needed to store
summer heat for Nov-Feb, eg in a 20' tall x 24' diam insulated water tower
with a floating foamboard draindown cover under a transparent dome.
Energy Plus weather stats for Aberdeen (N 57):
oct nov dec jan feb mar
Tavg 9.0 6.1 4.2 3.6 4.3 5.6C
Hdir 1052 890 499 632 1141 1616 direct | Wh/m^2-day
Hglo 1314 652 314 448 1017 2107 global | of sun on
Hdiff 967 452 246 330 703 1402 diffuse | the ground, vs
Hglo 3218 2145 1672 1956 2744 3785 global, for Phila, PA, USA
Phila is not a great solar heating climate, but it has about 3 times more
sun on the ground than Aberdeen in December.
> Lots of south facing windows, mine is a C shape with a garden room
> (vertical glass wall, insulated flat roof) filling in the C.
Like this, viewed in a fixed font?
--------------------------------- ---------------------------------
| | | | | |
| | garden | | | garden room |
| | | | | |
| | room | | |---------------------------------|
| | | | | |
| | | | | |
| | | | | |
| ------------- | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
--------------------------------- ---------------------------------
The one on the right can be less expensive and more efficient, with a lower
surface-to-volume ratio, without the south "wings." Garden rooms with plants
need to avoid freezing, but the ceilings might not need much insulation, if
they get cold at night.
> Airtight - use breathable membrane for an unventilated "warm roof"...
What do you mean by that?
> 300mm fibreglass on N, E, W walls
About 12", US R40, metric R7 (m^2C/W). A 16mx16mx2m tall airtight house with
R7 walls and ceiling and no windows(!) could have 16^2/7 = 36.6 W/C of ceiling
conductance + 128/7 = 18.3 for the walls, totaling 55. At 20C indoors and 5C
outdoors, it would only need (20-5)55 = 825 watts of heat, eg 200 watts from
4 half-time occupants + 625 watts from 625x24hx30d = 450 kWh/mo of indoor
electrical use. Maybe it doesn't need solar heat :-)
> Solar tiles for hot water / some space heating - e.g. Solex in the UK -
> approx GBP 100 per square metre + 300 for the controls.
How about heating water in a big unpressurized tank with a $35 car radiator
and its 20 watt fans in the garden room, and making water for showers with
a $60 1"x300' 13-gallon plastic pressurized pipe coil in the 140 F tank?
> Heat store - a vertical trench 200mm wide filled with closed cell foam
> insulation 1.2m deep, running round the West, N, E walls, but 2m inboard
A basement full of hot water would have a lower surface-to-volume ratio.
With no internal heat gains from people or their electrical use, you might
store 825Wx24hx30dx3mo = 1782 kWh in 1782/(60C-22C)/1.163 = 40 m^3 of water
cooling from 60 to 22 C in a 2mx10mx2m-tall tank lined with a single folded
piece of EPDM rubber roofing material.
Nick
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