The ultimate performance solutions are: 1) Isolate the solar gain space,
> to let it go cold at night. If you eliminate all of the times that the sun
> does not heat the room, you eliminate 100% of the backup heating, so you
> don't need high Rvalue windows...
Maybe no windows at all, just plastic film glazing.
2) Nighttime window insulation. Basically the same strategy, but you are
> closing the insulated door on the glass, instead of the whole room.
> There can be problems.. some of them human.
Historically, most people tire of moving insulation twice a day. Twice a year seems OK. Or automatically filling a glazing cavity with soap bubble foam at night. My favorite "movable insulation" is a big fan with 2 thermostats in an insulated wall between a sunspace and a living space.
3) Reduce the glazing area considerably, and get your Solar gain, via
> simple, low cost wall type air panels, or a single glazed sunspace,
> over the south wall.
We might rethink how we use spaces. People seldom look out windows at night. They cover black holes with curtains. A living space might only have 1-2% of the floorspace as windows for small views. Picture a core living space behind enclosed porches, or "viewspaces" with lots of glazing for large views. During the day, move into a viewspace and steal some heat or AC from the living space with an occupancy sensor and a thermostat and a fan.
A 32x32x8' tall living space with 16'-deep SE and SW viewspaces and a 48'x48' footprint might have 24ft^2 of R4 windows with 6 Btu/h-F. An R40 ceiling and R30 walls would add 32x32/40 = 26 and 33, with 30 more for
30 cfm of air leaks, if it's tight, for a total conductance of 95 Btu/h-F.
With 4 American Craftsman 6068-2 6'x80" U0.48 sliding glass doors ($269 each at Home Depot) or 320 ft^2 of R4 windows, a 16'x48' SE viewspace would have a 123 Btu/h-F conductance. Two more doors would give a 16'x32' SW space 61 Btu/h-F. The glazing might have overhangs to reduce summer sun and dark mesh curtains to reduce light levels for people, eg 80% greenhouse shadecloth, which preserves views, like a dark window screen.
If the average living space temp is 65 F and we spend 4 hours per day in each 70 F viewspace (Henry Mercer built bonfires on the roof and moved from desk to desk as the sun moved in his 6-story concrete castle in Doylestown PA) on an average 30 F January day in Phila, the house needs 24h(65-30)95
- 4h(70-34)123 + 4h(70-34)61 = 79.8K + 17.7K + 8.8K = 106K Btu/day of heat. With 34.1K from 300 kWh/mo of frugal indoor electrical use, we need 72K more solar heat, which might come from a solar attic.
The solar attics of Soldiers Grove (see
A new attic might have a $1/ft^2 corrugated R1 Dynaglas polycarbonate
20-year south roof with a 60 degree slope and 90% solar transmission. NREL says 620 Btu/ft^2 falls on the ground and 1000 falls on a south wall on an average January day in Phila, so 1 ft^2 of roof would collect
0.9(1000sin(60)+620cos(60)) = 1058 Btu/day.
Nathan Hurst's "Low-cost active heat storage" story in the July-September
2007 Issue 100 of ReNew (http:
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