A low mass sunspace is meant to serve as a heater, not a greenhouse for plants or a comfortable place for humans.
William A. Shurcliff:
It is hard to think of any other system that supplies so much heat at such low cost…
One could shorten the warm-up time of the enclosure and increase
the amount of heat delivered to the rooms by making the enclosure
virtually massless–by greatly reducing its dynamic thermal capacity.This can be done by spreading a 2-inch-thick layer of lightweight
insulation on the floor and north wall of the enclosure and then
installing a thin black sheet over the insulation. Then, practically
no heat is delivered to the massive components of floor or wall;
practically all of the heat is promptly transferred to the air.And since the thermal capacity of the 100 or 200 lb. of air in
the room is equal to that of one fourth as great a mass of water
(about 25 to 50 lb. of water), the air will heat up very rapidly.
I estimate that its temperature will rise about 40 F. degrees in
about two minutes, after the sun comes out from behind a heavy cloud cover.At the end of the day, little heat will be “left on base” in the
collector floor or north wall and, accordingly, the enclosure will
cool off very rapidly.
New Inventions in Low Cost Solar Heating–
100 Daring Schemes Tried and Untried
Brick House Publishing, 1979
This works well with airflow between the sunspace and living space
during the day and no airflow at night.
Tags: Chapter 3 - Alternative Building Strategies, Chapter 5 - Siting, greenhouse, Passive Solar, sunspace, william shurcliff
Nick Pine:
…Run a large window fan (eg Lasko’s $50 2155A, which moves 2470 cfm
with 90 watts on high speed) to circulate air between the house and the
sunspace when the house needs heat and the sunspace is warm, using a $15
line voltage 70 F heating thermostat in the house in series with an 80 F
cooling thermostat in the sunspace. The fan can move sunspace air into
the house through the upper part of a house window, with a passive
plastic film damper indoors to prevent reverse airflow at night. Air
might return to the sunspace via the lower part of a house window with a
plastic film damper in the sunspace that prevents reverse airflow at
night.
A 2-story sunspace might not have a fan, just upstairs and downstairs
windows and dampers… Btu/h = 16.6Avsqrt(H)dT1.5, with Av ft2 of
window area and an H’ height diff and a dT (F) temp diff. Av = 16 ft2
and H = 12′ and dT = 10 F will move 16.6x16sqrt(12)101.5 = 29.1K Btu/h
(8.5 kW.) If A ft2 of R2 sunspace glazing with 80% solar transmission
loses (80-30)A/2 = 25A Btu/h to 30 F outdoor air and gains 0.8x250A =
200A in full sun and 200A – 25A = 29.1K, A = 166 ft2, eg a 16′ tall x
12′ wide $400 transparent sunspace wall, at $400/8500 = $0.05 per peak
watt, about 100 times cheaper than PV energy. And houses need several
times more heat energy than electrical energy.
A 2470 cfm fan is like a 2470 Btu/h-F conductor, eg a 1ft2 R0.0004
wall. It can move 2470(80-70) = 24.7K Btu/h into a house with 80 F
sunspace air with A = 141 ft2, eg an 8′ tall x 20′ wide sunspace wall.