[Greenbuilding] low-mass sunspaces

[Nick Pine]

Rob Tom writes:

> Perhaps someone would care to 'splain eet to me, the wisdom of making 
> a "low mass greenhouse" because quite frankly (and shirley too) I 
> don't get it.

William A. Shurcliff 'splained the winsdom of a low mass sunspace:

   It is hard to think of any other system that supplies so much heat
   (to an existing house) 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.

Nick