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Re: solar house information



Jason M. Roth <jr4q+@andrew.cmu.edu> wrote:
>...here are the 4 basic solar systems:

>DG, Direct gain, which means sun-facing glass into the living space with
>thermal storage inside. Simplest and cheapest, but...

A poor performer, often reducing the backup heat for a house by less
than 30%, or even  increasing  the backup heat requirement in very
cloudy areas. Movable insulation helps, but you still have to live
inside the heat battery...

>AG, Attached greenhouse...

A low-thermal-mass sunspace, NOT a greenhouse full of plants, containing
thermal mass, is a better performer, by as much as a factor of three.

>TW, Trombe wall, a system developed by a Frenchman in which a thick
>concrete wall is placed on the sun-side with glass on the outside.

Another poor performer, compared to a low-thermal-mass air heater on
an insulated south wall. I put Trombe walls on my house 20 years ago,
when I didn't know any better.

>WW, Water wall, in which water-filled prisms (oil drums, plexiglass
>cylinders, etc) are just inside the sun-glass and act as thermal mass.

Again bad, in cloudy areas. If the water is just inside the glass, the heat
will leak out through the glass all night and during cloudy day periods.

>H2O is _the_ best storage mass (in efficiency, at any rate.

Agreed. Water is also cheap, and it can be easily moved around.

>Another option is less direct, in which you run pipes through solar
>panels and use that water to heat the house (radiant or baseboard or
>whatever);

Very expensive, and those panels up on the roof have lots of thermal
losses, which do nothing to heat the house, compared to a water heater
in the sunspace. And they may freeze, or heat up to 400 degrees if the
pump fails, ie during collector stagnation, which may break the glass covers.
It is better to have a solar closet as a deliberately stagnant collector,
IMHO.

>another includes a rockbed, in which heat is gathered and stored in a
>rockbed near the house, and the heated air is circulated up to the house
>(thermosiphoning).

How about putting the rockbed INSIDE the house, in an insulated
closet, on the first floor, and using thermosyphoning to heat it from
an air heater in the sunspace in front of it, and using 55 gallon
drums full of water instead of rocks. Drums are free, and last at least
20 years, and they are easy to stack up. Water has three times more
thermal mass than rocks, and the air spaces are bigger, so natural
convection or a small high-temp fan (eg Grainger's 4C861) works better
to heat these "rocks."

>That's a brief summary; just about any solar book will cover these.

I guess we need a new book. Perhaps John Allred will write one...

Nick