Unquestionably Confused wrote:
| Morris Dovey, wrote the following at or about 6/8/2007 6:07 PM:

|| In this shop, the insulated 6" concrete slab acts as a big thermal
|| "flywheel". Since warmed air "wants" to stay up near the ceiling,
|| the fan is necessary to shoot it down to warm the floor. When the
|| sun sets and the solar panel shuts down, the heat stored in the
|| floor radiates as IR to extend the daily comfort period and
|| prevent the shop temperature from dropping anywhere near the
|| freezing range overnight.
|
| Again, I guess I'm somewhat surprised that the concrete (insulated
| or not) comes into play that much. Would expect it, I guess, from
| basking in the direct sunlight behind a wall of windows, etc. but
| not so much with the air above circulating over it.

Normally (without the fan) the slab would not play such an important
role. The ceiling fan provides a whole collection of benefits, and
it's difficult to say that any one of them is more important than the
others.

By pushing the warm air away from the ceiling, it helps to reduce
conductive losses through the ceiling.

By mixing the warm air with the cooler air below it reduces
stratification and evens out the heat distribution throughout the shop
to make the whole more comfortable.

The continuous flow of warm air on the insulated slab warms raises its
temperature (stores energy in it) so that the it will begin giving up
its heat to the air as soon as the air temperature drops below that of
the slab. If the slab were left cold, it would still take some energy
from the air that touched it, but it would warm less and might
continue absorbing heat well beyond the point where the air felt
chilly.

|| It's important to panel efficiency to get the heat out of the
|| panel as quickly as possible. By designing to maximimize capture
|| bandwidth and to maximize the volume of air flowing through the
|| panel, the panel operates at a lower temperature and delivers more
|| heat. Operating the panel at a lower temperature reduces the black
|| body (IR) radiation back through the glazing, and lowers
|| conductive losses through the panel body. It's a balancing act,
|| but as you home in on the balance point, panel performance does
|| seem to peak spectacularly.
|
| Okay, that explains why the high efficiency panels are "more better"
| though they are operating at 140 degrees vs the discontinued economy
| panels that were running at 160 degrees.

Exactly! The concept you've grasped is of the utmost importance - that
heat (energy) and temperature are _not_ synonyms.

My current aim is to lower that 140F to 120F for a 6'-tall panel
without major cost increase. The Madison County installation won't
quite make it but I'm getting closer with every design iteration.
Interestingly, I'm not sure that achieving that goal will necessarily
produce a more efficient /system/.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/SC_Madison.html