Subject: A solar sauna? Date: 16 Jan 1999 10:17:01 -0500 From: [email-masked]
Newsgroups: alt.solar.thermal, alt.energy.renewable, alt.architecture.alternative

Here's an 8' cube with a 4x8' sauna and  ----------R15--WWW-------
sunspace and 5 1'x 2' double-pane       |    4'  |       8'       |
windows. With R15 insulation, it has a  |        |                |
thermal conductance of about 6ft^2/R2   |        |                |
= 3 Btu/h-F for the windows, 410/15     |  162 F W      70F    8' W 
= 27 for the walls and roof, and        |    ?   W                W
1ACHx768ft^3/55 = 14 for air leaks,     |  sauna W      room      W
so it requires about 24h(70F-30F)44     |        |                |
= 42K Btu to stay warm over a 24 hour   |        |                |
30 F day or 211K Btu to stay warm       |---WWW---------WWW-------|
for 5 cloudy days in a row, which       |         sunspace     6" | 
might come from P pounds of water in     -------------------------  
the sauna cooling from 120 to 80F, where           south
P(120-80) = 211K, so P = 5280 pounds, say 83 ft^3 of sealed water
containers in a stack 4' wide x 8' tall x 4' deep, heated and cooled
by sauna air. 

Over an average 6 hour 30 F January solar collection day in Philadelphia,
with an average amount of sun (1,000 Btu/ft^2 on a south wall), the
sunspace receives about 86K Btu of sun and provides about 10K Btu for
the structure and loses about 6h(T-30)96ft^2/R1 to the outdoors, so
86K-10K = 6(T-30)96 and T = 162 F, in this linear model.

The room temperature might be controlled during the day by opening the
window between the room and the sunspace or opening an outdoor window
if the room gets too warm. The sauna-sunspace window might be wide open
whenever the sunspace is warmer than the sauna. At night, an open sauna-
room window might warm the room, cooling the sauna by 32KBtu/5280Btu/F
= 6 F to 156. This could all be done automatically. 

The windows might be made from two layers of clear polycarbonate plastic.
The insulation might be 2 layers of 1.5" R7.5 Styrofoam with latex paint
on the outside and plywood or cedar flakeboard inside. The sauna wall and
roof might have an extra layer of insulation. The rooftop might be an EPDM
rubber pond which supplies fresh water for a hot tub with an ozonator
(Heliotrope General, (800) 552-8838)) in the room. A shallow pond south
of the sunspace might add about 30% more heat.

Nick