[Greenbuilding] A self-contained sunspace house heater

[Nick Pine]

An 8'-tall x 8'-deep x 24'-wide sunspace over a south house wall (as below,
in a fixed font) could provide heat and hot water. It might have a $100
modified stone floor over black plastic film on the ground and 10 $100 4'x8'
double polycarbonate film panel walls (how do we handle thermal expansion
of GE's HP92W lexan?) and a roof with 6 $50 4'x12' Dynaglas corrugated
polycarb panels over greenhouse polyethylene film and an 80% shadecloth mesh
curtain near the walls and under the roof for daytime comfort and privacy.

                                            4'
 ------------------------------------------------     
|                                       |        |   
|                                       |        |  
|                                       |        | 
|                                       |        | 
|           view from above             |  tank  | 8' 
|                                     2'|        |   
|                                    ---|---     |  
| SC                             3' h D RF  |    |  south
| 2'                                h   RF  |    |  house
 |||---------------------------------|||-hhh-----    wall
                                      RH                |
                         24'                            |       8'  
                                                        v
 ------------------------------------------------     ------------------
|               ...mesh...          |   RF  |    |      |FFF|           |
|                                   |   RF  |    |   DH |FFF| 2' view m |
|                                DS h----hhh     |      hhhh|    from e |   
|                                   |   | DH     |      |   |    the  s |
|         view from the north       | D |        |  8'  | D |    west h |
|                                   |   |        |      |   |           |
|---                                |---|--------|      |---------------|
| SC| 2'                            | R |  tank  |    3'R     tank      |
|   |                               | H |        |      H               |
 ------------------------------------------------     ---------------------

During the day, house air enters the sunspace through one-way convective
plastic film damper SC and flows through motorized damper DS (2'x3' of
foamboard over North-South hinges h, with a $10 windshield wiper motor
and limit switches) when it is in a horizontal position and flows through
a $35 car radiator RR and its fans FF and returns to the house through
motorized damper DH, open for house airflow when horizontal.

When the house is warm enough, vertical damper DH (with E-W hinges below)
blocks house airflow while the fans push air back down into the sunspace
to heat tank water to 140 F, or to heat the sunspace with tank water once
in a while. The 4'x8'x3'-tall plywood tank has a folded EPDM rubber liner 
with a $60 13-gallon 1"x300' black plastic pressurized PE pipe coil to 
heat water for showers.

The radiator slowly drains back into the tank for freeze protection, with
a 1/4" hole in the return pipe above the tank water line. A 0.5% ACI-100
non-toxic corrosion inhibitor solution from D. W. Davies allows using
an inexpensive cast iron pump like Taco's 1/25 HP 008-F6-1 (Grainger item
4PC92, $85.55), which can move 1 gpm with a 15' head and 14.5 at 1'.

On a cloudy day, the radiator heats house air that enters insulated
vertical duct D via register RH, with DS vertical and DH horizontal. 

In full sun on an average January day in Phila, the sunspace gains
0.8x250Btu/h-ft^2x8'x24' = 38.4K Btu/h. With 70 F air near the walls
(how can we arrange that?), it might only lose (70F-30F)40'x8'/R2 
= 6.4K Btu/h, for a net gain of 32K Btu/h in 1000 cfm of 70+32K/1000 
= 102 F air. The sunspace might be bigger, eg 32'x12'x16'-tall, with
a 102.4K Btu/h gain and a 17.9K Btu/h loss and an 85.5K Btu/h net 
gain and 156 F air. 

Nick