Re: Constructing collectors for a solar hot water system

 

For the whole stack? :-)


Nice...


I've never seen a commercial collector with baseboard fin-tube inside.
It's fairly expensive and doesn't collect well at low temp diffs.


Ideally, we'd want a small amount of fin-tube inside a large air heater, so
the fin color wouldn't matter much. David Delaney suggested something like
this with passive auto radiators and a vertical poly film airflow separator.



Lowes and Home Depot. With 2'x50'x0.018" rolls of Amerimax 69124 brown/white
coil for $78 and 10'x1/2" copper pipes for $10.85 and 3/4" pipes for $17.62
and 3/4"x3/4"x1/2" copper Ts for $2.34, the materials for a 10'x10' bare
collector with 18 10'x6.4" fins would be about $78+$17.64+18($10.85+2x$2.34)
= $375. Screwing it into 3 4'x8' sheets of 1/2" OSB into 3 4'x8'x1" foil-
polyiso boards onto a south wall might add $60.

A draindown version might look like this, viewed in a fixed font:

                              10'
in   -->-------------------------------------------
         |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
         |  |  |  |  |  |  |  |  |  |  |  |  |  |  | <-- 18 vertical
         |  |  |  |  |  |  |  |  |  |  |  |  |  |  |        10' fins
         |  |  |  |  |  |  |  |4'x8'|  |  |  |  |  | 4'
    57.6"|  | a|  |  |  |  |  |  |  |  |  |  |  |  |  
         |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
         |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
         |  |  |  |..|..|..|..|..|..|..|..|..|..|..|  
         |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
         |..|..|..|  |  |  |  |  |  |  |  |  |  |  |     10'
         |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
         |  |  |  |  |  |  |  |4'x8'|  |  |  |  |  | 4'
         |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
         |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
    57.6"|  | a|  |  |  |  |  |  |  |  |  |  |  |  |  
         |  |  |  |..|..|..|..|..|..|..|..|..|..|..|  
         |  |  |  .  |  |  |  |  .  |  |  |  |  |  |  
         |  |  |  .  |  | b|  |  .  |  |  |b |  |  | 19.2"
         |  |  |  .  |  |  |  |  .  |  |  |  |  |  |  
         |  |  |  .  |  |  |  |  .  |  |  |  |  |  |  
          -----------------------------------------|
             2'           4'               4'      |
out  --<-------------------------------------------

Cutting diagram:
                    19.2" 19.2"        57.6"
                   --------------------------------  
                  |     .     .                    |  
                  |     .     .         a          | 2'
                  |     .     .                    |  
               4' |  b  .  b  .....................|  
                  |     .     .                    |  
                  |     .     .         a          | 2'
                  |     .     .                    |  
                  |     .     .                    |  
                   --------------------------------  
                                  8'

This might be inside a 12'x12' frame on a south wall covered by 3 $84 4'x12'
sheets of U0.58 Thermaglas Plus twinwall polycarbonate with 80% transmission.

In 250 Btu/h-ft^2 sun and 34 F outdoor air on an average December day in Phila,
140 F fins with lots of water flow would gain 0.8x250x100ft^2 = 20K Btu/h with
144-100 = 44 ft^2 of parasite heating and no heat loss to 140 F frame air, so
back insulation is useless. If we simultaneously collect frame air to warm
the house and lower the frame air temp and raise the overall solar collection
efficiency, back insulation can raise the water collection efficiency.

Nick

 
Oops. This might drain better:


Or this, with some pipe squeezes (how deep?) on the left to equalize flow: