Posted by DJ on January 14, 2007, 2:23 pm
Actually, Nick, they don't destroy themselves in my experience, they
tend to cook and denature the glycol in the recirculation header when
Posted by Nick Pine on January 14, 2007, 6:56 pm
I'm thinking about a draindown system.
Posted by Jeff on January 14, 2007, 11:02 pm
Nick Pine wrote:
This is not a hot stop but a hot start problem? Why not put a thermal
cutoff and that is higher than the cuton switch? The worse that would
happen is you would lose a days heating. Computer backup powers supplies
have gotten pretty cheap if you have a lot of short outages and if you
have a long one than your day is probably shot anyways. It's been years
since I lost power.
Posted by nicksanspam on January 19, 2007, 11:16 am
I'm beginning to think it's a non-problem. After talking with SRCC about
their 30 day stagnation and thermal shock tests, it seems to me that any
certified system will be immune to those problems, but I'd look at
the guarantee and talk to the vendor before designing a draindown system,
since some vendors seem chary about that.
Posted by nicksanspam on January 14, 2007, 7:24 pm
Oops. With no room air circulation, the air in the box will be warmer, so
we can use a smaller collector, eg 0.195 ft^2 under 1 ft^2 of glazing.
Like this, viewed in a fixed font:
--- | R1 R1 |
|--|-->|---*---www---30 F ---www-----*----
--- | | I----------> |
225-43.9 | | |
= 181.1 w 1/(1.5x0.195) | w
Btu/h w = 3.42 - | Tt = 30+ w 3.42
w - | 181.1x1 w
--- | - --- = 211.1 F |
|--|-->|---| 140 F - | 140 F
--- | | 43.9 --->|
225x0.195 | | |
= 43.9 --- - ---
Btu/h --- ---
The collector gets 43.9 Btu/h of direct sun plus I = (211.1-140)/4.42
= 16.1 from the box air at Ta = 140+16.1x3.42 = 195 F.
Or run it at less than 140 F, for more DHW and less room heat.