Drainback vs. Closed Loop Circulators [RE-wrenches]

[Bill Loesch, Saint Louis Solar]

Todd et al,

Please don't confuse the issue with heat transfer between the two systems.
First, you need to decide if you want guaranteed freeze protection. If the
answer is yes, the only way I know how to provide _guaranteed_ freeze
protection is through the use of antifreeze. Both types of systems can use
antifreeze. Both types of systems then will have similar heat transfer
through their heat exchanger. 

To trust freeze protection of your thousands of dollar system to the
electric differential temperature control and/or sensors to not fail at a
critical time is not (for me) prudent or cost justified. Who pays for the
damaged system when a freeze does occur? The control manufacturer with whom
you've spent less than two hundred dollars with? I doubt it.

While the freeze protection prevents a dramatic failure, a much more
insidious risk is that of hard water in any of the systems. Hard water over
time, will produce a gradual loss of heat transfer which is likely to go
unnoticed. Unfortunately the scale acts as wonderful insulation. So, make
sure your water supply is appropriate for long term health of the SDHW
system, whatever system you ultimately choose.

I'm surprised Tom didn't point out that the tubular collectors don't shed
snow and frost as well as the flat plates.

Respectfully,

Bill Loesch
Solar 1 - Saint Louis Solar
314 631 1094


Message text written by INTERNET:RE-wrenches at topica.com
>>
> I have seen bad experiences with evacuated tube collectors. They are 
> fragile and the performance gain is not worth it unless you are trying to

> make steam. Flat plate collectors are heavy and take 2 to 3 people to
lift 
> them on the roof, but they last forever.
>
> Drainbacks are more efficient in terms of heat transfer, but the energy 
> for pumping is MUCH higher than a closed glycol loop. It is probably a 
> toss up as to which is better. What do others think about this?
>
> Todd
><


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