Drainback vs. Closed Loop Circulators [RE-wrenches]

[Todd Cory, Mt. Shasta Energy Services]

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The only caveat with drain backs is the possibility (albeit very small) 
of freezing. I agree with all the advantages mentioned about drainback 
systems versus glycol... but I do not think it wise to trust a snap 
switch and/ differential controller or its temp sensor to not accidently 
pump water through the system during times of freezing weather. Brazing 
leaks on a burst absorber panel is no fun.

Todd



Ken Schaal wrote:

>Let's be sure we are not confusing DRAIN DOWN -- using a motorized valve to
>shut off pressurized water going to the collectors-- with DRAIN BACK , which
>uses a pump to lift unpressurized water to the collector, and drains back
>into the reservoir/tank by gravity when the pump shuts off. The collector
>and piping must be sloped to drain [ even plumbers can understand that part
>! ] and there must be a way for air from the tank or reservoir to get into
>the return line, thus allowing the collector and piping to drain.
>
>Travis comments are right on target !
>
>The only time I have used glycol for a new system is when the bottom of the
>collector cannot be above the top of the water level in the tank .
>Incidentally, the first systems I installed in 1977-78 were draindown and
>then we started using various versions of drain back. A typical tank is
>shown on my website www.commonwealthsolar.com/cwhot.htm
>
>As for pumps and high power requirements that was /is a concern, although as
>Travis has shown the reliability and efficiency gains more than compensate.
>For years I used Taco 009B pumps, syphoning water from the bottom of the
>tank. Recently Taco has 'improved' the performance of these pumps head
>capacity, which made them more sensitive to cavitation. This got expensive
>and frustrating ! For 6 mos I have used Fluid-o-tech TMFR pumps which use a
>converter to provide 3 phase to the pump. Total watts on a Brand meter of
>20-30 at 30' head and 1-2 gpm. A bypass line is required to allow drainback
>.
>
>Please contact off-list for more info.
>
>Thanks to all for the chance for an old SHW guy to learn PV !
>
>Ken Schaal
>CommonWealth Solar,LLC
>804-798-5371
>  
>


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