Drainback vs. Closed Loop Circulators [RE-wrenches]

[Jeff Clearwater]

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Hi All,

We have been getting back into offering Solar DHW - mostly due to two 
factors that make it a doable business model in terms of 
installation, service and liability.

The first is switching to evacuated tube collectors.  They are light, 
easy to ship and handle and easy to install - I don't have to worry 
about cranes or major racking weight and it eases safety factors with 
my installers.

Second is going with drainback instead of closed loop glycol.   This 
eliminates having to service the glycol every 2-3 years and actually 
gives a chance that the system might live on when the folks sell the 
house etc.

However, I recently suggested drainback, closed loop to a low income 
zero energy home development we are working with and the thermal 
engineer came back with data saying that the drainback circulators 
used up to 1/3 of the energy harvested by the system in terms of 
electrical cost vs. gas saved!  I find that hard to believe. He 
claimed the closed loop circulators use less but still was showing a 
significant percentage.  I'm not sure whether he's just finding an 
excuse to go with what he is used to or whether there is a 
significant difference here.

So the questions for my esteemed wrenches are:

1)  Does anyone have KWH use figures for solar DHW circulators?
2)  Does anyone know of the most efficient circulators?  (are 
circulators positive displacement pumps?) - any models to suggest for 
drainback?
3)  Do folks recommend using PV direct pumping for drainback?  What 
controller would one use then?

Thanks!

Jeff C.

-- 
~~~~~~~~~~~~~
Jeff Clearwater
Village Power Design
Sustainable Energy & Water Solutions for Home & Village
http://www.villagepower.com
gosolar at villagepower.com
NABCEP (tm) Certified Solar PV Installer

530-470-9166
877-SOLARVillage
877-765-2784
72 Baker Rd.
Shutesbury, MA 01072
425 Nimrod St.
Nevada City, CA 95959
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