Drainback vs. Closed Loop Circulators [RE-wrenches]

Conrad Geyser conradg at cape.com
Mon Jun 5 22:21:40 PDT 2006


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Jeff, Travis and other Drainheads,

If you want to cut the power use more you can use two smaller circulators, 
cutting the second one out after 5 minutes (once you know you've filled the 
collector).
Tek-Mar controller provides for this through a programmable second 
output....
.
BTW, out of the several hundred 80's systems that we've serviced here in the 
northeast, there is yet to be one surviving drainback.
Some day I'll try to catalog this in the hopes of solutions.
for starters:
-corrosive drainback water?-circulators failing quickly and collectors 
corroding
-freeze ups

Those glycol loops sure hold up....

Conrad Geyser
Cotuit Solar

----- Original Message ----- 
From: "Travis Creswell, Ozark Solar" <ozsolar at ipa.net>
To: <RE-wrenches at topica.com>
Sent: Monday, June 05, 2006 3:52 PM
Subject: RE: Drainback vs. Closed Loop Circulators [RE-wrenches]


>
> Hello Jeff,
>
> We just did a drain back system with six 4x10 flat plates.  Calculations
> showed that we had to use Grundfos 26-96 to overcome the head and total
> pressure drop.  I carefully added up every foot of pipe, valve, elbow etc 
> to
> make sure I didn't oversize it.
>
> It's rated at 215 watts but we choked the flow down to ~9 gpm (1.5 per
> panel) and dropped the wattage to 135 as measured with a Brand power 
> meter.
>
> The pump would do almost 20 gpm with out reducing flow which was higher 
> then
> the charts said it would do so I assume there was a siphon effect adding 
> to
> the flow.  But you can't factor that into the pump sizing as you have to
> overcome the head initially.  And the next smaller pump left no room to
> safely overcome the head plus it didn't use much less wattage.
>
> I'll gladly use the extra energy to get all the benefits of drain back. 
> In
> the morning I saw a 20f delta t at 9 gpm.  Of course the Delta T drops as
> the days goes on but stays above 10.  That's 90,000 BTU's of heat for 460
> BTU's worth of electricity.  So the average of the day that's 1% of the
> energy collected is used to pump.  Share that with the "thermal engineer"
> and see what he says.
>
> The common circulation pump is centrifugal which is not a positive
> displacement type.  Very low wattage positive displacement pumps are
> available that can handle the temp but their flow rate limits them to a 
> max
> of several panels.  Ken Schaal of Commonwealth Solar can speak with direct
> knowledge of them.
>
> Best,
>
> Travis Creswell
> Ozark Energy Services
>
>
> -----Original Message-----
> From: Jeff Clearwater [mailto:clrwater at earthlink.net]
> Sent: Friday, May 19, 2006 7:56 AM
> To: RE-wrenches at topica.com
> Subject: Drainback vs. Closed Loop Circulators [RE-wrenches]
>
>
> 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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