Drainback vs. Closed Loop Circulators [RE-wrenches]

[Jeff Clearwater]

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Hey Conrad,

Is the drainback of the '80s a fair comparison to the drainback of today?

It's the failures of '80s glycol that pushes us to drainback.  But 
then again is the glycol of the '80s a fair comparison to the glycol 
of today?

The debate goes on.

Travis, you said "all the benefits of drainback" - Want to spell that 
out for us?

Conrad, game to do the same for glycol?

Still Learning,

Jeff C.



>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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>>
>>
>
>
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-- 
~~~~~~~~~~~~~
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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