Drainback vs. Closed Loop Circulators [RE-wrenches]

Jeff Clearwater clrwater at earthlink.net
Sun May 21 19:07:01 PDT 2006


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Hi Jeff, Bill, Todd & Tom,

I really appreciate all the great feedback on this!  That's why I 
love this list.  All of your experience is worth it's weight in gold.

Any more input from those that have had good experience with 
evacuated tubes before I reconsider what to recommend?

And on drainback vs closed loop?

Thanks!

Jeff C.


At 2:45 PM -0400 5/21/06, Jeffery Wolfe, Global Resource Options wrote:
>What we've seen with the evacuated tube collectors (which we have used,
>and don't any more) is the following:
>  - they work better in cold, cloudy weather. But in the great northeast
>(and most of the rest of "cold country"), we don't get much solar
>irradiance during cold cloudy weather. (as a percentage of overall
>irradiance. For example, from Nov. 1 to Feb 28 we get about 20% of our
>annual irradiance.
>  - the collectors are much more expensive than flat plate per BTU
>harvested on an annual basis
>  - collecting a theoretical higher percentage of the energy when there
>is not much energy available does not result in that many more BTU's. It
>may result in more BTUs when you need them, but our experience does not
>bear that out to any large extent.
>  - as was pointed out, they do NOT shed snow well. We've got some on our
>home, at a 50 degree installation angle, and they can stay covered for
>days (to high on the roof for me to get to, and those that do try to
>scrap snow of break tubes. We've had several customers learn the hard
>way even after our admonitions during training.)
>  - while they are lighter to carry to the roof, there are more trips, by
>far, up and down the ladder. And carrying a box of 7' long tubes up a 2
>story ladder is no simple chore either. With proper training and proper
>tools, the installation time and safety has not proven to be any worse
>with flat plates. (We do not use 4x10's on standard residential
>projects. Why exacerbate the problem!)
>  - the failure during warranty period has been high. Granted, one tube
>failure does not shut the system down, but it can create a radiating fin
>instead of a heat absorbing fin, reducing system capacity. The fact that
>we've had some failures, and that failures are fairly hard for an owner
>to see unless they pay careful attention to the system visually (the
>snow melts faster off a failed tube. That's about the only visual
>indication) they will not know about the failure. Where we have gone
>back for other reasons, we've too often found failure. This is reflected
>in other wrenches I know who have installed this technology for a large
>number of years in the past. The glass / metal seal is a weak point, and
>will always be a weak point.
>  - there is one new evacuated tube on the market that has a glass to
>glass seal. That might work. Only problem is, they are incredibly
>fragile, and very difficult to ship. Not my recipe for a good product.
>  - overall, we strongly believe (through modeling and anecdotal
>evidence) that high quality flat plate collectors perform about as well
>year round in our climate, have FAR fewer warranty issues, and cost no
>more to install safely.
>
>My 8 cents.
>
>Jeff Wolfe
>Global Resource Options, Inc., Solar Energy Solutions

-- 
~~~~~~~~~~~~~
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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