Drainback vs. Closed Loop Circulators [RE-wrenches]

Jeffery Wolfe, Global Resource Options jeff at globalresourceoptions.com
Sun May 21 11:45:31 PDT 2006


 
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


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