[RE-wrenches] Evacuated Tube-based SDHW

[Kurt Albershardt]

On 3/25/09 7:40 AM, Peter Parrish wrote:
>
> could we start a thread?
>
> My principal reason for looking into this technology is for 
> space-limited applications. Right now we are looking at trying to find 
> space on a crowded roof for about 100-120 sq-ft of conventional flat 
> plate collectors (e.g. SunEarth Empire 4’x8’ or 4’x10’), and 
> skylights, parapet walls and a PV array are getting in the way. 
> Climate is southern California coastal.
>

I asked for evacuated tube experiences on this list and have 
subsequently queried a number of installers and manufacturers over the 
past 2-3 years.  There were some facts, a lot of bad experiences early 
on, and plenty of opinions.  What I have distilled from all of this so 
far is:

ETs make sense when ∆T is high and when the location has a lot of 
overcast days.
ETs do not make sense when ∆T is low to moderate and when the location 
has few overcast days.
ETs cost more per square foot of aperture.
ETs present much lower wind loads than flat plates (potentially allowing 
installation using ballasted racking on low slope roofs.)
Stagnation and scale present bigger risks with high fluid temps.




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