Posted by Jonathan Mau on January 14, 2005, 8:55 pm
As above, I am interested in installing a commercial DHW system. The
question becomes whose?
I would like to get a greater than average solar fraction as I am looking
ahead to getting off-grid one day. I don't much see the point in turfing
the electrical utility, only to go out and rent propane tanks to run a
water heater. I would also like to do some space heating in the spring
and fall. Maybe the natural surplus in non-winter seasons will allow this
without oversizing the system.
I currently supply house heat with wood harvested on the property. Backup
heat is oil, but oil is getting to be more of a PITA every year- too
many government rules and insurance hassles- and I can see letting it go one
So ideally one day all my energy would come from solar, wind, and wood.
I am curious about these evacuated tube type heaters. On the face of it,
with ambient delta T of > 50 F degrees much of the year, combined with my
desire for a high solar fraction, these would off hand seem to be the way to
go from a technical viewpoint. I do not know of specific pricing, but the way
China is pumping out these units, I suspect the price is getting better
Unfortunately, DHW is mostly an European and Asian thing with not much
going on in North America, so it is hard to find anyone close with any
real experience with these systems.
What is the current thinking on these systems. Do the evacuated tube
types make economic sense, or does one just purchase more flat plate
collectors? Does anyone have any specific recommendations available in
Ontario, Canada? I would also be interested in specific commentary on
Sunda products as a local guy handles this line.
Posted by DJ on January 18, 2005, 5:01 pm
The evacuated tube heaters are cool, no doubt about it. From my
researching the technology, though, the big thing they save is roof
space, ie, if you have very little available space, vac tube is the way
to go. Otherwise, the flat plate collectors have the financial and
lifespan edge, installed correctly.
For Canadian applications, I'd suggest considering the
Thermo-dynamics.com (out of Dartmouth, Nova Scotia) or Solcan.com (out
of London, Ontario).
I've dealt with both professionally, and both are quality outfits.
Neither do the vacuum tube thing, though. Both deal in flat plate
For your overall plan to move off the grid, however, you should consult
a qualified professional to get a good plan together. A good place to
find one might be http://www.cansia.ca/ .
Posted by redstone on January 20, 2005, 6:24 pm
I am kind of in the same boat as I am building off-grid in Colorado,
probably within the next year. I am not only looking for DHW, but also a
little bit of heat for radiant floor heating. There's alot to consider. But
here's the way I am thinking right now (and this changes weekly :)
I have two main contenders for my solar water heating. One is the Thermomax
tubes and the other is the GOBI flat panel. You've outlined the pluses of
evacuated tubes pretty well below. On the negative, they are EXPENSIVE.
Also, if you want to have some btu's for space heating (i.e., many tubes)
you run into a real problem in dumping heat in the non-heating months (when
the sun is really cooking). They recommend a swimming pool or hot tub. With
a well at less than 1 gpm, thats not going to happen! Also, be careful with
the Chinese supplied tubes, you get what you pay for.
What I'm thinking right now is a water heater for DWH supplied by 30
thermomax tubes and also a pre-heater (internal coils) contained in a 300
gallon tank. The 300 gallon tank will be supplied by 2-3 GOBI panels and a
masonry stove water loop. While the masonry stove will be a primary heat
source, the 300-gallon tank will be the source of radiant heat for selected
portions of the house. The radiant floor is not enough to fully heat the
house, but ought to (hopefully) be enough to keep my wife's feet warm (her
only criteria; I know, alot of money for warm feet, but a small price
compared to my need to not be beholden to the power companies!). Both DWH
and space heating will need a propane tankless heater as back up to meet
requirements for insurance. The GOBI panels will be mounted vertically for
maximal winter contribution and to shield them a bit during the summer. They
may even be tucked under the eves of the house. The beauty, for my
application, is that in the short days of winter average production of hot
water (per thermomax data) drops from ~100 gallons to ~65 gallons (water
heated 60F), I will be supplying the Themomax water heater with pre-heated
GOBI panel water.
For your needs, look at the GOBI panels. they seem like they have pretty
good heat output in winter. Remember to ask any panel supplier about winter
output. Solar panels are kind of like the old VW heaters; they work really,
really well in the summer, when you don't need them :). Thermomax is pretty
cagey about letting their prices get on the internet, but it seems like you
can get 2-3 of the really big GOBI panels for the price of 30 thermomax
tubes and equipment.