Posted by Anti-Spam on May 11, 2007, 8:50 pm
Sorry just to drop in without doing any background research, but I am
doing a friend a favour. This friend of mine, has asked me to plumb in
a solar water heating panel and hot water storage tank (has two heat
transfer coils within the tank) , he has bought (whilst he is away
doing his job abroad). He lives off grid with a substansial
photovoltaic panel/battery system and a generator. He presently has a
standard electric water heater (the type that stores some 50 litres of
hot water), which he turns on when the generator is running. My
question is, where do I plumb in this water heating panel/storage
Posted by gary on May 11, 2007, 9:22 pm
How the plumbing all goes together depends on what kind of system it
is (drainback, closed loop, ...). In addition to knowing "where" to
plumb it in, you may need to know "what" to plumb in (e.g. expansion
tanks, PTR valve, fill valves, ...).
To avoid getting into trouble, I would recommend that you read the
Home Power Magazine solar water heating Basics articles. They are
very well done, and very hands on. They will give you all the info
you need to do it right.
You can find them all at the top of this page:
They are free downloads.
Posted by Anti-Spam on May 13, 2007, 3:22 am
On 11 May 2007 14:22:07 -0700, firstname.lastname@example.org wrote:
Thanks Gary, the system he bought is a evacuatred tube system which is
a complete system with tank and tubes on a stainless steel frame. I've
not seen it yet, but he told me it is a complete system. I will email
him and ask what type of system it is.
Posted by DJ on May 13, 2007, 2:50 pm
That's a bit tricky, as his electric tank doesn't always run and is
then usually full of cold water. Traditionally, though, the path goes
Cold source (well, lake, whatever). Then hot-water cold-water split.
The solar storage tank goes after the split, on the hot-water branch.
Some put in checkvalves at that split on the hot water side. The panel
recirculates through one of the two heat transfer coils in the tank.
The top outlet of that tank then goes on to feed the powered hot water
As he powers the powered tank intermittently, though, I'd advise a
different strategy. I'd recommend putting an electric heating coil in
the thermal storage tank (there are usually threaded ports for this).
Remove the old 50L tank from the system altogether or devise a bypass
strategy. Then use the electric in the solar storage tank to top up
whatever he doesn't make with solar.
The second heat transfer coil would probably be best used with a heat
recovery system through his wood stove.
Posted by flip+ on May 14, 2007, 8:14 pm
I think the answer is going to depend on how your friend uses the system,
what is expected in hot water supply, how big the storage tank is, how
much sun the collector receives (and ambiant temps), and how big the
collector itself is.
If the solar tank can supply water in sufficient quantities at an
acceptable temperatures, you might be able to eliminate the
generator powered heater altogether...
If usage is somewhat sporatic, and storage tank is large enough, that
If usage is more constant, i think solar heater as preheater to electric
might be the way to go.
Is the generator air or water cooled?
If the generator is water cooled, you might want to use the second HE
loop there. (of course, there needs to be some mechanism for dealing
with the heat when the storage tank comes to temperature.)
DJ's electric heater as second heat exchange source sounds like a good
idea, but that requires extra equipment.
Going the extra equipment route, if you had the solar tank as a preheater,
with a tankless heater to bring to temp should that source fail to keep
up with supply, you'll be golden. If the solar keeps up, the tankless heat
never kicks on... if it doesn't, then the tankless kicks in and keeps
the temp where you want it.
See if you can narrow down usage patterns/expectations. I'm just a
novice at this and I can think of multiple ways of doing this... The
really good folks/professionals here will be able to provide much
better advice with more detailed info.
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