A viable solar installation has solar collection, heat exchange, and storage.
I've proposed a system that combines heat exchange and storage, thus giving you efficiency of design. The storage tank and the draindown tank can be the same tank, thus removing a maintainance/failure item (glycol - which likes to leak, is less efficient than water as a heat transfer medium, costs $8/gallon (in the US)). Plus you are saving time as it looks like you are hunting around and experimenting with low percentage ideas (PVC/CPVC = PITA).
The proposed system does require a pump (you should be able to use two circulators in series - read your pump sizing charts). As to "DHW through excessive piping" - I presume you are talking about pressure drop. That is solved by taking your 3/4" supply and running it through three 1/2" loops in your heat exchanger. And you are only adding 100 to 120 feet of run, so the pressure drop should be manageable (even if you kept it a single 3/4" loop in the heat exhanger.
Tom
Ken wrote:
Tom,
Does a drain down system simplify anything other than the heat
exchanger and eliminate the use of glycol? Or course, you're adding
the drain down. It almost seems like a wash (there is a pun in there
somewhere, I'm sure). I would like to use my solar hot water for
space heating as well - either radiant heat or with a liquid to air
heat exchanger and blower. Either way, I think I'd prefer a closed
loop so that I'm not pumping DHW through excessive piping.
Am I missing something else?
> If the goal is to keep it simple, do two things differently than you are
> contemplating:
> 1 - make your heat exchanger by putting multiple loops of coiled copper in a
> polypropylene tank - at most you will need soldering skill if you want to
> break up a 3/4 or 1" flow into multiple 1/2" coils (surface area = good).
> One logical loop for (may be many loops of a smaller pipe diameter) for the
> load (ie DHW or hydronic heat) and (2 below)
>
> 2 - use a "drain down" open system instead of glycol. This allows you to
> use water everywhere. A pump (not a circulator) pumps the water up to your
> rooftop collectors when the system senses available heat (standard, cheap
> solar differential controls) and gravity drains it down when the system is
> not in use [this method requires that the panels be above the storage tank
> and that the pipes exposed to freezing are graded towards the storage tank -
> usually very easy to do] Note that the PP tank in step one above is the
> drain down tank and storage tank for your hot water (they can be separated
> if desired, and a larger tank/multiple tanks will provide additional
> storage, which is the key to effective solar hydronic installations).
>
> So you end up with one (open system) tank full of hot water from the sun,
> heating your coils of copper, containing the water from your (closed system)
> DHW. Similar technique (add a logical coil) for the hyrdonic side. Just make
> sure you don't always "preheat" your hydronic -sometimes the return water
> from your heating system will be hotter than your solar storage - you need a
> control to tell you whether there is heat available for the hyrdonic system
> (not an issue for preheating DHW - your solar storage temp will be almost
> always be above your groundwater temp).
>
Radiance Heating and Plumbing, Inc. (ROC 204149,204150)
Tom Scheel
928-380-6294
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