solar hot water heater problems

Steve G

Last year I replaced a solar water heater for a customer, same size and capacity. the problem is the relief valve trips and the anti freeze leaks out. I have increased the expansion tank with no change(from #15 to #30). I am averaging re-filling the system every 6 weeks. I have heard that a "dump zone" may be neccessary due to the solar panels producing more heat than the household needs. I hate trial and error methods and would like to find a definative source of info on this subject. thanks.

Nron_13

high pressure

test the tank and see if the heat exchanger is leaking to the solar side as this will over fill the system nomatter what you do , check your glychol level too it will show if its waterd down

hr

Does it have a pressure

and or temperature gauge on the solar loop? Did you check the precharge on the new expansion tank? what pressure did you charge the glycol too? Gebnerally 12 psi is sufficient. anything over that you may be reducing the expansion capacity of the precharged tank. If a # 15 tank has worked before, then the larger tank should not be an issue.

Typically the solar side has a pressure relief valve, usually 30 psi. Not usually a temperature relief valve. although the tank should have a temperature and pressure relief valve on the domestic side.

You could be air locked, or have a bad pump and not getting flow through the panels? You need an accurate pressure gauge to get some stable data.

hot rod

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[Deleted User]

A fix...

Back in the hey days of solar, this used to be a regular problem because the solar salesmen (former door to door vacuum cleaner salesmen turned solar technician overnight) would sell the system based on the tax credit potential and not the actual needs of the home/family...

Consequently, the systems were GROSSLY oversized. Generally speaking, the systems (closed loop) failed in the first year of operation while the family was away, vacationing in Dismal Land or Wally World. During the summer months, the system would max out the storage tank at 180 degrees F by noon, and then the loop pump would shut down, exposing the solar loop fluids to extreme stagnation temperatures (350 degrees F). The expansion tanks for the loop were NOT sized for this potential, and consequently, the pressure relief valve cuts loose with a big WHOOSH, scareing the living crap out of the family cat that just happened to be in the same room taking a dump in the cat box...

When the family returns from their vacation, they notice that the cat is skittish, and won't go down stairs to use the cat box any more, but more importantly, the red and green lights on the solar control are on during the day, so everything must be OKay, according to their solar salesman...

In reality, the loop is air bound and almost empty. There is just enough fluid in the system to keep the pump lubricated, so it continues to spin, making noise, causing the consumer to think that everything is OK...

The "FIX" is this. Bond a strap on aquastat to the return line coming back to the storage tank from the collector array. Set it to OPEN at 180 degreees F. Wire the storage tank sensor (just one wire) through the contacts, and when the fluid coming back from the collector gets up to 180 degrees, the control will open the circuit to the storage sensor, sending a false signal to the differential controller telling it that the storage tank is extremely cold. This will cause the solar loop pump to stay on, keeping the fluid moving, and avoiding a catastrophic melt down. Once the fluid coming back from the panels cools down to around 170 degrees F (re-radiation), the circuit closes, and the controller realizes that the pump should be off, and shuts it down.

At this point, the only thing that could cause the loop to blow down would be a long term power failure between the hours of 10:00AM and 2:00 PM, peak insolation period.

If you choose to use this method, I must caution you to install an antiscald tempering valve between the solar preheat tank and the auxilliary DHW tank. At times, the water temperatures in the tank could approach some pretty hot (200 degree F) temperatures, and if a draw should occur during this time period, AND you feed that hot of water into the auxilliary tank without mixing you COULD pop the ECO fuse on the auxiliary control, causing additional grief.

Now about that cat....

ME

Wayco Wayne_2

This is why a drainback

system might make more sense. I have very little solar experience but have been reading up. A drainback system drains down to a little storage tank when not in use. This is useful for preventing freezing problems and over heating the storage tank. My question is, how stressful is it to the solar panel itself to have sun shining on it but no fluid flowing through it??? WW

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[Deleted User]

350 degrees F...

does ALL kinds of strange things to insulation, rubber gasketing, chromium onyx an dmore...

But these components handle it much better than does glycol:-)

And you are correct that drain back is the bees knees, however, it doesn't fit in all situations, like where the colectors are lower than the mechancial package.

I just plucked 6 3X7 solar panels off of a roof. THree go on this house, and three go on the mountain home.

AHHhhhh more article fodder:-)

ME