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Simply Rad

I am reconfiguring a solar thermal radiant system.  There is no solar DHW in the system.  Right now there are 2 indirect water heater for storage. The buffer fluid is heating water and the HX are solar fluid.  I would like to change one of the tanks so that it can preheat the DHW.  Is there a problem with draining and flushing one of tank and then use it for potable water.  Is there a cleaning process I can do?   Thanks Jeffrey. 

Jamie Hall

Two preliminary questions: first, what is the "solar fluid"? Chemical description or MSDS? And second, which side of the heat exchanger in the tank is it on, and will that be the same side as the domestic hot water?

Simply Rad

Jamie 
The indirect coil is filled with solar rated glycol.   Right now the tank is filled with heating water.  I want to change the heating water to potable water 

mattmia2

Is it ethylene or propylene glycol?

Simply Rad

propylene

Jamie Hall

You're in luck. Propylene glycol, while not totally benign, is not regarded as particularly hazardous -- unlike ethylene glycol, which is.

There may, however, be other additives in there; it would be most wise if you could find the MSDS for the particular material you have.

That said, assuming there are no additives, I would be inclined to treat the tank with a very thorough flush. First drain, of course, and dispose of the fluid in a safe and approved way (probably a haz waste pickup). Do NOT under any circumstance dump it on the ground or in a septic tank or storm drain or something silly like that.

Then the flush. Figure the total volume to be cleared (you should have a nice estimate of that from the draining). Assuming the drain has been thorough, you will do well enough by flushing the system with at least 10 volumes of fresh water. If there were other additives, such as corrosion inhibitors, triple that at least -- or more. Consult the MSDS for potential toxicity of the additives.

mattmia2

A nontoxic hydronic system cleaner soak for the first refill wouldn't be a terrible idea either.

hot_rod

So the tank has plain water that was a heating fluid, and you want to make it potable water? The coils remain solar glycol?
I would add some bleach and let it set a day, flush and add potable water.

Simply Rad

Thanks everyone for the input. I did find that the heating system also has glycol. So I contacted the glycol manufacturer and got instructions on how to flush it for potable use. I am not a fan of glycol in conditioned spaces.

Tom_133

I agree I also don't like glycol when not necessary. Sadly, I have been burned at least twice, by not refilling a system that had glycol back with glycol. This lead to a pipe that was in an outside wall froze and split. I didnt know, the homeowners didnt know but we all know now that some of the heat lines were in outside walls. Make sure there was no reason for the original system to have glycol in it. Just a heads up.

kcopp

I was under the impression that if a water pipe or appliance that was used in a Non-potable application could not be used/ reused in a potable water application.
2015 IPC 608.10