solar thermal drain down ? relief vlv / vacume brake

5 Posts
Apr 22, 2009 09:31 pm
solar thermal drain down ? relief vlv / vacume brake

my question is i would think there would have to be some kind of vacume break at the top of the collector to be able to drain down. what is commonly done? is there a relief valve / vacume break combonation component avaiable?   Thanks 
Apr 23, 2009 09:18 pm
Re: solar thermal drain down ? relief vlv / vacume brake

Think of a drainback system as a hybrid of a closed and an open loop system.
There are drainback systems available on the market that do not require an automatic vacuum relief valve.
Having a vacuum relief valve would introduce air into the system that would have to be expelled as the water is pumped up to the collector from the reservoir and begins to heat and build pressure. There is good chance it would lose some fluid each time this happend. Most likely as steam. It would depend on the amount of positive pressure relief.
In a drainback system, once the pump stops running the liquid finds its way back down to the reservoir from the collector and any outdoor exposed piping without a negative pressure relief valve. It all has to set up just right to work properly though.
« Last Edit: Apr 23, 2009 09:28 pm by Thomas Allen Schmidt »
5 Posts
Apr 23, 2009 11:13 pm
Re: solar thermal drain down ? relief vlv / vacume brake

ok got it thanks alot when i put it all together ill make sure it works right.  pitching all exposed piping .25 " per foot for drainage should be my only concern then and a relief valve for safety. Thanks again
462 Posts
Apr 24, 2009 08:55 am
Re: solar thermal drain down ? relief vlv / vacume brake

David, they make a duo vent. It is both a vaccuum relief and air vent......
5 Posts
Apr 24, 2009 10:32 pm
Re: solar thermal drain down ? relief vlv / vacume brake

im confused do i need an air vent/vacume brake? the first reply says i dont. as i understood, the pump would carry enough presure to purge all the air back to the tank.  what is commonly done? or is either way excepted
19 Posts
Apr 25, 2009 08:21 pm
Re: solar thermal drain down ? relief vlv / vacume brake

It depends on the specific system setup whether or not you need a vacuum break.

On a truly 'closed loop' system you would most definitely want a vacuum break installed or the water wouldn't ever 'drain back' due to the vacuum created by bleeding air out of the system when the system is initially pressurized.

On an open loop system, or a system that drained back into a non-pressurized collecting tank where the input end of the tube was not submerged there would be no need for a vacuum break in the system, since as soon as the pump stopped, gravity would drain the liquid back into the collecting tank through the submerged 'output' end and air would be drawn into the line through the non-submerged 'input' end.
5 Posts
Apr 25, 2009 10:20 pm
Re: solar thermal drain down ? relief vlv / vacume brake

ok that makes sense (im a little new at this). im going for the open drain back system. seems the simplest with the least components. I need to think of some good ideas for the drain back tank now that i understand it better. i might try to use an old 15 gal elect. water heater (cut the top off) and fashion a heat exchanger from some 3/8 or 1/2 cpr tubing to put inside of it. ill use the drain as the pump supply and the releif valve as the return. i can just set it next to the preheat tank.  Thanks everyone for your help!
Apr 26, 2009 05:58 am
Re: solar thermal drain down ? relief vlv / vacume brake

Maybe this will help too.

Here is another page with a lot of interesting ways to utilize solar thermal energies. This one is full of links other pages and products and some those have even more links to other pages and products.

Did you know that it is possible to use the Sun to heat water up to 1,600 degrees Fahrenheit? A little extreme for residential purpose but its still fascinating to me. Here is another site that might be of interest. Its "roots" began in doityourselfism. Or would that be doityourselfinisticism? Anyway...

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