handling steam in a drainback

thoughtfulTom · August 2009

Greetings,

I build large residential systems to provide space heating and DHW. We only install drainback systems.

Currently we are using atmospheric tanks (plastic or EPDM lined). I am able to seal these, but when the water comes back as steam, the increased pressure blows my seals and I get a steamy room. I could use the controller to limit it, but with solar you want every BTU you can get. This only results from stagnation conditions, but in the fall and spring we might satisfy the tank by noon and want to top it off at 3pm.

So I would like to be able to handle the 1-2 minute steam bursts when they happen. I am considering making a still like cooling tower out of 1/2" copper, then taking that through a 1/2 trap and then wasting any remaining steam outside. Anyone solved this problem?

thanks,

Tom

hot_rod · August 2009

drainback stagnation

in a drainback the collectors should be empty and dry when the pump is off. How are you getting steam? When they first fill up and the collector is hot?

This is where a pressurized drainback works so much better. Keeping pressure, even 20PSI raises that boiling point to 259F. It also helps keep some pressure on the pump(s).

Limited application for plastic tanks in solar, as you are seeing.

hr

EricAune · August 2009

Have to pressurize

If you get any flashing then it is best to go to a pressurized drain back.

Royboy · August 2009

seems like pressurizing

would be a good fix. you could still use your large plastic/EPDM tanks if you had a separate drainback reservoir (small water heater?) feeding a coil HX in the big tank.

Roy

handling steam in a drainback

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