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handling steam in a drainback

thoughtfulTom Member Posts: 18

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?




  • hot_rod
    hot_rod Member Posts: 16,286
    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.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EricAune
    EricAune Member Posts: 432
    Have to pressurize

    If you get any flashing then it is best to go to a pressurized drain back.
    "If you don't like change, your going to like irrelevance even less"
  • Royboy
    Royboy Member Posts: 221
    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.

This discussion has been closed.