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Supposedly "green" residential hot water recirc systems aren't

Post in 'The Green Room' started by semipro, May 8, 2013.

  1. semipro

    semipro Minister of Fire

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    This is a pretty interesting finding out of a PhD dissertation at Virginia Tech. The basic result is that the hot water recirculation systems touted as "water savers" actually don't save water since extra energy is needed to for pumping and that requires water. Its a good technical read for the energy geeks here if you can get your hands on the the dissertation.

    http://www.sciencedaily.com/releases/2013/05/130501192939.htm?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed: sciencedaily/earth_climate/sustainability (ScienceDaily: Earth & Climate News -- Sustainability)

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  2. StihlHead

    StihlHead Guest

    Recirc hot water systems are about like aluminum siding. A lot of sales hype and wasted money. There was a recircirculating system in my house in California and I re-plumbed it to get rid of it. Lots of copper in the loop that I salvaged to run a new hot water heater in the garage (the old gas water heater was in a hall closet in the house!).

    On-demand water heaters are far better, use less energy, and cheaper. I never heard of recirc systems being green before. They are a convenience (fast hot water available) that just use more energy in my experience.
  3. Circus

    Circus Member

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    Instant hot water pumps green? What's amazing is that disproving it was good enough for a Ph.D. dissertation.
  4. begreen

    begreen Mooderator Staff Member

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    Just noted the article specifically points out "some" recirc systems cost more. The flaw in the study is that it only looks at energy costs and not water costs. That has to be accounted for if we are looking at savings. In some areas water is quite expensive.
  5. peakbagger

    peakbagger Minister of Fire

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    In my case with SHW and woodfired in the winter, the logic changes. I have a deep well, it consumes power when I run the water to the drain while its warming up., if a low head recirc pump equipped with a flow switch can reduce the amount of water pumped up from the deep well, there is a savings to me as the recirc pump uses far less power to overcome line loss than the deep well. Of course most of the home depot systems dont have a flow switch and run all the time so then folks are basically heating their house with whatever supplied hot water.
  6. GaryGary

    GaryGary Feeling the Heat

    Joined:
    Jul 12, 2010
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    Loc:
    SW Montana

    Interesting.

    This is my experience with the recirc system that came with our house:
    http://www.builditsolar.com/Projects/Conservation/Recirc/RecircEnergy.htm

    It wasted $3200 worth of propane over the 8 years we had it in operation -- this with the pump disconnected and just thermosyphon circulation.

    Gary
  7. EastMtn

    EastMtn Member

    Joined:
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    I also, would never have bought into that sort of hype. This is my first time with a recirc system on propane to boot. The house I bought is aesthetically pleasing with nearly floor to ceiling glass end to end in the common areas and master suite but energy efficiency is not its strength. ;) I think the builder installed a recirc system knowing full well that a high end home should not take very long to get hot water with this amount of money spent. However the propane water heater and both showers are at extreme ends. Without the recirc it takes 15min to get hot water to my shower.



    I got a tip from a coworker and installed a progammable timer on the recirc pump and that has made a huge difference. I set the timer for 4hrs in the morning and 4hrs in the evening to coincide with the times my wife and I are most likely to use hot water at home and it has taken $15 off my monthly electric bill and the time between propane fills in the summer has decreased by 1-2 months. Next year I intend on having a stainless steel, no anodes needed, propane modulating water heater installed to improve efficiency further.
  8. StihlHead

    StihlHead Guest

    SS has less heat conduction than plain steel does, and that will actually reduce the efficiency as opposed to plain steel glass lined tanks. The modulated part will improve efficiency, but if the runs are long to the showers, you may be better off with on demand heaters in the bathrooms.
  9. EastMtn

    EastMtn Member

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    An on demand point of use would be good. Re-wiring and re-plumbing those parts of the house makes me a little leery but I think it would pay off also.

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