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

semipro Posted By semipro, May 8, 2013 at 3:10 PM

Thread Status:
Not open for further replies.
  1. semipro

    semipro
    Minister of Fire 2.
    NULL
    

    Jan 12, 2009
    3,037
    463
    Loc:
    SW Virginia
    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)
     
  2. StihlHead

    StihlHead
    Guest 2.
    NULL
    

    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 2.
    NULL
    

    Jan 11, 2013
    217
    23
    Loc:
    EC Wisconsin
    Instant hot water pumps green? What's amazing is that disproving it was good enough for a Ph.D. dissertation.
     
  4. begreen

    begreen
    Mooderator 2.
    NULL
    
    Staff Member

    Nov 18, 2005
    61,315
    7,817
    Loc:
    South Puget Sound, WA
    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 2.
    NULL
    

    Jul 11, 2008
    2,537
    527
    Loc:
    Northern NH
    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 2.
    NULL
    

    Jul 12, 2010
    291
    18
    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
    Burning Hunk 2.
    NULL
    

    May 19, 2013
    205
    48
    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 2.
    NULL
    

    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
    Burning Hunk 2.
    NULL
    

    May 19, 2013
    205
    48
    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.
     
Thread Status:
Not open for further replies.

Share This Page