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  1. #1

    Desuperheater and recirculation piping

    Hey guys, questions about the correct piping for a HRU with a recirculation loop. I am going to run a hot water return line from the furthest fixture. Here is a diagram for the desuperheater piping: http://www.hotspotenergy.com/heat-re...thout%20TT.pdf

    Question is where do I pipe the recirculation line back to the tank? Tee into the drain also with the hru using check valves? Would it be better to add pre-heat tank, and if so, would recirc line plumb into drain of "main" tank?

    Thanks for your time

  2. #2
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
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    6,017
    Most off the shelf dhw recirc systems use the existing cold water lines for return.

    Since I have a hru at home I can say I wish I plumbed the return from hru into cold inlet to tank for this reason-

    Since the hru takes water from bottom (cold) and puts in the top (hot) if hvac system turns on while using hot water (showers) it quickly inhibits the temp of the hot water because of hru circ.

    I like your seperate preheat tank for this reason also. But id suspect if I took water out the drain and put it back in the cold side I may have better result as the heat should still rise to the top.

  3. #3
    Quote Originally Posted by SBKold View Post
    Most off the shelf dhw recirc systems use the existing cold water lines for return.

    Since I have a hru at home I can say I wish I plumbed the return from hru into cold inlet to tank for this reason-

    Since the hru takes water from bottom (cold) and puts in the top (hot) if hvac system turns on while using hot water (showers) it quickly inhibits the temp of the hot water because of hru circ.

    I like your seperate preheat tank for this reason also. But id suspect if I took water out the drain and put it back in the cold side I may have better result as the heat should still rise to the top.
    Thanks for the reply but I think you misunderstood. I am running another pipe from the furthest fixture then into a recirculation pump and back into tank. I am trying to avoid the entire passive system altogether.

  4. #4
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
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    6,017
    Quote Originally Posted by steelsparky View Post
    Thanks for the reply but I think you misunderstood. I am running another pipe from the furthest fixture then into a recirculation pump and back into tank. I am trying to avoid the entire passive system altogether.
    ok I understand but wonder why would choose this way over the passive way?

    i like how the desuperheater is piped in illustration...wish mine was done like that. I think my next project is going to be changing them.

  5. #5
    Well, I've heard you run the chance of making your cold water supply near luke warm. Plus all the added valves under every sink is not that attractive to me. I just had my house repiped so I can just follow their route back to tank with a new pipe. Pretty easy access. Wish I thought of this stuff earlier! Now I just gotta figure out the input of the recirc line. The more I think of it I'm just going to add a pre-heat tank, plumb return from hru to preheat drain, and recirc return into "finish" tank drain line. Does this sound correct?

    Any ways, how do you like your HRU? Save you much on electric? I am also in Florida. I found this thing brand new on ebay for $100 shipped and I'm also doing all the install myself so I'm hoping I still have some return on investment when I add another tank and recirculation pump, not to mention valves, pipe, time.

  6. #6
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,017
    You can add only one valve at the furthest sink and accomplish pretty much the same thing...I think. The water is only lukewarm for a few secs and then runs out cold as before. The good thing is the valve acts like a reverse TXV in that once the water is warm to valve it throttles down.

    I had DHW recirc like this before I had HRU....pretty much for my dishwasher. Boy were those dishes clean with instant hot water.

    I do get pretty much free hot water all summer and winter long. With long recovery rates (or nonexistant during mild weather) on only one 40gal tank as drawback . and the way its piped in hinders performance. The tag on my heater says about $400/yr electric with less than my local rates. So about $20-30 a month I would think less.

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