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Using a multi stage pump for Domestique Hot Water recirculation

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Henry
Henry Member Posts: 998
edited February 2020 in THE MAIN WALL
In the past 2 weeks, I have been called to look at recirculation loops and pumps at 3 large properties. Case 1 had two 22floor towers with multistage booster pumps. Looking at the plans of the newest tower (3 years), the engineer specifies a pair of Grundfos CR4-3 for 1 to 10 floors and the other 11 to 21 floors. In another section of the plans it is UPS40-240. But the plumbing outfit installed two Wilo Helix multistage. The other was a new large condo with 6 floors. The plumbing contractor sized a 1inch return for 14 risers and installed a Grundfos 18 GPM at 65 feet (according to the tag as we could not make out the model. The first tower would do with a UPS26-99 in S/S. The second one a UPS26-150 as there is too much restriction by the 1 line. The third tower of 22 floors had only one of three booster pumps working for recirculation for all 3 zones. Each recirculation line was 1 1/4 inches. Looking at the old plans, this tower needed 3 separate circulators UPS26-99: one at SPD1 for the recent 8 floor adition, one UPS26-99 SPD 2 for 1 to 10 and a UPS26-99 SPD3 for 11 to 21. In 44 years, I have never seen multi stage pumps used for recirculation even on 41 storey buildings.

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  • Jamie Hall
    Jamie Hall Member Posts: 23,668
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    The only reason I can think of for multistage pumps would be if the head loss in the circuit were too high. Which to my way of thinking would be wasteful. Was someone (not you, @Henry !) thinking they needed to reach the top with the pump? Static pressure does that -- all the pump does is stir the stuff around.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Henry
  • hot_rod
    hot_rod Member Posts: 22,498
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    Seems overkill. The head and gpm are the sizing criteria.

    Head of course determined by piping path. GPM is all about the temperature drop. Is it all uninsulated copper supplies and recur lines? If so it could require a lot of flow. it is a hydronic hosting loop with bare copper :)

    Sounds like a system headed towards some erosion and pin hole issues?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Henry
    Henry Member Posts: 998
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    Jamie, the engineers figure they need to overcome static pressure. So 22 floors at 5 PSI per floor plus 25 PSI for good luck. The pump outlet pressure gauge shows 135 PSI. They don't realise that it is a closed circuit! The last one has pinholes in copper pipes on the lower floors
  • Henry
    Henry Member Posts: 998
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    The pump repair company sent a quote for a new pump that would provide 45 GPM (in an 1 1/4 inch return, normal max is 14 GPM) due to the fact that there are so many apartments!
  • mattmia2
    mattmia2 Member Posts: 9,974
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    Did a EE size the pump or something? Even we should know water in a closed ckt just needs something to pus it around, not to lift it...
  • hot_rod
    hot_rod Member Posts: 22,498
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    How does the water get to the top floors, 150 incoming or boosted psi with prv's every 4 floors or so?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Henry
    Henry Member Posts: 998
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    There are booster pumps at the water entry. There is a PRV for the first 10 floors in both locations. The 6 floor unit has 80 PSI city water.
  • Jamie Hall
    Jamie Hall Member Posts: 23,668
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    Just use the booster (or city) pressure to fill the system -- and purge it -- and then your circulators don't have to have any more head capacity than needed to move the water in the pipes.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England