Using a multi stage pump for Domestique Hot Water recirculation

Henry

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.

Jamie Hall

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.

hot_rod

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?

Henry

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

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

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

How does the water get to the top floors, 150 incoming or boosted psi with prv's every 4 floors or so?

Henry

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

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.