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sizing pump for solar system

mark schofield
mark schofield Member Posts: 153
My 30 year old grundfos UPS20-4 for the glycol loop on a Grumman sunstream system is almost gone. I cant find a cross reference or pump curves for that model. So when figuring the head and gpm for my system, how much might I add for the head in the collectors and how to figure the gpm/btu delivered relationship. It seems that a pump with a very low curve like a Taco 006 is fairly close but I'm just guessing. The Grundfos sight doesn't go back to include my pump number. Thanks,   mark s


  • SWEI
    SWEI Member Posts: 7,356
    UPS20-42 replacement

    Grundfos shows the UPS15-42 as a replacement for the UPS20-42.  Curve is roughly equivalent to a Taco 008.  If the budget allows for an HEC-2 (Bumble Bee) I'd use one of those. 
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Recalculate, don't just replace

    Remember, pumps are often oversized because someone was being overly careful and inserting a dose of CYA.

    So it can be a mistake to replace as existing pump with an equivalent pump. You might be able to save first cost and pumping energy by finding the right pump.

    The head loss in the collectors is probably negligible depending on the collector and if they are piped in parallel. To estimate it, count the risers. If there are 20, then the flowrate through each is the total flow/20. Use that flowrate for the pipe size of the riser to find the head loss. The head loss in the header is harder to figure, but could be estimated by using half the flowrate through that size pipe.

    If you can find the mfrs. headloss spec., use that. But if they are piped in parallel, it's the headloss of only one collector, no matter how many there are.

    There was an error rendering this rich post.

  • hot_rod
    hot_rod Member Posts: 22,505
    what type of controller?

    If you replace the pump, consider changing the controller to a newer version that modulates the pump speed to the conditions. As the collector warms, the pump speed increases. Start with a 3 speed circ like the Grundfos 15-58 or another brand with a close curve.

    Chose the speed to provide adequate flow and allow the control to modulate the speed. this will save energy, reduce pump cycling, and put the system on "cruise control"

    I know there are folks on here with Grumman experience, what type of HX or tank is it connected to?

    With some pump and control tweaks you may be able to wring some additional performance from the system.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • solsean
    solsean Member Posts: 18

    heat exchanger and pump module boards are one of the last ones standing from the 1980's but there is more to consider than just the pump.  Others have mentioned pumps and controls to upgrade but the issue I've seen is the tube and shell HTX becomes scaled on the rifling and there is very little delta T.  Descaling the water side of the HTX is an option but with the higher efficiency modern options I would modernize.
  • mark schofield
    mark schofield Member Posts: 153
    solar quuestions - thanks

    Thanks for the replies. I finally got a Grundfos distributor in Mass. to send me an old sheet from the factory with the UPS20-42 specs and the Grundfos 15-58 seemd like the closest match. Also being 3 speed I can experiment. The B&G  was a bit small. About a year ago the sigma-rho controller started failing so I replaced it with a Goldline GL30 which basically duplicates the original controller. The literature I have shows nothing about head thru the collectors so I figured it as negligibly as was suggested. I'm guessing that there is no scale in the heat exchange unit because of the noticeable temperature differentials between the various pipes and the incredible speed with which the temp in the storage tank rises. Presently the tank feeds solar preheated water to the inlet of the tankless coil on a WM WTGO3. In the New Haven area durring april -november I usually get 120deg + exiting the storage tank on sunny days. And thats with hot water draw durring the day. Some day I'd like to connect the top electrical element on the storage tank ( a Whirlpool 50 gallon electric heater not electrified at the present) and shut the boiler off from april to november and see what happens.  Presently the boiler (non cold start) maintains a minimum set point during the off season and supplies the heat for hot water during cloudy days. I wish I was younger and was starting from scratch. It would be fun to build a completely integrated system. But at the present the system works well and has had only two mechanical repairs in the past 35 years. Thanks again for the replies. And SWEI, I'm presently fighting my desire to put a Bumbelbee in my 3 zone heating system.
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