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Pumps in series

What would be the effect of a Grundfos Alpha 2 on a manifold in series with a Grundfos UPS15-58 on a baseboard zone with a balancing valve?
Think of it as a booster pump. 4 monoflow tees and baseboard resistance on that zone and a short injected infloor radiant loop (75'), too.


  • STEVEusaPASTEVEusaPA Member Posts: 4,109
    Why do you think you need two in series. What does the math tell what size (btu's, flow head) you need?
  • HomerJSmithHomerJSmith Member Posts: 889
    Good question, Steve. It is an old baseboard system with a Lochinvar fire tube boiler. This particular zone is the longest in the 3 story house with the boiler on the bottom flr and the heating loop on the 3rd story. I set all the zones to a flow of 2 gal/min. (seven zones) with the balancing valves. That all works fine. The on the longest zone I added 6' baseboard, 2 flat panel towel bars, 2 toe kick heaters and a 75' 1/2" Pex injection loop. It has 4 monoflow tees for the towel bars and toe kick heaters. I have no idea what the pressure loss is on that zone is without putting on pressure gauges. I would prefer adding the UPS 15-58 which the homeowner has and checking the flow thru the balancing valve for that zone and setting it at 3-4 gal/min. I am a little afraid that with the homeowner insistence on the added extra radiation that I will run out of heat energy which is why I want to increase the flow. Technically, pumps in series increases the head energy. The ECM would supply the UPS 15-58 and the other zones and the UPS 15-58 would be dealing with the pressure loss in that zone at the desired flow.

    I think this idea has wings, but then again. I've been fooled so many times before.
  • STEVEusaPASTEVEusaPA Member Posts: 4,109
    I think the toe kicks, towel bars and the mono flows are creating a lot of head, but you can calculate it.
    An accurate pressure gauge at the boiler will tell you your system pressure, so you can first calculate how much static (fill) pressure you need to start with. If you're pumping into the expansion tank, that may be the bulk of your problem.
  • Jamie HallJamie Hall Member Posts: 12,710
    The pump on that one zone will effectively reduce the head loss "seen" by the main pump for that one zone. Without knowing the head loss vs. flow characteristics of that zone, and the head gain vs. flow of the two pumps, one really can't figure out what you will get -- particularly if any other zones are calling at the same time (it is even possible that you have the new pump on that zone effectively pulling water from other zones).
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • HomerJSmithHomerJSmith Member Posts: 889
    Steve, I would never pump into an expansion tank. That's one thing that the original installer did correctly.

    Jamie, I didn't consider that possibility of pulling water from the other zones. I don't want reverse flows. I would think that the alpha would speed up as the pressure dropped in the manifold and the balancing valve on the 15-58 zone would limit the flow in that zone.

    I'm going to give this some more thought. Thanks guys!
  • I've been thinking about this for while (a constant speed circ and delta P circ pumping in series).

    I can't say with 100% confidence this won't work but the issue will probably be that a delta P circ looks at pressure differential across the circ. So, if the upstream circ has anything less than a flat curve the downstream ECM delta P circ will hunt while the upstream circ is changing flow and differential pressure (following it's constant speed curve). A delta T circ wouldn't care as it only looks at delta T, not differential pressure.

    Keep us posted if/when you use a constant speed and delta P circ in series. Interested in the results.
  • ZmanZman Member Posts: 5,737
    If it is possible to create a separate primary/secondary loop, that would be a safer bet.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • HomerJSmithHomerJSmith Member Posts: 889
    edited December 2019

    ZMAN, I was a little concerned as there wouldn't be hydrolic separation between the pumps. It is already a primary and secondary sys with the Alpha 2 supplying the zone valves (7) on the primary manifold. I plan on keeping the Honeywell zone valve on that zone and placing the 15-58 on the discharge side of the zone valve and having the end switch turn on the circulator thru a relay. It will be a while before I can get this done. I guess I'm an adventurist.

    Steve Thompson, I was thinking that the balancing valve on that circuit would limit the flow and keep it from changing. That would keep the ECM from constantly hunting. I was thinking once the flow is set at a fixed head the 15-58 wouldn't be moving up or down the pump curve.
  • HomerJSmithHomerJSmith Member Posts: 889
    edited December 2019
    REPORT Back:

    Well, I got the top floor mast. bdrm circuit purged and working with both pumps in series and the flow set at 2 gpm.

    It works like a charm. The 15-58 is set at med speed which is close to the fully open position of the Taco Acuflo balancing valve.

    Notice the fan center controlling the 15-58 and the end switch.

    Like my Daddy use to say, "Sometimes I surprise myself."

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