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Circulation problem

veeder1
veeder1 Member Posts: 10
in Oil Heating
Just wondering if any of you experts out there have ever had a problem like this and if so how did you solve it. Our company installed a new oil fired boiler for a customer. There were 6 zones using circulators on the return side of the boiler. The customer had an outdoor woodstove so we piped the heat exchanger in series on the return side between the circulators and the boiler. We also installed a system circulator between the heat exchanger and the boiler. That circulator runs whenever any zone circulator is running. The boiler maintains 175 degrees just fine. The problem is that when all 6 zones are running we lose flow in many of the zones if not all. There were 6 taco 007 circulators in the system. We replaced them to Grundfoss 3 speed circulators and that did not improve the situation. I was thinking about putting in a variable speed circulator for the system circulator and put in zone valves. Could we be over pumping. The zones are all 3/4" and the main header is 1 1/4". We are talking about a small 3000 sq ft house. Any ideas??

Comments

  • Zman
    Zman Member Posts: 7,611
    Are you pumping towards the expansion tank?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    GroundUp
  • veeder1
    veeder1 Member Posts: 10
    Yes
  • Zman
    Zman Member Posts: 7,611
    The expansion tank is the point of no pressure change (PONPC) in the system. Your pumps are converting electrical energy into mechanical energy as you can see by the pressure differential on either side of the circulator.
    What is likely happening in your case is that because you are pumping into the expansion tank and you have a combination of circulators is series and parallel, you are creating negative pressure at your zone circulator inlet. This is either air locking or cavitating your zone circs.

    Dan does a much better job of explaining this in this book https://heatinghelp.com/store/detail/pumping-away-and-other-really-cool-piping-options-for-hydronic-systems.

    The right way to fix this is to move the expansion tank so you are "pumping away" from the expansion tank.
    Does the problem go away if you de energize the new circ you installed?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • veeder1
    veeder1 Member Posts: 10
    Problem seems to appear when all 6 circulators are running. Very random but one of our techs had 4 zones operating at once. When another one came on all zones were lost. When only a couple are operating those zones seem to be ok. Do you think that this system could be balanced by turning on one zone at a time and regulating flow in that zone to achieve a 20 degree delta tee to minimize the total flow? Back in the day most systems were piped so that you were pumping into the expansion tank as the circulators were installed on the return side of the boiler. What your saying makes sense.
  • veeder1
    veeder1 Member Posts: 10
    Thanks for the link Zman!!!!
  • Zman
    Zman Member Posts: 7,611
    I think you have a combination of over pumping and incorrect expansion tank location. If you post a drawing with all the details, we can dig into the circulator sizing.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 23,400
    what type and size heat exchanger? that could constipate the entire piping circuit.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • veeder1
    veeder1 Member Posts: 10
    Good morning guys. Here is the specifics for this job.


  • Zman
    Zman Member Posts: 7,611
    Have you tried turning all the circs to speed 1?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • DZoro
    DZoro Member Posts: 1,048
    Plate may need to be primary/ secondary piped, in this situation. Use your system pump there instead of on the main return.
    D
  • Jamie Hall
    Jamie Hall Member Posts: 24,873
    Not to be slightly harsh, but where you are pumping into the expansion tank like that, as several have noted when you have enough zones on line the pump inlet pressure drops below what they require. If they haven't already been ruined by cavitation, they will be -- soon.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Zman
  • veeder1
    veeder1 Member Posts: 10
    Thanks for all the suggestions. I have had initially 6 taco 007 pumps that were installed. I changed them to the 3 speed grundfoss and I did have them all on low. Didn't make a difference. We still lost zones once the system got up to over 3 or 4 running at once. I also had piped the system in a primary/secondary configuration initially. I did it on the supply side of the boiler. By doing that I could only get a max supply temp of 158 degrees. The way I have it piped now I am getting 175 degrees to the zones. Hopefully I will get the chance to return to this job and relocate that expansion tank so we are pumping away from it. It makes a lot of sense what you guys are saying. Hopefully a simple fix. Thanks for all your input and help!!!

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