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    A flow problem (21 Posts)

  • NathanVt NathanVt @ 10:45 AM
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    A flow problem

    So here is the setup:
    1" iSeries 4-way Cv 9.3
    008 delta T pump
    20' 1" pex to the manifold
    Mr Pex manifold with 5 loops, highest head is 6.7 ft
    Flows are:
    .8 (set)
    .9 (set)
    .85(wide open and longest loop 1/2" at 188 ft) needs 1.0
    .85 (wide open) needs .9
    .85 (wide open) needs .9

    The question is why am I not getting enough flow? I have closed off all other zones and set pump to full speed. By my calculation 4.5 gpm requires: .54 for iSeries, 1.6 for 1" Pex, 1.4 for manifold adjustment valve and 6.7 for longest loop. So 4.5 gpm at 10.24 ft head is easily within the range of a 008, capable of about 14 ft at 4.5 gpm.

    Any ideas?
  • Zman Zman @ 11:15 PM
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    Are you...

    Are you running 100% water?
    Is the circ mounted with plenty of staight pipe on either side.
    I am suspicious of the mr. Pex data.
    Carl
  • Rich Rich @ 7:12 AM
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    Nathan

    Do you have a picture of the near boiler piping for us ?  What piping arrangement is this , what type boiler ? Where is the circulator located in the system ?
    You didn't get what you didn't pay for and it will never be what you thought it would
  • Ironman Ironman @ 7:49 PM
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    I Series and Delta T Circ.

    Why would you need both? It seems like they would fight each other trying to regulate the flow rate.
    Bob Boan



    You can choose to do what you want, but you cannot choose the consequences.
  • Rich Rich @ 8:30 PM
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    Ironman

    Could you clarify what you were trying to say in that comment ?  The I series regulates temp and will flow whatever the circ pulls through it .
    You didn't get what you didn't pay for and it will never be what you thought it would
  • Ironman Ironman @ 9:48 PM
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    Flow

    Yes, and the delta T circ is also attempting to regulate flow based on its delta T setting. Thus, you have two different devices both trying to regulate flow, one based on outdoor reset and the other on delta T. Every action by either device will cause a reaction by the other that in turn causes another reaction by the other in its attempt to compensate. Simply put, they're fighting each other. It's kinda like democrats and republicans fighting over obamacare: whatever one does, the other attempts to counter based on its logic.

    I don't think you should have both devices in the same circuit.
    Bob Boan



    You can choose to do what you want, but you cannot choose the consequences.
    This post was edited by an admin on October 11, 2013 9:53 PM.
  • Zman Zman @ 10:47 PM
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    Good call

    I did not notice the delta t circ. I believe you are correct.
    Carl
  • Eastman Eastman @ 1:37 AM
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    hydraulic separation?

    "I have closed off all other zones and set pump to full speed. "
    You closed four of the five zones on the Mr Pex manifold?  Or are these zones external to this circuit?

    Is the 4 way mixing valve hydraulically separated from the rest of your system?  If not, I think you are potentially missing more terms in your estimate.

    I don't see an inherent incompatibility between mix valve and delta T pump control.  Why would they interfear with each other?  --they're effectively regulating different flows.
    This post was edited by an admin on October 12, 2013 2:03 AM.
  • Rich Rich @ 7:35 AM
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    Bob

    I can certainly see your reasoning , explained in that way .  I have been doing this when it makes sense for quite awhile and have not encountered the problem you anticipate yet .  I also use the smallest I Series possible without making head losses too great for pump to deal with and let the Delta T pump do its' job , the pump will be dealing with Delta T's that are always changing regardless of mixing method or where it is done . Many are using the I Series within injection loops with great success , Taco also supports this use . Should we never use a Delta T circ there either ?  The supply temp should not change that much if at all during a call for heat and it should not be and is not an issue thus far on my systems . Using a  device that is smaller than the piping it will be connected to is not an issue either and in fact is desirable , you lessen the amount of water that it has to regulate allowing it to achieve the proper temperature faster . As long as you don't go with a Cv that is too low .  Maybe this makes sense to yourself and Carl , hope it does .      
    You didn't get what you didn't pay for and it will never be what you thought it would
  • Rich Rich @ 7:39 AM
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    Nathan

    When you said you set pump to full speed , what do you mean ?  Check all your values again also  .
    You didn't get what you didn't pay for and it will never be what you thought it would
    This post was edited by an admin on October 12, 2013 8:19 AM.
  • NathanVt NathanVt @ 9:03 AM
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    Heres a pic

    Thanks for the posts so far, see the pic for my setup. Boiler is off to the right, a WM97+ operating with the internal primary/secondary valve open, hydraulically separating the boiler. As you can see the system is not complete, but I am running with the three zones shown. The question of why don't you use the boiler for outdoor reset is due to having the zone in question run on a lower temp from the unfinished flange you see. Running 100% water, all copper is 1".
    Removing the valve control from the iSeries and manually operating it does not resolve the flow problem.
    Each zone sentry controls a Mr Pex manifold, no actuators involved.
    All of the original pressure losses are checked. Removing the return sensor from the delta T circ will cause it to run full speed, much greater than 10 deg delta T it is set for.
  • Rich Rich @ 9:49 AM
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    Nathan ,

    This pump must be located within the mixed temp portion of the piping arrangement , it seems as though none of these manifolds /loops will be receiving even a fraction of the heated water they require . You also must install some means of purging the air from this system .  If these zone valves all have a manifold at the other end of them with multiple loops you better be sure that what you described to us is in fact the greatest head pressure in the system and remember to add all GPM rates . When multiple manifolds are served by a single circ the head losses for all should be pretty close to each other , I am not certain that the Deltas will be as tightly controlled as I am sure you had wished either . Again , start out with purge set up and relocating that pump between the Zone valves and the I Series .  After performing these things let us know how it is responding then .
    You didn't get what you didn't pay for and it will never be what you thought it would
    This post was edited by an admin on October 12, 2013 9:54 AM.
  • Ironman Ironman @ 10:09 AM
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    Air bound?

    How do you purge each loop individually with that setup? Are zone valves on the return or supply?
    Bob Boan



    You can choose to do what you want, but you cannot choose the consequences.
  • Rich Rich @ 10:29 AM
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    it looks

    like the sensor for the I Series is on the zone valve header Bob .  Nathan  You have given us the numbers for one manifold , what are the GPM requirements for the others along with the one you have told us about ?  That 008 VDT will only pump in the mid to high 7 GPM range at 10.? feet of head . If your requirements for the whole system exceed those GPM for all manifolds you will need to increase the pump size .  I do not believe that you will have the control over Delta T that you were hoping to accomplish in any case with only the single circulator .  
    You didn't get what you didn't pay for and it will never be what you thought it would
  • Zman Zman @ 2:25 PM
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    Considerations

    I think there are a few things you have overlooked in your calculations.
    Head loss to the zone valve
    Head loss to the pex transition fittings, isolation valves and other 90's
    Head loss to the pipng on the other side of the I valve.
    You are only considering one of the zones attached to the system, the math will change significantly when the other zones are operating.
    Your piping should be sized for a flow rate of 4 ft/sec. The "headers" that distribute water to and from the zones, should be sized at 2 ft/sec.
    From a cosmetic point of view, keeping the near boiler piping level and plumb tends to give the homeowner the warm and fuzzy feeling that they has hired a true professional. I like to make the copper to pex transitions above eye level.
    Carl
  • NathanVt NathanVt @ 2:47 PM
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    Only one zone needs consideration

    The delta T circ is on the system supply side of the iSeries, noted by the triangle on the valve body. The zone valves are on the return side of the system. Purging is done at the manifold, where each manifold has a purge/fill valve. I do not believe this is an air problem as the loop flow gauges all show a flow and when the other two zones open there is a slight decrease in the flow of my longest loop. When I isolate the zone with the highest required head and flow (both variables in the same manifold) I am unable to obtain more than 4.5 gpm @ 10.24 ft of head, this does not include the loss for the zone sentry (Cv 8.9) and the 1" head stock. Lets exaggerate the numbers and say 12 ft of head, that should still give me up to 6 gpm of flow.

    I am not looking for a perfect delta T, just trying to figure out why I am not flowing what I should be. I have been running the system for a few days and the heat is being delivered, but I am concerned if I cannot get the flow when I hit my design temp I will not receive adequate BTUs.

    The picture was not taken square. as you can see the edge of the boiler on the right, I am tilted a little to the left. It is more plumb than the picture shows. Thanks for the tip on the copper though.

    And the pex fittings are minimal see page 13: https://www.ppfahome.org/pdf/PEX%20Handbook_draft_rev_2008.pdf
    This post was edited by an admin on October 12, 2013 2:49 PM.
  • Zman Zman @ 3:05 PM
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    BTU

    I would be surprised if the system under performs. You are only slightly below you design flows. You may end up with a slightly higher delta t than you designed.A slight increase in water temp will compensate for that. There are plenty of folks out there designing for 20 degree and thinking they are superstars. You would be surprised how many don't know what delta t means, they just design by "rule of thumb" As long as the flows don't tank when all the zones are on line it should work just fine.

    Carl
  • NathanVt NathanVt @ 4:00 PM
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    Design meets reality

    Should I consider a change in pump?

    I want my system to meet my design, I know reality is much different from theory. If my pump is under sized I would need to make a decent jump in size from the 008. If 4.5 gpm is being reached at 13 ft should I consider the 0011 to meet the head and eventual total flow of about 8 gpm. Seems like overkill, but I fall in a bad area in that chart.
    Ok, reading what I just put down and checking the pump curves, I way undersized with the 008 for total flow.
  • Zman Zman @ 6:02 PM
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    The whole picture

    Nathan,
    The math doesn't lie. The reason you are not getting the flows you are looking for is that there is resistance in your system that you are not considering.
    What does the piping on the other side of the 4 way look like? Is this the only circulator? What kind of boiler? I picture or drawing of the entire system would help.
    Carl
  • Rich Rich @ 9:08 PM
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    What

    could the total system flow be at design ?  How many BTU is the entire load of the building ?  
    You didn't get what you didn't pay for and it will never be what you thought it would
    This post was edited by an admin on October 12, 2013 9:30 PM.
  • SWEI SWEI @ 12:50 PM
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    Smallest iSeries possilbe

    is a good point.  I would spec Cv of 9.3 for a design flow of roughly 19 GPM.  Oversized control valves do not settle well as they are operating near one end of their curve most of the time.
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