what's up with the flow

Discussion in 'HVAC Heating & Cooling' started by rrekih, Dec 16, 2009.

  1. rrekih

    rrekih New Member

    Messages:
    46
    Location:
    Canada
    I have installed a underfloor heating system that is running off of the tankless hot water system. The heating box is of the closed loop type.
    At the moment I have 5 zones being used from the manifold.
    The loops are from 200ft to 300ft. of 1/2in pex.
    When running one zone, the shortest, the flow meter shows just a little bit better than 1/2 GPM.
    This is measured by the flow meter on the Watts manifold.
    When opening up another zone the flow goes down to half or less.
    I am running about 30psi at the moment, when at first I was at about 15psi and the flow was quite a bit less.
    If I open any more zones I don't think I will have any flow at all.
    The pump is an Armstrong E9B.
    Flow range: 0 to 38gpm
    Head range: 0 to 42.4ft.

    Attached Files:

  2. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
  3. rrekih

    rrekih New Member

    Messages:
    46
    Location:
    Canada
    What can I say, I'm in it deep now.
    What is the last link? www.calleffi.com

    Can you give me some of the big mistakes?
  4. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    To start with, just how big do you think those passages in the water heater are? Those alone are enough to restrict the crap out of the flow. You needed to pipe the heater to a buffer tank.
  5. rrekih

    rrekih New Member

    Messages:
    46
    Location:
    Canada
    I believe that I don't need a buffer tank as the heat system is fully modulating.
    17,000 to 160,000btu's. From what I understand a buffer tank is to keep the boiler from short cycling.
    The connection stubs are 3/4in for the out and in of the heat system. I have just kept the same size.
    The supply and return from the manifold etc. is 1in. and I have kept that the same.
    One thing though I have put in a PRV in the 1in supply to the manifold, would this restrict the gpm?

    Thanks for your response.
  6. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    Yes, big time. Normal boilers normally have an 1-1/2" or larger feed and return. The buffer tank in this case is not to buffer water but rather to give you a larger vessel to pump from. You are asking an appliance with some pretty small passages to handle way mor flow than it's capable of.
  7. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    I don't see any other system circulators besides the ones in the heating box. The ones in the heating box are there for the tankless and the exchangers and are only capable of a basic primary loop outside the heating box to supply the secondary circ(s) for the system, and in this case your radiant manifold. You need to change some piping and add an appropriately sized secondary zone pump(s) for the radiant.

    Is that really a PRV in the supply line? Why? that is your biggest problem, it cant be there! I think you meant to add a PRV tee'd into the supply line to maintain system pressure (12# cold), not inline.

    Other than that everything looks OK
  8. rrekih

    rrekih New Member

    Messages:
    46
    Location:
    Canada
    Thanks for your response, I know that if I work out a few more details I will get it right.

    http://www.navienamerica.com/PDS/ftp/HeatingBox/HBC-100-Spec-sheet.pdf
    There are 2 circulator pumps one for domestic water and one for heating system. The pump is a Armstrong E9B.

    Just to get this straight:

    There is a pump in the tankless system, this pumps job would be to circulate the water between the tankless system and heating box?
    The pump in the heating box is for the primary cct. to the manifold supply and return?
    I need to add one more pump for the secondary system, the actual heating circuits? How do I plumb this in? I will have 8 circuits in total when I am finished.

    Yes I screwed up with the PRV, I will be moving it to the city supply line. In this case I have put the city supply line into the return side of the manifold, is that alright?
  9. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    The heat side circulator in the heating box is adequate to pump to a typical hydronic coil, baseboard loop, and and a few other similar applications but may not meet the requirements of your multiple loop radiant system. Only you would know that after calculating flow and head requirements based on the heatloss and comparing all that with piping to the pump performance curve.

    I believe you may be reading spec's and believe that the circs you have in the heating box are armstrongs but take a closer look, the circ I see in the picture are identical to the A model tankless and all those are actually Navien's own SS circ, which fall performance wise between a Taco 007 and 009.

    The pump in the tankless only circs inside the tankless to maintain hot water in the tankless to allow no delay or minimum flow requirement. Or if used but not in this case because of the heating box, a external DHW loop. In your case because of the heating box, the A model with pump and internal tank was a waste of money. One circ in the heating box creates flow through the tankless to create domestic hot water.
    The second circ in the heating box serves as a heating pump but is limited to a certain flow/head. Since the tankless is capable of fairly high BTU's but has maxed out flow of about 5-6 GPM because of piping, plate heat exchangers, etc. in you case the radiant may need higher flow, thus the need for a seperate zone pump.

    I would first remove the improperly placed PRV, make sure the feeder fills the heating side to 12#'s cold and try the heat before possibly needing the repipe a bit and add another pump. While there are better places than some to connect the heat side fill, any place you can is better than none.
  10. rrekih

    rrekih New Member

    Messages:
    46
    Location:
    Canada
    Yes big difference 0 to approx. 25 ver: the Armstrong 0 to 42.
    I did remove the PRV and there is now a bit more flow, but not enough.
    The flow meter's read less than 0.25gpm, and how accurate are they, which at that flow I get very little heat back on the return.
    Where to place the second pump?
    If I put in the supply to the manifold wouldn't it be like the heat box pump supplying the secondary pump?
    Also when you say "make sure the feeder fills the heating side to 12#'s cold" are you meaning to connect it to the supply to the manifold?
    Thanks very much for your input.
  11. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
  12. rrekih

    rrekih New Member

    Messages:
    46
    Location:
    Canada
    Pump is a Everon KDP-CTH0650, couldn't fine anything on the web.
    Flow: 50L/min max. or 13.2 gpm
    Head: 6M max.or 19.68 ft
    So I am shopping for a pump.
  13. Doherty Plumbing

    Doherty Plumbing Journeyman & Gas Fitter

    Messages:
    810
    Location:
    Penticton, BC
    deleted......
    Last edited: Dec 21, 2009
  14. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    Yes you wont find that circ for sale, its exclusive to Navien equipment.
    I would put a UPS26-99 Grundfos on it. It's 3-speed allowing you to turn it up. Right now the system looks to need low or med speed and later you may need med or high.
  15. rrekih

    rrekih New Member

    Messages:
    46
    Location:
    Canada
    Thanks much for your inputs Z1700.

    Now just a thought, if the UPS26-99 Grundfos were to fit in the same space as the old pump in the heat box, do you think that would work?
    I know it would probably void the warrenty.
    I will be contacting Navian about the change in pumps that are specified, considering the new style is only have of what they have spec.
  16. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    No like I said and provided the link, change the piping and add the secondary pump external to the heating box.
  17. rrekih

    rrekih New Member

    Messages:
    46
    Location:
    Canada
    I have talked to Navian and they are willing to supply the Armstrong E9B pump as the spec's are showing this pump.
    With that if you look at page 11 this is how I have my system plumbed. As a closed loop system.
    So before I change everything I will try the Armstrong and see if it does the job. I am only doing about 1500sqare ft. of space.
  18. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    The Navien drawing shown is an example of design. When drawn it couldnt possibly know all system installation perameters (length, # of loops, # of bends, heat load, .......).
    A hydronic system designer with experience and knowledge always trumps system designs. For example why do you think they show the install also that I suggested you use?
    You wont like the Armstrong pump once you get it installed
    Good luck
  19. Dana

    Dana In the trades

    Messages:
    2,933
    Location:
    01609

    You have it broken up into 5 zones- just how much mass do you have in your smallest zone, and how big it it's average heat load relative to 17KBTU? (17K is more than half the design-day load at my house, and many times the heat load of my smallest zone.) Odds are NONE of your 5 zones have a 17K heat load, even on design day.

    If you're not getting at least 5 minute burn (or 10 gallons through the Navien) at a time, you're losing efficiency. Every ignition and flue purge cycle takes it's toll... (Which is why in the real-world a condensing Navien rarely breaks 80% average efficiency in a residential hot-water only application.)

    Buffer tanks have very low head, so using a buffer as the hydraulic separator you can use small pumps on the boiler loop and get all the flow you need, and properly set up with the gpm & temp dialed for your design heat load, the Navien will modulate well on the average load working with the mass of the buffer. It'll likely reduce the number of burn cycles in a 5 zone system by half, and set a minimum burn based on the raw mass of the working volume.
  20. rrekih

    rrekih New Member

    Messages:
    46
    Location:
    Canada
    The design on page 12 shows a hook up for a open loop system.
    The one on page 11 is closed loop, this still could be done as a primary / secondary system.
    I will listen to what you have to say about the armstrong pump, maybe this is why they don't use these anymore.
    You haven't said anything about a buffer tank as in the post after you by Dana, what are your thoughts on this.

    So a buffer tank would be added to the primary / secondary system?
    The primary system would supply the buffer and the secondary would draw off of it?
    Right now I have 5 cct's all running 250' to 300', I will be adding 3 smaller cct's in the near future.
    What size would I make the buffer?
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