Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

New radiant system high Delta T

Rob760
Rob760 Member Posts: 1
edited January 21 in Radiant Heating

I have 5 loops of 1/2” pex B at 300' per loop. I have a bluefin manifold feeding them and the company that I bought the system from told me to use 3/4” pex B from circulator to manifold. My delta T is around 45 degrees and outside air temp is 0F. My thoughts are to get rid of the 3/4 pex and go to 3/4 copper to gain a bit more volume. Any help is appreciated

Comments

  • Ironman
    Ironman Member Posts: 7,540
    How about some more info?

    Is this a slab or wood floor? If a slab, how well is it insulated?

    What size pump is feeding the manifold? What’s the heat source and how many btus is it?

    Some pics would help.

    Changing to copper won’t drastically increase the flow rate, but non barrier pex should not be employed.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    Rich_49
  • EzzyT
    EzzyT Member Posts: 1,342
    The 3/4” copper might not due the job either, might have to go with 1” all depending on the overall length from the manifold to the mechanical room piping.
    The circulating pump might also needed to upgraded, pump curve middle 3rd to match system curve 
    E-Travis Mechanical LLC
    Etravismechanical@gmail.com
    201-887-8856
    Rich_49
  • GroundUp
    GroundUp Member Posts: 2,099
    edited January 20
    What are the actual supply and return temps? What are the flow rates on each loop? How long has the system been running? What is the ambient indoor temp? How is it piped and with what sort of heating unit? There is nothing wrong with 3/4" pex for only 5 loops, you may just have the supply temp too high or simply need to wait for it to warm up if it's a recent startup.
  • hot_rod
    hot_rod Member Posts: 23,341
    Do you have a design that shows how many gpm each loop needs?

    For example
    5 loops at .50- .75 gpm as a range would be 2.5 - 5.75 gpm

    This calculation shows 80' (40' each way, 4 elbows)of 3/4" pex at a 5.75 gpm flow = 13' head.

    Here is a common circulator Grundfos 15-58. Find 5.75 gpm on the bottom, run up to the top speed 3 line and left to 13'

    But more details would help see exactly what you have for a boiler, mixing valve?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Teemok
    Teemok Member, Email Confirmation Posts: 677
    5 -1/2" loops is .7 to 1 gpm per loop. So under 5 gpm. 4.6 GPM is about max flow rate for 3/4 @4ft per sec. Seems like it should work. How long the 3/4" runs are is critical. You may not have enough pump to create the flow rates needed to achieve lower deltas in the loops and in turn higher btu delivery.
  • Teemok
    Teemok Member, Email Confirmation Posts: 677
    The relationship of your heat emitters Delta T and the out side air temp isn't all that connected except to say it's cold outside. Lot's more info needed to say what's likely happening. If your boiler is full fire dumping heat into a huge mass, it's very normal to see high deltas for a long while. If the boiler is just low fire cycling you have a flow rate problem.
  • hot_rod
    hot_rod Member Posts: 23,341
    Teemok said:

    5 -1/2" loops is .7 to 1 gpm per loop. So under 5 gpm. 4.6 GPM is about max flow rate for 3/4 @4ft per sec. Seems like it should work. How long the 3/4" runs are is critical. You may not have enough pump to create the flow rates needed to achieve lower deltas in the loops and in turn higher btu delivery.

    News to me , recently discovered this table shows max. velocity of 8 fps in pex.
    Although a foot note suggest 5.5 as the industry standard for hydronic systems.
    Also noted, above 8 fps may cause erosion in metal components in the system.

    I think the 2 fps for DHW was recently slipped into the table? :)

    May want some water hammer arresters on the urinal flush valves seeing 10 fps
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Teemok
    Teemok Member, Email Confirmation Posts: 677
    Just because Uponor brags it's pex can handle it doesn't mean we want to design for the head pressure needed to push 8 ft/sec through it. I did say "around" Don't know where Supplyhouse got their chart. I suppose there's a difference between concerns of erosion, noise and efficiency.

  • hot_rod
    hot_rod Member Posts: 23,341
    Teemok said:
    Just because Uponor brags it's pex can handle it doesn't mean we want to design for the head pressure needed to push 8 ft/sec through it. I did say "around" Don't know where Supplyhouse got their chart. I suppose there's a difference between concerns of erosion, noise and efficiency.
    To vague and conservative 

    The Online PPI calculator for pex allows you you to put in size, length, fittings and gpm

    gives you feet of head, psi drop  and velocity 

    https://www.plasticpipecalculator.com/PressureDropHeadLoss.aspx

    Engineering toolbox.com has copper and steel pipe tables
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Teemok
    Teemok Member, Email Confirmation Posts: 677
    Too vague and conservative for what? I agree it's a little conservative.
    Yes, I've got the PPI calculator.
    The pumping costs vs velocity balance creates the sweet spot. If you "need" to be outside of that range? Fine, push it but it's not free.
    If someone posted that they designed for 6.5ft+/sec in 3/4"pex home runs, you'd want to know what the head loss is.
    There's nothing wrong with conservative pipe size design.
    When does noise become a concern with higher velocities in pex?

Categories