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New radiant system high Delta T
Rob760
Member Posts: 1
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
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Comments
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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.1 -
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 curve1 -
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.0
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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 dream0 -
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.0
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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.0
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News to me , recently discovered this table shows max. velocity of 8 fps in pex.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.
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 fpsBob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
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.
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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.
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 tablesBob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
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?0
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