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# Pipe sizing

Member Posts: 18
I was thinking about (and will) use 3/4" pipe. It works better with pump flanges and what not, plus it will give me extra capacity if needed in the future. BTW at a delta T of 20 degrees the flow rate is 3.3 gpm which is at the low end of 3/4" at 2 fps.

I did calcs. on the different panels, the flow rates vary, but yes they are small. I'm going to put another post as to the manifolds, but here it is for you. The panels have balancing valves built in. Do I need an expensive manifold that has flow meters and balancing valves or can I go with a simple copper manifold and due the balancing at the panel? There is a huge cost difference in manifolds.

Pete

• Member Posts: 18
Pipe Sizing

Have 32,000 BTU heat loss and will use 9 panel radiators in a home run zone. Supply temp of 140 degrees and Delta T of 40 degrees. I am coming up with a flow rate of 1.6 GPM. At between 2 fps to 4 fps I could go with 1/2" pipe on the secondary loop for the panel zone.

The pipe size seems small, am I missing anything here?

Pete
• Member Posts: 2,398
The math works out OK

and I applaud your use of wider delta-T's than the conventional 20 degrees. It would not hurt to go to 3/4" to the manifold just to keep your transport losses to a minimum, assuming that you are not using a circulator on the manifold but the primary circulator to move all water. Gives you a margin of capacity for expansion too, for not much cost.

Here is my practical side coming in: How far down can you meter water to each radiator? You are dividing 1.6 gpm amongst nine radiators, that works out to 0.18 GPM per radiator assuming they are all equal.

A hamster with an inflamed prostate could pee more than that.

You have to be able to confidently balance each radiator including homerun pressure drops to a point where they all get what they need, consistently. To meter down to those small flows means some pretty tiny valves and/or flow meters.

I am suggesting that you may wind up delivering more flow overall to assure balance and let local TRV's take what they need. Mind you, I am a huge fan of not moving too much water, but you still have to "measure it to manage it".
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"

• Member Posts: 552
Pete m

Hey pete m are you in new jersey if so you know who i am drop me a e mail if so have not heard from you in a dogs age peace and good luck clammy RDEUZA@aol.com
• Member Posts: 2,398
Metered Manifolds

are a great way to go, so long as the meters are capable of enough turn-down. I have a radiant manifold in my house piped to Climate Panel (so 10 MM or 3/8" nominal tubing). With one circuit, the meter is practically all on or off. Hard to get the flow to a reliable level (it works, flow quite forgiving mind you). But it seems that the smallest "tweak" triples the flow sometimes.

If you DO go with copper manifolds, see if you can get maybe 1/4" needle valves. You may not actually measure the flow but you can at least distribute it accurately. In the end you will likely be "measuring" by Delta-T over time.
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"