TRVs, direct return, and balancing valves

dave123

So it seems there are opposing opinions about this question, depending on where I look. With panels rads piped direct return, each with a TRV, is a balancing valve needed on the return branch coming from the radiator, or not?

Some seem to say that the TRV removes the need for a balancing valve, but it seems to me, on a design day temp, when all the TRVs should be open, the radiator at the end of the run is going to see a significantly lower water pressure than the first of the run, and so lower flow and lower avg temp.

Am I missing something?

hot_rod

One radiator per branch? Or are some in series

EBEBRATT-Ed

@dave123

What you said about full load is true. The trvs will control better if the flow is balanced.

Weather you need them or not would depend on how out of balance the system is without them.

If you had reverse return I would skip them. With direct return I would put them in.

dave123

This would be 7-8 rads per zone, direct return. Parallel only, no series.

Would simple globe valves suffice for balancing?

hot_rod

Are they piped with H valves? They often have balance function. Some TRV have a balance function. Really any valve can be a balance valve, balance specific type will have ports to connect a meter for best balance accuracy

Good, better, best options are available. What type of flow rates are you needing?

dave123

Yes, H valves. But I thought those were like ball valves and weren't really designed to limit flow (?). I thought they were meant to be just open/closed.

hot_rod

There are numerous ball type balance valves out there. The popular B&G Circuit Setter is a ball type, as is the Caleffi Quicksetter. Dahl mini ball valves are often on radiant manifolds used for balancing. I don't imagine you are making a huge adjustment or flow limitation so that ball isolation valve may be adequate.
Where else would you mount a balance valve for the radiator, back at all the connections to the main loop?

dave123

All of the piping would be accessible from the floor below, so there'd be room for balancing valves on the return leg from each rad to the main return trunk.

I had been thinking to using the caleffi 3010 as the isolation valve. I guess since flow through each rad would be pretty low overall, maybe throttling with the isolation valve (where needed) would be okay.

hot_rod

I think for a small adjustment that valve would work. You don't want to choke a ball type valve way down or they wear quickly with the edge of the ball exposed to the flow.

Here is an example of a Dahl mini ball/ balance, it has a fine thread and a pin that drops for s bit better flow path.
All sorts of pipe connections available, this one is sweat by 1/2 pex.

dave123

Thx, I'll look into that one.

One other question I had is whether or not a balancing valve is needed on the last, or maybe even the second last radiator of the zone. Seems like they would be unneeded or of very little use, as opposed to the balancing valves on the first/second/third rad of a parallel piped zone. Is that right?

hot_rod

I think with H valves and TRVs you should have enough adjustment. Do you kn ow required flowrates, or just going to balance by feel?

dave123

The prelim design is for oversized rads to keep the water temp down. Total design load 53K. That would mean a pretty low flow needed through each rad, on the order of about 0.3 gpm, give or take depending on the rad.