direct return, with or without diverter tees?

sgriffis

Hello all!
I am putting together a simple 3 zone direct return system for my home.
I am running a Bosch greenstar boiler to restored cast iron radiators (some have TRVs).
For piping I plan on using 3/4" vega barrier pex for supply/return and 1/2" for each radiator branch.

Do I need diverter tees for each branch?
Or are regular tees fine

How far can I run a branch off from the supply/return loop?
In other words dose the supply/return loop need to run directly under each radiator?

SuperJ

I would use regular tees, diverter tees don't make sense since your not looping your rads together. Each rad is connected directly to the supply and return so each rad has access to the undiluted SWT. A traditional diverter tee loop don't mesh well with the benefits of a modcon. But you should consider how you are going to achieve balanced flow.

There isn't really a specific limit for your branches. It has more to do with pressure drop. Figure out the flow you need at each rad and do the math based length. A low flow zone may be able to have substantially longer branch tubing than a high flow zone.

I did something similar in my house, I ran about 30' each way 3/4" pex to a remote manifold from my mech room, and then up to 50' each way to pick up various panel rads. In my case the rads all had balancing valves and TRVs so it was a cinch to setup with a delta P pump.

You don't want to have to start adding pumps or using ridiculously large pumps just because you skimped on piping though.

hot_rod

Why not a home run system?

Harvey Ramer has fine article in this months PHC on a home run cast radiator retro. He dug deep into how TRVs and ∆P circulators work together.

https://www.phcppros.com/articles/7804-when-old-tech-meets-new-tech

SuperJ

That article sums up my experience pretty well. When I first installed my panel rads with TRVs and a AutoAdapt Grundfos pump, I had my ODR set too aggressive and TRVs set too low. Once I started thinking of TRVs as a high limit rather than my primary control, things evened out nicely. And the rads stayed warm all the time rather than hot or cold, and the boiler ran longer cycles at lower temperatures.

hot_rod

I think this dynamic TRV is designed for variable flow, ∆P circulator systems like that. First you set the desired Cv, for the various flow requirements at each radiator. The valve has a pressure independent balance function that assures it is always getting correct flow as other TRVs modulate or shut down.