primary loop flow control

[rotaxman]

attempting completion of my first radiant design but I have one question that has me stumped. Maybe it's obvious, we'll soon see.

My design has one circulator and 3 zone valves and what I would like to do is control the flow of the by-pass on the primary loop.
The primary loop flows through 1.25 pipe and has the DHW heat X in that loop. head loss or resistance is very low and this is where my concern is. If one or more zones are calling, (3 zones total head loss of 10 @ 8 gpm), I'm worried that the path of least resistance will be right back to my OWB and I'll get little or no flow to the zones.
I would like to keep the return temp to the boiler as high as possible so the by-pass cannot be shut down, just slowed down. Is there a valve that can vary the flow? as pressure reduces, the by-pass valve reduces flow at by-pass and increases flow at zone manifiolds.
Having no experience, I am looking for guidance on the best strategy. I looked at the nofossil design and the by-pass is controlled by a zone valve, I assume that it's either open or closed, which wouldn't work for me.

or maybe I'm worrying for nothing and as zones open, I'll have to control the flow at the manifolds and the bypass flow will be self regulated. nahh, thats too easy.

If I haven't been clear, please say so and I'll post a drawing when I get home

TIA

 

[Nofossil]

They make an adjustable pressure 'relief' valve for that purpose. You'd have to put it in series with the DHW exchanger. Hopefully someone will have a link to an actual example.

 

[Gooserider]

Drawings are always helpful, but the other thing I'd suggest is going to the Caleffi website, and look for their "Idronics Magazine" section - they have one issue on zoning that goes through a lot of different options... Their layouts assume a conventional boiler, but really the heat source doesn't matter to the rest of the system, so you should still be able to get some good ideas.

Gooserider

 

[rotaxman]

Actually......I have most of their web site material printed and in a binder. Looking at their products, I could install a pressure differential valve in the bypass and it sounds like this would work. They also have a flow switch, and this could measure a desired flow and signal a valve to partially close but I haven't found any variable valves yet. Another option could be to have the controllor signal the 15-58 3 speed pump to bump up one speed if the 1, 2 or 3 zones are open, depending on the flow required. These are all theoretical ideas for me since I have no practical experience. What sounds good in my virtual world may be a real bad idea in real life. Maybe a few others will share their ideas.


thanks for the Caleffi tip, their web site is fantastic and I will certainly be buying their products