System piping and bypass valve question

[tropostudio]

I've installed a Westinghouse WBRUNG080 modcon system, using Uponor manifolds and Myson T6 radiators. It is pretty much a home-run system, with each emitter having its own TRV, except for a couple locations where I installed a pair of emitters in series, using a Myson bypass valve at both units in the pair.

The sketch labeled 'Current Emitter Piping' shows how it's set up now. The sketch explains issues with the system, and need to have a minimum 1 gpm for the boiler even if all loops closed down. Sketch labeled 'Modify Emitter Piping System?' shows my thinking to help make system easier to balance, and to simplify adjustment of a 1 gpm flow to boiler if all loops were closed. I welcome any critique, or suggestions for other options.

FWIW, there are actually 3 manifolds, each with 5 loops, to cover a 3 level house. The other 2 manifold are in parallel with the example shown in the sketches. CH is operated off one Grundfos Alpha pump. No primary-secondary. I currently have that running in constant pressure mode on low, which gives 1 gpm. Running it in AutoAdapt brought the flows below 1 gpm. DHW is provided via na Amtrol tank with Grundfos 3-speed circulation pump, set on medium speed (did the head loss calcs to pick that speed). Call for heat is insured by a single Tstat wired to boiler, set at a temp higher than all TRV's. Outdoor re-set is used, although it's not optimized yet.

 

[NY_Rob]

Not commenting on the emitter layout at this time, but that 1 GPM minimum figure through the UFT's HX is only good for very low fire rates.
If you're at anything above maybe 40-50% fire output- you'll fry the HX (Heat Exchanger) with 1 GPM flow. Run it with the front cover off and you'll hear sizzling... that's not good!

Try at least CP II speed on the Alpha... that should get you a couple of GPM through the HX.
With the front cover removed- listen to the HX when the boiler is firing at near max... if you hear sizzling... you need more flow.

If your heatloss on DD is less then the 80K boiler output, use function 18:cb on the installer menu to limit the boiler capacity to something closer to your expected load. You can also enable "Step Modulation" (install menu item 37:CM) to slow the fast rise to high limit.
Both the above will let you flow less water through the HX without damaging it.

 

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[tropostudio]

Not commenting on the emitter layout at this time, but that 1 GPM minimum figure through the UFT's HX is only good for very low fire rates.
If you're at anything above maybe 40-50% fire output- you'll fry the HX (Heat Exchanger) with 1 GPM flow. Run it with the front cover off and you'll hear sizzling... that's not good!

Try at least CP II speed on the Alpha... that should
get you a couple of GPM through the HX.
With the front cover removed- listen to the HX when the boiler is firing at near max... if you hear sizzling... you need more flow.

If your heatloss on DD is less then the 80K boiler output, use function 18:cb on the installer menu to limit the boiler capacity to something closer to your expected load. You can also enable "Step Modulation" (install menu item 37:CM) to slow the fast rise to high limit.
Both the above will let you flow less water through the HX without damaging it.[

Thanks, Rob -

I had to go to CP III on my Alpha to get 2 gpm on it's display.
My calculated Q with a -8F design temp is 59kBtuh. Haven't come close to -8F this season Should I set 18:cb to 75-80%? And 37:CM to ON?

I made good use of your system diagram when I put together my system - thanks for that. You use 3 zone valves, but I didn't see a differential pressure bypass.

Running the numbers on my entire system, 3 floors, gives me 3.5 -4.5 gpm flow with all circuits open for delta T from 30F to 25F. My emitters are almost 100% oversized so I could run supply at 140F at -8F outdoor design temp.

Now for really stupid questions: If all my emitters are closed down because the TRV's have hit temp, and I have no bypass, my boiler gets no return water. That's bad. If I have a diff bypass, or as in case of my current diagram, an effectively fixed bypass, my boiler gets hot return water and says "I'm done" and shuts down, right? My Tstat set high connected to boiler TT tells boiler there is still a call for heat, but boiler ignores it if return water is about as hot as supply, right? Or am I confused? (highly possible).

 

[NY_Rob]

"My calculated Q with a -8F design temp is 59kBtuh. Haven't come close to -8F this season Should I set 18:cb to 75-80%? And 37:CM to ON?"
Well, it's worth trying to limit boiler output in many cases, there's just no reason to throw 80K BTU's at your HX with 2GPM flowing through it. It also depends on the max CH water temp on your ODR curve. If your max CH water is 140F on DD and you emitters can only put out 50K BTU's at 130F AWT... why throw 80K BTU's at it- then hit high limit- and then have to modulate down.
Same goes for step modulation... instead of starting at full fire, it starts at 40% of your max output (based on 18:cb) and gradually steps up to full fire (if needed). Sometimes you might notice you don't even get up to step six because you're approaching high limit... it may stop climbing before even hitting max.
Over time you'll find the control logic on this particular boiler isn't so great... you may be running at high limit and a couple TVR's close... now you pass high limit and the boiler can't modulate down fast enough.... so it stops firing, only to restart a just few min later because other emitters are still calling for heat. It's worse with zone valves when a large zone shuts down leaving only a small zone running at high boiler output.

 

[NY_Rob]

"I made good use of your system diagram when I put together my system - thanks for that. You use 3 zone valves, but I didn't see a differential pressure bypass."

Don't need a DP valve with zone valves and a CP circulator pump like the Alpha. It will maintain minimum flow as the zones open and close.

If all zones close, TT contacts are open and boiler stops firing unlike TRV's where all could close but the thermostat is calling for heat and the boiler and CH pump would still be running.

 

[NY_Rob]

"If all my emitters are closed down because the TRV's have hit temp, and I have a diff bypass, or as in case of my current diagram, an effectively fixed bypass, my boiler gets hot return water and says "I'm done" and shuts down, right? My Tstat set high connected to boiler TT tells boiler there is still a call for heat, but boiler ignores it if return water is about as hot as supply, right? Or am I confused? (highly possible)."
Makes sense, because with no radiation to shed BTU's you would quickly hit high limit and it would stop firing till it cooled down to below the differential (HL-15 or 20 deg) and it would fire up again. Doesn't sound ideal though....

You might be better off with a P/S setup via a Low Loss header and discrete boiler pump?
Your boiler can control a boiler and system pump in a P/S environment.
In P/S setting you can keep the boiler pump at a fixed speed and never worry about cooking the HX, and the boiler would control both pumps as intended, you would also have better control of the flow in the CH loops since it's not tied to the boiler any longer.

Honestly, at this point I'm not comfortable offering advice because I have no experience with TRV's.

Perhaps post your diagrams and ideas at the other popular heating site to get some more eyeballs on the project- the pros there have no doubt dealt with circuits like you have...

https://forum.heatinghelp.com/

 

[tropostudio]

Thanks for your help, Rob.

One of the reasons I chose the WBRU was the low loss across the boiler and ability to set it up with a single circ pump. I picked the Alpha to use with homeruns and TRV's at all emitters because it won't deadhead if the emitters all close down. It seemed like a simple system, despite the Hydra of PEX coming into 3 5-loop manifolds. Except now I have the concern about maintaining min 1 gpm across the HX. That's why I was thinking a DP valve, but maybe a way to open the TT contacts and end the call for heat is better. Right now I have a basic thermostat set to 80F that's acting as a switch, so its always closed

I'll see what folks at The Wall have to say.