Radiant heat flow meter setting - general guidelines?

[sevensandeights]

I just typed a long post but lost it somehow so here is the shorter version:

I just figured out after a year that the flow meters on my professionally installed radiant system were set at zero during installation. Needless to my system didn't work very well last year. I was starting to have similar issues this winter so I did some research and realized my boiler was short cycling. I actually opened my eyes when during the visual inspection of the system (compared to the last 100 times I looked at it) and found the issue with the flow meters.

My building is 60'x40' and I have 8 loops of 1/2" Pex all on one zone. 7 loops are about 285' and one is about 200'. I am using a high efficiency 75k BTU boiler with a Grundfos pump (currently set on HI).

Is there a general rule as to where to set the flow meters to start?

 

[Highbeam]

Start at 0.5 gpm per loop.

 

[sevensandeights]

Thanks, that's where I'll start.

I'm assumimg the next step would be to measure delta T between supply and return loops. From what I've read the goal is 20 degrees. My current boiler output temp is 108 degrees. Is there a way to determine maximum efficiency for output temp and flow?

 

[anthony666]

what's your boiler make & model ???

all your flow meters show 0 ?? is the pump working ???

 

[sevensandeights]

Flow meters were set to zero, or very close to it. Pump was "on" so I assumed it was working but don't have a way to test output.

Boiler is a Utica SSC 75k BTU.

 

[anthony666]

'on' doesnt mean anything .. feel the pipe on either side of the pump .. they should be equally hot or theres no flow .. a cassette type pump can seize and snap the impeller shaft and you'd swear they were working, which they are, but there's no flow

what brand of manifold is it ?? is the manifold hooked up right ?? 0 flow is full if the return and supply are backwards

pictures speak volumes

 

[sevensandeights]

System works fine now, I am just trying to get it dialed in to maximize efficiency.

 

[Highbeam]

System works fine now, I am just trying to get it dialed in to maximize efficiency.

Amazing what some flow will do.

Optimizing the system will require more information, a condensing boiler is most efficient with low system temps and long run times. What is your thermostat set for? 20 degree delta seems to be the rule of thumb. Ideally you would measure the out and in temps for each loop and adjust flow in each loop to match up the temps. An infared temp gun would be a great tool.

 

[anthony666]

System works fine now, I am just trying to get it dialed in to maximize efficiency.

good news

 

[sevensandeights]

Ok, I bought an IR temp gun. With 0.5 gpm flows, Initial readings across all 8 circuits were pretty consistent at 90 degrees supply and 70 return. I increased flows to 0.9 gpm and temps changed to 90 supply and 80 return.

My t-stat is set to 60 degrees and is located 5 feet above the floor. I think my maximum boiler output is set to 110 degrees.

Any suggestions other than turn the flows back down to 0.5 gpm.?

 

[anthony666]

google 'low loss header'

 

[98ssuck]

Most likely you need a way to decouple the flow between your boiler and your system. Hence the low loss header or a heat exchanger. Pics would help. Was your system professionally designed as well as installed? If so they should have left you with each zones flow rating.

 

[Highbeam]

Ok, I bought an IR temp gun. With 0.5 gpm flows, Initial readings across all 8 circuits were pretty consistent at 90 degrees supply and 70 return. I increased flows to 0.9 gpm and temps changed to 90 supply and 80 return.

My t-stat is set to 60 degrees and is located 5 feet above the floor. I think my maximum boiler output is set to 110 degrees.

Any suggestions other than turn the flows back down to 0.5 gpm.?

Your system sounds perfect at 0.5 gpm per loop. Nice and low temp, perfect temp drop, nice low flow for low head loss. What more would you want? You're there?

 

[anthony666]

well i dunno what boiler he's running exactly, my only clue was 'high efficiency', but since he asked for suggestions .. imho his boiler would be a happier boiler at a higher output temp and the best way to accomplish that at this juncture would be a low loss .. to me a buck ten is a low temp for a modern boiler

 

[Highbeam]

to me a buck ten is a low temp for a modern boiler

Even a modern condensing boiler? I was under the impression that gas condensing boiler efficiency is maximized at lower temperatures. More heat is stolen from the flame with a lower temperature sink.

 

[anthony666]

without knowing more about his specific boiler it's really just conjecture i guess .. high efficiency is a pretty vague term

anyway, i might be old school, but i like a nice hot relatively quick burn, obviously without dipping into the short cycling trap, to keep the flue and heat exchanger clean .. and i aim for a fairly wide delta at the boiler, obviously depending on the design specifics of the boiler, to keep it condensing .. the biggest mistake in operating efficiency i see is not decoupling the boiler .. floors and boilers do not like the same kind of hot/cold inputs, keeping them slaved to each other usually just compromises both to perform out of spec and decoupling them allows them the freedom to properly work efficiently .. easy way to achieve that in an existing system is to build a low loss header .. i've personally seen gas bills drop by a third by decoupling

anyway, enough generalized hydronic theory; op, what boiler you have and lets see a pic or three of the piping

 

[anthony666]

scrolled back, saw 'Utica SSC 75k' .. read the brochure, it has a built in primary secondary

ignore what i said, not applicable in your case .. my bad for generalizing

 

[anthony666]

that looks like a decent rig .. how much plastic is inside it ?? the quietsides look great on paper til you get a look inside