Measuring supply run for circ size

Brad White_9

I think there is enough to work with. Zone 1A seems to define the highest pressure loss but we can check each. I will ignore the "express returns" as you state.

What will the system look like in it's final stage? May I assume (ahem) that you will be pumping away? And will there be balancing valves on the express returns to prevent short-cycling? You might now be starving your further radiators and short-cycling your boiler due to higher HWR temperatures, if I gather things correctly.

Anyway, let me get cracking on this in some spare time.

Later!

Brad

D107

Dan's method of length divided by 6 for head very helpful but

I'd like to know precisely where you stop measuring. End of last rad? or the whole run from boiler back to boiler? Seems to me pump has to push water all the way around. (Re: Monoflo system.) In direct or reverse returns systems would you measure returns as well?

2. Also, Dan's method assumes an extra 50% length for fittings, etc. So that also allows for (let's say in monoflo) the branch takeoffs/returns to and from the rads from the supply? That could be up to 6ft total additional for each rad from what I've seen.

3. Finally, in the case of a split zone--one that divides at boiler--does that smaller section get figured into the circuit length measurement, or do you measure only the longer zone?

Seems to be no end to my lack of knowledge,

Thanks,

David

Brad White_102

All good questions, David

The pump head is defined by the longest complete circuit: From your circulator discharge, through the mains (MonoFlo in your case, including all of the tees in series), back to the circulator, plus your longest branch run to and through the furthest radiator... does that make sense?

By "furthers radiator" I do not mean necessarily "distance"; for example one radiator may be 50 feet away with mostly straight pipe and a few elbows. Another may be 25 feet away and require flow through tees, elbows, valves and terminate in a kick-space heater with a high pressure drop... That is the circuit that counts.

In split zones, only take one zone, the worst case. If you have enough pressure differential to do the worst case zone you can do the lesser ones. Pressure is parallel, flow is cumulative.

As one of my co-workers once said, "If you can stand in your garden with a water hose and water the flower bed at the far side of the yard from where you are standing, you will be able to water the vegetables at your feet."

In the end, though, the short-hand way of "length plus 50%" is borne out in actual practice as "close enough". Personally I only use that during the preliminary stages of a job to get my arms around things, then calculate them in detail, segment by segment, before the job goes out.

No end to my lack of knowledge either, David. We hope to keep learning until we die, right? Or until our heads explode, but that would be the same think, I think...

D107

thanks, yes mostly clear

except you say, including 'the mains PLUS your longest branch run to and through the furthest radiator.' Well in this monoflo one pipe, all the rads--as far as I know are basically three or four feet away from the main and probably all would have the monotees, requisite elbows and shutoff valves. So once I measure the main from circ discharge back to boiler, you're saying add the additional 6-8 ft of run to the rad that has the longest supply and return branches if that's the longest I can ascertain?

This question came about--you may not have seen that post--because I suddenly discovered upon examination that it's not straight monoflo. The supply run feeds the first three rads, and then for some reason the 1/2" return branch of the third rad pipes into a capped reverse 3/4" return that goes right back to boiler while the main continues on. I'd guess this was done to supply hotter hot water to the rest of the circuit but don't know if combining monoflo with a semi-reverse return is usual. Plus I found the zone itself splits at boiler to feed via 3/4" supply the last, largest rad in the system--living room/entry hall--and the branch 1/2" 4' long return from that rad pipes into the end of the 1" monoflo main coming back to boiler. That makes sense to me; otherwise living room might take too long to heat given the pipe route. But in terms of pump head, I understand that you say don't worry about the small living room run, but as far as the reverse return after the first three rads, am I measuring that one for the pump head calc?

Does this sound like a gerry-rigged piping system? Perhaps this was done after they added two large basement rads.

Thanks,

David

Brad White_102

This is worth a diagram, David!

I missed the details of the post but did see the fitting. I suppose the right answer is between our assumptions.

If the multi-emitter branches are in series there is an additional twist of temperature drop, perhaps another issue.

But you know what? We and a few others could analyze this and come up with different outcomes. In the end, given the system being so limited in size and scope, you are likely to wind up with a Taco 007 or a Grundfos 15-58 and it will work just fine. Just my projection!

But if you can send me a diagram or post one, I think we can come up with a reasonable calculation.

D107

If you can call this a diagram....

I think I drew better in kindergarten....
I was out at the house yesterday and had a guy look at the piping. He surmised that the reverse return was installed to improve the flow to the kitchen powered convector which was added to the system and at one time also served as an AC unit. The split loop feed to the living room radiator also serves almost as a separate zone to the largest room/entry hall in the house and gives it heat immediately instead of being last on the run.

Formula I used for gpm = mbh x .1042 (Steamhead’s chart.)
Zone 1:
11 convectors 75K kbtu off 1” monoflo main with half-inch feeds to rads;
Total 151 linear ft Dan’s formula: 151/6 = 25ft head, 8gpm
(Note I didn’t the count the extra 3/4” reverse return run from kitchen powered rad (15ft) or Zone '1B' 3/4” direct split zone supply to living room powered rad (15ft.)
Main supply has about 11 90deg L’s, each convector has one shutoff and supply feed. Fittings?
Currently Taco 008 F6 (Flow: 0-14gpm; Head: 0-16ft.)
With new boiler: Taco 0011, GF UP26-99F ????

Zone 2: (Porch only)
163 ft 3/4” straight circuit with 26Kbtu baseboard. (that’s supply and return combined.)
90Ls: 23, 1 shutoff
Dan/Steamhead formula: 27 ft head, 2.75gpm.
Currently Grundfos UPS 20-42 on speed 3. (Flow rate: 0-21gpm; Head: 0-14ft.)
With new boiler: Taco 0011, 009, or GF UP26-99F ????

When you’re calc-ing gpm, that’s really for main pipe, yes? So for 1” it’s 8 gpm but less will flow through the ½” feeds to the rads I assume..

As I believe you once said even if the sizing is 50% off you can get 90% of your heating. Most contractors don't seem to spend so much time on this for retro-fits for small 2100 ft houes. But I agree why not take a few measurements and get the circ size as close as possible?

I thank you for your input on this.

David