Figured out the GPM and Head; now which circulator?

D107

Heat Loss: 47K Gain: 100K. 2 Zones. Proposed boiler: Buderus G-115/21. (3 section: DOE Output 74mbh; net: 64mbh)

NOTE: I EDITED OUT SOME INCORRECT INFO BELOW AFTER TONY'S POST AFTER THIS ONE CORRECTED MY CALC METHOD.

Main zone 1” monoflo to 11 convectors; Loss: 39mbh; Gain: 75mbh.

Zone 2 3/4" loop via baseboard to porch on slab only. Loss: 7.5mbh; Gain: 26Mbh

Zone 3 for DHW Buderus ST-200

I see some curves are straight and others convex; don't know how to translate that. I gather best efficiency is in center third of curve--speaking left to right--but perhaps more on the left side. While pipe width seems to determine gpm,it doesn't seem to determine head. Also on Zone 1 monoflo, gpm is based on one-pipe main size, not the 1/2" feeds to rads etc. so I assume flow rate will decrease when it leaves the one-inch into the 1/2" feeds.

Before I start looking at a more precise calc for the head, measuring fittings, etc. I just want to get a good idea if I'm approaching this correctly.

Thanks,

David

Tony_23

It seems

Your head calcs are pretty high. I think you're dividing length by 6. Rule of thumb is 6ft/ 100 ft of pipe.

Your main zone may need a NRF-33, being monoflo. The PL series is a bit much, IMO.

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D107

thanks for the correction -- big difference

There seems to be some debate about whether to base gpm on the emitters or the heat loss. Makes a big difference. Steamhead uses emitters in his table. The effect in my case might reduce the Delta T to 10 degrees instead of 20. Since this is an atmospheric boiler that may or may not be desired. I will have outdoor reset; the Buderus G115 can handle down to 104deg. supply temps with the Logamatic control.

So if I re-calc head as per your correction and if I determine GPM by the heat loss and not emitters:
Zone 1: 8ft head with 4 gpm: best pump = NRF-33 or NRF-22, but both overpump a bit.
Zone 2: 11ft head with 1gpm: best pump = NRF-33
Zone 3 ST-200 indirect: 4.3ft head with 17.6 gpm max = NRF-22

Thanks,

David

CC.Rob

numbers

HO here. I can't speak to the monoflow loop, but the numbers for the 3/4" loop look odd to me. Last winter I did a bunch of head/flow calcs for my system (2 zones, series loops, 3/4" piping, fin/tube convectors). The major lesson was _never_ to use a rule of thumb. There is a very straightforward guide for doing a head/flow calc at the Taco site. 10 minutes measuring and writing down, 20 minutes in excel and you're done.

http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf

If that loop is 176 ft of straight pipe, throw in some elbows, fittings, etc. and you probably come out with a TEL of, say, ~225-250 ft, which for a flow rate of ~4 gpm, is a head loss of about 7-8 ft. Note that in 3/4" copper you want a flow rate of 3.2-6.5 gpm (2-4 ft/sec) to keep entrained air moving to the elimination point.

Given the very low BTU/hr demand of the loop, I'm guessing you probably want to stay at the low end of the flow range to achieve at least some delta-T. In which case, at just over 3 gpm, a 250 ft TEL loop has about 5 ft of head. Small pump. Taco 006 or 005? Comparable Grundfos?

Just some thoughts, totally open to correction!

Steamhead (in transit)

The reason I used the emitters

is because they are full of water that needs to be moved, as are the system's pipes. This must be accounted for, especially in a converted gravity system. The actual basis for the calcs came out of an old Bell & Gossett Handbook. I just presented them in such a way that you can use any manufacturer's circ.

When selecting circs for existing systems, the type of distribution system and emitters only determine how the circ is selected. Always size the boiler to the calculated heat loss. If the system's flow rate is not the same as what the boiler requires, use a primary-secondary setup which uses separate circs for the boiler and the system.

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