Were the Dead Men Wrong?

Alan (California Radiant) Forbes

This is a continuation of a thread about a Bell & Gossett replacement circulator.

Based on everyone's great advice, I replaced a 79-year-old B & G circulator that was leaking with a Grundfos 15-58 because I wanted a choice of speeds in case low or medium didn't work (see performance curves below). I added 30# gauges on the suction and discharge sides of the pump to determine pressure drop and the results were surprising.

I added the gauges out of curiosity. I didn't know the actual pressure drop of the system. Three-eighths tubing in the plaster ceiling was known, but was it 3/8" o.d. or i.d.? And how long were the loops?

As I said, the results were surprising. The pressure drops were:

Low speed: 7 feet
Medium speed: 9.3 feet
High speed: 11.7 feet

At low speed, the Grundfos satisfies the heating requirement of 3 gpm. I shot the ceiling with my infrared camera and it was all aglow.

The owner saw the replacement of his massive B & G circulator with the much smaller Grundfos and told me he wanted to keep the B & G "just in case".

If the installer had known what I know now, he could have used a B & G Series 100 circulator to satisfy the system requirements and reduced the owner's utility bill. But he probably wanted to make sure his system worked properly and erred on the side of expediency although the B & G "1½ HV" is really a high volume pump, able to flow over 35 gpm.

gerry gill

My guess is that the dead men did just that...guess

Solid_Fuel_Man

I'll take a stab that 90% of residential jobs are massively over pumped. The math doesn't lie, but it doesn't take much flow to move heat. The emitters only care what the average water temperature is, more pump and all you get it higher return temps.

Dont you just love hydronics? So much heat can be moved through such small pipes (3/8")!

Tinman

Pressure diff x 2.31 = ft of head
7 x 2.31 = 16.17 ft of head
👍

Alan (California Radiant) Forbes

Steve Minnich said:

Pressure diff x 2.31 = ft of head

7 x 2.31 = 16.17 ft of head

👍

That's the formula that I used, Steve. The pressure differentials were 3, 4 and 5 pounds respectively.

hot_rod

Nice use of those ported iso-valves
Maybe they were designing for a 3- 5° ∆ with that large circulator.

Alan (California Radiant) Forbes

hot_rod said:

Nice use of those ported iso-valves
Maybe they were designing for a 3- 5° ∆ with that large circulator.

Thanks for turning me on to them, HR. I just wish they were ¼" tappings instead of ⅛".

Danny Scully

They make 1/8” gauges @Alan (California Radiant) Forbes

STEVEusaPA

Good work you mad hydronic scientist!

Tinman

F you want to be even more accurate, use a single gauge piped in parallel to the pump with a ball valve on each side. It lessens the margin of error.

Alan (California Radiant) Forbes

It's great. It was the first time I could draw a system curve on a pump performance curve.

Oh, the things I get excited about!

Tinman

For the performance curve, did you use B&G's System Syzer?

Alan (California Radiant) Forbes

The pump performance curves are shown on the lower image above.

I used the pressure drops to plot the duty points on each curve and ran a line through them to give me the system curve.

jumper

Not that difficult to determine a system curve and then select pump. But this obvious method is rare even on million dollar projects. Hope that Henry from Montreal sees this post.

hot_rod

And most important the system curve over the pump curve defines the OP operating point of the circ.

Notice 5.5 where two circs would give you the correct flow, a high head and a flat curve, which would you select?

STEVEusaPA

hot_rod said:

And most important the system curve over the pump curve defines the OP operating point of the circ.

Notice 5.5 where two circs would give you the correct flow, a high head and a flat curve, which would you select?

#2?

Alan (California Radiant) Forbes

#2 as well. Circulators with flat curves are more desirable when using zone valves . Flow will not change drastically as a function of opening and closing zone valves.

jumper

Alan (California Radiant) Forbes said:

#2 as well. Circulators with flat curves are more desirable when using zone valves . Flow will not change drastically as a function of opening and closing zone valves.

For main circulator. Opposite situation for coil circ.

JohnNY

Great post/thread.

bob eck

Where did you buy the flange with 1/8” tapping.

Steamhead

Solid_Fuel_Man said:

I'll take a stab that 90% of residential jobs are massively over pumped. The math doesn't lie, but it doesn't take much flow to move heat. The emitters only care what the average water temperature is, more pump and all you get it higher return temps.

I'd say you're right. Check this one out:

https://heatinghelp.com/systems-help-center/adjusting-the-flow-rate-for-an-old-gravity-hot-water-system/

which led to this:

https://heatinghelp.com/systems-help-center/sizing-circulators-for-old-gravity-hot-water-heating-systems/

Alan (California Radiant) Forbes

bob eck said:

Where did you buy the flange with 1/8” tapping.

Calefactio (means "warming" in Latin) is in Montreal and I couldn't find any out West, but finally scored in Salt Lake City. Hajoca at (855)982-1408. Ask for Vern.