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Were the Dead Men Wrong?

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Alan (California Radiant) Forbes
Alan (California Radiant) Forbes Member Posts: 4,106
edited June 2019 in THE MAIN WALL
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.








8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

Two btu per sq ft for degree difference for a slab

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  • gerry gill
    gerry gill Member Posts: 3,078
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    My guess is that the dead men did just that...guess
    gwgillplumbingandheating.com
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

    Zman
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    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")!
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • Tinman
    Tinman Member Posts: 2,808
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    Pressure diff x 2.31 = ft of head
    7 x 2.31 = 16.17 ft of head
    👍
    Steve Minnich
  • Alan (California Radiant) Forbes
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    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.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • hot_rod
    hot_rod Member Posts: 22,483
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    Nice use of those ported iso-valves :)
    Maybe they were designing for a 3- 5° ∆ with that large circulator.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,106
    edited June 2019
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    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".
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Danny Scully
    Danny Scully Member Posts: 1,430
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    They make 1/8” gauges @Alan (California Radiant) Forbes :wink:
    Alan (California Radiant) ForbesSeanBeans
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
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    Good work you mad hydronic scientist!

    There was an error rendering this rich post.

  • Tinman
    Tinman Member Posts: 2,808
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    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.
    Steve Minnich
    Alan (California Radiant) ForbesSolid_Fuel_Mandelta T
  • Alan (California Radiant) Forbes
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    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!
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    Solid_Fuel_Mandelta T
  • Tinman
    Tinman Member Posts: 2,808
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    For the performance curve, did you use B&G's System Syzer?
    Steve Minnich
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,106
    edited June 2019
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    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.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • jumper
    jumper Member Posts: 2,333
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    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
    hot_rod Member Posts: 22,483
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    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?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
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    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?

    There was an error rendering this rich post.

  • Alan (California Radiant) Forbes
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    #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.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • jumper
    jumper Member Posts: 2,333
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    #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
    JohnNY Member Posts: 3,244
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    Great post/thread.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
    Classes
  • bob eck
    bob eck Member Posts: 930
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    Where did you buy the flange with 1/8” tapping.
  • Steamhead
    Steamhead Member Posts: 17,008
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    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/
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    Solid_Fuel_Man
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,106
    edited June 2019
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    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.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab