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Author Topic: Pump speed  (Read 2401 times)

MD20/20

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Pump speed
« on: November 22, 2018, 07:49:16 AM »
I have a 275 ft of Rehau 1” going to a 80 plate heat exchanger. What speed should my Grundfos 26-99 run? I guess I need to measure return temps??
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Central MD

wreckit87

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Re: Pump speed
« Reply #1 on: November 22, 2018, 08:04:42 AM »
275 ft of 1" and an 80 plate do not go hand in hand. What is the heat load on the plate? With the 26-99 on speed 3 you'll only be able to move about 70,000 BTU which a 20 plate would be able to transfer. If the plate was sized to the load, you're going to have a rough go with return temps being far too low and there is nothing that can be done about it besides digging up the pipe and replacing it with the correct size. The heat load in the building will determine though, I'm hoping the plate is just way oversized
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RSI

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Re: Pump speed
« Reply #2 on: November 22, 2018, 08:05:59 AM »
It will depend on your heat load.
I would guess high would be around 9 gpm, medium 8 gpm and low around 6 gpm.

It looks like a 15-58 on high would give you the same or slightly more flow than the 26-99 on low speed.

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RSI

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Re: Pump speed
« Reply #3 on: November 22, 2018, 08:08:08 AM »
Those numbers are assuming you have full 1" ID pipe, not CTS pex.
1" CTS size would be around 6 gpm on high.
« Last Edit: November 22, 2018, 08:27:50 AM by RSI »
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MD20/20

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Re: Pump speed
« Reply #4 on: November 22, 2018, 08:29:35 AM »
 I went from 3/4 “ on the initial install, which at the time was the recommendation from Nature’s comfort. Beside the pipe being worthless, the return temps were too low. I got the true 1 inch ID fro RSI, and the stove is performing well. I’ll double check return temps, but reallly doubt I need to take up my newly installed Rehau. I’m heating my house which is about 7,000sq ft quite easily.
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wreckit87

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Re: Pump speed
« Reply #5 on: November 23, 2018, 06:03:41 AM »
If it measures 1" ID, that is 1-1/4" Rehau not 1". 550' round trip is 24ft of head from friction loss alone, which puts you right at 8GPM on high with a 26-99. Figure in a handful of elbows and exchanger, you're closer to 30ft of head and out of the usable curve of a 26-99, meaning 4-5 GPM. Speed 3 is going to be your only option with that pump. 7,000 sq ft if all calling at once, is likely going to flatten that in a hurry and leave you with 50-60 degree delta T. Try it on high and check delta with everything calling simultaneously; if it stays above 140 on the return at the bottom of a cycle (say your setpoints are 170-180, need to figure from the bottom AKA 170) You'll be okay, but my prediction says you'll be looking for a bigger pump. Maybe something like a B&G PL-45
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