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Author Topic: Just wanted to say thanks, project complete  (Read 5607 times)

E Yoder

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Re: Just wanted to say thanks, project complete
« Reply #15 on: June 07, 2018, 01:22:44 PM »

Yeah, I think you're right, one feed, through both loops, two returns.
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E Yoder

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Re: Just wanted to say thanks, project complete
« Reply #16 on: June 07, 2018, 07:29:26 PM »



Yeah, should have done the bucket test, don't guess flow can be calculated from head pressure on a gauge then.


There are guys smarter than me on this but I think you would need a gauge on each side of the pump. Then it should be accurate.
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RSI

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Re: Just wanted to say thanks, project complete
« Reply #17 on: June 07, 2018, 07:46:16 PM »

I don't think a second pressure gauge would do any good. Just have to check with pump off and then with it running.
I am guessing when you are at such a low pressure, it will be hard to find flow that way.

With only 27' of pipe, you should have pretty good flow rate. I just wouldn't have guessed that much.
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E Yoder

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Re: Just wanted to say thanks, project complete
« Reply #18 on: June 07, 2018, 07:51:50 PM »

I guess the inlet would be negative pressure, outlet would be positive, the difference should be where you land on the pump curve?
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greasemonkoid

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Re: Just wanted to say thanks, project complete
« Reply #19 on: June 07, 2018, 10:51:44 PM »

For your entertainment:
 Units = PSI

Static head pressure - 2.1


Circulator pump low, both loops - 2.6

Circulator pump med, both loops - 2.8

Circulator pump high, both loops - 3.0

Circulator pump low, circulation loop only - 3.0

Circulator pump med, circulation loop only - 3.7

Circulator pump high, circulation loop only - 4.0

Both pumps low, both loops - 3.4

Both pumps high, both loops - 4.5

Both pumps low, circulation loop only - 4.5

Both pumps high, circulation loop only - 6.5



So the question is - at what gpm does the static pressure of 2.1psi return to 0? Might be where that extra gauge comes into play.

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RSI

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Re: Just wanted to say thanks, project complete
« Reply #20 on: June 07, 2018, 11:21:57 PM »

I am confused. Isn't the pressure sensor after the pump? If so, why would it ever return to 0? If it is 2.1 psi then that means the gauge is a little under 5' from the top of the water in the boiler.

I didn't look at the pics enough to figure out exactly what is going on there. What valves were open for the pressures listed above? It sounds like the pumps are working at least somewhat in parallel from those numbers.
Where is the pressure sensor located?
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E Yoder

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Re: Just wanted to say thanks, project complete
« Reply #21 on: June 08, 2018, 05:17:55 AM »

With having two returns I can see how the pressure wouldn't climb as quickly. I think (and I'm not super smart on these things) that having the pump halfway around the loop from the expansion point (point of no pressure change), then the majority of the restriction (when both returns are being used) is upstream before the pump and not showing up on the gauge. It's moving the loop mostly by suction.
I realize some of the scenarios listed were with one return and the pressure climbs more quickly on higher speeds.
If the pump was at the supply outlet on the stove one gauge on the outlet would be fairly accurate (I think). I wonder if you subtracted the static pressure off the total, then doubled the number left  to account for the drag of the supply line, you could be fairly close to an accurate number for accounting for total pressure drop for the whole loop. Convert to feet of head and you could find gpm on a pump curve.
I'm probably off by a mile.. :)
« Last Edit: June 08, 2018, 05:25:00 AM by E Yoder »
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greasemonkoid

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Re: Just wanted to say thanks, project complete
« Reply #22 on: June 08, 2018, 06:28:03 AM »

Mentioning a flow rate which equals zero pressure is in regard to the feed line to the pump - the pressure on that line only. At 2.1psi you'll have,  up until a certain flow rate, positive pressure. Yes? Beyond that flow rate the inlet pressure goes from positive to negative pressure, then you have suction and the pump is basically pushing uphill at that point.

The gauge is on the heat exchanger loop with the crossover line connected, the valves are closed on the exit of the exchanger loop manifold end, so nothing actually flows through there, but pressures can act on the gauge. This scenario is for using the circulation loop only.

Both loops typically remain open and the circulator loop pump runs 24/7, the heat exchanger loop pump runs about every several hours to reheat the hot water tank.
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E Yoder

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Re: Just wanted to say thanks, project complete
« Reply #23 on: June 08, 2018, 06:29:07 AM »

Using the method I described above using one return I come out around 5.5 - 6 gpm, single pump low speed.
But I could be way off.
Edit: I was writing this during your response so it may not make sense. You're right, on lower speeds the inlet of the pump would possibly still have positive pressure, but not much.
« Last Edit: June 08, 2018, 08:01:47 AM by E Yoder »
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RSI

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Re: Just wanted to say thanks, project complete
« Reply #24 on: June 08, 2018, 07:56:41 AM »

The pressure should never drop to 0 on the inlet line. If it does or goes negative then you will have short pump life. (gravity needs to supply more GPM to the pump than you are pumping)
I was thinking about the pump mounted at the boiler before when I said no return sensor would be needed where there would be no pressure drop.
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E Yoder

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Re: Just wanted to say thanks, project complete
« Reply #25 on: June 08, 2018, 12:17:54 PM »

Makes sense.
My guess factoring in the pressure drop of the single incoming line using one return line you'd be at 5.5 or 6 gpm, two return lines at 6.5 or 7 gpm. Low speed on a 15-58. A bucket test at the height of the fill/overflow pipe would be interesting!
The short loop really helps get flow rates up and reduce electric consumption. I cringe when folks talk of circulating 300+' and wonder why the pipe costs so much and they have to burn a lot of juice keeping that loop turning.
BTW, thanks for posting this stuff greasemonkoid.
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greasemonkoid

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Re: Just wanted to say thanks, project complete
« Reply #26 on: June 08, 2018, 03:22:36 PM »

You're quite welcome. Thank you guys for tossing around ideas, it's great to hear what the gurus have to say.  :)
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