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Author Topic: loop question  (Read 2772 times)

willieG

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loop question
« on: June 28, 2017, 07:00:06 PM »

lets say you have a circuit of 10 loop and you decide to add another ..all loops on the same header and all loops the same length and size, will this added loop cause more head or only take away from the flow on the other loops?
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NaturallyAspirated

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Re: loop question
« Reply #1 on: June 28, 2017, 07:19:39 PM »

lets say you have a circuit of 10 loop and you decide to add another ..all loops on the same header and all loops the same length and size, will this added loop cause more head or only take away from the flow on the other loops?
The head loss across the primary header entry and exit will remain the same, the gpm per loop will change (decrease) and thus change your btu output per loop.
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RSI

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Re: loop question
« Reply #2 on: June 28, 2017, 07:28:20 PM »

Head pressure and flow on each circuit will drop. Overall on the entire system flow will increase some and head pressure drop. (You are just shifting a bit on the flow curve of the pump)
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willieG

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Re: loop question
« Reply #3 on: June 28, 2017, 07:59:58 PM »

ok now some major thinking on you guys now....instead of heat, think cool water, lots of it

a large chilling unit with a 2 inch centrifugal pump driving it, feeding into a three inch header with (now) 14 loops of 5/8 plastic pipe of 600 feet per loop. about 30 psi on the "out" of the pump and only 2 psi on the return at the pump side. the unit is working well and water must be moving quickly, the cooling area of these loops is only 8 feet wide and 2 feet high (like a plastic tepee, in full sun) cooling water is entering at 40 degrees f and returning at no noticeable change, tent is 14 degrees cooler that outside of tent.  now the owner is thinking of adding another 28 loops, so I  guess mu question would be if there will be enough pressure on the return side as to not cause cavitation at the pump?
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RSI

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Re: loop question
« Reply #4 on: June 28, 2017, 10:12:48 PM »

Would need to see the pump curve but I would think the inlet pressure would drop a lot and the return would go up. I would guess each loop is running about 5 gpm. (estimating based on 3/4" pex which should be close to the same ID)
That is 70 GPM for the 14 loops.
To get a similar flow, you would need a pump capable of 210 GPM at close to 70' of head pressure.

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willieG

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Re: loop question
« Reply #5 on: June 29, 2017, 06:41:07 PM »

 I think we would be happy with 2.5 or 3 gpm, we should have it all hooked up by early next week, I wont know the true gpm but I will post pressures and inlet and return temps

there is a lot of pipe and each loop is only about 3.5 wide so there are sharp  90's on the ends of all the loops.  With the one set of loops running the pump has settled at 40 psi leaving the pump and only 2 psi at the return (gauge is three feet from suction of pump)
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RSI

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Re: loop question
« Reply #6 on: June 29, 2017, 10:27:55 PM »

Is it possible to find the flow curve for the pump?
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willieG

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Re: loop question
« Reply #7 on: June 30, 2017, 02:31:40 AM »

Is it possible to find the flow curve for the pump?

I will see if I can find any numbers on it today, the chiller came in as a rental unit and is painted over but maybe they didn't paint the name plate
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willieG

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Re: loop question
« Reply #8 on: June 30, 2017, 05:35:33 PM »

I didn't get the pump info but we have our three main headers and all our pipe in the system we added enough water to keep the pressure up a little to keep the system full  and allow a few air bubbles still in the system to hopefully settle in the top of the cooler where we can drain them off.

anyway,, all loops are moving water as you can see some small air bubbles moving through the 3 inch semi clear return  lines from each loop. best guess is water is moving in these hoses 2.5 to 3 feet a second. thee inlet pressure at the pump is 30 and the pressure at  the return side  of the pump is about 15. if the pump  is shut off pressures equal on each side 
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