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#1
01-20-14, 09:24 AM
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Join Date: Nov 2013
Location: USA
Posts: 35

I need a pump recommendation…but I’m ignorant when it comes to calculating head.

I need to circulate water from an open 75 gallon tank. The loop is approximately 300’ of 3/4" poly pipe. Approximately 10’ of the loop is vertical.

#2
01-20-14, 10:40 AM
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Join Date: Oct 2006
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Posts: 23,539
This really doesn't 'fit' cleanly into the heating forum.

In addition to the information that you have given, you also will need to know the GPM (gallons per minute) that you are pumping. The friction of the water moving through the pipe also counts as 'head' and this varies with flow.

Being an 'open' system, not only the 10' vertical part, but any additional 'rise' in elevation needs to be accounted for as well.

Unless I'm misreading something here... just because the tank itself is open doesn't necessarily qualify that the 'loop' is 'open'. If you are only pumping water around a loop, and both ends of the tubing are submerged in the media you are pumping, then it's not an 'open' system technically.

Why not explain to us what it is exactly that you want to accomplish?

#3
01-20-14, 11:27 AM
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Join Date: Nov 2013
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Thanks Trooper.
Yeah, not really a home heating/boiler question.
The concept is to warm an insulated outdoor plumbing trough using the warm water in the open tank. I’m just trying to keep the temperature in the trough above freezing.

Both ends of the loop are indeed submerged in the tank...
The outlet is 3” from the bottom of the tank…
The tank’s outlet is 30” above the floor. The pump can be installed below the tank.
Loop supply and return runs 10’ vertically, remainder of the loop horizontal, approx 280’.
Flow can be as low as 3 gpm.

#4
01-20-14, 01:07 PM
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Have you considered an electric stock tank heater? Farmers use them to keep livestock tanks open from ice.

I'm having a little trouble visualizing what you are trying to do. What is a "plumbing trough"? What is the source of the hot water going to be that you will pump? Can you post a sketch of the proposed system?

#5
01-20-14, 01:23 PM
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How warm is the water in the tank?

How quickly will it be reheated?

I don't think that 3 GPM is going to do it for you because once that warm water starts heading down that tubing it will start to cool. I'll bet it will be useless cold by the time it gets half way round that loop.

At 3 GPM on 3/4" poly tubing you are looking at about 2-3 feet of head per 100'.

The 10' rise and fall is irrelevant, they cancel each other out... that's the beauty of a closed system.

The head goes up raised to the power of 1.73, it's not linear at all, so if you try to pump say 6 GPM, it won't be double the head at 3 GPM.

more later..................

#6
01-20-14, 02:31 PM
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Join Date: Nov 2013
Location: USA
Posts: 35

Gilmorrie,

As Trooper surmised, this is not a home heating question. It’s for my car wash business.

High and low pressure plumbing (hoses and tubing) from the equipment room to the car wash stalls is routed through the flat roof into the trough. The trough is 12”wide x 10”tall x 100’ long, insulated with poly-iso on the inside.

In freezing weather the hoses need protection and my heat solutions seems to fail at the most inconvenient time. So…I’m brainstorming for a different solution. Hot(warm) water heat!!!

The water tank is maintained at approx 110F by a large RayPak tube-fin boiler. Rather than purchase a small electric water heater and pump to circulate the loop, I thought I might circulate the water from the already heated tank.

The tank has an unused 1” outlet near the bottom of the tank. I envision a 1” brass nipple to a pump flange > pump > flange > 1” x 3/4” hose barb > 3/4" poly pipe.

Trooper...
I was just guessing at the flow rate.
I suppose it could be as much as 10 to 12 gpm...just to make sure it warms the entire length of the trough. BTW, the equipment room is in the middle with 4 stalls on either side so the loop would be double pass.

(I'm hoping a 007 would fill the bill)

#7
01-20-14, 03:28 PM
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I suppose it could be as much as 10 to 12 gpm
I don't think you can get that much water through 300' of 3/4" tubing without HUGE head losses, meaning HUGE pump, and very fast flow in that size pipe, maybe 12-15 FPS. You'll be tearing plastic off the inside of the pipe!

At 9.5 GPM you're at about 17.5' head per 100 feet... times 3... more than 50' of head, ain't gonna happen.

Step up to 1" and you're down to 5.4' per 100 ... times 3 ... around 16' ... MIGHT be workable, but not for a 007.

Up to 1-1/4" and it's about 1.5' per 100, 007 would be up to the task.

Here's the thing though... let's pull a number out of the hat and say that with 110° water running through that pipe that you MIGHT get about ohhhhh... let's use a SWAG of 100 BTUH per foot of heat out of it. Times that by 300' and you are looking at 30K BTUH.

I'm too foggy right now to do all the ciphering and figure out how cold the water coming back to the tank will be, but in order to maintain the tank at 110F that boiler will have to be able to put 30K BTUH back into the tank in order to maintain the temperature. And this is WITHOUT anyone washing their cars!

That 100 BTUH is a GUESS, could be more, probably less, have no real way of knowing.

I dunno if what you want to do is feasible or not... I'm thinking not... the amount of heat you get out of that tubing might not do what you want it to do, and the fuel to do it even if it could might well be astronomical.

#8
01-20-14, 03:31 PM
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Rather than purchase a small electric water heater and pump to circulate the loop

Electric water heaters run 4500-5000 watt elements. That's only about 15K BTUH. After a few minutes of circulating, the tank would be cold and no way would those little electric elements be able to keep it at temperature.

#9
01-20-14, 03:59 PM
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Join Date: Nov 2013
Location: USA
Posts: 35
Thanks for the "bring me back to reality" Trooper.

I've just found a "better" heat tape solution...and for not much more than I paid for the old stuff.

Too bad though...I really wanted the hot water loop to work.

Best regards

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