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# Can someone explain head and flow..

#1
12-22-08, 05:13 AM
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Join Date: Oct 2008
Location: NYC
Posts: 433
Can someone explain head and flow..

Can someone explain head and flow.

#2
12-22-08, 06:23 AM
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Join Date: Nov 2005
Location: USA
Posts: 2,458
Flow is how fast the water moves. Usually expressed in terms of volume (gallons per minute) or velocity (feet per second).

Head is the resistance to flow and is a function of the flow speed, the diameter and length of the pipe, the roughness of the pipe interior, and other restrictions such as elbows, tees and valves. Usually expressed as feet or psi. One foot of head equals 0.433 psi. One psi equals 2.31 feet of head.

#3
12-22-08, 07:42 AM
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Join Date: Oct 2008
Location: NYC
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I understand, not in detail but I understand.

I have a couple of questions now....

I have 8 - 1/2" loops about 200 feet each inside a concrete slab running to a manifold that is fed with a 1" return and supply line.
I want to be able to heat the area with the most amount of heat and as quick as possible.

I am looking for a Taco pump to push the water through, I was considering an 011 or 013 with ifc of course, can someone tell me if I'm on the correct track without going into complex calculations. Can I have overkill on the pump? All help is appreciated.

#4
12-22-08, 07:44 PM
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Join Date: Nov 2005
Location: USA
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OK, no complex calculations. The pumps are huge overkill.

You should first determine the desired (or needed, since you already have piping installed) temperature drop of the circuit to satisfy the heating load, which dictates the flow rate, which dictates the resistance in the specified piping, which dictates the pump size.

There, no math!

And of course you don't want the floor surface temp more than 85F or it feels uncomfortable.

And of course a high-mass radiant system like this typically takes a day or two to stabilize, and because of the high mass is inherently very slow to respond to changing heat load.

So "most" and "fast" are basically the opposite of what the floor can do.

#5
12-23-08, 10:01 AM
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Join Date: Oct 2008
Location: NYC
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The only thing I have is the heat loss calculation and that is about 40,000 btu. It probably souns alot but that is what it is. There are alot of windows and it is facing the water.

#6
12-23-08, 11:50 AM
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Join Date: Mar 2006
Location: Wet side of Washington state.
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You're screwed. Two hundred feet is insanely long for 1/2 inch tubing, at least twice as long as would normally be allowed for 1/2 inch tubing.

Furthermore, one inch supply is way undersized to feed eight loops, you should have nothing smaller than 1-1/2 to feed eight 1/2 inch loops.

Xiphias gave you the straight scoop on masonry slabs, they heat and cool slowly. How fast it CAN warm up is dependent on several factors, including the size and spacing of the tubing in the slab.

With those extremely long loops of undersized tubing you are going to need a high-head pump to get your required flow. And because the tubing is so small it will take a high flow to keep from having too high a temperature differential from the loop inlet to the loop outlet. The high flow rate will eventually cause erosion in the tubing and that will lead to leaks.

Your system has fatal design flaws. You may be able to get it to work to some degree but it will never work properly.

Sorry.

#7
12-23-08, 02:06 PM
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Join Date: Jan 2006
Location: San Jose
Posts: 2,175
Your 200' loops of 1/2" are fine (with about 300 to 330' being the maximum length you can go). A 1" supply and return to the manifolds has a capacity of 80 MBH which is more than enough for your needs.

An in slab radiant system is not nor ever can be what anyone would describe as a responsive form of heating. It has very high mass so the best way for it to run is steady. It won't lose heat very fast but it can't gain heat very fast. Kind of like an oil tanker, it takes a long time to get up to speed and a long time to stop.

Set the t-stat and forget it or look to some other forms of supplemental heat like an air handler or loss mass rads.

#8
12-23-08, 02:37 PM
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Join Date: Oct 2008
Location: NYC
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I had to run downstairs and look at the manifold. I havent looked at it for over 6 months. It's actually 5 loops and from what I remember they are spaced at 6". I poured the slab maybe 18 months ago so I forgot. ALso, I remember talking to the uponor guy about the lengths and he had told me that 200 feet would be fine. So it is 5 loops hooked up o the Uponor manifold. Now back to the pump.....any suggestions?

#9
12-23-08, 03:06 PM
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Join Date: Jan 2006
Location: San Jose
Posts: 2,175
Yes 200' is the norm for 1/2" no issue there...

Now back to the pump.....any suggestions?
Yeah start typing and tell us a heck of a lot more than what you have posted so far because we really have nothing to go on.

When you say "the" pump should we assume you are doing RFH with just one pump? What have you got for a boiler? How is it piped? What pump(s) are currently being used? Who installed everything? Was it ever working right?

The biggest challenge for us in trying to help you is actually understanding what is the actual issue.

#10
12-25-08, 02:36 PM
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Join Date: Oct 2008
Location: NYC
Posts: 433
I am remodeling my house and have added a new kitchen(40k btu heat loss) along with a new master bedroom.

I have a heat loss calculation of 400k btu.

I have a large 300k btu burnham now that I will be replacing with a 2 boiler buderus system.

I have 2 seperate zones of radiant floor heat and at least 6 zones of conventional cast iron radiator heating

I will be using a primary/secondary boiler piping system.