Supply & Return header sizing

Shawn Forlenza

I was trying to get some info on making sure my supply and return mains for our radiant job are sized adequately.Does anyone have a program or calculation to figured what each size pipe will handle? I know my circs are good, and I have my GPM & headloss figured, but I'm questioning using 1" mains as opposed to 3/4. Any experience would be appreciated.

Brad White_9

Typical Principles

No chart do I have, but typically, when sizing headers, you strive for minimal head loss compared to the head losses within the outfeeding/incoming zone branches.

The idea is that regardless of flow rate combinations from any zone or group of zones, the headers shall not see any appreciable pressure change. This is to minimize the effect of one zone or groups of zones on any others.

As a place to start, I use no less than 1" in any header, even if I am handling only two 1/2" lines.

My other rule of thumb is to size the header for the sum of cross-sectional (transverse) areas of all connecting branches.

Example: Say you have five (5) 1/2" branches and two (2) 3/4" branches at sum areas of 1.27 Sq. inches and 1.032 Sq. inches respectively. Total is 2.302 Sq. inches. A 1-1/2" line would be 1.831 Sq. inches (barely too small) so I would use a 2" pipe at 3.17 Sq. inches to be conservative and cover unknowns, future expansion or adjustments to flow in any zone. (Short pipe, buy it once.)

Another check-figure is to size the header for at least one size larger than the cumulative flow rate would indicate.

In the above "transverse area" method, say the sum of potential flows would be 10 GPM. A 1-1/4" pipe would be indicated for that flow rate. Go up a size and you are at 1-1/2". My area method would trump this so I would tend toward the 2" size.

In either case, the pressure drop rate of 10 GPM in 2 inch pipe would be less than 0.30 feet per 100 feet, while my "branch rate" may be in the 2.4 to 3.5 feet per 100 feet rate.

If you used 1-1/2" size your PD rate would more than triple to 1.08 feet per 100 feet of pipe. The rule of the square is a good thing!

All of these are based on Type L copper tubing by the way.

Unknown

Mains Made Easy

1st Size your mains for no noise:

1/2=1.5GPM
3/4=4.0GPM
1=8GPM
1-1/4=14GPM
1-1/2=22GPM
Find an easy chart for this and for zoning at
http://fhaspapp.ittind.com/literature/files/810.pdf

2nd - Varify that the size and length you are using will not exceed your TDH on your circs. Find a sizing chart for this at: http://www.bellgossett.com/BG-SystemSyzer.asp

Hop this helps

Steve

Shawn Forlenza

Thank You both for the input , but if I could clarify a bit. The system is in floor radiant, one zone is only 1.2 GPM w/ 1.6 ft head loss. the remainder of the zones are similiar. This zone has a manifold with 5 equal loops.Do your formulas still work?

Brad White_9

Formulas

always work! (That is why we call them that )


Check them out with your own parameters and see what you get. If the flow rates per branch do not change (ie: do not have telstats or control valves) you may not need that last "go up a size" urge if the flow is just a little bit over.

Otherwise, a size up is cheap insurance.

Unknown

3/4inch

SO if you follow my rules, run 3/4 copper. Every 100 feet will only add .82TDH to your friction.

Empire_2

Hi Shawn

Check out B&G web sight and order the circuit setter (slide calculator). Everything you need to accurately design and implement your Ideas. They also have a software program that I think is free. Let me know what you find.

PS Brad: I think you would like this tool to. I am almost positive it is free for the asking.:-)

Mike T.

Ted_9

info

As a side note here, Viega's radiant wiz and I think Wirsbo's have this in there program.

Massachusetts

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Weezbo

here is a thought..

you can size pipes accordingly buh..if you can go Large Burger king kinda deal...you have less wear on the pipe and it also helps the circs out a bit. uping the pipe size can actually be cost effective:)