Need second opinion on this matter 1

[Harry2k14]

I was calculating the pipe sizes of a down-feed water supply system of a 3 storey-commercial building and I came up with this sizes:

For a total probable demand = 47.56 gpm
2 1/2 inch distribution pipe
1 1/2 inch branch pipe @ 2nd flr.
2 inch branch pipe @ ground flr.

For a total probable demand = 32 gpm
2 inch distribution pipe
1 1/2 inch branch pipe

Pipes used are G.I pipes.

And another question is, can the gravity tank supply the 3rd floor fixtures?

Are those pipe sizes calculated even realistic? or did I over calculated it?
Calculation is based on the National Plumbing Code Handbook (1957) by Manas.

Thank you.

 

[Ron]

Why are you using such an old reference?

Unless the gravity tank is above the level of the third floor, it will not supply. You will have to pump.

Your pipe sizes do not seem standard, at least for my area. What area are you working in?

 

[bimr]

You would never get enough pressure from a gravity tank in or on top of the 3rd floor. You probably do not need a tank unless the water supply is not adequate or reliable.

Would expect that you would have booster pumps on the first floor.

The plumbing code (and the plumbing fixtures) have changed since 1957.

 

[bridgebuster]

One thing hasn't changed: $#!+ still flows downhill.

 

[Harry2k14]

Tnx guys.
@RON. I used the graph provided by the code which is also being used in other book references. I thought its easier calculation, am I wrong instead? the graph im talking about is the one relating to pressure loss per 100 ft. pipe length and the total water demand. As the rule of thumb dictates that 1 in and 1/2 in is being used in residential only, so therefore in commercial buildings, such pipe size may increase? im kind of thinking a 2 1/2 is no longer economical, that is based on calculation but in experience I dont have any idea if its too much or adequate.

@BIMR. The thing that I didnt use booster pump is that for economical reason, booster pump consumes too much energy, maintenance cost, and the lot area is very limited, and would be useless if the power gone off.

@BRIDGEBUSTER. That is why its called gravity. Lol

Are there any calculation methods that you would suggest then?

Thanks in advance

 

[jgailla]

You need to get a copy of whatever plumbing code is in use in your area, which is probably the latest International Plumbing Code if you are in the US.
Your local building/code official can tell you the governing code.
Whether you need pumps is dependent on your system pressure. It is possible but unlikely that you can get adequate pressure at the third story.

 

[msquared48]

bridgebuster:

Not if there is a plug in the line and gas starts building...

Mike McCann, PE, SE (WA)

 

[LittleInch]

Harry,

for anyone to have an idea if you've got it right you have only supplied one of the four elements required - flow rate. Why two demands?

We also need:
total pipe length and equivalent length of your fittings - "commercial building" is very vague and could be a small office block or a large warehouse
head difference from top of lowest water level in your tank to the output point (tap / connection)on each floor 3rd / 2nd / 1st or ground flr)
Thickness or grade of your GI

Also is there any minimum or maximum pressure requirement on your 3rd floor / ground floor to see if it could supply the water or not.

I'm assuming ground floor = 1st floor?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[boo1]

School or owner question?

 

[bridgebuster]

Mike,

Good reply! First I wasn't going to post it, then the voice in my head said "are you losing your nerve? Post it before Mike does". [flush]

Funny thing, I was at a meeting last week about renovating a sewage treating plant, owned by a Catholic church. Some one said "Bishop, this plant has enough capacity to flush 17 toilets for 24 hours straight every day". His reply "That's more than I need to know."

 

[Harry2k14]

jgailla:
I'll try to find one, and looking through the web for national codes.

boo1:
Both

littleinch:
Yes, there are two demands because I separated the line from the kitchen sinks (comprised of a foodcourt) from the line from the comfort rooms.

1.)eq. lengths = 241.186 ft. and min.pressure from tank 4.232 psi ; head difference = 21.325 ft.
2.)eq. lengths = 130.387 ft. and min.pressure from tank 2.822 psi ; head difference = 21.325 ft.

Yes sir, ground floor = 1st floor.

 

[Ron]

Harry2k14....the internet is not the place to look to determine the applicability of a certain code....that is done by your local building department or other local jurisdiction. Find out what is applicable in your area and then apply it.

The chart you are using for head loss is probably a standard one. Validate it by other means, such as Cameron's Hydraulic Data (also an old reference, but one that stands the test of time). If you are considering PVC or other piping, the head loss tables for iron/steel pipes do not apply.

 

[bimr]

Here is a presentation on the Philippines plumbing code. I assume that is where you are located.

http://www.slideshare.net/Liguidliguid/presentation-plumbing

You can download the plumbing code here:

http://www.fileswap.com/dl/3ve10YVfBD/80960884

The pressure on the third floor will be marginal, but should work as long as you do not have the Sloan type flush valves. The flush valves need pressure in order for the valves to close. You probably do not have those type of valves anyway.

You can size the water supply piping from the pumps with a maximum velocity of 8 ft/sec. The distribution piping from the tank should be sized for 3-4 ft/sec.