Water Mains Calculation/Formula

[barronbathrooms]

Evening all, I am currently quoting for a refurbishment of 10 apartments which are currently offices. Each flat will need its own metered water supply to feed a direct 160 litre unvented cylinder which feeds one bathroom in each apartment. The building currently has 2 x 25mm water mains entering it. I have not tested these yet and there is no information in the specification about them just a disclaimer to say it is the responsibility of the contractor to make sure flow rate and water pressure is "suitable".
My problem is i have no idea how i can size the main. I cannot install a CWST and a booster setup as there is no provisions within the building, there is a service riser hatch i could install a manifold in but i would still need to know how to calculate this. Or do a ask Water Suppliers for an extra 6 mains(huge cost i would imagine) I have plenty of commercial experiance but the drawings and calculations were always done for us. Any of you guys/gals have any idea how much it would cost to get a M&E engineers in to supply the info.
I queried this issue with the developer as they have just finished an identical development on the same block. he informed me they "just split the 2 mains up). its a 5 storey building i don't think that 2 x 25mm water mains would be enough, again i don't know the calculations to mathematically prove my theory.
Any advice is appreciated!
Wish i listened more in my college days..

 

[AWheating]

If you want it to work as designed you probably want 10 separate mains or a 63mm main with manifolds. 25mm to first 3 floors, 32mm to others. Looking for a water pressure of 4bar and 20lpm to each flat.

If they want you to split the two existing mains then put it in writing that you recommend the above and what they want is wrong and any performance issues are not your responsibility.

Also speak to local board and see what they would be willing to give, where they want the meters etc.....

 

[barronbathrooms]

Thanks for the advice, it's been frustrating me All week that I am unsure how to size it. Still is!! I had an idea what I needed through experience but I wanted to prove it mathematically to put in a disclaimerand e-mail to them. Again thank you for your help.

 

[AWheating]

Tbh the water board won't do any maths when telling you what they advise. They use a table out a book for most jobs. You can measure the incoming supply and calculate the losses on the pipe work based on cylinder min requirements. But the supply pressure and flow are out of your hands normally.

 

[barronbathrooms]

Where would I find reference material with that I info? I can do the equations for gas but never had to worry about mains water before.

 

[Masood]

Where would I find reference material with that I info? I can do the equations for gas but never had to worry about mains water before.

The WRAS water regs guide has a table but definitive source is BS6700:1997

A couple of useful methods here:

https://www.dropbox.com/home/shared docs/pipe sizing/Water

 

[barronbathrooms]

Cheers how do I access the Dropbox?

 

[hammers4spanner]

Last few jobs I have been on where flats are involved it's all been off a manifold from the main that the water board have been involved.
sure it was off 63 mm main on last one with 25 mm going up 5 floors to top flats .
worked a treat

 

[Masood]

Cheers how do I access the Dropbox?

PM'd you

 

[barronbathrooms]

Cheers everyone, I will contact water board tomorrow see what they say, anyone have and idea what they charge for this type of work ?