Pressure balancing

[vij36]

We have a 2 floors building and another 4 new floors are being constructed.
We would like to have a booster pump at the second floor.

The 7th floor is at the height of 24 meters. Here the hot water tank is being proposed.
We are evaluating the pump options.

The booster pump is planned to setup at 2nd floor.

First options to have top 4 floors through booster and the bottom floors through gravity.
The booster pump is 1.5 HP with 7500 LPH. Pressure is 2.2 - 3.6 Kg/ cm2

Second option is all floors are through booster with pressure 2.4 - 4.4 kg/ cm2

Here will there by any pressure differences arise for hot water and cold water ? How to handle both the pressures at the wall mixer ? Are there any standard calculations or best practices available?

Thanks,

 

[LittleInch]

Can you draw this in section so we can understand your options better.

What do you mean by "hot water tank"?? AN open top tank to deliver hot water via a tank on the roof? Or some sort of pressurised tank?

Whatever you do, having cold and hot water at the same pressure is required to allow units to work and prevent back flow.

Also be aware that the min pressure on the top floor probably needs to be 1kg/cm2 to allow control of flow, but pressure more than 3 on the ground floor might be too high so you might need some pressure regulators on each floor.

How many apartments etc on each floor?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MJCronin]

Any plans to put a swimming pool on the top floor ?

MJCronin
Sr. Process Engineer

 

[vij36]

Yes you are right, the hot water tank is pressurized.

It is a dormitory kind of building.
There are about 9 rooms on each floor with about 30 occupants each.

Gravity pressure from overhead tank expected (in kg/cm2)
Ground Floor - 2.73
First Floor - 2.39
Second Floor - 2.06
Third Floor - 1.72
Fourth Floor - 1.38
Fifth Floor - 0.98
Sixth Floor - 0.64
Terrace

hot water for Ground floor, 1st floor and 2nd floor are planned to have through gravity.
third through sixth are using booster.

Attached the SLD.

 

[chicopee]

Print the layout of your ACAD file in CutePDF so that everyone attempting to answer your OP can open it up. Not everyone who is attempting to answer has a copy of your ACAD version but most will have PDF.

 

[vij36]

Thanks for the input.

Attached pdf version.

No plan to have swimming pool

 

[vij36]

any inputs please ...

 

[LittleInch]

I still don't understand what is going on here.

What is the turquoise line?
Why is it connecting to the cold water line from the roof tank?
What is this intermediate thing
Where is your booster pump?

Where you have large changes in flow rate throughout the day like a dormitory, a large water tank on the roof is usual as the change in flow can be accommodated more easily than a wholly pumped system.

But for that many users, you really need some good design work here.

You've got nearly 2000 people here. They won't be happy if the hot water runs out every morning and evening.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MJCronin]

Wow .... I read 11+ meters between floors ....Is that correct ?

Its gonna look like a cathedral in this dormitory.... Will the bunk beds be 6 - 8 tiers high ?

... and you are going to put all of this massive, flexible structure on top of an existing structure ?

Fortunately, this building will not be constructed in a seismic area ... right ?



MJCronin
Sr. Process Engineer

 

[vij36]

What is the turquoise line?

Hot water inlet to Hydro Pneumatic pump.

Why is it connecting to the cold water line from the roof tank?

This is a drafter's mistake. Please refer updated dwg attached.

Where is your booster pump?

It is located one floor above ground floor on the conical roof. Box with green border lines.

You've got nearly 2000 people here

Sorry, it is 30 persons per floor. So around 200 persons entire 7 floors.

Wow .... I read 11+ meters between floors ....Is that correct ?

The top floor is at 24 meters (78 feet) height.

... and you are going to put all of this massive, flexible structure on top of an existing structure ?

The structure above the conical roof is detached from conical roof. Because of place constraints it is done like this. Initially the idea was to flatten that conical roof. But that equipment cost is much higher. So a structure is planned above this conical roof with support from heavy columns and beams.

yeah you are right. the area does not come under earth quake sensitive.

Now the thing to find out is if hot water supply for all 7 floors is through booster pump then what will be the hot water pressure at ground floor, 1st and 2nd floor. will the gravity pressure adds to pneumatic pressure and overrides the cold water pressure. Please advice.

There are two provisions for hot water. One is through gravity and other is through pneumatic. In case of power cutoff issues change over can happen to gravity line.

 

[LittleInch]

What I see here is that you have a top floor tank fed by some means ( the dark blue line)

Then I can only assume that the feed from that tank to the hot water system doesn't normally flow, only when water in is less than water out fot he hot water or cold water systems.

Normally the pressure in the hot water system comes from your pump on the 2nd floor.

So the hot water pressure will be whatever pressure comes out of the hot water system PLUS the impact of gravity.

Now what that pressure is you don't say or how you plan to control it.

The problem is that with a PRV on the cold water supply, the cold watr supply pressure is fixed by gravity from the roof tank and will be those pressures you listed a couple of posts ago.

This could be quite a lot lower than the hot water pressure and or the hot water pressure could go up and down depending on the number of users / flow variations.

to keep the two pressures more or less the same I would remove the PRV and install an NRV on dark blue line to stop reverse flow in this line. Then if you pump fails or the water supply fails, the water will flow from the roof tank for both hot and cold water at the same pressure.

The pressure though will be quite a lot higher in the ground floor than the top floor. 0.64 bar isn't a lot for normal domestic fixtures so the flow up there could be quite low when used from the tank. however if on pump operation you set that to say 1.5 bar, then the pressure on the ground floor would be well about 4 bar.

I think you should have Pressure regulating valves on all the floor set at say 1.5 bar on both hot and cold supply lines to make the distribution of water more even otherwise those on the ground floor will simply "steal" all the water to the detriment of the top floor. They won't be happy.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MJCronin]

Mmmmmm........ " Because of place constraints it is done like this" ......

Where will this building be located ????/

MJCronin
Sr. Process Engineer

 

[vij36]

.however if on pump operation you set that to say 1.5 bar, then the pressure on the ground floor would be well about 4 bar.

Dear sir, I really would like to know how this estimate is made.

I was going through some calculations in theweb.
Link

Are these formulae can be of any help.

 

[LittleInch]

I simply added the positive pressure at the hot water system to your calculations about static pressure.

Now you've not mentioned anything about frictional losses before now so the link is interesting, but ins this case not of benefit to us as we know ZERO about your frictional losses 9 water flow, pipe size etc.

In any case with a multi layer building and a single pipe, the calculation gets complex if water is being taken off at each floor.

So in reality the flowing pressure on the ground floor, if you pump delivers 1,5 barg at the roof top would be less than 4 bar due to frictional losses. They could be anything from say 0.5 bar to 3.5 bar.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.