water supply booster pump 1

[Neel.mech]

hello everyone ,

i have been trying to find the booster pump discharge for a township of villas , i have tried using Hunters method in IPC .
the capacity says to be 208 gpm .Now consultancy is not satisfied with the pump size , they are recommending to recalculate as it is very high as per them.
do i have to consider any factors while considering discharge as calculation is as per individual fittings discharge. Can you guys please help me out to resolve this issue .
i have checked previous calculation for the same , but i don't have an idea how my ex colleagues could could settle the discharge by 35 gpm .

please give me your advises , am i right or wrong ?.

Basil

 

[Neel.mech]

please find the attachment.

 

[PEDARRIN2]

Hunter's curve was designed to be used for a single building, not for a group of buildings.

The probability of use in a single building will not replicate easily over several buildings.

There are other methods for sizing this type of distribution, typically available to the civil engineer responsible.

 

[bimr]

You have to estimate the daily flow to each villa. Then add up the number of villas to come up with a total average flow per day for the community.

You then estimate the peak hourly flow. There are curves in textbooks where historical data has been used to develop peak hourly flows based on the size of the population. A large population has a peak hourly flow of 3-4 times the average daily flow while a small development has a peak hourly flow 7-8 times the average daily flow.

 

[Neel.mech]

Dear all ,
thanks for all your comments. But when i try to add each villa of 9 gpm at least, i have around 40 villas , that gives me a even bigger value of 360 gpm.
can guys please you suggest me a method so that i can submit calculations .how can i calculate demand for each villa ? as fixture method is not working here.

thank you

basil

 

[PEDARRIN2]

I do not know if you have flush valve toilets or flush tank toilets, but if you have the former, 9 gpm is not going to do it. 25 gpm is more appropriate.

But if you have calculated each villa at 9 gpm and have 40 villas, you could have an instantaneous load of 360 gpm. But I would not size your pump for this, because if your peak load only lasted 1 minute per hour, your pump would operate for one minute every hour which is far too short of a time and soon need maintenance.

Bimr stated a peak hourly flow of 7-8 times - so that would be ~72 gallons per hour or 1.6 gallons per minute.

If I was sizing a pump for a single building, I would likely size the pump for 25 or 50 gpm, to take into account two flush valves operating simultaneously. Sizing a pump for multiple buildings is different because there is typically storage involved.

In these situations, and I would want someone from a civil background to verify (or correct me), you calculate a daily consumption based on the quantity and type of buildings. Say it is 1,000 gallons per day. Then you provide a storage tank of 500 gallons, which would handle half a day's requirement. Then you size a pump that will refill the tank when it gets to 100 gallons and take about 20 minutes to refill. Your pump would be 20 gpm (400 gallons/20 minutes). Your pump then only runs twice a day for twenty minutes and you have supplied water to your villa.

These numbers are all hypothetical, but the approach is correct.

It is a similar approach to how storage water heaters are sized, a balance between generation and storage.

The tank would have to be elevated to provide enough static when it is at its lowest volume to provide adequate pressure for flush valves, taking into account any pressure losses.

 

[jgailla]

100 gallons per person per day times 3.5 people per villa times 40 villas is 14000 gallons per day average use.
14000/24/60=~10 gallons per minute. With a peaking factor of 4, that's a design flow of 40 gpm.
bimr's right, though. Something this small should use a higher peaking factor. I've never designed anything this small.
Usually you have a fire flow for a community of this size which will be well above the domestic flow.

 

[Neel.mech]

thanks everybody for all your advises, i appreciate u all . so it should be safe to go for 40- 50 gpm pump ?
so i can go for a smaller pump with by ignoring the other methods.

 

[jgailla]

basilbn,
You must have documented calculations based on your state or local code.
No, it's not "safe" to go for a 40-50 gpm pump.
If your local code is obscure, you can use an Army Corps Technical Manual (now know as Whole Building Design Guides).
Since you have such a small development, you may want to look at the International Plumbing Code and see their approach for generating demand for buildings.
PEDARRIN2 is on the right track with the storage tank. That approach will likely be cheaper than providing a larger pump.

 

[bimr]

One problem is that we do not know where you are located. In the developed world, water consumption is much higher than in undeveloped countries. Urban areas also have higher water use than rural areas. How big are these villas? Is this permanent housing or vacation villas?

Please provide a better description of your project.

 

[PEDARRIN2]

He was using Hunter's method in the IPC which will help him size individual building gpm, but will not tell him gpd.

I agree with using the Whole Building Design Guide or even EPA guidance on design of small public ground water systems, which gives general gpd for various buildings.

 

[Neel.mech]

Thank you , Every one for all your replies.
.
Bimr , my project is in Saudi Arabia , there we have reverse osmosis plant installed for water supply .In Saudi , all standards are same as american standards.
so this is an industrial area, for a petroleum refinery . so all these are accommodations for staff.
i believe Saudi is a developed nation as far as i know , not quiet sure though , average water usage per person is 400 liters as per their building codes.

so , i go like this ,

number of people = 40 x 3.5
total water consumption = (40x3.5 ) x 400 liters
gpd = 40x 3.5 x 400 /3.785
peak factor = 4
so , gpm = (40 x3.5x400/3.785)/(24x60)= 10.27 gpm
pump capacity = 4x10.27 = 41.097 gpm
is that correct method ?

thank you

 

[bimr]

It is probably in the range.

Industrial staff will use less water than residential consumers. There is also no lawn watering which cuts the peak usage as well.

 

[Neel.mech]

thank you very much guys ....