Water network for High Rise building area

[waseem19]

Hi,

I'm kind of new at designing water network and would appreciate the help in doing the design for this. I'll just talk about my design and assumptions which would be great if you comment on.

I'm planning to have a pumped system only, so I will not be pumping to elevated storage tank, instead I will be pumping to ground tanks which the building owners will have to build according to specification we give them, so I don't have to worry about fire flow as well, cause the fire hydrant or sprinkler system will get the flow from the ground storage tank inside each building. The daily fluctuations in demand will also be handled by the pumps installed near these ground tanks.

now, I'm confused on what should I pump from my main pumping station and for how long ? should I size my network to carry only daily average flow pumped during 6 hours of the day ? or do I need to make sure that the main pumping station and the network can handle the peak flow ?if yes then which peak ? maximum day or hour ?

I don’t really have data on the pattern of this community, I’m now assuming that any average flow will be multiplied by 3 to give me the peak flow.

I cannot build elevated storage tanks cause there is no space.

 

[sese]

You can estimate the peak flow base on the population of the committee that you designing for, so if you tell the size of the population. On the other hand if the population is small you could estimate the water consumption pattern by spreading a questionnaire about their daily domestic activity.
In our country we have a roof tank and the water pumped into the system 3 days a week.

 

[cvg]

peak flows will be handled by the building owners, so your task is simply to keep the tanks full. Or at least, maintain them half full. Depending upon the energy costs, you may find that pumping at night to fill the tanks is more cost effective, so an 8-hour pumping cycle during the night may be recommended. Size your mains to fill the tanks in 8 hours or less.

 

[stanier]

You can use Epanet, a freeware program to model such a system. The tank levels can be mapped to show levels during diurnal demands.

A book available from

http://www.haestad.com

called Advanced Water Distribution and Modelling and Management is worth investing in. Do the Civil quiz and get a discount on the book. Haestads Watercad is based on the same engine as Epanet so no need too invest in their software unless you need help all the time and have a bottomless wallet.

 

[bimr]

You have not provided enough information to make detailed comments. However, some comments can be made:

1. You don't have to be concerned about peak flows since you have the water tanks.

2. The water tanks should be sized for fire flows and emergencies. Fire flows depend on the types of buildings being protected and is obtained from insurance underwriters. For light commercial and residence fire flows, the fire flow will be maybe 3,000 gpm for 1-2 hours. The total tank volume in the storage tanks should be 2-4 days of average daily flow.

3. You probably will have minimum flows at night if you are talking about a residential area. Your daily peak flow at the residences will probably be on the order of 5-6 times the average daily flow, especially if you have a smaller populated area.

4. It probably makes sense to plan to fill the ground storage tanks in one work shift or 6-7 hours.

 

[waseem19]

cvg , Bimr :

you both mentioned that I don't have to worry about peak flows , I think you both meant the hourly peak but shouldn't I multiply my average demand by "say 1.25" to get my maximum day demand over the year ?

the existing system is already pumping 24 hours, I'm only tapping from it so does it make sense to keep my mains small and assume that I'm getting my flow over a 24 hours ? if I'm to assume 8 hour shift then the flows will be 3 times more and all of my network up to the ground tanks will have to be a lot bigger.

thanks for your valuable comments

 

[bimr]

waseem19,

Yes, we were referring to the peak hourly flow. You need to design for the yearly maximum day flow.

You should add an allowance for the maximum day. The maximum day will vary with the season and will depend on seasonal commercial and industrial activities in the area serviced. You also should add an allowance for future population growth. If you are working with a resort area, the maximum day may be as high as 2X the annual average day. You best guide for estimating the maximum flow is to review old records.

Lacking records of water use and with no unusual seasonal variation, the rule of thumb is to use 150 gallons per capita per day for the design basis.

Pumping 24 hours per day will work fine. The proposed 8 hour pumping shift is probably the most economical staffing option not necessarily the most economical pumping option. The assumption was that this is a small pumping station and not likely to be staffed around the clock.

 

[cvg]

also - in some areas of the country, off-peak rates for energy can be substantially lower. Therefore pumping at night would be cheaper