OVERHEAD WATER TANK AND CISTERN TANK COMBINATION

[inkospire]

GOOD DAY!!

I just want to raise a question here bout overhead tank combined with a basement cistern.
I was assigned to design a 15,000 gal capacity sprinkler system, the problem was the source of supply consists of this: two(2) 5,000 gal overhead tank and one(1) 5,000 gal capacity basement cistern tank. The building is three-storey approximately 40 ft high. How can I meet the system requirement for the design, specifically to combine the upstream and down stream supply..
Appreciate to get feedbacks...thnks.

 

[stookeyfpe]

1) Install one pump to supply the two overhead cisterns from the basement tank and calculate the sprinkler demand based on a gravity flow and the head pressure of roof cisterns?

2) Disregard the basement cistern tank and use a municipal water supply to fill the overhead cistern tanks? Employ option 1 to meet the sprinkler demand

3) Calculate the hydraulic demand at the 3rd floor and if the static and residual pressures are great enough from the municipal water supply to meet the hydraulic demand, disregard the cisterns completely?

Have you calculated the hydraulic demand for the residential sprinkler system using NFPA 13R? Based on a 4-sprinkler design area your total flow should not exceed 100-120 GPM assuming 20 ft x 20 ft sprinkler spacing.

 

[Sdpaddler50]

Regarding the filling arrangement for the tank, you may want to check out the FM Data Sheet on break tanks. Sounds like your water demands are very low, so not a big issue here. This Data Sheet has good specs for the amount, and type of fill lines. For an office bldg for example, .10/1500 and hose, it asks for 3 separate fill connections if i remember correctly - 2 auto (activated by tank level) and one manual. I have not looked at this Data Sheet for awhile, so dont quote me on any of this.

 

[inkospire]

to stookeyfpe:
the system demand is 198 gpm w/o considering the hose allotment and demand pressure of 42 psi. if the overhead tank alone, only 20 psi approximately is available against a demand of 42 psi, from my point of view the overhead tanks are not sufficient enough to meet the system demand.
here is installation scheme, a 10hp fire pump at the ground floor to supply 5,000 gal from cistern @50 psi. the total capacity is 15,000 gal for 30 mins. minimum running time. 5,000 gal from the cistern will only last more or less 10 mins. 10,000 gal for two overhead tanks is sufficient enough to supply the remaining demand. but, it cannot meet the pressure demand of the system. do i need to add a booster pump for the overhead tanks?

 

[inkospire]

to: Sdpaddler50
sir, can i ask for a link for that FM data sheet for break tanks?
thanks in regards.