Water Well Pump sizing to feed large storage reservoir

[Mech110]

Hi everyone,

Need help on sizing a pump to feed water from bore to storage tank.

I have a underground storage tank of 200,000 gal. capacity. My water supply demand is 650 gpm. Reserving 60,000 for Firefighting I am left with 140,000 gal which will be supplied to the fixtures using 6 booster pumps of 120 GPM each (1 standby). Is my Booster pump sizing ok?

Now the real question: what should be the flow rate of the vertical inline pump (any other recommended type for this application?) I should be using to feed storage tank? What are the guidelines in selecting that? Currently, I used the following approach. Need expert guidance on this.

If I select a 1000 gpm pump, and set the pump cut-in level to 80,000 gal. of water left in tank (reserving 60,000 gal. for FF and 20,000 gal of domestic water just to be on a safer side in case of pump malfunctioning or downtime; 20,000 gal. will give approx. half an hour of backup - 20,000/650 = 31 mins.) 1000-650 = 350 gpm will be the rate at which tank will be filled. So it will take around 5.7 hours to fill while water supply is on and then that 120,0000 gal. will be emptied in 120,000/650 = 184 mins = approx. 3 hrs.

What about the duty cycle of the pump in above case? its ok or I should change the pump size?

Thanks in advance for any help.

 

[ashtree]

If your water supply demand is 650GPM and is constant why use 6 pumps to deliver that. What i suspect you are saying is that the average demand is 650GPM. Whether the 6 pump configuration is correct or not depends upon the variations in that demand above and below the average. If there is absolutely no variation use two 650GPM pumps in a duty/standby arrangement. If there is very large fluctuations use more pumps, but you must have enough pumping capacity to meet your max demand and keep at least 1 spare on standby.

Some of the consideration for the borehole pump should be about what the bore is able to supply. I assume that you know that the bore can supply 1000GPM. In my opinion the bore should be set up so that it stops and starts infrequently and would ideally be running continuously at the lowest rate able to meet demand. Now that may not be possible unless you want to invest in variable speed drives etc and you flow match water coming in with that going out speeding up and slowing down the bore pump as required. Either way the bore has to be able to supply more than the average demand otherwise you will never be able to fill the tank.

You don't mention what you are actually supplying with this, but you need to decide for yourself if the 31 mins reserve is enough time for the application. I would think its a bit small and won't allow much time to resolve even a small problem.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[LittleInch]

You need to reference your two other posts on this issue to give everyone the background.

Are you now going for a direct pumped design and not the tank on the roof of the building?

You don't seem to have understood that the 650 gpm is a max flow for possibly only a few minutes at a time. Total daily water demand is probably around 100,000 gal for 1000 people in the building.

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

 

[cvg]

based on the previous thread, 650 is the peak, not average or constant demand. Most of the time your demand will be much less. Suggest you estimate what your peaking factor is and then use average daily demand so you can more accurately determine your storage and supply requirements.
thread407-441756

you need to be able to meet your peak demand of 650 and any extra margin for safety that you want. Say 700 gpm would be adequate for the well pump. But this needs to be validated with a pump test in the well.

I agree with Ash that 31 minutes is totally inadequate, however I suspect that if you are to use an average daily flow rate instead of the peak, then you will have a lot more than 31 minutes of reserve.

 

[ashtree]

Yes that other info would have been nice to know.
Most likely if the max demand is 650gpm and such peaks are of small duration you may even be able to go smaller with the bore pump than what CVG suggests (700gpm), but i agree with where he is coming from.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

Your borehole (water well) should be sized for the expected maximum day demand. The maximum day demand (MDD) represents the maximum consumption during any one day of the year. You should have two boreholes in the event that one borehole or the borehole pump fails. One online borehole and one spare borehole. Unless there is an alternate supply of water. It may take several weeks to repair a borehole and/or borehole pump.

Water Supply

The fire water volumes should be determined by the insurance company's fire protection engineer based on the type of building structure.

 

[cvg]

the post title says "water well" pump which is also being referred to as a "bore" pump and a "vertical inline" pump. My interpretation of this is a "vertical line shaft" pump installed in a deep well. not sure how you would have a spare in a well. Maybe more clarification would help.

 

[Mech110]

I am really getting some fruitful conversations in this and other threads and I am really thankful to all of you for your generous support.

Yes 650-700 GPM is the peak flow occurring for a small time during a day. I wonder why UPC or IPC do not define it clearly in their code and furthermore, there is no data available on the estimate of duration this load would occur. Anyways, what is average daily demand? if calculated using 100 gal/person/day then I have approximately 926 people in residential area, considering 2 persons per bedroom. Furthermore, I have some public area comprising shops and 18 restaurants. How the average daily demand of a restaurant will be assumed? Any standard/thumb rule?

Using multiple small booster pumps will lead to operation of fewer pumps in times of lesser demand.

The above discussion is again leading to 2 opinions. One is based on max. demand which leads to using bore pump of approx. 700 GPM but the other one suggests using smaller pump of say 400-500 gpm. Again, do we have a consensus on this? What is the standard approach used in industry? The question still stands: What should be the pump size???

 

[PEDARRIN2]

Six booster pumps seems excessive. I would recommend a triplex variable speed set up where each pump is sized for 50% (325 gpm). The control panel would alternate lead/lag between the three.

The bore pump does not have to match the booster pump flow rate, but should replenish the storage tank so it has a consistent stored volume.

 

[bimr]

Your ID indicates that you are from Pakistan, is that correct?

You will need to use the building codes that are adopted in the location where the project is located. The UPC or IPC may not be the correct building/plumbing codes. The 100 gal/person/day metric may not be appropriate for Pakistan especially if there are no private lawns.

In some parts of the world, water wells are know as boreholes. Water wells may have only one pump so if you only have one borehole (water well), you need a 2nd borehole (water well) which should be the same capacity. Owners typically alternate the operation of the borehole (water well) and spare.

Your knowledge of this type of work appears to be limited and you should employ a competent engineer to assist you. Otherwise, you may make some expensive mistakes.

The question still stands: What should be the pump size???

Your borehole (water well) should be sized for the expected maximum day demand. The maximum day demand (MDD) represents the maximum consumption during any one day of the year. You will need a second borehole (water well) in the event an alternate or emergency water supply is not available.

Suggest that you review for guidance and definition of maximum day demand:

Water Supply Design