Well pump & pressure tank for fire hall 3

[DomDoucet]

I am helping to design the plumbing systems for a new municipal building in Eastern Canada (New Brunswick) that will house a volunteer Fire Department and the municipal offices. The Fire Department requires roughly 200GPM of water flow from the well in order to fill their trucks. The building includes washrooms, showers, janitor closet and a kitchenette. The building is occupied by a max of two persons, Monday-Friday, 8-5. The building may be used for other activities on weeknights. We are concerned about sizing the pressure tank for the domestic water system based on the pump, which is 20HP. That would be a very large pressure tank. The reason for this is we are worried that with so little demand on a typical day (assume 16 gals a day max), it will take quite a long time for the pressure tank to deplete and the pump to kick in. We don't want stagnant water. We want to specify a VFD well pump with an 80 gal pressure tank. I am looking for suggestions on how to design this or opinions on our preliminary design.
thank you very much

 

[BigInch]

Using a VFD on a well pump flow of 16 gal/day to 200 GPM is not reasonable.
Even if turned down to 100 gpm will get you only 1/4 of the way up to the surface.
The VFD turned down to 20 gpm will hardly get the water out of the pump.
Use the well pump only to fill the fire truck tanks.
Get a small separate water tank and have a commercial water service truck bring potable water once a month.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[dicksewerrat]

Two pumps? one for trucks, one for domestic use.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[DomDoucet]

Thanks for the feedback on the VFD. Two pumps would be ideal. Not sure we would be able to fit two in the well, casing is 8".

 

[bimr]

You should put in separate wells. You can use a 4-Inch well pump. A separate well installation may cost $3-10K.

 

[DomDoucet]

What about having the 200GPM 20HP pump serving a water storage tank (open to atmosphere)? The storage tank could have a small pump to maintain pressure in the building domestic water piping. When the tank is down to say 25%, the well pump fills it up. When the Fire Department needs to fill their trucks, a separate line from the well pump to the fill station feeds their connection directly. This would avoid having to have another well drilled.

 

[Artisi]

Not too open if it is to be used as potable water .

A storage tank makes sense with a level control system to keep the tank filled for the domestic service, float isolating valve to shut off the storage tank when the tankers are being filled, connect a small domestic pressure pump / system to the storage tank for domestic service.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[BigInch]

I think he said that such a system would not guarantee that the water would remain as fresh as he liked to have.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[FACS]

Note on "two pumps in a well":

When I worked for the water well industry, we visited a guy in Oregon that made an apparatus so that you could put two pumps in a well; One on top of the other.

let me know if you want information on something like this. If it's a one time thing, I remember enough about it to explain the design. It was easy enough to manufacture.

Charlie

http://www.facsco.com

 

[dicksewerrat]

How large is the pipe from the well for the Fire Dept.? How far into the water table is the pump? You could probably get both pumps into the 8 inch casing. Use a 2-3 inch pump for domestic and a 4-5 inch pump and pipe for the Fire Dept. Just make sure the Fire Dept. pump is lower than the domestic pump. Need offset pump dischage connections. I know my well has about 130 feet of water in it and my pump is down into the water 50 feet.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[Artisi]

"The reason for this is we are worried that with so little demand on a typical day (assume 16 gals a day max), it will take quite a long time for the pressure tank to deplete and the pump to kick in."

How long do you envisage that it will take the water to become stagnant - and is the water from the well drinkable anyway?

Have you considered of a deep well ejector pump surface mounted with a pressure tank. The drive pipe and return pipe require very little space in a well casing. Should be available off the shelf from a number of supplier.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[TenPenny]

I think the solution is to have a tank with a booster pump to use for filling the trucks, and use a relatively normal sized pressure tank for the potable water. That way, you'll have relatively fresh water for drinking, and still have the capacity for filling the trucks.

 

[Artisi]

That's 3 pumps when you can get by with 2 units.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[jonr12]

One pump, constant pressure valve, 80 gallon diaphragm tank, all you need.

 

[BigInch]

So then, that's back to running 20 HP pump to fill a diaphram tank.

We've gone full circle.


"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[DomDoucet]

Happy to see so many suggestions. Keep them coming! Here are my thoughts:
- The storage tank would not actually be "open to atmosphere"; just a standard water storage tank, same as a cistern. It would be fairly small, say 80 gals. This would eliminate our worry for freshness of water for domestic purposes.
- A separate well is still our worst case scenario option. We were given a quote of roughly $9,500 for the well and pump.
- Regarding the idea of two pumps in the well, the well driller told us it would be very difficult and did not recommend it. He was concerned over having to remove the top pump in order to service the bottom pump. The well casing is 8", the fire department line is 4" and the domestic water system requires 1-1/2" to 2" max. The well is 200 feet deep with the casing down to 130 feet.
FACS: if you could forward me that information, that would be great!
- Yes the well water is drinkable; further to this, we are specifying carbon filters at the faucets.
- TenPenny: I agree with what you are suggesting, but the large capacity of the pump required for the fire hall vs the small pressure tank is what is concerning us at this point. Essentially, even with a soft start drive on the 20 HP pump, it will only take 30 seconds - 45 seconds for the pump to fill the 80 gal tank. Based on our calculations, this would happen 2-3 times a week, so we aren't terribly concerned about short cycling the pump. Just trying to get a feel for how this surge will affect the system in whole.
- jonr12: How would the constant pressure valve protect the domestic system from the surge of water from the 20HP pump? I assume the valve would release when pressure of 60-70psi is reached?
- We are also considering a small expansion tank to help with water hammer.

 

[TenPenny]

In my opinion, you only need one pump in the well, to supply both potable water and the trucks, and one booster/transfer pump to fill the trucks from the storage tank.

The storage tank needs to be sized appropriately considering what capacity you need to fill the trucks, and at what rate you can refill this tank.

Out of curiousity, where in NB is this located?

 

[jonr12]

A constant pressure valve or CPV will start and stop the pump at 5 GPM, no water hammer at all. 80 gallon diaphragm tank holds 20 gallons of water. The CPV is set at 50 PSI with a 40/60 pressure switch attached to the tank. When using water domestically, the CPV makes the pump work like a 5 GPM pump. It starts and stops the pump at 5 GPM, and refills the tank at 5 GPM, which takes about 2 minutes at those pressure settings. Not very efficient to run a 300 GPM pump at 5 GPM, but you only use 16 gallons per day, so who cares. Because the amps are reduced the motor gets plenty of cooling at 5 GPM, and won’t be damaged. When you need to fill a truck, the CPV will open up and supply as much water as the pump can produce while holding 50 PSI. In this way one pump can do both jobs.

 

[rickfer]

I agree with TenPenny.

If you pump from the well to a booster tank, Potable water will be renewed every time a truck is filled.

If there is enough space, you can pump from the well to an elevated tank, and fill the trucks by gravity. This way you will save a pump.

If the elevated tank is big enough, you even can use an smaller well pump. (But will be pumping more time).

 

[BigInch]

I would imagine that he knows the frequency of fire truck refills and that's exactly upon what he based his stale water opinion and that small demand for water just won't justify a two pump solution.

The aquarium in my living room has half a month's supply.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek