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

 

[Artisi]

Your best option is a deep-well jet pump as suggested earlier.
No need for any above ground tank with water available on-demand for your building.
Link below describes the operation etc of a deep-well jet pump - costs probably a few hundred's, easy to install and maintain.

http://inspectapedia.com/water/JetPumps2Line.htm

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]

Deep Well jet pumps are extremely common in rural New Brunswick, I grew up with one, and had one at my previous house until the foot valve died one January day, we replaced it with a submersible.

The issue I see is that he needs to have fresh water for potable use, and a reservoir tank for filling the trucks. You could do this with one pump, all you have to do is separate the plumbing above the well head, so that the potable water comes directly from the well. Why not just use check valves, so that the pump kicks on when there is demand either from the potable side or the truck supply side, but that neither downstream use will cross feed the other? I don't see why two pumps are needed.

 

[Artisi]

If there is a reservoir tank for both requirements, unless it is well elevated you will need a second pump to pressurise the building supply and the truck fill operation (a 200GPM requirement) - back to 2 pumps.

To use the well pump for the building supply is over-kill, open a tap for a drink of water and you bring a 20HP pump on-line for 5 - 10 seconds.

I see only one reasonable solution, the well pump dedicated to filling the tanker, and a seperate deep well pump with pressure tank to service the building.

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.)

 

[Compositepro]

Can the well even supply 200 gpm, and for how long? It seems wasteful to use a 20 hp pump when a 3/4 hp pump and an elevated plastic storage tank will suffice. All that horsepower is required because you are trying to lift water from depth at high rate.

 

[BigInch]

Ya. I think that was at least half the reason for the OP's post. After all, it is somewhat obvious that two pumps could be used, or a small tank off the large tank, etc. etc., all seemingly extreme overkill for providing only 500 gal/month.

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

 

[77JQX]

I agree with jonr12. You only need the 80 gallon pressure tank, the 20 HP well, and a control valve. Sure it's not efficient, but we're talking about wasting about $10/year on electricity by using the large pump for domestic water. With a bladder pressure tank, there's no worry about stagnant water. (How old is the groundwater before you pump it?)

 

[Artisi]

How old is the groundwater, probably many billions of years old.
Anyway seems the OP has given up.

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.)

 

[DomDoucet]

- Didn't give up, just got sidetracked! Thanks for all comments up to date! Very informative.
- Yes, the well can provide 200 gpm. Well is 300' deep.
- We are looking into the deep well pump option. Do I understand correctly that a submersible pump could be installed in the well in conjunction with a deep well pump? We are back to two pumps on a single well; other than capital cost, what are the cons to this setup?
- We can't count on potable water being replenished when the trucks are filled; the fire department does not get that many calls.
- Trucks are 1250 gals (2), 2800 gals (1) and a future 4000 gals tanker (1). The client wishes to have capacity to fill one 2800 gal truck at this well.
- What is the advantage of using a storage tank for the truck fill? Why not pump directly from the well?
- Here is our current design, comments are appreciated:
20 HP submersible pump to 4" line into building, 4" line ran directly to fire truck fill stations, 1-1/2" line tee-ed off from 4" main to 80 gal pressure tank for domestic use, control valve located on 1-1/2" line prior to pressure tank. Pump complete with soft start drive. Pump rep is not concerned about burning out the pump, as it will only turn on every few days to replenish the pressure tank. For the amount of time is will run for domestic use, we are not overly concerned about operating costs either.

 

[77JQX]

Sounds good to me. I'd add backflow prevention to the truck fill as well, ideally as an air gap, but sometimes the truck guys prefer a direct connection. With a direct connection, our regulators would require a reduced pressure principle backflow device.

 

[DomDoucet]

Good point, we have specified a double check backflow preventer, which suits local regulations here.

 

[BigInch]

Hey, why not just install a tap on the truck.

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

 

[DomDoucet]

A tap?

 

[jonr12]

Your making this harder than it needs to be. You don't need a soft start panel, and I am guessing that 1.5" control valve you mention is a pressure relief valve, that won't help. Also the truck fill guys will need to open the line all the way or the pump will cycle rapidly. I have done several of these and it works great.

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.

 

[DomDoucet]

Sorry to be a pain, I haven't used a constant pressure valve before. It does seem adequate for what we need. But the pump has no VFD, how will it work like a 5GPM pump? If the pump is only pushing 5 GPM, it will not even get the water out of the well.

 

[jonr12]

It is so simple it is hard to explain. I found this graphic which might help.

http://www.cyclestopvalves.com/simple/municipal.php

 

[DomDoucet]

Wow thanks for the link! That really makes it easy to understand. I think this is our solution.

 

[BigInch]

Those 16 gpd are going to be produced using starting current amperage.
Starts and stops of the pump are the worst duty cycle possible.

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

 

[jonr12]

An 80 gallon pressure tank will hold about 20 gallons of water. With 16gpd the pump will come on once a day, and will run about two minutes to refill the tank. So it won’t short cycle. I have also found that starting a pump against a closed valve will make the motor start under a no load condition, which reduces the starting current equal to or even less than a soft start panel.

 

[Artisi]

Seems the problem has been solved so lets see it put into practice.

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.)

 

[DomDoucet]

BigInch: short of putting in two pumps, do you have any other suggestions?