Small/Mid-Size Water System Design - hydro tank vs. elevated storage?

[murdock]

Hello all,

I have been tasked with providing options for an expanding a small campus's water system. My previous experience with potable systems is for much larger operations, with 100k gal elevated reservoirs serving a population on the order of 6,000 people. This project is related to a 50-person learning institution expanding to around 125. Currently the campus is connected to one well which is fed to a building's pressure tank, which is then piped to another building (with pressure tank). Several new buildings with water services will be constructed. A primary concern is being able to still use water during power outages.

The client(s) are debating between constructing a reservoir tank above the campus and gravity feeding everything and the construction of a pump house with a large hydropneumatic tank and generator. The terrain above the campus is steep, forested and full of ledge, so construction costs and buildability are a concern with that option. However, I am not as familiar with pressure tank design, especially when the local regulations require water storage. Among the questions I've been asking myself/the internet: Where does the reservoir go, before the hydro tank? after it? will it need an additional pump besides the well pump to be able to transfer all of its water to the users or hydrotank?

I am leaning towards the hydrotank option at this point, but not sure how it should be pieced together. Looking for some advice or other examples on how a system like this would be designed.

Thanks in Advance,

- smm

 

[bimr]

Before you do anything, you need to understand the fire scenario. Who is responsible for supply fire water?

An elevated storage tank is a luxury that most small systems can not afford. If you have terrain that may accommodate such an installation, you are extremely fortunate.

If you have a ground storage tank at grade, you may pump directly out of it, then through a hydropneumatic tank. As an option, you may use a VFD system and skip the hydropneumatic tank. The well pump will pump into either the elevated storage tank or the ground storage tank. You may need a new well pump with the elevated tank. With the ground storage tank, an additional pump set will pump out of the ground storage tank into the distribution system.

The size of the hydropneumatic tank depends on the size of the water system.

 

[hydrae]

Hydro pneumatic tanks larger than 119 gallons are classified as pressure vessels. So they require a ASME B&PV stamp, which also require an annual internal inspection by the state inspector (assuming USA)
So if you go with the pressure tanks, install 2, so each can be inspected without taking the system out of service, or go with several of the 119 gallon units
But as Bimr stated, since you have the elevation, that is way better

I you go with a VFD, I suggest pressure tank storage that can last long enough for the generator to startup and transfer load

Hydrae