Need advice on a funny design received.

[DJVS]

Here is the design “as received” for a renovation project. I knew that it’s funny-noncompliance design. However I am trying to get your thoughts/advice on this.

(1) Below ground tank is existing which doesn’t have sufficient capacity, there is no chance to modify the underground tank in any ways.
(2) Existing pump is horizontal split case with below ground water storage - AJH agreed with this since its already been installed long back ago.
(3) Above ground tank is newly proposed to increase water storage tank to comply with AHJ requirement.
(4) Concept is already approved by AHJ.

Does anyone have any comments / input / thoughts / workable solution if any, kindly share.

Thank you for your valuable time.

 

[KoachCSR]

I take it the picture is more of a schematic representation of the system? I say that because my first observation is that I'm having trouble visualizing how the balancing pipe is going to function between the underground and above ground tanks...I'm assuming it's a given there's an elevation difference between the two, so the above ground take will constantly be draining to the underground tank (i.e. no real free board, and the underground tank will pressurize equal to the static head imposed on it by the above ground tank). Has the underground tank been evaluated for this condition? Note that that the above ground tank won't begin to fill until the underground tank is full as it's currently depicted.

If that's the intent and has been evaluated as acceptable, I'm not really seeing the point of the duty and standby transfer pumps...why not just fill the above ground tank and allow it to supply the underground tank?

If that is not the intent, the design of the system will need to be changed...either some type of level control valve implemented on the balancing line, or the system design perhaps reversed to supply the underground tank from the above ground tank utilizing the existing level signals...this approach would likely result in a less expensive centrifugal pump as it would not need to be self-priming.

 

[TravisMack]

Whether AHJ approved or not, you can not have more than -3 psi at the pump suction gauge per NFPA 20 and that is only to allow for friction losses between the tank and pump suction flange.

I would run from this situation or re-configure it with a vertical turbine pump.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, LLC

http://www.mfpdesign.com

 

[chicopee]

My opinion would be if the water supply from the municipality water main supplying fire hydrants is adequate why not tie up a line with a fire pump (if necessary0 to replenish the underground tank with all necessary controls to fill the tank while the sprinkler is activated. With regard to your drawing, is the underground water tank capable of withstanding the additional pressure from the above ground tank. Is the supply of the above ground storage tank capable of providing water during the required duration. Can the connecting pipe capable of sustaining the water supply in the lower tank for the required duration. How much sediment has accumulated in the lower tank over the years, sediment which can reduce the lower tank capacity.

 

[LCREP]

Do you have fire pump annual flow test data say for the last 5 years? That will give you an idea of pumps performance, the pumps maybe toasted and need replacement. As others have said has an internal tank inspection should be done, how much build up in the bottom of the tank and condition of the intake screens, I hope they have them??

A few questions???
Is this in the USA
What is the occupancy
Ratings of pumps
Sprinkler and standpipe demands