Pressure of the system in Churn Pressure Condition. 1

[GeorgeMech]

Hi, I have a simple problem but I don’t know if I'm using the correct formula or procedure.
I have a fire pump rated at 14 bar with a churn pressure of 16 bar, the consultant wants to give the pressure at each tapping point for each building (16 buildings in site), the piping runs straight from the pump discharge line to the last building, so the question is, if the pressure in the discharge outlet of the pump is 16 bar, is the pressure at the inlet of the furthest building is also 16 bar during non-fire condition or should I consider hazen william formula to calculate the friction loss in piping from the discharge header up to the inlet point of that building.


Thanks!

 

[stookeyfpe]

Given the water is an incompressible fluid, hypothetically speaking, the churn pressure at the most remote building should be 16 bar. However, you need to adjust delta P for friction and elevation change.

 

[chicopee]

Stookeyfpe, at churn you should not have any flow once the pipe is filled with water and the pipe end where the remote tap is placed is shutoff , therefore friction should not be considered; however I do agree with you about the difference in elevation.

 

[stookeyfpe]

Correct, but we don't install fire pumps so they sit in churn mode. We install pumps to increase pressure to meet a specified hydraulic demand, which requires the water to move at some time during its service life. I was just trying to help the fellow understand the basic design ramifications because he/she will need to flow water during the acceptance and annual ITM tests.

 

[chicopee]

Stookey, altho. at Churn point there is no substantial flow, there will still be a trickle of water to prevent the pump from overheating during fire pump tests.

 

[GeorgeMech]

Hi, Thanks for the reply, actually I was worried only about the location of the PRV on the sprinkler system since my pipes, fittings, valves,etc are having a rated pressure of 12.1 bar (175 psi) only, but after I determine the location PRV for each floor per each building, I will run the calculation in the supply mode to check whether the minimum pressure for the most remote sprinkler and standpipe (separate riser inside the building) would still be enough as per NFPA requirement. So the the bottom line is that during non-fire condition (static condition), the system pressure of the system (considering the churn pressure) for the furthest building would be the same unless there will be a change in elevation and also this difference in pressure is only applicable if there is a flow in the system.