Common header- Differential Pressure

[jrrocks]

In a chiller plant , 4 CHW pumps are connected to common headers in Parallel. Each pump has DP of 5 bar (return 2 bar and supply 7 bar, flow 70 l/s, supply return pipe diameter 200mm). Common header flow when all pumps are in duty, flow is 280 l/s and pipe diameter is 400mm. How to calculate DP at common header?
Note: Network design pump head is 5 bar, at 280 l/s. So, pumps are running at full load.

 

[GT-EGR]

It sounds like you have the differential pressure between your supply and your return headers (7-2 = 5bar). Not sure I understand the question.

 

[willard3]

The problem is not presented clearly, I don't understand it either.

 

[danschwind]

If I understood correctly what you are asking, you will have 7 bar at common header, 2 bar at return header and a DP of 5bar.

 

[jrrocks]

The pressure I am getting at individual pump IN (2bar) and OUT(7bar). Pipe size is 200mm. This, including all other 3 pumps connected to common header which has 400mm Diameter. On supply side common header if i put the pressure guage its not 7 bar. the reason is the bigger pipe diameter. How to calculate the pressure in supply and return based on the different flow and pipe size. I tried using below formula -
Head= flv(sq)/2gD. This gives me a almost correct value

 

[GT-EGR]

You have to follow your pump inlet and discharge from the point of pressure measurements that you currently have all the way to the header. Since you know your pump flow, calculate the pressure drop through the fittings, piping, and valves, and then subtract that from the pump discharge pressure or add to the pump inlet pressure and that will give you the theoretical pressure at each header

 

[danschwind]

Ok, so what you are asking is what the pressure at a given point at the common header is. You didn't specify any lengths so me and I think all other colleagues assumed that those lengths were so small that any pressure drop from any of the pump's outlet up to the header were insignificant.

If you want to calculate the pressure at any given point in your system, you need to perform a hydraulic calculation. I suggest you get a copy of CRANE TP-410.

 

[jrrocks]

Thank you all..!!