Centrifugal Pump Calculations Energy loss in discharge valve throttling
System 1 : Pump E selection ( Exact to reaction )
We have requirement for pump with 68m³/hr flow and 47 meter height
So we had selected Pump E with 60% efficiency.
Here
ϱ = density = 1000 liter / hr
g = gravitional force = 9.81 m/s²
H = Head = 47 meter
Q = Flow of fluid = 68 m³/hr = 68 m³ / 3600 sec
η pump = 60%
η motor = 90%
Motor power = ( 68 x 47 x 1000 x 9.81 ) / ( 1000 x 3600 x 0.6 x 0.9)
= 16.1 kW
System 2 : Pump A selection ( Oversize )
We have same flow and head as previous but efficiency is 50%.
Here
ϱ = density = 1000 liter / hr
g = gravitional force = 9.81 m/s²
H = Head = 76 meter
Q = Flow of fluid = 68 m³/hr = 68 m³ / 3600 sec
η pump = 50%
η motor = 90%
Motor power = ( 68 x 76 x 1000 x 9.81 ) / ( 1000 x 3600 x 0.5 x 0.9)
= 31 kW
Extra power consumption
= Oversize pump A - Exact size pump E
= 31 - 16.1
= 14.9 kW extra power consumption.
Extra cost of pumping
= 8760 hr/yr * 14.9 kW
= 1,30,524 kWh/Annum * Cost of unit power
We can see that new pump installation cost is less than oversize pumping.