Pumping system operating efficient operation is important to reduce operating power cost. Considering a typical 5 year lifecycle of 100KW and above pumps, spent on power contributes to more than 90% of total ownership cost. Therefore it is important to consider operating efficiency of pump. Pump efficiency is always a major consideration while pump procurement, but because of no of reasons in many cases pump efficiency drops while operation. lets check, How to operate pumping system efficiently.
Reason for efficiency drop can broadly be divided in two categories:-
- Best efficiency point shift as per system requirement.
- Pump efficiency deterioration.
Let us try to estimate pump operating efficiency step by step:
STEP-1 Measure and collect pump system data as below
- Operating Flow
- Operating differential Head. (Discharge head – suction head)
- Fluid type
- Motor power withdrawn and shaft power.
- Pump curve
STEP-2 , After collecting data measure pump efficiency
Efficiency of pump is calculated by
Pump efficiency = Ph(kw) / Ps(KW) X 100
Where, Ph(kw) is hydraulic power & Ps(KW) is shaft power
Hydraulic power
Ph (KW) = ( (Sprg X Q ) X H X g) / 3600
- Q = capacity in m3 /
hr
- spgr = specific gravity (water =1)
- H = differential head in mtr
- g = gravitational acceleration in m / sec 2 (g=9.8)
Ps (KW) = motor measured power X motor efficiency
STEP 3 Example with a typical pump data
Data collected as per below format and pump efficiency calculation
| Sr. No | Description | Unit | Design | Operational |
| 1 | Pump Flow | M3/hr | 1200 | 750 |
| 2 | Spgr | 1 | 1 | |
| 3 | Differential head | Mtr | 30 | 37 |
| 4 | Power | KWhr | 113.5 | 109 |
| 5 | Pump efficiency | % | 86.5 | 74.5 |
| 6 | Efficiency loss | % | 12 |
Pump flow 750 m3/hr,
Differential head = 37 mtr,
Measured power = 109 KW
Motor efficiency = 93%.
Ph (KW) = 750X37X9.8/3600 = 75.54 KW
Ps (KW) = 109X.93 = 101.37 KW
Pump efficiency =75.54 / 101.37 =74.5%
STEP 4 Identification of Problem
| Sr. No. | Case | Condition | Reason for efficiency drop |
| 1. | Pump efficiency is low | If pump flow, head and power follows pump characteristics curve. | Best efficiency point shift as per system requirement. |
| 2 | Pump efficiency is low | If pump flow, head and power does not follows pump characteristics curve. | Pump efficiency deterioration |
STEP 5. Solution to pump efficiency drop
| Sr. No | Reason for efficiency drop | Condition | Solution | Disclaimer |
| 1 | Best efficiency point shift as per system requirement. | Flow is high, Head is low | Pump needs to be replaced with suitable design. | |
| 2 | Best efficiency point shift as per system requirement. | Flow is low (constant) , head is high | Impeller trimming may be done. | Impeller tripping will shift pump operating condition to Best efficiency point |
| 3 | Best efficiency point shift as per system requirement. | Flow is low( But Variable) , head is high | VFD can be planned | |
| 4 | Pump efficiency deterioration | Flow is low, Head is low | Wear ring clearance increase. | Need to replace wear ring |
| 5 | Pump efficiency deterioration | Flow is low, Head is low | Pitting and wear of impeller and casing | Surface coating can be done. |
Pumping system operating efficient operation can be achieved by identification and elimination of reason for efficiency drop. Operate pumping system efficiently to reduce power consumption and save on operating cost.
For understanding pump coating to further improve efficiency, Please click here
Sample Pump curve
