Pump Performance Testing and Benchmarking Database
Electricity accounts for over a quarter of the direct greenhouse gas (GHG) emissions caused by human activity today. Pumps that are running inefficiently results in wasted energy and loss of capacity. Pump efficiency improvement costs are typically much less than cost savings from the efficiency gains. Any reduction in energy, through pump efficiency improvements, will benefit not only the ‘bottom line’, but also obligations as a responsible and environmentally conscious organization.
Various metrics are in use or have been proposed, for measuring the energy efficiency of pumps and pump systems, and for performance benchmarking. Data quality limitations lead to corresponding errors in the calculation of metrics, and will possibly be too high for accurate measurements of energy savings, or for identifying improvements. An indication of the scale of the problem is found from the large amount of data filtering that was employed in the WSAA and WRF programs, which used the conventional method for pump performance measurements.
In contrast, the data obtained by the thermodynamic method in OPA program was much more consistent.
A new pump performance benchmarking database, relative to the level of service pumped, has been developed using highly accurate and reliable in situ pump performance measurements from Australasian water utilities.
The pump performance indicator total dynamic head (PPI_TDH) is calculated by dividing the motor power consumption (in kilowatt-hours) by the volume pumped (in millions of litres) and the head difference across the pump (or total dynamic head [TDH]) in meters; the units of PPI_TDH are kWh/ML/m.
The PPI_TDH indicator normalises the specific energy against the head produced by the pump, thus providing a more consistent comparison across pumps of different pressure ranges and independently from pump type or speed.
The thermodynamic test data was obtained using the Robertson Technology P22 system which meets standard ISO 5198:1999 Code for Hydraulic Performance Tests - Precision Class. The thermodynamic technique measures the pump efficiency, uncertainty of down to 0.5%, directly via differential temperature and pressure measurements across the pump. The flow rate is calculated from the pump efficiency along with pressure and power measurements captured.
For multiple pumps operating in parallel, pump efficiency and flow can be measured simultaneously for individual pumps to determine the overall pump efficiency using the thermodynamic method. The thermodynamic method is suitable for both water and wastewater pumps which are either dry mounted or installed in a wet well.
Testing aims to cover the full operating range/pump curve via. valve throttling or variable motor speeds controls (then the data is adjusted using the pump affinity laws) to obtain measured head, power and efficiency vs. flow curves to compare the manufacturer’s curves to provide an assessment of the pump performance.
The PPI_TDH deteriorates until the pump is refurbished, indicated by an improvement in the PPI_TDH and how much of an improvement depends on the effectiveness of the refurbishment. The condition of each pump and potential for improvement can be quantified by comparing actual PPI_ TDH at the pump operating point with the maximum possible value PPI_TDH_MAX that would be achieved if the pump was operating at the manufacturer’s pump BEP.
The parameters that can change where a pump is operating on its curve include pump speed, pump combination, friction losses in pipework and pump impellor size. The PPI_TDH values in the database vary from 3.1 to 5.3 kWh/ML/m and a value of <3.7 is defined for when pumps are operating efficiently, based on the 50th percentile of the database.
If the PPI_TDH exceeds the 75th percentile, in this case, a value of 4.1, an energy performance improvement opportunity might exist for the particular pump and further analysis should be conducted.
The benefits of this programme are that inefficient pumping systems are identified early, and the cost benefits of remediation are known with accuracy, with up to 20% energy savings realised in some cases.
Typical improvements made possible from pump performance testing include:
- Pump overhaul timing based on actual energy consumption and efficiency, flow and pressure, run hours, cost of refurbishment/replacement, cost of electricity and inflation.
- Operating pumps within their Preferred Operating Region (POR).
- Identification of pump system problems e.g. excessive wear, suction/discharge recirculation, air entrainment, blockages, leakage etc.
- Preferentially operating the most efficient and best-matched pump(s) and speeds that meet flow demands at the lowest energy and maintenance costs.
- Confirm that pumps recently installed are operating as they should and provide a benchmark for energy consumption.
- Pump replacement that ensures the most efficient pump is selected to suit the measured pump station system curve as like for like replacement may not be the best option.
The ability to identify the actual operational pump condition with these investigations can be directly linked to planned maintenance activities, which provides better value for these works over fixed time scheduled maintenance programmes. This will reduce critical asset failures. At the same time, these inspections confirm that the pump is fit for its purpose, that it complies with its designed duty at the intended efficiency.
For more information contact
Sector Lead - Water Infrastructure (Australia)
Senior Mechanical Engineer (New Zealand)