Our client was looking to improve efficiencies of its water pump sets. Programming a simple algorithm enables us to establish an online monitoring system which cycles through the pump sets and triggers alarms when efficiencies fall below an acceptable level.
CASE STUDY 3: PUMP STATION EFFICIENCY
Experience has shown us most pump stations are equipped with enough measurement instrumentation to make online pump efficiency calculations possible. Therefore, it is a relatively simple process for any business to achieve power savings by monitoring pump efficiency.
Most water pump stations consist of the following elements:
• A supply reservoir where water is sourced from
• Pumps to pump water to a higher level
• A delivery pressure gauge
• A delivery flow meter
• Power monitoring on the pump station (optional)
Because often only one pump is running at a time the flow, pressure across the pumps and power consumed in the pump station can all be assigned to that particular pump. Therefore, calculated efficiency can be allocated to the pump running at the time.
The combined mechanical and electrical efficiency of a pump set is a simple calculation. Where the inlet pressure isn’t measured it can be calculated by using the relative levels of the pump set and the suction water level.
Most pump stations also cycle the duty of the pumps which gives us an opportunity to calculate the relative efficiency of each pump to the other. So, if there are three pumps in a pump station cycling duty once per day, after three days of online efficiency monitoring the calculated efficiencies of the three pumps can be determined.
One of the many advantages of online efficiency monitoring is that worn or defective pump sets can be identified.
As an example, from our online efficiency monitoring information in our client’s case we found Pump 2 has a much lower efficiency than the other two pumps.
We can also see that running Pump 3 most of the time can increase the average efficiency by 7%. On a pump set of 630kW that is a whopping 44 kW reduction in power.
From our experience, we know the following algorithm can easily be programmed into any control system:
• Day 1: Set Pump 1 as Duty 1, calculate and store efficiency at a benchmarked point
(I.E. Destination reservoir 80% full)
• Day 2: Set Pump 2 as Duty 1, calculate and store efficiency at a benchmarked point
(I.E. Destination reservoir 80% full)
• Day 3: Set Pump 3 as Duty 1, calculate and store efficiency at a benchmarked point
(I.E. Destination reservoir 80% full)
• Day 4 to 14: Set most efficient pump as Duty 1
All efficiencies should be logged into a historical database and alarms generated when the benchmarked efficiency drops below acceptable levels.
Online monitoring of efficiency has also saved the day for our client when the outlet valve of a pump wasn’t shut due to a valve defect. Water was recirculating through that pump while another pump was running. Because of the online efficiency monitoring, an alarm was triggered as soon as the efficiency of the running pump dropped and the overall result for our client has been a 4% power saving achieved in a relatively short time.
Without the alarm, this situation may have continued for several months until routine maintenance caught up with the fault.
