It’s no secret that pumping consumes by far the most electrical energy for water companies – often around 20% of treatment operations. With energy consumption / energy waste and the zero carbon goal remaining in the spotlight, this makes knowledge of pump performance a truly vital metric.
Historically, the cost of energy has been subsidized by the environment. As the effect of this has taken hold, there has been a disproportionate increase in the cost of energy to consumers. In the UK, for example, the average increase in household water charges has increased by 64% over a recent ten-year period, while at the same time there has been an increase of 91 % for domestic electrical energy. The industrial tariff for electric power has increased by around 200%. The only option for a water company to maintain its profits is therefore to reduce the unit cost of delivery by increasing efficiency.
Just as a SAT-NAV system works for drivers, pump performance monitoring can be used in conjunction with a decision support system to provide real-time instructions. This can then help guide operators to the minimum possible operating costs for a pumping system.
There are many methods and types of equipment available to measure pump performance under different circumstances, roughly in two categories.
Conventional (Pressure / Volume)
The conventional method calculates the output power of the pump by measuring the differential pressure and the volumetric flow through the pump.
These features include:
- Resilience for all heads goes from zero to the top.
- Therefore requires the flow measurement; suitable and precise for a test loop and generally unsuitable for on-site use due to the lack of straight tubing in the main line of the individual pump.
- Any error in measuring motor efficiency propagates directly to an error in calculating pump efficiency.
- Expensive to implement on site, requiring a flow meter on each pump, which is generally not possible due to physical space constraints, which also limit the accuracy of the application.
Second, this method was first documented by a French scientist in 1912. The then-named “thermometric technique” used an enthalpy / entropy mapping method to determine the efficiency of the pump without the need to measure flow. The premise is rooted in fundamental thermodynamics in that if you measure two thermodynamic state variables (TSV) (which include temperature and pressure), you can calculate any other TSV (which includes enthalpy and entropy).
Here is a summary of the characteristics of this method:
- The purchase cost is lower and regardless of the size of the pump.
- The installation cost is low.
- Pump efficiency can be measured by a ½ inch BSP thread on each side of the pump.
- Does not require straight lengths of pipe (as required for the conventional method).
- Suitable for on-site and on-site pump performance monitoring.
- Precision at higher heads.
- Accuracy at low heights less than 33 feet is variable.
- Limitations of the head to obtain the best precision.
The results are the same for each method (measurement of head, power, efficiency and flow), but each method is suitable for different applications.
So, for a century-old technology, why is the thermodynamic method not more widely deployed in the pumping industry? The main reason has been the need to measure very small temperature differences, which has improved a lot in recent times with the advent of the semiconductor industry. Another reason is not related to the measurement technology, but to the software decision support system, which produces a result from the measurement. Great advances have been made in the methods of hydraulic analysis and, more importantly, in the way pumping station personnel interact with such a system to overcome the cultural barrier to adoption.
Although the thermodynamic method has been around for over a century, a groundbreaking case study emerged only recently when an international organization operating a UK water company commissioned Riventa to install a heat pump efficiency monitor. in real time.
In this large high-lift station, there are 11 pumps (two of which are not used), rated at motor power between 1005 HP (750 kW) and 2145 HP (1600 kW), with seven driven units by traditional variable speed drives. The drop height ranges from 262 feet (80 m) to 311 feet (95 m) and normal flow rates range from 33 million gallons per day to 66 million gallons per day.
A one month pump monitoring evaluation period to understand the current operating regime showed that there were large variations in hydraulic and financial operating behavior. A 244% variation was observed in the operating cost to deliver 2.2 million gallons for the large pumps (9, 10 and 11).
The pump efficiency of the large pumps varied from 32% to 89%, due to the current operating regime. A variation of 16% was observed in the operating cost to deliver 1 million liters for the small pumps 3, 6 and 7.
The current annual energy bill – before implementation – is estimated to be around $ 5.1 (£ 3.7million). Therefore, the savings from real-time scheduling are 13.7%, or around $ 0.7m (£ 0.5m) per year.
An evaluation of the Green Pump Index (GPX) showed that currently, for every $ 1.4 spent on electrical power, only $ 0.66 is used to successfully deliver water to customers’ homes. The rest are losses. With the appropriate investment in properly specified best practice technology, it has been calculated that the annual energy cost could be reduced by up to 46%, or $ 2.38 million, through the deployment of the best pump technology, engine, drive and decision support.
Another successful example of the thermodynamic method has been demonstrated in Nevada. To help the Las Vegas Valley Water District (LVVWD) optimize its water supply, Riventa recently identified potential savings of 12%, equivalent to $ 254,000 per year. The pumps were monitored with Freeflow thermodynamic technology at the Hacienda Water Pumping Station (WPS), a strategic part of the district system that is also part of the Southern Nevada Water Authority (SNWA).
Previously, it had not been possible to accurately assess the efficiency of the seven fixed speed dry pumps that transfer potable water to a regulator tank at another site, but the team quickly established that 7.4% savings would result from refurbishing four of the pumps. .
Savings of at least 4.8% can be achieved through pump programming at Hacienda WPS, which was built in 1981, with assets modernized in 1996.
The Hacienda WPS is well designed, with pumps to match the system, but using Freeflow the team were still able to identify hidden savings typical of water treatment facilities in the United States with equipment such than pumps and fans of a certain age. Initial data showed that the least efficient pump was used the most during the first two weeks of the project period. Using all the data, the team made real-time recommendations for pumping suits, based on demand, achieving 4.8% savings that could be achieved through pump planning. Three pumps required no maintenance, while four were considered a priority for retrofit, resulting in additional savings of 7.4%. The technology now provides LVVWD’s operations team with the information they need to operate aging assets and stations as efficiently as possible.
Technological improvements have the potential to help greatly with the mandate of guiding operators towards the minimum operational cost possible for a pumping system, but proper selection and deployment can often only be achieved through actions leading to a informed decision.
As Lord Kelvin rightly said in 1880, “If you can’t measure it, you can’t improve it.