This article originally appeared in the October 2021 issue of WQP under the title "Measure Twice, Cut Once"

So far, water pumps consume the most electricity for water companies—usually about 20% of process operations. This is no secret. With the constant focus on energy use/energy waste and the promotion of carbon zero, this makes knowledge of pump performance a truly important indicator.

Historically, energy costs have been subsidized by the environment. With the gradual realization of this impact, consumers’ energy costs have increased disproportionately. For example, in the United Kingdom, the average household water bill has risen by 64% in the last 10 years, while at the same time household electricity has risen by 91%. The industrialization rate of electric energy has risen by about 200%. The only option for water supply companies to maintain profits is to reduce unit delivery costs by improving efficiency.

Just like the SAT-NAV system that works for the driver, pump performance monitoring can be used in conjunction with a decision support system to provide real-time instructions. This can then help guide the operator to minimize the operating costs of the pumping system.

There are many methods and types of equipment to measure pump performance in different environments. Broadly speaking, they are divided into two categories.

The traditional method calculates the output power of the pump by measuring the pressure difference of the pump and the volume flow through the pump.

Second, the method was first documented by a French scientist in 1912. The method called "temperature measurement technology" at the time was to use the enthalpy/entropy mapping method to determine the pump efficiency without measuring the flow rate. The premise is rooted in basic thermodynamics, because if you measure any two thermodynamic state variables (TSV) (including temperature and pressure), then you can calculate any other TSV (including enthalpy and entropy).

The functional summary of this method includes:

For Thames Water, Riventa emphasized the deterioration of blower efficiency.

The results of each method are the same (measurement of head, power, efficiency, and flow rate), but each method is suitable for different applications.

So, for a 100-year-old technology, why is the thermodynamic method not more widely used in the pumping industry? The main reason is the need to measure very small temperature differences, which has recently been greatly improved with the emergence of the semiconductor industry. Another reason has nothing to do with measurement technology, but with the software decision support system, which produces results from the measurement. Great progress has been made in hydraulic analysis methods, and most importantly, how pump station personnel interact with this system to overcome cultural barriers to adoption.

Although the thermodynamic method has existed for more than a century, a breakthrough case study recently emerged when an international organization operating a water company in the UK contracted Riventa to install a real-time thermodynamic pump efficiency monitor.

In this large high-lift station, there are 11 pumps (two of which are not in use), and the motor rated power is between 1005HP (750kW) and 2145HP (1600kW), of which 7 are driven by traditional variable speed drives. The head range is between 262 feet (80 meters) and 311 feet (95 meters), and the normal flow rate is between 33 million gallons per day and 66 million gallons per day.

The one-month pump monitoring and evaluation period to understand the current operating conditions showed that there are large differences in hydraulic and financial operation behavior. A 244% change was observed in the operating costs of delivering 2.2 million gallons of large pumps (9, 10, and 11).

Due to current operating conditions, the pump efficiency of large pumps varies from 32% to 89%. A 16% change in the operating cost of pumping 1 million litres of water for small pumps 3, 6, and 7 was observed.

The current annual energy bill-before implementation-is estimated to be approximately US$5.1 (£3.7 million). Therefore, the cost savings through real-time scheduling is 13.7% per year, or approximately US$700,000 (£500,000).

A Green Pump Index (GPX) assessment shows that for every $1.4 spent on electricity, only $0.66 is used to successfully deliver water to customers’ homes. The rest is loss. Through appropriate investment in correctly designated best practice technologies, it is calculated that by deploying best practice pumps, motors, drives and decision support technologies, annual energy costs can be reduced by up to 46%, or $2.38 million.

Nevada demonstrated another successful example of the thermodynamic method. To help the Las Vegas Valley Water District (LVVWD) optimize its water distribution, Riventa recently identified a potential savings of 12%, equivalent to $254,000 per year. The Hacienda Water Pumping Station (WPS) is a strategic part of the regional network and part of the Southern Nevada Water Authority (SNWA), using thermodynamic free flow technology to monitor pumps.

Previously, it was impossible to accurately assess the efficiency of the seven fixed-rate dry-well pumps that transport drinking water to a regulator tank at another location, but the team quickly determined that refurbishing the four pumps could save 7.4%.

Hacienda WPS was built in 1981 and its assets were upgraded in 1996. Through pump scheduling, a savings of at least 4.8% can be achieved.

Hacienda WPS is well-designed and the pump fits the system, but with Freeflow, the team is still able to identify hidden savings, which is typical for water treatment facilities across the United States, which have pumps and blowers of a certain age. The initial data showed that the least efficient pumps were used the most during the first two weeks of the project period. Using all the data, the team recommends pump combinations in real time based on demand and found that pump scheduling can achieve 4.8% savings. Three pumps do not require maintenance, and four are considered priority refurbishment, which will further save 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.

Improvements in technology have the potential to greatly help guide operators to minimize the operating costs of pumping systems, but proper selection and deployment can usually only be achieved through measurements that lead to wise decisions.

As Lord Kelvin rightly said in 1880, "If you can't measure it, you can't improve it."

Steve Barrett is the managing director of Riventa. You can reach Barrett at [email protected].

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