This article explains how to reduce the Total Cost of Ownership (TCO) with a limited investment can provide reductions in pumping systems TCO while maintaining sustainability objectives. By Lionel Gaudrel, strategic marketing manager, and Arnaud Savreux, offer application expert manager, Industry Business, Schneider Electric
Wherever pumping systems are present — in environments such as buildings, water/wastewater, and oil and gas facilities — energy consumption exerts a major influence on cost. Despite the fact that electrical energy cost represents 40 percent of the TCO of pumping systems, many organisations fail to introduce the proper steps to leverage cost reduction through efficiency improvements. To solve this dilemma, the following major barriers need to be recognized and addressed:
- Lack of proper metrics — Energy efficiency has traditionally not been used in assessing performance. In most organisations, the responsibilities of energy procurement and efficient operations are separate and consistent/standardised metrics are not utilised.
- Knowledge gap — A lack of awareness in energy efficiency opportunities is prevalent and, as a result, potential savings and other benefits are missed.
- Fear of investment — Operations personnel often struggle to present attractive large or even small investments to their finance organisations.
Any sound energy plan should take into account the following three steps:
- Energy efficiency management
- Asset management
- Energy cost management
For the purposes of this article, the scope of a pumping system will be defined as encompassing all related elements starting from the point of the electrical utility connection down to the point of end use. This article will illustrate how energy management best practices can result in a 20 percent reduction in TCO and a return of investment within 24 months.
Step 1: Energy Efficiency Management
Energy efficiency is now a global high priority for both industrialised and emerging countries. The Rio conference and Earth Summit of 1992 and the Kyoto Protocol of 1997 resulted in the signing of a global treaty that sets binding targets for reduction of greenhouse gas emissions. The International Energy Agency and various governmental and nongovernmental organisations agree that the reduction of CO2 emissions and the resulting energy savings can be achieved through the deployment of energy efficient products and systems.
The challenge, however, is that the nature of production in industrial environments is in a constant state of flux. Production cycles, for example, are influenced by variables such as market demand, weather, and local regulations. As a result, factory and building operators need to understand how and when energy is used in order to minimise consumption and related costs.
The pump system energy management approach discussed in this article will review the nature of efficiency loss not only for individual components within the system, but also for the system as a whole, integrated entity.
In pumping systems, most inefficiency comes from:
- A mismatch between the pump deployed and the actual system requirement (ie: undersized or oversized)
- The improper use of throttling valves and damper technologies to control the flow of liquids
These two elements imply that the way pumping systems are controlled plays a major role regarding how efficiency can be improved. Control systems themselves are composed of both hardware and software components. On the hardware side, variable speed drives are a primary enabler of high-efficiency performance.
Determining pump efficiency is only a first step in identifying system performance levels. Monitoring efficiencies via software can detect operating points that are not suitable for the pump. Access to such data can help improve both system energy efficiency and reliability.
Summary Of Pump Energy Efficiency Management Best Practices
The energy efficiency of a pumping system can be improved by implementing the following simple actions:
- Replace fixed drives with variable speed drives to boost efficiency. Connected to a pump, a variable speed drive can control speed, pressure, and flow in conjunction with dynamic process and production requirements.
- Monitor production data and energy consumption data via software dashboards. Continuous tracking of the deviation between production output and energy consumed allows for rapid and cost-effective decision-making. Intelligent Electronic Devices, such as variable speed drives that are tied into the monitoring system, play a major role in reporting data related to operation, production, and energy in real time. Monitoring points should be close to the load because that is where most of the power is consumed. The closer the monitoring is to the load, the more insights can be acquired relative to cost savings.
- Monitor the operating point of the pump and its efficiency on a continual basis in order to visualise trends. Observance of the trends can then lead to sensible actions that improve efficiency and verify the impact of improvements to the system.
- Use proper metrics to identify an increase or decrease in efficiency on particular systems and to compare efficiency performances of different pumps in multiple sites. A recommended key performance indicator metric is the specific energy consumption metric (in kWh/ m3).
Efficiency Standards: Motors
In the realm of efficiency improvement, motors play an important role as part of the overall pumping system. In 2008, the International Electrotechnical Commission (IEC) introduced the IEC 60034-30 and IEC 60034-31 standards as an efficiency classification system for motors. Countries have published laws and regulations based on these standards and require the usage of more efficient motors in order to reduce CO2 emissions.
Over the next several years, government regulations will require higher efficiency motors. European Union (EU) countries that require IE2 motors today will require either IE3 or IE2 motors with variable speed drives in 2016. An IE3 motor will increase efficiency by 2 percent for 4 kW/5 HP motor power when compared to an IE2 motor, and by 1 percent for a 90 kW/125 HP motor. Although these gains are significant, if variable speed drives are deployed, the potential for further efficiency gain is greater.
Efficiency Standards: Pumps
As with motors, new standards and regulations have been adopted in the domain of pumps. The European Commission (EC), for example, has adopted regulation n°547/2012 under Directive 2009/125/EC in regard to eco-design requirements for water pumps. The EC regulation is intended to suppress the availability of low-efficiency water pumps. It is applicable in the EU to rotodynamic water pumps for pumping clean water.
The EC regulation defines a Minimum Efficiency Index (MEI) for affected pumps. The MEI is a criterion based on evaluation of European pump manufacturer statistical data, technological aspects, fluid dynamic laws, and operating points included between 75 and 110 percent of the BEP flow rate.
In order to further expand efficiency gains, the EU has requested a new directive that defines a broader view of the pumping system. Moving forward for efficiency measurement purposes, a pumping system will include the pump, the motor, the load profile, and the variable speed drives. This will result in a potential savings of 30 percent compared to 3.6 percent with the current ‘pump only’ approach.
The IEC regulation n°547/2012 does not yet include firefighting pumps, self-priming pumps, displacement pumps, pumps for private and public wastewater and for fluids with a high solids content, pumps for swimming pools, pumps for fountains, and clean water pumps larger than 150 kW. (In many of these areas preparatory studies are underway for the future development of new efficiency standards.)
Other regions in the world have defined their own minimum energy performance for pumps. The calculation method in Brazil is similar to the EU approach. In China, the regulation GB19762-2007 is applicable for clean water pumps. That regulation defines three grades where grade 1 is used for very high-efficiency-pumps. Grade 3 is the minimum efficiency authorised. The method of calculation used to define the grade is different from the method used by EU regulation. The US Department of Energy (DOE) has begun work evaluating new energy standards for pumps. The DOE has published a rulemaking framework and has shared documents regarding commercial and industrial pumps with manufacturers, consumer groups, federal agencies, and states in order to gather feedback.
Step 2: Asset Management
Physical assets such as pumps need to be maintained on an ongoing basis. Maintenance costs represent 25 percent of TCO, therefore maintenance practices warrant examination in terms of contribution to energy-influenced savings. Maintenance costs are unavoidable due to the wear of components during system operation and because the cost of downtime attributed to loss of production would threaten the solvency of the business. In pumping installations, many moving parts mean that proper maintenance of motors, drives, pumps, and associated pipes is crucial. Numerous steps can be taken to assure that maintenance costs are kept at a minimum while integrity of the systems is kept stable.
All pumps should be operated within the parameters of a given pump’s specifications (often stated in the pump supplier’s instruction manual/data sheet). As discussed, pump efficiency varies according to operational parameters. The pump is designed for optimal operation at the BEP but 75 percent of the pumping systems are oversized by around 30 percent.
Variable speed drives can help to keep the operating point close to the BEP and also protect the pump against destructive forces generated by inefficiencies. Extreme situations, such as dry running, low flow operation, or cavitation (due to low net positive suction head), which can cause instantaneous damage, are avoided. Monitoring the operating point of the pump and its efficiency provides diagnostics that can help predict when potential system problems will occur.
Wear is unavoidable due to mechanical parts that are moving and to the action of the fluid being pumped. Erosion is generated by the speed of fluid and could be increased by slurries (sand or bigger particles). Corrosion is due to chemical or electrochemical reaction that attacks the pump materials. Even treated drinking water causes corrosion in cast iron casings as a result of the catalytic effect of bacteria. Erosion and corrosion mostly impact the pipes, the impeller, and the case (which are key operating components).
Efficiency drops by 10 to 15 percent for an unmaintained pump. Moreover, the major loss in efficiency occurs in the first few years of the pump’s life. Regular maintenance avoids losses in efficiency and capacity that can occur before the pump fails.
A number of approaches are available that can help to address the issue of maintenance in a cost-effective manner. Preventive maintenance implies the systematic inspection and detection of potential failures before they occur. Condition-based maintenance is a type of preventive maintenance that estimates and projects equipment condition over time, utilising probability formulas to assess downtime risks. Corrective maintenance is a response to an unanticipated problem or emergency.
Condition-based maintenance monitors system data on an ongoing basis and provides an accurate assessment of the health or status of components, devices, and/or the complete system.
As it relates to pumps, variables such as suction pressure, discharge pressure, pump speed, power, flow, and temperatures are monitored to detect a loss of efficiency. Identification of the potential problems is possible by combining the efficiency trends and process variables.
Variable speed drives have the capability of measuring process variables, temperature, and power with high accuracy and to assess the pump efficiency. If connected to the automation system, they continuously monitor the health of the system and can indicate in a precise manner when proper maintenance is needed.
As part of the overall pumping system, pipes are also subject to issues such as overpressure, leakage, or pipe burst. An overpressure situation can be caused by poor pump control. A situation called ‘water hammer’ can also occur. Water hammer is caused by a pressure or shock wave that travels through the pipes, generated by a sudden stop in the velocity of the water. This sudden acceleration and deceleration on the motor can be avoided with the help of a variable speed drive (sudden variation in flows is avoided). Leakage can also be reduced by automatic adjustments to pressure when appropriate.
Protection against mains voltage and frequency fluctuations can help maintain the integrity and extend the lifetime of motors. In cases where motors are equipped with variable speed drives, those electrical disturbances are not transmitted to the motor.
Protection against high-temperature conditions can also extend the life of the motor assets. Devices such as thermal relays, PTC, or PT100 thermal sensors can help and are manageable through the variable speed drive.
In cases where long motor cables are used in conjunction with motors and variable speed drives, it is recommended that filters be installed in order to avoid the dv/dt and motor voltage surge effects.
Step 3: Energy Cost Management
Building owners, water/wastewater, and oil and gas facilities operators are presented with utility bills that have multiple components. These can include power demand charges, energy demand charges, time-of-use charges, ratchet clauses, cost-of-fuel adjustments, power factor penalties, customer service charges, and national, regional, and local taxes. A misinterpretation of utility rate structures can lead to poor management of electrical consumption and higher costs.
Most energy bills cover similar basic elements. Familiarity with the terms can help show where the opportunities for cost reductions exist.
By pursuing best practices in energy efficiency management, asset management, and energy cost management, TCO of pumping system networks can be reduced by up to 20 percent. One simple technology, the variable speed drive with embedded energy management functionality, has the capability of being a major contributor to achieving achieve the TCO target.
The variable speed drive is fully integrated in the numerous steps that can be taken in order to implement an effective energy management plan. These include adopting energy efficient technologies, implementing condition-based maintenance practices, and optimising cost control of the electrical bill. The linking of pumping processes to energy systems helps improve business performance through better energy management.
Organisations that are ill equipped to jumpstart an energy efficiency program should seek the assistance of mission-critical subject matter experts. The alternative invites unnecessary delay, risk, and expense.
To achieve operational sustainability, organisations must act quickly to assess their current programs and begin building an operational methodology that emphasises improvement in energy efficiency.