Summary
Water supply systems are responsible for 2 - 3 % of the world's energy consumption. Efficiency savings are crucial to meet national targets for reducing greenhouse gas emissions (GHG) and to decrease EU dependence on imported energy sources. The first step to energy management is to conduct an energy audit in order to assess energy performance and identify energy saving opportunities. Therefore it is necessary to establish a cost-effective methodology for conducting energy audits. This fact is reinforced even further by the new desired legislative framework for energy demand management (Directive on End-use Efficiency and Energy Services), which states that energy audits are fundamental in the promotion of energy efficiency and energy services in buildings and industry.
A new approach to energy management was tested on two water utilities in the North of Portugal. The analysis of the 21 pumping stations allowed the identification of electricity cost savings by better procurement, potential changes to pumping regimes and load management, future pump replacement programmes and the need for a computer-based energy monitoring system.
Results
Costs savings by reducing electricity price and tariffs
Improved understanding of the electricity demand profiles of the installations, enable a reduction in electricity costs from 3% to 12% from new tariff option, interruptible contracts and change of electricity supplier.
Improve equipment and operation efficiency
The energy analysis techniques were used to identify periods of different electricity consumption patterns and to quantify costs of these changes. This allowed the calculation of how much could be saved by avoiding the use of several pumps at the same time. This information was used to inform and encourage operators to reduce, as a much as possible, the time pumps are running simultaneously. However this is not always possible, due to limited water storage capacity and other constraints associated to management of water reservoirs. Nevertheless, it was possible to quantify savings from increased pumping energy efficiency achieved by an extended water reserve capacity.
The investment cost associated with typical energy efficiency measures for these type of installations, such as: the replacement old motors for new higher efficiency ones, installation of variable speed drives to control pump speed and flow, refurbishment of pumps and the coating of internal components of pumps was found to be quite high. Most of the installations in this study are quite new, under 4 years-old, and more importantly, the water utilities were not interested in financing energy efficiency measures associated with high investment. Pumps are replaced only when seriously damaged. This fact alerted us to the importance of promoting energy efficiency at an early stage, when the initial planning and design of the ductwork, pumping and water treatment stations is being prepared.
Energy efficiency and operation monitoring
The implementation of a computer-based monitoring system was not in place at the time of the study. The use of time series energy analysis techniques informed the operators and managers on the advantages of energy M&T. In consequence the utility managers decide to integrate in the existing Supervisory Control and Data Acquisition System (SCADA) an energy management module.
The new energy management system will collect short-time series data, typically in 15 minutes intervals, on a large range of signals, such as energy consumption, pressure, flow, reservoir levels, etc, from several sites. Energy and production information is synchronised and integrated in the same 15 minutes intervals. All this information is then collected and monitored real-time at a base station and then stored on a computer database.
The energy management system includes graphic analysis tools, using energy M&T techniques (bivariate analysis together with CUSUM); it also has the facility to perform electricity tariff analysis, power demand monitoring and assess individual pump/motor performance and global efficiency of the water supply system. This computer-based energy monitoring system triggers alarms for unexpected values of the measured parameters. In summary, the energy management system will enable a continuous and timely detection of cost saving opportunities in these multi-municipal water supply systems.
Energy management action plan
The output of the study was an energy policy statement and a management action plan for the two water utilities. The energy policy was integrated in the environmental policy of the companies and signed by top managers. The creation of an energy management team in both utilities, which includes a representative from all the departments (operation, infra-structures, environment and finance) and external experts, was responsible for the development of an energy management plan. This energy management plan was based on the outputs of the energy study conducted. Some of the energy management measures are: provide training in energy management to head of departments and technicians, regular electricity procurement activities, continuous integration of energy issues into the quality and environmental management systems, regular assessment of water pumping efficiency, investigate opportunities to integrate renewable energy technologies in the water supply system, develop a new methodology for the design for future water pumping stations and establish energy reporting procedures. The energy management system, will act as the support tool for all the future energy management measures in the future.
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Case Study (148 KB PDF)