By Morris Liu, City of Calgary
The Canadian Water and Wastewater Association conducted a national survey on large-scale pumping system optimization. It identifies what products/practices are used, and what drives investment.
Water utilities operating a system with multiple pressure zones and pump stations encounter challenges to their financial resources as well as environmental impacts. Operators have to make instantaneous decisions in selecting optimal pumps/pump combinations to respond to demand changes or other system needs.
A large-scale pumping system uses an extensive amount of energy. Proper operational guidance and technical support is the key for efficient operation that can reduce energy consumption and greenhouse gas emissions, while ensuring safe and secure water supply.
A variety of pump station optimizers or pump schedulers are available in today’s market. However, water utilities often find it difficult to choose an appropriate solution to their system. A non-biased knowledge of their peers’ practices and experiences could help them in such situation.
The Canadian Water and Wastewater Association (CWWA) conducted the survey among its members in February 2017. It targeted water utilities with multiple pressure zones and pump stations and focused on pump station optimization software (functionality, experience and preference).
Eighteen municipalities responded with information on their drinking water systems and optimizing practices in pump stations operation. Participants shared information on their main drivers, methods, preferable control strategy and major challenges in optimizing large-scale pump systems.
Twenty percent of the participants have an existing pump system optimizer. Twenty percent said they use pump optimization solutions other than software. One-third of the remaining participants are interested in investing in pump system optimization software.
Among the “No” responders to the “interest of investing” question, 40% either conducted pump tests recently or installed monitoring devices for the energy consumption of individual pumps. The “No” responses appeared neither correlate to the scale and complexity of a municipality’s pump system, nor to the population served.
High-energy cost is the primary driver to invest in pump system optimization. Population growth and demand increase is the second main driver. Other drivers include reduction of carbon emissions, reduction of pressure fluctuation and overpressure incidents, building resiliency and redundancy in the system, inadequate staffing and losing experienced staff due to retirement.
Two-thirds of survey participants use one or more pump system optimization solution in their water transmission system. The solution can be software, an operational practice, or both. Software products providing advisory recommendations are slightly preferred over software that takes full or partial control of a pump system.
Level of Automation with Software
To understand what type of pump system optimization software is desired among municipalities and utilities across Canada, three options were provided. These are Fully Automatic Control by Software, Advisory Only and Hybrid.
Advisory software was the favored option. However, the municipalities / utilities who already have optimization software implemented all select the Hybrid option.
Other optimization solutions included:
- Operating pumps during off-peak periods
- Thermodynamic testing of pumps to establish real-world up to date pump curves
- Running VFD in the most efficient energy and flow zones
- Continuously monitoring pump efficiency in conjunction with pump retrofits (Fig. 5&6)
- Proper pump selection during design stage
- Educating operators and providing the most efficient pumping schedule and combination
Utilities across Canada are facing diverse challenges for pump system energy management including:
- aging infrastructure,
- difficult to maintain adequate storage for potential sudden demand increase,
- oversized pumps,
- pipe leakage,
- difficult to obtain reliable demand prediction and current pump curve,
- pump operating far from the Best Efficiency Point,
- high water demand often occurred during on-peak hours, and
- raising water over an extensive amount of height.
The survey yielded results that may benefit water utilities facing financial constraints when making decisions in capital investment. It showed the significance of the energy and energy efficiency issues today to water utilities, provided examples of optimizing solution in large-scale pump systems with multiple pump stations and reservoirs, displayed preferences in software’s level of automation and shared current practices among participated water utilities.
This survey was funded and supported by the Canadian Water and Wastewater Association and its Water and Energy Efficiency Committee. The author would like to thank Rita Zhang with the City of Calgary, for her significant contribution in this project.
Morris Liu is with the Water Resources Department at the City of Calgary.