Water and wastewater facilities consume approximately 3% of the power used in the United States. For many New England communities water and wastewater facilities represent their largest energy demand. The cost of energy is a major factor driving conservation considerations. Historically, the potential to save money was often not sufficient to gain public support for energy conservation projects because of the required up front capital cost. Today, public interest in sustainable infrastructure; reducing our carbon footprint; lessening dependence on foreign energy sources; and taking advantage of energy efficiency incentive programs; along with bottom line savings, has given energy conservation efforts new life.
It’s all about the pumps
Water facilities use the majority of their energy in the pumping of water. Many of the pumps used in the water industry were designed over half a century ago. The key to conserving energy is to optimize pump selection, operation and maintenance. Pumps should be selected so they are operating at their ‘best efficiency point’ (BEP). To make the proper pump selection, it is important to understand the conditions under which the pump will operate. Developing a water distribution hydraulic model is a great tool to assist in selecting the finished water and booster pumps.
Optimize pump efficiency
Once the most efficient pump is selected, there are a number of ways to maintain high efficiency, including:
- Avoid the use of throttling valves for flow control
- Use variable frequency drives (VFD’s) to vary flow to match demand
- Use automated controls to optimize the run times of pumps
- Set up an asset management system to track maintenance of your pumps
- Replace inefficient motors with premium efficiency motors
- Complete pump efficiency tests on a yearly basis
- Monitor pump vibration and bearing temperature on a quarterly basis to look for early signs of loss of efficiency
- Conserve energy by reducing lost water
Another energy conservation strategy is to reduce the amount of water pumped by reducing lost water in the distribution system. One community reduced lost water from 25% to 15%, which resulted in a 10% reduction in power use and treatment costs. Setting up a regular leak detection program is a key component for reducing lost water. Modern methods of electronic leak detection devices and use of computers to pinpoint leaks have made leak detection a worthwhile investment.
Optimize the distribution system
Another method to reduce pumping costs is to optimize your distribution system. Using the water distribution hydraulic model, you can evaluate opportunities for reducing the pumping head your pumps have to overcome. A reduction in pumping head will directly reduce energy consumption. The model can be used to adequately size pipes; look for areas to loop the distribution system; and, determine if rehabilitation or replacement of corroded water mains will have a positive hydraulic benefit. Another potential energy savings is to develop multiple pressure zones within the distribution system. Operating each area of your water system within a 35psi to 65psi +/- range may reduce the overall energy of pumping water.
There are many other strategies to reduce energy consumption at water facilities. The best way to start is with an energy audit of all your facilities. Energy audits come in all shapes and sizes, from simple in-house review of energy use, to complete process audits. In general, energy audits review the following:
- Document current energy usage
- Identify low cost operational adjustments
- Find opportunities for using instrumentation for better monitoring and control
- Assess building lighting
- Assess HVAC
- Assess building insulation
- Process audit
- Complete a payback analysis on equipment replacement and upgrades
There are a number of public and private programs that help fund energy audits and energy conservation measures. If are considering energy conservation improvements, you will want to explore these programs.
Conserving energy is the most economical, and has the most positive environmental impact.