Zero and Low Cost Energy Savings Opportunities From Demand Management

Authors:

  • B. R. Lisk, H. Long - Hazen and Sawyer

Figure 1 shows the demand profile for the South Durham Water Reclamation Facility (City of Durham, NC) blower building electric utility service.

Reducing energy costs is rapidly becoming a major priority for water and wastewater utilities. Many water and wastewater utilities are implementing energy management projects to optimize their facility’s energy efficiency and resource utilization (i.e. biogas) to reduce energy usage. Demand management is another energy management opportunity that is often overlooked and can provide significant energy cost saving opportunities at zero or low capital cost. Demand management strategies that can be used in the water and wastewater industry to reduce energy costs include qualizing influent flow, managing filtrate return timing and flow, managing filter backwashing timing, managing biogas storage and utilization, managing water storage, interlocking intermittent loads, and utilizing onsite power generation to manage demand. In order for demand management strategies to be effective, the demand management strategy must not have any negative impacts to the treatment process and the demand management strategy must be coordinated with the energy billing rate structure(s).

To illustrate how demand management can result in energy cost savings, Figure 1 shows the demand profile for the South Durham Water Reclamation Facility (City of Durham, NC) blower building electric utility service. As shown on Figure 1, the City was managing their demand by stopping one electric blower and starting a biogas fueled engine driven blower during the on-peak period when the demand charge was $15/kW (off-peak demand charge is $1/KW). After developing an average demand profile from interval demand data supplied by the electric utility, it was found that the City was stopping the electric blower ~10mins into the on-peak period which increased the billing demand to ~437kW. The result was an extra $20,000/year in electrical demand charges. The City made it their procedure to stop the electric blower 15 minutes before the on-peak period which resulted in a ~$20,000/year savings in electrical demand charges. This change in operations was a “no cost” change that resulted in significant energy cost savings.

The purpose of this paper is to describe the elements required to develop effective demand management strategies for water and wastewater treatment facilities. This paper will present multiple demand management strategies that were identified and implemented from multiple energy management audits performed for multiple facilities.

The results of multiple demand management case studies will be presented with an emphasis on demand management strategies that provided a payback period of 1 year or less. Specifically this paper will include the following as a minimum:

- A description of common electric utility rate schedules (i.e. Time of Use, Demand Ratchets) and how electric utility rate schedules impact the demand management strategies for water and wastewater treatment facilities.

- Typical demand management practices commonly used by water and wastewater utilities including process modifications, peak shaving, and operations management.

- Utilizing on-site power generation systems such as standby power generators and biogas fueled CHP systems as a part of the demand management strategies to reduce energy costs and generate revenue streams from electric utility capacity credit programs and coincident peak billing rates.

-The role power monitoring capabilities has on the development of demand management strategies.

-The results of multiple case studies where demand management opportunities resulted in a payback period of one year or less.

For more information, please e-mail the author at hlong@hazenandsawyer.com.

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