Water Authority Sharpens Performance with Energy Audit

The Steelton Borough Authority was able to reduce energy consumption at its water treatment facility by more than 16 percent through implementation of energy conservation measures suggested after an energy audit of the facility.

Steelton Borough is located near Harrisburg in Dauphin County, Pa. The authority owns and operates a 3.0 mgd conventional water filtration plant designed and constructed in the early 1970s. The authority serves approximately 5,500 customer connections via a distribution system that includes more than 35 miles of pipe ranging in size from 11/2 inch to 16 inches in diameter. Raw water for the plant comes from the Susquehanna River.

Plant equipment includes screens, a raw water pumping station with two 30 horsepower pumps, pre-chlorination, chemical conditioning (with an "Instamix" inline mechanical mixer), two flocculation clarifiers, four dual media filters, a clearwell, disinfection by chlorine dioxide and two 250 horsepower finished water pumps. Plant equipment also includes two backwash water pumps, each of which has a 20 horsepower motor; two backwash drain pumps with a 11/2 horsepower motor; and miscellaneous pumps including sump and vacuum pumps. All pumps at the plant and at the booster pump station are constant speed devices.

The plant purchases power (480 volt service) from the Pennsylvania Power and Light (PP&L) Company. Power is distributed throughout the facility from a switchboard and a single Motor Control Center (MCC). The Borough negotiated with PP&L in 1998 to obtain more favorable energy pricing for all of its facilities under the Pennsylvania energy choice program.

Herbert Rowland & Grubic Inc., (HRG) designed the water filter plant and is the authoritys retained engineer. With a goal of reducing costs and optimizing customer service, the authority directed HRG to conduct an energy audit to identify how, where, and when energy was used at the plant.

Energy Audit

The audit team included the plant superintendent and a team of engineers from HRG. The HRG team included a client manager, a process/controls engineer and an electrical engineer. They reviewed process, mechanical and electrical drawings prior to the field audit. The HRG team also obtained a copy of each of the energy bills for the previous year for all Steelton Authority facilities and created a database from the information. The database included:

• Month, year, and number of days in each billing cycle.
• Kilowatt, kilowatt hours, and KWH/day.
• Bill amounts in dollars.
• Plant flow in gallons (for the billing cycle).
• kwh per 1,000 gallons processed.
• Load factor.

Work on site began on Oct. 20, 1998. After discussing the audit process with the Steelton Authority staff, all of the team members participated in a preliminary walkthrough of the plant. The team then conducted a detailed investigation of the site and equipment.

Power measurements were taken for each piece of equipment with a motor of 10 horsepower or greater. Data on the run cycle of equipment (hours per day, days per week etc.) was recorded. Pump curves were obtained, and pressures and levels were measured and verified for accuracy. Equipment with installed spare capacity was rotated so that performance of online and standby equipment could be checked and recorded. Aside from process equipment, lighting was evaluated for adequacy, operating cycle, and type. Heating and air conditioning were reviewed as well.

After the data was collected, the team conducted a brainstorming session which yielded numerous options for evaluation. Assignments were made and due dates were established.

Energy Conservation Measures (ECMS) were created for each energy saving opportunity. Each ECM includes a narrative that describes the existing conditions, as well as the proposed or modified operating scenario. Each ECM is tied to a spreadsheet that includes the following information:

• Process name.
• Equipment name.
• Equipment make and model.
• Motor Data (horsepower, nominal efficiency, voltage, speed, full load amps etc.).
• Measured kw for motors 10 HP and greater.
• Calculated kw for all other motors and equipment.
• Annual operating hours.
• Calculated kwh and annual utility cost(at time of audit).
• Calculated kw, annual operating hours, calculated KVM and annual utility cost (after implementation of the ECM).

The above data combined with an estimated cost of implementation allowed the calculation of a cost payback for each conservation measure.

The ECMS, along with other data that were collected, were incorporated into an Energy Conservation Analysis Report. The report included sketches and a spreadsheet that compares energy use per 1,000 gallons of water produced. This value was used as a yardstick to monitor the plants progress. The goal was to reduce energy use without sacrificing customer service. Consideration was given to both process and non-process ECMS. Payback and capital cost were used to prioritize implementation of the conservation measures.

A total of six ECMs were developed. The first involved installation of power monitoring equipment to enable the plant staff to monitor their efforts and progress on the project. A GE Multilin Power Quality Monitor was installed to provide data on use of energy throughout the facility.

The second measure included retrofit of plant lighting. Much of the existing lighting was outdated. Retrofit recommendations included the installation of T8 fluorescent lamps and electronic ballasts in lieu of existing fluorescent lamps. The project also included the replacement of incandescent lamps with compact fluorescent lamps, and the addition of occupancy sensors in key areas. A payback of slightly over 31/2 years is projected for this ECM. The payback calculation includes an O&M credit associated with the effort.

ECM 3 involved heating and air conditioning. The existing air-conditioning system covers only the office area but is old and inefficient. All of the heating is accomplished by electric unit heaters. The ECM recommended a capital project to retrofit HVAC plant wide. On an interim basis, thermostats were adjusted in several of the process areas that are seldom occupied. A cold weather temperature of 50 degrees F now is maintained in the flocculation/clarifier area.

ECM 4 included retrofit of raw water pumps with Variable Frequency Drives (VFDs). The current method of flow control in the plant is to use a throttling valve to obtain the desired amount of flow. The estimated payback for this ECM was six years. The relatively long payback is the result of the project imposed requirement to retrofit both the online and standby pumps with VFDS.

ECM 5 included retrofit of the Coagulation/Chemical Feed system. An in-line mixer, chemical tank mixers, and chemical feed equipment were evaluated for need, size, use, and effectiveness. The team recommended that one in-line mixer be eliminated after testing determined it could be removed with no adverse effect on the process. Other recommendations included replacement of chemical feed pumps with more efficient units.

ECM 6 was the most complex measure. It included a combination of equipment modifications, process and piping modifications and operational revisions. The goal of this ECM was to minimize the number of backwash cycles and to minimize the energy required to backwash. Tank and piping modifications were recommended that would result in reduced backwash pump head requirements. New backwash wetwell level instrumentation and pump controls were recommended. The instrumentation would result in better control over pump operation and would enable cost effective interlocking of pumps to minimize or eliminate simultaneous operation of backwash pumps and drain pumps. Finally, operational modifications were recommended. They included modifications to the scheduled backwash performed on the filters. This ECM provided a five year payback.

During the same timeframe as the energy audit project, the authority was replacing its high service pumps. HRGs client manager was involved with the project and coordinated efforts with the energy audit team. As a result, the new high service pumps also provided substantial energy savings.

Results

The energy conservation measures suggested by the audit are currently being implemented. On a per gallon basis, the plants current energy use is 16 to 30 percent less than it was before the project began. As other conservation measures are implemented, the Authority looks forward to savings of 20 to 35 percent.

About the Authors:

Joseph Anthony Guagno, P.E., and Bradley James Straub, P.E., are engineers with Herbert, Rowland and Grubic Inc. Paul Wintergrass works for Steelton Borough Authority.