Figure 1: Sample rate classes for a Northeast utility.

As electrical utility de-regulation accelerates, energy managers may want to look again at their electrical systems to discover how changing utility rate schedules will affect their energy management plans.

Significant energy savings have been achieved in the last twenty years and finding areas to reduce electrical energy cost is more difficult now. The fast pace and diversity of regulation changes make these efforts even more challenging. However, even under these circumstances, knowledgeable and alert facility managers can still find electrical energy savings.

There are three strategies that energy managers can used to find energy savings in their facilities:

• Increase electrical system efficiency

• Achieve better control of the electrical system

• Upgrade the electrical system

Individual projects must produce sufficient savings to pay back in a reasonable time. The existing or proposed utility rate schedule will help determine how feasible a project may be and how quickly it will pay back. Reducing energy costs also means improving business operation efficiency. In a period of low inflation, efficiency is one key to business success.

Electrical Energy Savings Analyses

When assessing a facility electrical system, the following information is required to evaluate system performance:

• Complete set of electrical system drawings with equipment nameplate ratings

• Hourly demand profile or monthly peak demand

• Monthly electrical usage for last three years

• Monthly electrical billing for latest 12 months

The electric utility can usually provide monthly peak demand and usage data along with power factor for medium and large users.

In addition, trend logs of HVAC equipment and three-hour temperature profiles help correlate comfort equipment operation to weather data. In addition, production data and work schedules relate energy use to production. If 12-month data are not available, a snapshot of a typical period during the peak demand months will suffice.

If electric use data are not available, a thorough analysis cannot be done until data collection is completed, which will take six months to a year. In-house staff or a consultant can do this work, using modern instruments.

Based on a preliminary assessment of needs, the facility manager may decide to monitor certain circuits, motors, buildings, or lighting circuits. The recording instrument can be moved weekly, taking snapshots of a particular load. When working with motor loads, the output of the machine or system needs to be recorded at the same time as the input power to the motor.

Electric use and power demand should be recorded at regular intervals, depending on the requirements of the survey. Production machinery and HVAC equipment are often monitored on an hourly basis. Other equipment may only need daily monitoring. Temperature data and other variable data should be recorded to provide data to correlate with the HVAC systems. Inexpensive data loggers can gather all the needed data. The power density (kilowatt per square foot) and energy intensity kilowatt-hour per square foot can be calculated as a baseline for individual buildings or the whole facility and compared to usage and demand.

A thorough survey, assessment, and analyses of every major electrical system, electrical machine, or branch circuit can locate energy savings opportunities in one or more of following areas:

• rate schedule

• lighting upgrade

• power factor correction

• motor efficiency

• motor control (asd)

• peak shaving

Facility managers should also examine their mechanical systems. Oftentimes the electrical survey will also reveal opportunities for savings in the mechanical systems.

Utility Rate Schedules

Figure 2: Energy strategies and their cost effect.

A facility that has expanded rapidly may qualify for the large commercial/industry or bulk rate schedule. Many facility managers mistakenly believe that the electric utility will notify them when they qualify for a better rate.

To determine whether a facility qualifies for a better rate, the facility manager should check with the utility representative and compare rate structures. The plant may need an upgraded voltage rating and switchgear to qualify for the better rate schedule. A cost-benefit analysis will determine if the upgrade is cost-effective.

Figure 1 shows demand charges for two classes of service for winter (October-May) and summer (June-September) for a utility in the Northeast.

A customer with demand of about 2000 kilowatts (kW) rate would receive savings from switching to a more favorable rate:

When transmission and other charges are included, the total annual saving would be approximately $150,000. If the switch gear upgrade project costs $450,000, then the simple payback is:

$450,000/$150,000 = 3

Lighting Upgrade

Lighting accounts for approximately 30-40% of the total energy for most commercial facilities. Because of heavy process and motor loads, the lighting in industrial facilities will consume only about 5-10% of the total energy. In either case, upgrading lighting is an attractive strategy and is usually the first option most facility managers select.

A lighting survey or audit is the place to start. The audit evaluates the current lighting systems and judges how well they perform compared to state-of-the-art systems. The basis for comparison is lighting power density (LPD). Current standards for state-of-the art office fluorescent lighting T8 systems are at 1 watt per square foot (W/ft2) or less. When the LPD of an existing office lighting system is 2 W/ft2, the potential savings is 1 W/ft2. This potential savings can be multiplied by the area of the desired upgrade.

For facilities that have not upgraded lighting systems, the energy audit is an excellent way to identify electrical energy cost savings. The most popular upgrade converts T12 fluorescent systems with magnetic ballasts to T8 fluorescent systems with electronic ballasts. Savings of 40-60% have been documented, and 2-3 year paybacks are common.

LED (light-emitting diode) exit signs that replace or convert incandescent or compact fluorescent (CFL) exit signs also save energy. Energy Star-labeled products operate at a maximum power of 5 W.

When existing signs use two 20-W incandescent lamps, the savings for each sign are 35 W. Exit signs operate 24/7/365 (8760 hrs/yr), so the energy savings ($25 at $.08/kWh) pay back the purchase and installation of new signs in less than 3 years. With virtually no maintenance for at least 10 years, maintenance savings reduce the pay back to less than 2 years.

HID systems in manufacturing or warehouse facilities can be effectively upgraded using either the new pulse start metal halide system or the new high-bay fluorescent fixtures. (See "Re-lighting Manufacturing Facilities" EUN, November 2001).

PF Correction

Many electric utilities penalize commercial and industrial customers for failing to maintain a power factor (PF) above a specified level. The penalty can easily be eliminated by increasing PF to the defined level.

The average power factor, without correction, for a typical small commercial or industrial facility is about 82%. If a power-factor-correction capacitor bank is installed to bring the power factor over 90%, a 10% power demand reduction can be realized. Normally, the cost can be paid from savings in less than 2 years. When feasible, PF correction is usually one of the fastest payback projects and should be at the top of the priority implementation list.

In addition, many utilities base their demand charges on kilovolt-amperes, not kilowatt.

Power factor correction reduces the demand charges by the same percentage as the increase of power factor, so a facility can still reduce its energy costs even when it cannot meet the utility's PF penalty threshold.

Improving power factor from 70 to 100% reduces heat losses by (70/100) 2, or 49%, saving 51%. For example, a facility using 500,000 kWh, with losses of 4%, will reduce its heat losses by: 500,000 kWh x 4% x 51% = 10,200 kWh.

Higher PF means lower waste current in the electrical system. All electrical equipment such as breakers, buses, fuses, transformers, conductors, current transformers (CTs), and potential transformers (PTs) will carry less current. Reducing the electrical burden will reduce heat generation, extend service life and reduce maintenance cost.

Care must be taken when applying PF correction capacitors. Improper application can damage an electrical system. Capacitors can cause fuses to blow and can amplify system harmonics. Every system is unique and requires carefully study and analysis by a power engineer.

When the volt-amp reactive (VAR) contribution is caused by large motors, the capacitor can be installed close to the load-at the motor starter. The PF capacitor can be applied at the distribution bus when the VAR contribution is from a distribution transformer. Systems that experience large load swings, throughout the day or month are prime candidates for switching correction units that automatically correct the PF as load variations occur.

High-Efficiency Motors

The efficiency of electric motors has improved substantially in the last fifteen years. The largest motors in an air-conditioned facility are usually the chiller motors. Significant savings can be realized by replacing older motors with newer, more efficient units. Data provided from a major chiller manufacturer in a recent chiller replacement project show that a new chiller can produce one ton of chilled water at 0.51kW (0.51 kW/ton). Twenty years ago, chiller loads were at least 0.7 kW/ton.

Using 0.71 kW/ton for convenience of calculation, a chiller rated at 1000 tons, upgraded to 0.51 kW/ton will reduce demand by 200 kW, a 30% savings. For facilities with 20-year-old chillers that are near end of service life, this savings provides a good reason for upgrading. For more incentives, the local utility may have an energy improvement incentive program available.

Other motors are also potential candidates for motor upgrades. For example, fans or pumps can have improved efficiency from 5 to 15%-the smaller motors having the larger improvement. Old motors can be phased out by a schedule or replaced with high-efficiency units when they breakdown and need repair. However, the decision to replace or repair should not be made at the time of breakdown, since replacement motors usually take some time to obtain.

For more information on motor analysis and replacement strategies, go to the Motor Challenge program website at: http://www.oit.doe.gov/ bestpractices/motors/

Adjustable Speed Drives

If a sizable motor is subjected to wide load swings during long operating hours during a year (such as HVAC systems) and the system can accommodate variable flow, then the system may be a candidate for adjustable speed drives (ASD). Examples of HVAC equipment that can use ASD are water pumps, central air handling units, exhaust fans, cooling tower fans, and chiller compressor motors. Savings vary based on the motor operating profile throughout the year.

Equipment and installation costs usually have an inverse relationship with the motor horsepower. For larger motors, the cost per horsepower is less. Motors of 100 horsepower and greater are candidates for an ASD upgrade. Smaller motors may need replacement.

Just as with most energy management projects, a detailed engineering design and a cost/benefit analysis have to be conducted. ASD and motor sizing, motor winding, coupling and load characteristics have to be reviewed. The first step in conducting the benefit analysis is to collect a reliable annual load profile for the specific application.

Peak Shaving

Thermal storage is often considered with other HVAC upgrades. As part of a chiller plant upgrade, ice storage cannot reduce the need to add chiller capacity. The ice storage system can make ice during off-peak periods to produce cooling for the next peak cooling period. A cost-benefit analysis based on cooling load profiles, rate schedules, and the cost of installation determines the savings from thermal storage.

An on-site peaking generator can be implemented for peak shaving as well. The facility must be on a rate structure that justifies the installation of a peak generator. This option must be carefully considered, taking into account all operating and maintenance costs, power quality, interfacing with the existing power distribution system, fuel, noise and vibration, and environmental regulations.

The demand profile can identify any heavy machinery that is operated a few hours a day that could be operated off-peak. Changing the operating hours of any heavy equipment operating on-peak can eliminate the need to purchase and install a peaking generator.

For example, a large manufacturer operated several large heat treat ovens on a 24-hour cycle. Upon closer examination, they determined that the process really consisted of three 8-hour operations, with each operation being completed by a different shift. By changing the firing operation of all units to off-peak, large demand savings were realized for little to no investment.

EMS and/or BMS

Building management systems (BMS) or energy management systems (EMS) can turn systems or selected equipment on or off based on time-of-day schedules or variable parameters, such as temperature. These systems may be connected to other building systems such as fire alarm, security/surveillance, or access control. They can also monitor other critical systems such as elevator control or other utilities management systems, such as water.

EMS and BMS systems are versatile and sophisticated controls for a small building or large office or college campuses. With current technology and sophisticated software, many points can be monitored for temperature, pressure, humidity, voltage, current, and switch or relay status throughout a facility. These BMS/EMS systems can be programmed to provide room comfort in the most economic way or to perform a number of energy management strategies, such as temperature setback. Applications employing energy management strategies have produced significant electrical energy savings that have resulted in a return-on-investment (ROI) in three to four years.

When the facility is served under a utility time-managed rate schedule, these systems can be set to turn off major equipment or motors during peak hours. The BMS/EMS not only can be used as an energy saving tool but also can be used to shave peak demand, saving energy cost. These systems also can generate a variety of utilities and energy consumption reports and analyses.

On-Site Generator/ Cogeneration

An on-site peaking generating unit may be feasible for facility having a load of 15-20 megawatts (MW) or more. For loads of 25 MW or more with an [adequate] requirement for steam, a co-generating plant may be considered.

Some large facilities, such as a college campus or major manufacturing plant, have built combined-cycle cogeneration power plants. The plant uses either a diesel engine or gas turbine generator for the first stage electrical power production. The exhaust gas (1000 ?F) or higher) is piped to a heat recovery boiler with supplemented fuel for steam production. In addition to providing a heating process or application, some steam is used for the second stage electrical power generation using a steam turbine. Steam from the steam turbine is also used for heating. This is the most efficient mode of cogeneration operation. Compared to traditional cogeneration plant efficiency of about 33%, the combined-cycle cogeneration plant can reach around 70%.

Of course, a thorough feasibility study has to be conducted to assess the facility need, operation, maintenance, environmental impact, and regulatory considerations.

Summary

When evaluating electrical energy management strategies, consideration should be given to that part of the electric bill that would be affected most by implementing each strategy.

With this approach, the manager can create a priority list of strategies to implement projects that benefit the facility and provide a reasonable payback on investment. Not all of the strategies may be implemented by any one facility, and the manager has to carefully evaluate the facility and choose those strategies most suitable for their applications. Some managers bundle several strategies together, so that the short payback projects help pay back the longer payback projects.