Today's facility managers have come to see controlling energy costs in a new light. No longer content with mere conservation, enlightened plant engineers now practice an integrated energy-management plan that factors energy use and demand. It's an approach that will work especially well after electrical utility deregulation, when energy consumption rates become more directly tied to peak power patterns.
To best exploit savings from this patterned approach, facility managers, engineers, and consultants should get together to develop a plan that minimizes unchangeable demand and controls changeable demand. Basically, the energy usage associated with voltage drop (line, or I2R, losses), low power factor, high-loss transformers, low-efficiency motors and low-efficiency lighting should be well known so that better system designs and specifications can be prepared. Let's carefully study these individual elements.
Line losses can account for 3% to 4% of the peak demand, so they deserve a good deal of attention. Factors directly related to voltage drop are high current (caused by low power factor and/or distribution at a lower than practical voltage) and extra resistance (caused by long circuits and small diameter conductors).
The National Electrical Code (NEC) allows a 5% total voltage drop from the service entrance to utilization equipment, with a limit of 3% in either the feeder to the distribution panel or the branch circuit to the equipment. By simply applying the NEC ampacity requirements for conductors in feeders and branch circuits, the 3% limit on losses can be satisfied. However, long-branch circuits often can be redesigned and studied for ways of reducing these line losses.
It is possible to gain a large reduction in I2R losses and reduced electrical demand if a 480 V/277 V, three-phase, four-wire main distribution system is used instead of a 120/208, three-phase, four-wire distribution system designed to Code requirements.
Whenever possible, 277-V lighting branch circuits should be used. And if No.10 AWG conductors, instead of No. 12 AWG wire, is used on lighting and appliance branch circuits, the total impedance of these circuits can be appreciably reduced. This concept can be applied to any circuit or feeder, but the larger the conductors involved, the smaller the percentage gain. Also, the available fault currents on these circuits will increase and have to be accounted for in equipment ratings.
* Utility power factor is generally improved by placing capacitors in the circuit close to the low-power factor load. The best place to connect power-factor-correcting capacitors at a motor is between the overload relays and the starting contacts of the starter. Thus, they will be switched with the motor. Also, the overload settings will not have to be adjusted because they will be downstream of the capacitors. Obviously, the starter should be located as close as possible to the motor. In some cases, the capacitors may have to be switched separately from the motor to prevent pumping action between the motor and the capacitors.
If the power factor of a motor is raised from 0.85 to 0.95 at the motor, the current flow to it will be reduced by 11% and the demand reduced by almost 21%.
* The use of higher efficiency transformers that have lower temperature rise may be advisable. These units have lower internal losses, but they are more expensive. Therefore, it is useful to do a cost analysis covering the fixed cost of a transformer versus operating savings by using a lower-temperature-rise but more efficient transformer.
* High efficiency motors have already proven themselves, and they are required by the latest energy codes. There are certain points, however, that should be considered before you make any capital investments. Motors should not be oversized because lightly loaded units operate less efficiently and at very low power factor. They should be specified with a power factor correction of .95 at full load.
* Retrofitting of exit signs is an important way to reduce operating and maintenance costs in a building because they operate 24 hours a day. Exit sign retrofit kits use low-wattage incandescent, compact fluorescent (CFL), or light emitting diodes (LEDs) as their light source, thus making the change out simple. A CFL type sign generally will have a pair of 7-W lamps and a ballast consuming about 6 W. Many LED signs use only 1 or 2 W, and none require more than about 5 W.
However, a number of factors should be considered when evaluating which type of exit sign retrofit kit to use for a facility. An exit sign must meet a number of standards, and a retrofit kit should be listed by UL in one of two categories, Classified or Listed Product. Classified means that the kit is approved solely for the fixture that was submitted, and Listed Product means that the kit is approved for any fixture with dimensions equal to the submitted fixture. With the recent introduction of the first UL 924-listed LED retrofit kit, any type of light source can now be used.
Although LED-type retrofit exit signs have a higher first cost than other choices-$60 or more for a new or retrofit LED sign, compared to $20 to $25 for an incandescent or CFL sign-their energy efficiency and low maintenance needs make them economical over time.
* Today lighting design focuses on three factors-system efficiency, better controls and target footcandle (fc) levels in all areas, as recommended by the Illuminating Engineering Society of North America (IES). A lower level of general illumination (30 fc in the main work area and 50 fc in task areas requiring more illumination) is usually recommended in offices. Remember that lighting efficiency can be evaluated not only on its direct energy use, but also by its impact on the sizing and energy use of other systems, particularly HVAC equipment.
Lighting systems using T8 lamps and electronic ballasts are in the forefront of efficient design for illuminating office