The climbing cost of electric powerconcerns all facilities today. This article offers some suggestions on where to look for opportunities to reduce unnecessary energy use. These suggestions may not be applicable to every plant and building, but some may trigger other ideas that can be put to use by electrical contractors, plant engineers, maintenance personnel, and system designers.
Electric utility deregulation is changing the way building owners look at energy management techniques and their use of electricity. To take advantage of the opportunities offered by deregulation, a facilities manager must have access to information on energy use and the ability to monitor and control that energy use.
Although monthly utility bills show how much electric power was used, what the peak demand was, and when the peak occurred, facilities managers need more information about their site if they are going to negotiate with an electricity provider in the future. Consider using an energy management system (EMS) tied into electrical meters to provide that information. Data from the meters or submeters can be routed through the system and stored in a computer. Data can then be set up in different formats for evaluation and presentation.
Basically, an EMS helps trim electric-energy consumption by tracking electrical demand and allowing the facility to reschedule the operation of electrical equipment or to curtail the use of equipment.
A full functioning EMS can provide this data in real time, and some of the products available make use of Internet technology. For example, a number of companies have energy control centers operating 24 hours a day using real-time, two-way communications over the Internet.
The control of your electric-energy demand offers excellent opportunities to cut power costs. Energy demand is defined as the greatest amount of power (kW, not kWh) required by a facility, over a preselected short period, usually 15 minutes. Most utilities impose a demand charge to discourage excessive demand peaks that could result in taxing their generating capacity. The demand charge is for the maximum rate of energy use, in addition to the charge for total amount of energy used.
One way to reduce power demand is to use a procedure called load shifting, in which some electrical loads are operated only during off-peak periods-when demand for and the cost of electricity are relatively low. A load curtailment procedure can automatically turn off electrical loads, such as air handlers, chillers, or freezers, sometimes on a rotating basis.
A recent study on the use of demand-side programs found that half of the large commercial buildings surveyed in the Midwest included a building automation system (BAS). Although a BAS can also be used to control lighting, the apparent complexity of these systems and interoperability failures limited these applications in the past. However, a modern BAS-controlled lighting system can provide energy savings greater than the savings seen with the use of occupancy sensors, photo sensors and timers.
Most BAS units are essentially distributed control systems (DCS), meaning all their computing hardware and software functions are distributed throughout the network. The programming "intelligence" is shared among a number of control modules and/or personal computers.
Each of the modules uses direct digital control (DDC) technology to communicate with each other and to function as an "intelligent" whole. Thus, all the lighting in a facility can be operated from a single central monitor, and the central monitor can supervise the HVAC system, security, elevators, and even smoke detectors.
A DDC module can be attached to any type of building load or sensor, such as an infrared occupancy sensor. By integrating the sensor and its associated lighting circuit into a BAS, its information can be shared with other systems within the building. For example, after business hours, if an occupancy sensor node tells the network a certain private office is occupied, the BAS can turn on the hallway lights on that floor, adjust the temperature in that office, and alert the security staff the room is occupied.
One of the biggest questions involved in setting up a BAS is the method of connecting all the devices together-with installation cost being a major concern. Low-voltage, twisted-pair copper conductor cabling is the most widely used wiring/communications method. Additional methods are: coaxial cable, fiber-optic cable, narrow band or spread-spectrum power line carrier (PLC) signaling, radio frequency (RF) transmitters and infrared (IR) transmitters.
Routers are also used to extend a control network over standard or dedicated telephone lines via modem, or over a transfer control protocol/Internet protocol (TCP/IP) network, such as a corporate intranet or even the global Internet.
These wiring/communications methods, or media, can be mixed in a network, so the best option can be used for each network section. Media with greater bandwidth, such as twisted pair or fiber-optic cabling, provide higher data transmission rates, which are needed for real-time monitoring and control.
Of course, a BAS can be rented, leased, or purchased. Some energy management firms call for little or no up-front payment in exchange for a share of the monthly savings in energy costs that the system returns, over the lease period. Additionally, some electric utilities may help pay for a system in exchange for the ability to monitor the power system and shed some electric loads in peak demand periods.
Control network A control network is a group of things (nodes-each with one of more sensors or actuators, plus localized computational capability) that communicates (over one or more media, using a standard protocol) to implement a sense and control, sense, or monitoring applications.
A control network can be a seatbelt warning system, or an electric power distribution control system, or a city's traffic management system.
Communication among the nodes on the network may be peer-to-peer (distributed control) or master-slave (centralized control). In either case, intelligence in the nodes (computational capability) permits the distribution of processing loads. A sensor can be "intelligent," for example, doing local data analysis, conversion and normalization, and reporting only unusual changes in status. If the control functions are also distributed, as mentioned above, both the system functional performance and reliability can be greatly enhanced.
BACnet and Lon Works are among the most popular communications protocols used by direct digital control (DDC) networks. A communications protocol is defined as the language allowing the control modules to "talk" to each other. Both protocols are effectively open standards, meaning any manufacturer of components can use them, and their products should be compatible with any other devices using the same protocol.
BACnet (Building Automation and Control Network) was developed specifically for HVAC control networks by the American Society for Heating, Refrigeration and Air-Conditioning Engineers (ASRAE). The protocol is described in ANSI/ASHRAE 135-1995. It was set up to allow the interoperability of various manufacturers' existing distributed control systems for HVAC.
A key feature of BACnet is its ability to send its signals over the wiring of an existing Ethernet or Arcnet local area network (LAN). BACnet signals can even be transmitted over a LonWorks network. However, Lon Works devices cannot interpret BACnet signals; they can only pass the signals along to a BACnet device. BACnet is also a prestandard within the European Committee for Standardization. However, lighting control components using BACnet are not yet widely available.
A development of the Palo Alto, Calif.-based Echelon Corp., LonWorks is used with virtually all types of control systems. More than 2000 companies around the globe use this protocol [technology] for applications ranging from manufacturing process control to supermarkets. Off-the-shelf components serve lighting security fire safety, access control, and HVAC. Although LonWorks and BACnet components are not compatible in the same network, a LonWorks control network can operate as a subset for a BACnet network.
Instead of requiring manufacturers to include a software interface in their control system, as BACnet standard does, Echelon "hard coded" the information into a chip called the Neuron chip, which manufacturers can include in their control-system assemblies. Echelon also has its own messaging protocol, called LonTalk, which is analogous to Ethernet and Arcnet. Although not an ANSI standard, an industry consortium, called the LonMark Interoperability Association, handles the protocol rules. The protocol is included in EIA-709, The Electronic Industries Alliance (EIA) Control Network Protocol Specification, and it is also recognized as a transport medium in the BACnet control standard.
With nearly 4-million devices (chips) installed worldwide, the LonWorks network has become a de facto standard because of their wide acceptance in the controls market.
Power factor correction The improvement in power factor can help avoid having your power company impose penalty charges for low power factor. Low power factor increases the power company's cost of supplying actual power because more reactive current must be transmitted; you can determine the status of your system power factor by studying your power bills. Low power factor can occur where feeder and branch-circuit runs are very long, when there are a great many motors on the system, or when motors are operated lightly loaded. This equipment will draw excessive reactive power, which is wasted power. A local apparatus service firm or engineering company can survey your power system for low power factor. An economical and practical solution to the problem of low power factor is to install capacitor banks. In most cases, savings in reactive power charges justify the installation after a relatively short period of time.
Modernize with variable frequency drives Adjustable speed drives, or electronic variable frequency drives (VFD), are now used for many loads, and also for control of tension, torque, position and other variables. These VFD units can significantly reduce electric power usage and bring cost savings when compared to mechanical-type adjustable devices such as fan dampers, throttling valves, belts and pulleys, gears, magnetic clutches and hydraulic drives.
However, be sure your motor and VFD are compatible! You could select a VFD to operate an existing motor and not have a real solution. Or you can select a new motor and a VFD for a particular application, and still have a problem. This is because not enough thought was given to how the motor, VFD, and load will work together.
The most popular type of VFD being made today produces AC via pulsewidth modulation (PWM), which chops up the sine wave into DC segments of constant amplitude every half cycle. A full cycle consists of one-half positive and one-half negative voltage segments (between 800 Hz to 15 kHz dc voltage pulses for each half cycle) rectangular shaped pulses. This high frequency pulsation is called the carrier frequency.
You should be aware of possible negative effects caused by high frequency pulsing on an existing motor. These include additional heat, audible noise, and vibration. Also, PWM circuitry, which causes a high rate of voltage rise of the carrier frequency, can cause insulation breakdown of the end turns of motor windings as well as breakdown of feeder cable insulation.
Consider changeout to more efficient motors The Energy Policy Act of 1992 (EPACT) now outlaws the manufacture of most standard efficiency motors, so only premium-efficiency motors can be made. The term "premium-efficiency" appears to be replacing the commonly used terms "energy-efficient" and "high-efficiency" when referring to motors with higher efficiency than standard-efficiency motors. The law, which took affect in October 1997, applies to any general-purpose, T-frame, single-speed foot-mounted polyphase induction motor of Design A and D configuration that is continuous rated and operating at 230/460 V, 60 Hz.
Some manufacturers and consulting firms offer on-site energy audits or assessments of existing motors to justify motor replacement. In such an audit, the surveyor establishes the operating characteristics (work load and efficiency) of the existing motor. Then, the audit becomes the basis for projecting energy savings and ROI (IRR, payback, or other financial measurement) when replacing with a "premium" motor.
On their Web sites, motor manufacturers offer application tools to help figure the payback you can enjoy by converting your standard-efficient motors to energy-efficient motors. Manufacturers also have different grades of energy -efficiency levels among the various motor models. A good, better, best system is not uncommon
Cut lighting usage intelligently Lighting is an obvious target for a campaign to cut electric power usage; the key technologies that can help in this effort are T8 fluorescent lamps and electronic ballasts. A T8 lamp and electronic ballast retrofit for a typical T12 and magnetic ballasts system will provide 30% to 35% reduction right off the top. A change out to a three- or two-lamp fixture with a specially designed reflector to optimize light distribution can provide a further reduction. A typical two-lamp T8 fixture uses about 58 watts, which is a saving of up to 70% in energy compared to a typical four-lamp, T12 and magnetic ballast system.
These products are an important part of the Energy Star Building's program Stage One Green Lights energy retrofit. The Environmental Protection Agency's 2600 Partners, representing 7.5-billion sq ft of commercial space, are showing some impressive savings, cutting their lighting energy costs per sq ft from 60 cents to 20 cents, with at most a three-year payback.
But T8 technology is now being overtaken by the T5 fluorescent lamp, in combination with an electronic ballast, as an even greater energy reducer. With a small cross-section (5/8-inch lamp diameter), a high efficacy and other desirable characteristics, T5 fluorescent lamps have become the standard for fluorescent fixtures in Europe. A 28-W T5offers about 104 lumens per watt, and a comparable 32-W T8 offers 88 lumens per watt, thus the T5 system provides more lumens per linear foot, and greater optical control and luminaire design flexibility.
Because of the T5's success in Europe, Dorene Maniccial, program manager at the Rensselaer Polytechnic Institute's Lighting Research Center, foresees the increased application of T5 in the United States in the coming years. The T5 lamp is produced in millimeter lengths, so it requires new fixtures to optimize light output and properly control source glare.
Primarily an incandescent lamp replacement, the compact fluorescent lamp (CFL) has grown slowly in application. Demand-side management programs helped develop the market in the early and mid '90s. CFLs are notable for their efficacy, using a quarter or less of the wattage of the standard incandescent and for their long lives. New developments in CFLs include dimmability and incandescent-like appearance-a bulb shape and color rendering close to an incandescent.
Future energy gains will come from the wider use of high intensity discharge (HID) lamps, especially the metal halide source. New developments in metal halide arc tube technology brings advantages of lower wattage and full dimmability, achieving efficacies similar to high-pressure sodium lamps but with much better color rendering. Over the last several years, lighting upgrades have provided many opportunities for facility owners and managers to reduce their lighting electricity loads by 20%, 30% and even 40% or more. Basically, the three most popular fluorescent systems used today are:
85-CRI (daylight has a CRI of 100), 4-ft F32T8 lamps with high power 1.15 to 1.20 ballast factor (BF) electronic ballasts
40-W to 55-W biaxial lamps with electronic ballasts
triple-tube compact fluorescent lamps with electronic ballasts In addition, one fairly new system is gaining a great deal of attention. At present, three manufacturers are marketing induction (fluorescent) systems featuring long life, good color, and energy efficacy. They use either an induction coil to create a magnetic field or microwaves to excite the mercury in a lamp in order to produce ultraviolet energy that in turn excites a phosphor coating on the bulb's inside surface. Depending on the lamp, manufacturers make claims for lamp life from 10,000 to 100,000 hours. Life is primarily limited by the degradation of the phosphors.
Lighting control for energy efficiency Controls allow users to operate lighting loads according to specific needs. Accessible, well-planned switches and dimmers allow an occupant to create the pattern and intensity of lighting that is most comfortable and productive.
Two states, California and Washington, have specific requirements for the type and operation of lighting controls within their energy codes. At this time, other states (and the federal government) are considering such regulation.