Superior office lighting an unusual approach
Integrating an advanced lighting system into the overall office environment produced far better lighting and slashed energy consumption from 2.5 W/sq ft to only 0.7 W/sq ft.
When energy costs began to get out of hand, Citicorp, the parent company of Citibank, set up an Energy Management and Conservation Department (EMAC), with a mandate to reduce energy costs throughout the worldwide organization. After EMAC finished with the HVAC systems, they tackled lighting. Their initial approach, like that of so many others, was, “a 2 x 4 fixture with four lamps? Take out two lamps. A 1 x 4 fixture with two lamps? Turn alternate fixtures off.” The energy costs went down, but so did the amount and quality of light—often to an unacceptable degree.
Citicorp then called in Designetics Associates, Inc. of Secaucus, NJ, who had done the lighting design for the public spaces in the 59-story Citicorp Center building, a New York City showplace noted for its unusual and attractive lighting. David Liametz and his Designetics team, working in conjunction with EMAC, studied the most advanced lighting systems and their application. He reached the conclusion that for maximum effectiveness the lighting system should not be considered alone, but as part of the overall environment—what Liametz calls the holistic approach. Holism is the theory that whole entities are more than just the sum of their parts, and a holistic approach to lighting emphasizes the functional and aesthetic relationship between each interdependent element and the whole to produce a superior total result.
In the office lighting design system being developed, that meant that each space had to be lighted effectively for its function, with easy modification possible as space and functions are rearranged. It meant taking advantage of daylight where available. It meant ease of maintenance and long life. It meant coordinating the hung-ceiling design, floor, window, and wall treatments, furniture layouts and finishes, and all colors, to contribute to the overall result. The goal was to improve the working environment while conserving energy, by incorporating the latest technology into an aesthetically satisfactory whole.
The resulting system has as its basis an unusual lighting fixture with a specially selected lamp, driven by a highly sophisticated, solid-state, high-frequency ballast. The ballast is controllable over a wide range, locally or remotely, to vary the light output. This ballast, fixture, lamp, and control system is fully integrated with the overall office environment.
The Citibank approach
Not only did Citibank require energy conservation, but they also hoped to cut down the electrical construction costs of their frequent office space re-arrangements. In 1980, at their 399 Park Avenue main office building in New York, their records showed actual bills paid of $176,000 for ceiling lighting and electrical work not including the cost of partition and furniture changes for space rearrangements. These are actual costs for a total office area of one million sq ft for one year. In some of this renovation work, the lighting fixtures were taken down carefully and reused. The actual cost of removing, storing, cleaning, relamping, and reinstalling these fixtures came to $119 per fixture. It was cheaper and better to rip them down and throw them away, replacing them with a new fixture.
The common approach of removing lamps or shutting off some fixtures for energy conservation did not work. Better, but still unsatisfactory, was the use of low-loss ballasts and lower-wattage energy-saving lamps; unless there was too much light to begin with, the result was too little light, of poor quality, causing visual discomfort. This was the brute-force method reduce wattage and hope enough light remained to see by. The Designetics team decided to try something different to completely renovate the space, with artistic goals and good design, implemented with the best lighting technology. Quality of light and environment and aesthetic effect came first, then energy saving. The usual 100 raw foot-candles of maintained lighting as a standard was abandoned.
After many studies and experiments, the basic complete system was developed. A mockup of 2000 sq ft was installed on the 2nd floor of Citibank’s 399 Park Avenue building, incorporating the modular ceiling, specific fixtures, lamps and ballasts, color schemes, furniture arrangement, and daylight and other control systems. The results were so convincing that a prototype installation of about 7000 sq ft was made on the 7th floor and carefully monitored for initial and operating costs. Analysis indicated a payback in less than two years from the electrical energy savings alone, completely repaying the cost of removing the old ceiling and lighting and installing the new hung ceiling and lighting and control system. This calculation did not include neither the additional savings in air conditioning as a result of the reduced heat (wattage), nor the savings in future rearrangements of the office space resulting from the modular and flexible ceiling and lighting system. The building was originally designed based on a lighting load of 3’/2 W/sq ft, typical for office buildings before the energy crunch, and the prototype lighting load was less than 1 W/sq ft. In new construction, the design would take into consideration the reduced heat output and lead to a smaller HVAC system. Also, the cost of later office rearrangements would drop dramatically.
The installation required internal coordination between the EMAC group and the interior design group. Previously, lighting was lighting and interior design (walls, window treatment, furniture) was interior design. This approach tied the two together, and cooperation between departments made it work. The resulting system was so successful that it is recommended by EMAC as a lighting guide standard for Citibank offices throughout the world. In addition, similar lighting programs have been produced by Designetics for McGraw-Hill and New Jersey Bell Telephone Co. facilities.
The fixture
It early became apparent that to obtain good office lighting with low energy consumption a parabolic reflector type of fixture, with “batwing” light output distribution, was necessary. Equivalent sphere illumination (ESI) is glare-free, visually effective light, measured in ESI foot-candles, as opposed to “raw” foot-candles. ESI lighting reduces veiling reflections (caused by light reflected at a bad angle from a work surface) that lower contrast and visual acuity and cause visual fatigue and discomfort. Parabolic-reflector fixtures have a light output pattern that effectively produces high ESI ratings when properly applied.
The selected fixture also had to have a high efficiency. Fixture efficiency is the measured total fixture output lumens as a percentage of the total lamp lumens produced. Typical 2 x 4 fixtures have an efficiency of 55 to 60% when new. However, the paint finish ages, dropping in reflectivity from as high as 88% to about 65%. Dirt further reduces output, measured by the luminaire dirt depreciation (LDD) factor. At Citibank the original fixtures in the test areas measured efficiency in place of about 46%. The fixture chosen for this system has an efficiency of 79.5% when first installed, and the unpainted, highly specular finish results in low LDD and high maintained efficiency. The open top and bottom, increasing air flow through the fixture, lessens the dirt deposit on the fixture and lamps, improving the LDD.
The highly specular, mirror like finish of the fixture is important. It results in less light diffusion and more precise light control than the semi-specular, slightly matte finish usually standard in parabolic fixtures. This results in low fixture brightness (direct light) and less contrast with the ceiling surface. The ceiling itself has less contrast. If the finish were semi-specular, all the fixtures would appear white and brighter. A ceiling with low overall brightness provides a visually comfortable and efficient environment.
The fixture measures 1 ft x 4 ft. In most cases, it is used with one lamp in a 5- x 5-ft module to cover 25 sq ft. However, the single lamp socket can be replaced directly by a two-lamp socket, and the same fixture can be used with two lamps to cover 50 sq ft or provide higher lighting levels where required. The two-lamp configuration results in little change to the desired light output pattern. The parabolic louvers and reflector provide refined light control to supply the batwing distribution necessary for good ESI lighting. Many ESI lighting installations require exact furniture placement. In this 5- x 5-ft modular arrangement, there is enough light overlap from fixture to fixture at normal office ceiling heights to make furniture placement non-critical, although the person at a workstation should preferably be facing along the lengthwise direction of the fixture. The 5 x 5 module lends itself to practical office partition rearrangement without changing the existing lighting and ceiling.
This fixture is listed by UL for through-wiring, permitting the lighting installation to be wired with a minimum of labor and materials. Provision for return air is inherent in the design, eliminating unsightly return-air louvers. It can, if desired, be used for supply air as well, using an available boot to connect to the air-supply system. The design operates the lamp at its optimum wall temperature to obtain the greatest lumen output. Although for a given space the initial cost of the fixtures is high compared to the common 2- x 4-ft, 4-lamp troffer on 8- x 8-ft centers, the overall effectiveness of the system in comfort, productivity, appearance, and especially reduced power consumption make it well worth the cost.
The lamp
The lighting system will perform as desired only when the fixture, lamp, and ballast are carefully matched. They must be coordinated for proper lamp wall temperature to produce maximum light output and efficiency. Originally, consideration was given to using some of the newer reduced-wattage lamps, in conjunction with low-loss, low-heat ballasts. These lamps are available in 34- and 28-W ratings, instead of the conventional 40 W. While these lamp-ballast combinations are highly efficient in terms of lumens per watt, their actual total light output is lower than that of conventional lamps and ballasts. They can be used in many retrofit applications because the original lighting was frequently over designed and the somewhat reduced light output is adequate. These efficient lamp-ballast systems are designed to operate best in the standard 2- x 4-ft, 4-lamp fixture. In the open parabolic fixture, air flow might cause the lamp wall temperature to be undesirably low, resulting in a considerable reduction in light output.
Color of the light was another important consideration, from both an aesthetic and visual-comfort point of view. Liametz feels that the standard cool-white (CW) fluorescent lamp, with a color temperature of 4000° K is too cool— not enough red light and too much blue. Conversely, he feels that the warm-white (WW) lamp, with a color temperature of 3000° K is too warm—too much red and not enough blue. He wanted a lamp with a color somewhere between CW and WW. This color output would also result in improved color rendition. Other factors desired in the lamp were efficiency, long life with low lamp lumen depreciation (LLD) with age, sufficient lumen output, and reasonable cost.
The final choice was a new tri-phosphor, high-efficiency lamp that meets all these criteria. The three-phosphor coating produces a color of 3500° K just halfway between WW and CW lamps. This is the color desired aesthetically, and it provides excellent color rendition, making objects appear close to their true colors. The color rendering index (CR1) is 73, as opposed to a CR1 of 52 for WW and 62 for CW lamps. In addition, the rated total light output is 3350 lumens for the selected lamp, compared with about 3150 lumens for both WW and CW lamps. The lamp has a high maintained lumen output over its life, helped by the fact that the cathodes are internally shielded.
The combination of high efficiency, high light output, and long life with low LLD, excellent color, and reasonable cost (a moderate premium over standard CW or WW lamps) makes the chosen tri-phosphor lamp eminently suitable for this application.
The ballast
The heart of the entire lighting system is the controllable electronic solid-state high-frequency ballast. The many capabilities of this type of ballast make the lighting system responsive to theenvironment and the lighting requirements of each area, permitting the flexible control that results in the extremely low energy consumption of this system. The ballast was chosen first and the fixture and lamp selected to take maximum advantage of its characteristics.
The solid-state ballast has been near at hand for several years. Early models were too unreliable or too costly or developed other problems. One manufacturer recently went out of the business when a purchased electronic component of his ballasts developed frequent failures with age, causing extremely high warranty replacement costs. (He is suing the supplier of the component.) The solid-state ballast selected for this system has a good experience record, is listed by Underwriters Laboratories (UL), and meets Federal Communication Commission (FCC) requirements for radio-frequency and electromagnetic interference. No NEMA, ANSI or CBM standard yet exists for electronic ballasts.
There are fundamental differences between the two types of ballasts. The standard ballast uses a magnetic iron core and coil to produce and control the necessary voltage and current, and operates the lamp at 60 Hz. The solid-state ballast uses an electronic circuit to generate and control the required voltages, converting the 60-Hz input to a high-frequency output to operate the lamp at about 27,000 Hz. Solid-state ballasts have many advantages over conventional ballasts. Although they cost more, the cost differential is narrowing. As the price of electronic devices continues to come down and the performance and reliability continues to rise, today’s conventional ballast will be obsolete sometime in the near future. This happened with circuit-breaker trip units; solid-state trips have replaced all dual-magnetic types and are today replacing most of the larger thermal-magnetic units. The era of the electronic ballast is rapidly approaching.
One of the most important advantages of the electronic ballast is that it can easily be controlled to dim fluorescent (and HID) lamps. Full-range dimming from 100% down to 10% of rated light output or less is simple and inexpensive with the electronic circuitry; it is difficult and costly with magnetic ballasts and does not work too well at low light levels. Dimming is critical to the operation of this lighting system.
The electronic ballast has low losses only about 40% of the losses of the conventional ballast. This results in low heat, low operating temperature, and long life. Manufacturers expect average life to be at least as long as conventional ballasts, and possibly considerably longer. The manufacturer of the ballast used in the Citibank system has a standard two-year warranty, with warranty up to 10 years available for a small premium. The high operating frequency, above the human audible range, and the absence of iron cores and coils results in very low, almost inaudible noise output compared with the low but audible 120-Hz hum of conventional ballasts. Also, the high frequency eliminates any visible flicker, even when dimmed to 10% of full output. Standard ballasts produce 120-Hz flicker that is subliminally noticeable and more noticeable when dimmed. When cathode-ray-tube (CRT) screens are viewed in ordinary fluorescent light, both the CRT display and the light flicker at power-line frequency, but rarely exactly in phase. This out-of-phase flickering, called the strobe effect, has been shown to produce eyestrain, discomfort, and fatigue. The high-frequency ballast eliminates this problem completely. Third-harmonic distortion in conventional ballasts is about 40% to 45%. The solid-state ballast used in this system has considerably less than half that—about 15% third-harmonic distortion.
The electronic ballast is designed to operate the lamps at optimum bulb temperature in a cool fixture, such as the parabolic open fixture used in the Citibank system. In fact, the ballast initially drives the lamp to 106% of rated lumen output, as opposed to 92 to 98% for a conventional ballast, as a result of high frequency and optimum bulb temperature. That is, the ballast factor is 106%, compared with magnetic ballast factors of 92% to 98%. As the lamp is dimmed, the lamp heaters are driven harder to maintain proper filament temperature and to improve lamp life.
The electronic ballast has a high power factor, greater than 90%, as do the better magnetic ballasts. It produces a far more steady light output for input voltage variations. For voltages 10% below normal, light output drops only 0.3%, as compared with a 4.5% drop using a conventional ballast. For voltages 10% above normal, light output increases only 0.2%, as compared with a 3.1% increase for a conventional ballast. The temperature regulation is also excellent. When used for dimming, the electronic ballast maintains a high efficiency, measured in lumens per watt, down to about 50% of full output of the lamp. Below 50%, the efficiency drops, but the actual wattage is also low so the lower efficiency means little.
The control system
The electronic circuitry permits lamp dimming from the ballast itself (each ballast has a built-in control potentiometer), or from a remote controller such as a lighting programmer or photocell. This is the capability that is used to produce a lighting system of great effectiveness and low energy consumption. If the ballast is the heart of the system, the controls are the brains.
The lighting levels are set by three different control systems—photocells, programmable controllers, and building-management system controllers.
The task lighting levels that have been found entirely adequate and comfortable are 50 foot-candles (fc) for office areas and 14 fc for lobbies, aisles, corridors, storage areas, and reception areas. (A 20-fc level was initially used in these areas but was found to be unnecessarily high). For maintenance and cleaning, 10 fc was found satisfactory (20 fc was also initially used here, and later reduced). While these levels may seem low, the high ESI rating and evenness of illumination, with little glare and veiling reflection, have resulted in great visual comfort and employee satisfaction.
The ability to adjust individual fixtures, either at the ballast or through the programmable controllers, is especially useful where a word processor or computer terminal has a CRT display. Because of the parabolic fixture design and cut-off angle, the reflection of the ceiling in the CRT will not usually show direct brightness or glare from more than one fixture. This fixture can be dimmed to reduce the glare. The Eastman Kodak Company found that when they eliminated CRT glare, productivity went up 12% at the CRT workstations.
Photocells are used to maintain a given light level as required by the task. They can control a single ballast or a group of ballasts, depending on the size of the zone. They will compensate for daylight by dimming to maintain constant total light, reducing power consumption and automatically correcting for variation with season, weather, and time of day. Photocells also compensate for fixture and lamp lumen depreciation (LDD and LLD) by increasing light output as the system ages, to keep task lighting constant. Initial power consumption is low, and increases with time. Conventional systems have constant higher power consumption, with excessive light in the beginning that decreases with time to the desired level or lower (see Fig. 1). The photocells operate through the programmable controller.
Programmable controllers are used, one on each floor, to provide overall control. Each controller has a microprocessor base with software control and can be set to control the lighting on its floor for a full year with, of course, manual override for any zone at any time. These controllers, with their power supplies and terminal cabinets, make up the light monitoring and control system (LMCS). Many variations are possible, and the units can be customized as desired. Input can be from a local or remote keyboard; a CRT display can also be local or remote. A modem with a standard RS-232 interface can be used for external input, monitoring, or reprogramming by tele-phone or other communication. Each controller has 32 photocell inputs, 32 ballast control channels, 16 digital inputs, 16 digital output channels, and 24 ON.OFF type input/output points. Each ballast control channel is capable of dimming smoothly up to 50 ballasts.
The controller can take data, log it, and transmit it as desired, on up to 16 internal or external parameters. Each zone can be operated individually in the automatic or manual mode. The software will permit any photocell to control any zone or zones, and the rate of dimming can be varied to avoid sudden changes in lighting intensity. A built-in clock with battery backup can be used to time events in complex sequences through the microprocessor. Minimum and maximum light levels in each zone can be set. Internal calibration means, self-checking, and status monitoring of each zone are provided, along with many other standard or optional features.
Where a building management system or other large, computerized system is installed, it can be used to signal the individual units of the LMCS. This is especially effective if demand control is used for peak shaving to reduce the electric utility demand charges. It has been found that a demand controller can reduce the light output up to 20% for brief periods with the variation being almost imperceptible if done slowly, rather than suddenly.
At Citibank, control wiring from the photocell sensors to the LMCS units and back to the dimmed ballasts used twisted-pair wiring. This shielded wire, insulated with low-smoke, low-flame material and so classified by UL, often (incorrectly) called “plenum” wiring, is permitted by the NEC and NY City code to be run in hung ceilings without conduit or other raceway. Each pair of wires could control up to 50 ballasts. A later installation, being done for McGraw-Hill in Colorado Springs, CO, takes advantage of a recent improvement carrier-current power-line communications (PLC). This eliminates the need for control wiring, sending the control signals in digitally coded form over the power wiring. The manufacturer is developing this equipment gradually, integrating it with the LMCS controllers. One PLC module transmits photocell data to the LMCS; another PLC module controls the ballasts. Initially, there will be 32 ballast-control channels, with future capability of 1028 channels (addresses controlled) on one frequency. It will take no more than ‘/2 sec to address any channel. Up to 11 frequencies are available. As initially installed, the PLC units are separate from the ballasts. Later, it is expected that the circuitry will be built right into the ballast unit.
Overall, this control system provides a flexible, easily adjusted lighting scheme that can be varied for the most-comfortable and economical lighting and changed as tasks change, such as for cleaning and maintenance, and as office space is altered. The control system can be designed to meet the needs of any user or installation.
The environment
For maximum effectiveness, visual comfort, and aesthetic satisfaction, this entire system must be integrated with the environment. The use of daylight means that windows should be large but of heat-resisting, solar-screen glass. The office spaces should be an open plan, taking advantage of the daylight contribution up to 30 ft from windows. Daylight varies, of course, with height, orientation, surrounding buildings, and other influences but, properly utilized, can be significant in reducing energy consumption. Walls, carpeting, and ceiling colors should be light, as should furniture finishes for minimum light absorption. Dark colors should be used for accent only, along with plants and works of art.
The results
The Citibank installation more than met expectations. The primary objective, lower electrical energy costs, was exceeded. The design goal was 1 W per sq ft; actual measured consumption in the prototype area was less than 0.7 W per sq ft. If the entire Citibank building at 399 Park Ave were converted to this system, the actual measured lighting demand load of 2400 kW would drop to below 700 kW. In the initial 2000-sq-ft test area, which is the building office, the space has been rearranged more than 10 times, including converting some storage space to a drafting area. No fixtures had to be moved and no ceiling work done for these changes. All that was necessary was resetting of the light levels. Similar results were obtained in the 7000-sq-ft prototype area, in the personnel department. An employee store was moved to a different part of the area, the original space became office space, and other changes were made — all without ceiling or fixture work, merely reprogramming controls. The costs of space rearrangements dropped drastically.
Actual readings in these areas were 40 fc with the original lighting and 50 fc with the new system. The areas were more attractive, there was less CRT reflected glare and strobe effect, and less heat was developed, reducing the air-conditioning load. This improved environment meant better comfort and productivity, with a 70% reduction in energy consumption. Additional benefits are reduced maintenance costs for lamp and ballast replacement and lower construction costs for space renovation.
In the McGraw-Hill building in Colorado Springs, which will use the PLC ballasts, the air-conditioning load was reduced by between 10 and 20 tons based on the reduced heat from the lighting. The connected lighting load is only 1.2 W per sq ft, and the anticipated actual operating load is expected to be less than 1 W/sq ft—probably close to the Citibank 0.7 W/sq ft.
The holistic approach taken by the Designetics team has set a standard that optimizes both low cost and beauty, with neither sacrificed for the sake of the other.
By ARTHUR FREUND, Senior Editor
REPRINTED FROM NOVEMBER, 1983 ISSUE
ELECTRICAL CONSTRUCTION AND MAINTENANCE
© Copyright 1983 McGraw-Hill, Inc. All rights reserved
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