Field data on lighting system power consumption and load profile will become more important as utility rebates are withdrawn; also, retrofit projects have to be economically justified on their merits.
The economic benefits of retrofitting a building with a more efficient lighting system can be significant. In addition to offering reduced operating costs, the various new (and relatively new) products that have proven themselves in the industry can frequently enhance both aesthetics and productivity at the same time.
While the retrofit of an inefficient and aging lighting system can bring many benefits - such as a return on investment within two years, if carefully planned - there are two cautionary factors to consider.
First, you must include all project expenses in your economic analysis; otherwise you'll be misled by the "apparent" cost savings of the proposed retrofit. Such unsuspected expenses as hazardous waste disposal of PCB-containing ballasts and mercury-containing lamps as well as the costs of a comprehensive system survey, analysis, and design often can defeat a well-intended project. Yet, they're integral parts of a good lighting retrofit program.
Second, you must carefully evaluate new and evolving technologies, such as dimmable electronic ballasts and microprocessor controls. In reviewing potential equipment, you should consider only those products having a reputation for reliability and performance. In fact, some specifiers refuse to recommend a technology unless it's been successfully used in a commercial application for at least one year.
Survey technique is important
A site survey using test instruments is important to gain an exact knowledge of the existing lighting system's condition, which will help determine what maintenance/upgrades are worthwhile. In addition, the survey gives you a benchmark for determining how effective the improvement is after the completion of any retrofit design, considering your electric energy costs. Here are some considerations.
Fixture characteristics. The type of fixture mounting (recessed, track, pendant surface-mount, etc.) and lamp type (fluorescent, incandescent, HID, etc.) must be noted for each fixture. The type of lens or louver used also should be noted. (The photometric report of the fixture can be used to determine how much light is actually sent out of the fixture enclosure.)
Fixture condition. The condition of existing fixtures should be noted. For example, are lenses yellowed or cracked? If so, they are probably at the end of useful life.
Ceiling characteristics. The type of ceiling (suspended, concealed spine, lay-in T-Bar, dry wall, plaster, etc.) should be noted to determine if the fixtures can be tandem wired if multilamp electronic ballasts are used. Special frames may be needed for certain types of recessed fixtures.
Lighting control. Verify what type of lighting control system is used and if the system is expandable or upgradable.
Work surfaces. Check all work surfaces with a light meter to see if they fall within established light levels. Note the color of walls, ceilings, and floors.
Site survey example
Let's consider an office building hallway having two lighting systems in its ceiling. One, which provides direct downlighting (essentially ambient light), is a layout of 10 2 x 2-ft recessed fluorescent troffers, each having standard two-lamp magnetic ballasts, two FB T12 cool-white (CW) fluorescent lamps, and a prismatic acrylic plastic lens. Control of this fluorescent circuit is provided by a single-pole toggle switch.
Here, a decision can be made to lower the light output of all 10 troffers. Or every other troffer can be deenergized, and an occupancy sensor device can provide the control.
The other lighting system includes 12 cylindrical cans mounted on two separate tracks, with each can housing a 150W R40 incandescent reflector flood lamp. The fixtures, controlled by a manual dimmer, are aimed at artwork on the walls.
At this point, the information about the original design should be considered. When the space was first occupied, there were 12 paintings illuminated, but because of a later redecoration, only eight paintings are now hung. So, four of the cylinder cans are unnecessary and can be removed, while the remaining eight cylinders can be repositioned. The reflector lamps can be replaced by 75W or 90W tungsten halogen PAR lamps, reducing the wattage load while maintaining the decorative appearance of the walls.
Test instruments are important
When it's necessary to measure voltage, current, and power consumption on a lighting branch circuit to accurately determine anticipated savings, you should keep a number of points in mind.
If a simple rule-of-thumb estimating technique is used, errors as great as 25% to 40% can occur. These errors are a result of the following.
The energy used by a fluorescent system can differ by 5% to 25% from energy use figures given in manufacturers' catalogs, which are based on lab test data.
The actual hours that lighting systems operate are usually quite different from simplified assumptions.
The impact of the lighting load on the HVAC system is often estimated incorrectly or completely omitted from the analysis.
Thus, selecting the right metering equipment and analysis methods are important to get accurate data. It's best to use an instrument that will accurately read voltage, current, and power - and take into account the harmonic currents on the branch circuit conductors.
A simple method is to connect a watt-meter [TABULAR DATA OMITTED] to a lighting branch circuit and take readings at particular time intervals.
Use your head with retrofit products
A variety of new products can be used in a maintenance/retrofit project. However, proper application of these lighting tools is not always as simple as it seems. In fact, basic engineering savvy and good common sense are needed to avoid some pitfalls that can cause unsuccessful installations.
For example, suppose a space with 2 x 4-ft recessed troffers is already overlit, but you want to maintain the appearance of a fully lamped fixture. Appropriate delamping (with the change to higher efficiency lamps and ballasts) and the installation of a specular reflector may seem like a good solution. However, specular reflectors alone do not significantly improve the efficiency of an existing fixture. They can provide up to a 16% improvement in fixture efficiency, but only in a fixture that is clean and in good condition before retrofit.
Task equipment can wreak havoc on a "good" lighting retrofit design. For example, if new fluorescent fixtures are being considered in office areas where computers are widely used, you must satisfy two major requirements. First, the luminaire should have a reasonably high efficacy; second, glare must be controlled so that required visual tasks are not defeated.
A major problem associated with using a computer is having reflected images appear on the video display terminal (VDT) or screen. Commonly, the screen will show both the computer-generated image and a reflection of the lighting fixture(s) located overhead, behind the worker. The two images compete for the attention of the computer operator; thus, he or she engages in repetitive focusing - or, more accurately - accommodation and vergence adjustment by the eyes. To counter this problem, the selected fixture should reduce the reflected image while maintaining the computer-generated image. (See Sidebar "Task Lighting With Computer VDTs In Mind," on page 34.)
By looking at the Table (on page 35), which lists five different 2 x 4-ft, 3-lamp, T8 luminaire designs, and noting the percent of lumens above 60 [degrees], you can understand how effective the shielding media is in controlling glare. You also can see that good glare control can be achieved in a luminaire without a large sacrifice in luminaire efficiency.
Be careful when specifying a fluorescent ballast changeout
New designs in fluorescent ballasts have received a great deal of attention because they can provide dramatic energy savings. These products are available with three levels of performance or grades.
Improved (energy-efficient) magnetic ballasts use components and high-quality materials that reduce inherent internal losses. Thus, up to 8W can be saved per ballast.
Hybrid ballasts cut off power to the lamp cathodes once the lamps starts, saving 2W or more per lamp in a two-lamp ballast.
Electronic ballasts (EBs) use a power control system that supplies power to the lamps at 20,000 Hz rather than 60 Hz, to more efficiently convert power into light.
EBs are very popular in retrofit programs, but you should consider a number of factors before choosing a specific make of EB.
Lamp operation. Generally, EBs are designed or optimized for either the T8 or the T12 lamp, but some can operate both types. If a ballast for the T8 lamp is installed and T12 lamps are inserted instead, a problem in lamp starting and light output can result. Conversely, if T8 lamps are installed on a T12 ballast, the life of the lamps can be appreciably shortened. Check for compatibility.
Ballast factor (BF). BF is the comparison of relative light output of a lamp served by a given ballast to that from a reference or laboratory ballast. Most magnetic ballasts have a BF of at least .925, while EBs range from .75 to 1.28. A suitable EB should have a BF of between .8 and .93.
Ballast efficacy factor (BEF). BEF is an overall efficiency rating, and is the BF (expressed as a percent) divided by the input watts. So, understanding that (old) standard ballasts have a BEF of 1.0, the ratings of the three types of ballasts mentioned above are 1.1 for energy-saving magnetic ballasts, 1.1 to 1.38 for hybrid ballasts, and 1.25 to 1.5 for EBs (serving two T-8 lamps).
Total harmonic distortion (THD). THD describes how much the ballast alters the sine-wave as it draws power. Magnetic ballasts are not a problem, but EBs can have a THD from as low as 5% to more than 30%. High THD can cause a multitude of problems on the power system and an appreciable increase in current flow on the neutral conductor of shared-neutral, three-phase, 4-wire branch circuits.
Current crest factor (CCF). CCF represents the shape of the current waveform delivered to the lamp. A perfect sinewave has a CCF of 1.4, while most ballasts deliver a waveform with a CCF of 1.7. (An EB can be 1.5 or less). A high CCF can degrade the cathodes of the lamp, thus reducing its life.
Exit sign retrofitting
Retrofitting of exit signs is an important way to reduce operating and maintenance costs in a building. 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 7W lamps and a ballast consuming about 6W. Many LED signs use only 1W to 2W, and none requires more than about 5W.
A number of factors should always be considered, however, when evaluating which type 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. The term "classified" means that the kit is approved solely for the fixture that was submitted; the term "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 with $20 to $25 for an incandescent or CFL model), their energy efficiency and low maintenance needs make them extremely economical over time.
Note that the lifetime of an LED is not rated according to burnout, but according to the point in time when it produces one half of its original light output. Thus, the life of an LED is estimated to be about 11 years; however, some manufacturers claim their products will last from 20 to 25 years. Because the technology is so new, it's too early for a comprehensive life test on a sign to have been completed. So, while the lifespan claims may be accurate, no one can be sure of the LED's longevity. Premature failure on units can occur, the same as with any other electronics-based product.
LED signs are available as direct view, reflective, and edge-lit panel. You should understand that, to save costs, a manufacturer sometimes will increase the power to each LED (generally an LED is rated at 30 mA), and compensate for the brighter luminance by using fewer LEDs in each sign. This can be a problem because overdriving an LED will shorten its life, with the reduction directly related to how much it's overdriven. The reflective and edge-lit designs are most likely to be overdriven.
Industrial lighting needs
Often, a contractor or engineer needs a technique to quickly determine the payback of a proposed industrial lighting retrofit. Basically, it would be useful to have a simple method that can be applied to come up with a projected payback on a project.
Let's look at a proposed retrofit in a 100,000-sq-ft industrial plant where the visual task is the fabrication and inspection of metal parts. The existing general lighting is provided by 1000W mercury vapor (MV) lamps in open bottom hemispherical fixtures mounted on 30 x 30-ft centers. Thus, each fixture covers an area equal to 900 sq ft. The aged system is unsatisfactory, and the owner wants an 18-month payback for a retrofit.
Step 1. In this case, the IES recommended illuminance for the task is 30 footcandles (fc), and you know that the existing system was satisfactory for the first few years. Initial output of an MV lamp is about 63,000 lumens. Since a good rule of thumb is to consider that half of the total lumens from a lamp reaches the workplane, a practical figure to use is 31,500 lumens. Dividing that figure by the 900-sq-ft area served by each fixture yields about 34 horizontal fc level on the workplane (since footcandles are lumens of light per sq ft of surface).
Step 2. The next step is to use the design fc information (rounded to 30) to estimate how many new fixtures would be required. That number is found by first multiplying the area (100,000 sq ft) by 30 to get the needed total lumens, which in this case is 3,000,000.
A 400W high pressure sodium (HPS) lamp is rated at 50,000 lumens; according to the rule of thumb applied before, half of that figure, or 25,000 lumens from each HPS fixture, would reach the workplane. Dividing 3,000,000 needed lumens by the 25,000 lumens reaching the workplane yields a requirement of 120 fixtures.
Step 3. The final step is to estimate savings. Since the new fixtures ($300 each) can use the existing wiring layout, the installation cost is estimated at $36,000. With the old system, each fixture consumes 1080W; with the new one, about 470W per fixture are consumed. Thus, the wattage saved at each fixture is 610W (1080W minus 470W).
The task then is to figure the total wattage saved in a year. Using an 18-hour day, the lighting system operates 4680 hrs a year (18 hrs per day times five days per week times 52 weeks), and the kWh savings per fixture per year is 4680 times 0.610 or 2855kWh. The task then is to plug in the average cost per kWh (use 10 cents/kWh) to derive power cost savings in a year. Thus, dividing the cost per fixture ($300) by the annual dollar savings ($285.50) yields the simple payback period, which should be a little more than 12 months.
RELATED ARTICLE: TASK LIGHTING WITH COMPUTER VDTS IN MIND
The Illuminating Engineering Society (IES), in its Recommended Practice for Lighting Offices Containing Computer Visual Display Terminals, states that the average luminance produced by direct lighting luminaires should never exceed the following values: 850 cd/m(sq) (candelas per sq meter) at 65 [degrees], 350 cd/m (sq) at 75 [degrees], and 175 cd/m (sq) at 85 [degrees]. (Note: Angles are expressed in degrees from vertical; that is, vertical walls are 0 [degrees], and the horizontal ceiling is 90 [degrees].)
These recommendations on brightness of the ceiling refer to a 0.6 m x 0.6 m (24 in. x 24 in.) area. The notation "cd" is an abbreviation for candela; one candela is equal to one lumen per steradian. A steradian is a solid angle (a plane) of a sphere used to define basic terms used in lighting, such as footcandle and lumen.
In addition, these recommendations cannot be properly evaluated without also considering the contrast - in terms of brightness - between the luminaire and the ceiling area surrounding these fixtures.
To control reflections of luminaires in a VDT screen, the IES recommends that direct luminaires in the reflected visual field behind the VDT operator have cut-off angles no greater than 65 [degrees]. As stated, the preferred maximum average luminance at 65 [degrees] is 350cd/m (sq), and under no circumstances should the luminance exceed 850 cd/m (sq). These conditions are seen in the figure on page 33.
RELATED ARTICLE: AVOID THE PITFALLS OF AN INDUSTRIAL LIGHTING RETROFIT
A machineshop has a 160 x 200-ft production area in which medium to fine machining work is routinely performed. The existing lighting system consisted of stem-mounted, 8-ft high-output (HO) fluorescent fixtures in continuous rows on 12-ft centers. These fixtures provided a uniform horizontal maintained lighting level of 70 fc.
A consultant advised the plant facility manager that lighting energy costs could be reduced by 50% if the existing fluorescent system was replaced with a high-intensity-discharge (HID) lighting system. Specifically, individual 400W HPS lamps in pendant fixtures mounted at a 25-ft height above the floor were proposed.
Because the amount of energy savings was attractive, the retrofit lighting system was installed. Almost immediately, however, plant employees began complaining about poor visibility at their workstations.
Thus, another consultant was called in, and he began his problem solving by taking light meter readings, studying the photometric data of the installed HPS fixtures, and noting the fixture mounting locations. After analyzing the data, two important design practice violations were found.
First, the illuminance level, which ranged from 10 fc to 40 fc on the horizontal work plane, was far below that recommended by IES for the type of work being done. In fact, the calculated average uniform illuminance level was only 38 fc, far below the 70-fc level of the original installation. Although the visibility requirements for the best productive work activity are somewhat subjective, the fact that no employee complaints occurred before the lighting retrofit reinforced the judgment that the HPS fc level was too low.
The second error was that the minimum spacing-to-mounting height ratio as recommended by the manufacturer was not followed. This was found after studying the candlepower distribution curve of the fixture data sheet. The fixture, which has a hemispherical reflector and a prismatic refractor lens enclosing the lower part of the housing, delivers most of the light within a 25 [degrees] -angle on either side of the nadir, and thus it is called a sharp-cutoff fixture. As a result, at this mounting height, most of the lumen output falls only within a 20-ft dia circular area of the floor, directly below the fixture. Ideally, this fixture should be used at height of 40 ft or more.
Additionally, some of the HPS fixture locations caused the operator to block a portion of the light that was intended to reach the work area around a machine, such as a lathe.
Other HPS fixtures were studied as part of this review, and one fixture model shown in a catalog was judged to be a better choice for this application. But replacing each of the sharp-cutoff HPS fixtures with the fixture having a wider light distribution would not totally solve the problem, since the average maintained illuminance level for the space would still remain below the recommended 70-fc level. Increasing the fc level could be accomplished only by raising the total lumen output of the lighting system.
In the end, the facility manager decided to reinstall the original HO fluorescent fixtures, but retrofitting them with electronic ballasts to obtain a 25% reduction in energy consumption. One reason for this decision was that the original HO fixtures provided adequate light levels for the tasks, but now in an energy-saving operation.