Retrofitting office lighting controls
Lighting controls have many options, and can save building owners money by reducing electric costs.
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Lighting controls are becoming popular tools for reduction of energy usage and, thereby, reduction of the electrical utility costs in today's office environments. While most codes are not retroactive, some building owners opt to go for the obvious energy savings by reducing the total lighting “ON” time, reaping a secondary benefit of positive publicity by showing an interest in having their buildings become more green and, therefore, more attractive to prospective tenants.
This article covers control functions and options; it does not cover lighting control protocols, such as Digital Addressable Lighting Interface (DALI). These topics may be covered in a future article.
Controlling interior lighting (and the law)
Since the adoption of the International Building Code (IBC) and its reference to the International Energy Conservation Code (IECC), there has been an ever-increasing interest in the engineering design community in automatic shutoff control of lighting. Specifically, the IECC now requires that every space in a building have either occupancy controls or a timer-controlled lighting contactor, multi-pole relays, or low-voltage relays so that all lights may be turned off during unoccupied periods of the day.
In lieu of a simple timer, there is a wide range of more sophisticated, centralized control systems that can be dedicated to lighting control with a wide variety of programming options. In addition, many of the BAS have interface units that enable them to not only control heating and cooling in the building, but also provide lighting control as sophisticated as the stand-alone lighting control systems.
While most jurisdictions that have adopted the IBC, many also have adopted the IECC, making the lighting control requirements enforceable by the local authority having jurisdiction (AHJ). However, a few jurisdictions (such as Pennsylvania, which will be used as an example in this article) have adopted the IECC requirements as an enforceable law, upgrading its status from merely a code.
This change allows the authority to make changes and allow adjustments out of the jurisdiction of the AHJ, and the lighting control requirement enforceable by law (and, although not addressed in this article, the associated lighting wattage power densities as well). While the actual enforcement authority and potential penalties seem to be relatively obscure, the potential for monetary fines and imprisonment should make adhering to the IECC requirements much less arbitrary for the design engineers than if the same requirements were only a code.
Lighting control options
The available options for occupancy-sensor controls (OC) for office lighting are quite varied and can provide a wide range of flexibility as to coverage and sensor types, with each option allowing precise tailoring of control to fit the areas to be covered and the types of activities in those areas. As outlined above, the options for control of office lighting using contactors and some type of control system are relatively straightforward; further exploration of the specifics may be discussed with the manufacturer's representative of the individual systems.
The simplest OC for retrofit applications is the wall-box mounted sensor, which replaces the light switch that controls the lights in that room. Each unit comes with a lensed sensor to provide the coverage range that is required by the application. Most of these units also have an integral override switch to turn the lights off, no matter what motion is sensed in the area, and a timer that allows an adjustable time between the last detection of occupation or motion in the area and shut-down of the lighting in the area.
Three general types of sensor technologies are used in these wall-box sensors, each with its own advantages and/or disadvantages: ultrasonic, passive infrared, and combination technology.
The ultrasonic sensing element provides the most complete coverage of an area, but it has the disadvantage of no clear cutoff for the coverage. Therefore, it is possible for people or moving objects in an area adjacent to the control zone to trigger the sensor while there is actually no one in the covered area.
The passive infrared sensing element eliminates the false lighting activation because it has a precise area of coverage that may be adjusted by blocking off sectors of the sensor to adjust the angle of coverage. However, because of this precise coverage, personnel movement or presence behind stationary objects cannot be detected, so low partitions or large objects in the covered area can prevent the sensor from staying energized when its beam cannot “view” the occupants directly.
Combination technology, sometimes referred to as dual technology, uses both passive infrared and ultrasonic sensing technologies to activate the area light fixtures so that the false trigger problems of the ultrasonic are eliminated. The lights are turned off only when neither the ultrasonic or infrared sensors indicate movement, thus eliminating nuisance extinguishment of the lighting in the area.
For larger spaces or rooms with unusual configurations (such as the long, narrow, high corridors in high-bay warehouses), there are specific styles of sensors that are designed for optimal coverage. The issues noted above on zones of coverage and false triggers (either on or off) also apply to the OCs for these spaces and, they face the added issue of needing an adequate range to detect the entry or exit of personnel. When the spaces are larger and have a number of occupants, multiple sensors, connected to form a network, may be used to control a single group of light fixtures.
The installed cost of the many options can vary from relatively inexpensive for a single, wall-mounted occupancy sensor to the expensive full-function, programmable lighting control system that can control a multitude of lighting circuits, each with its own set of timing, day-lighting variations, multiple levels, special event scheduling, and multiple location manual override capabilities. For most installations, the use of a single, large contactor controlling the lighting panel or the distribution panel serving a number of lighting panels will be the least expensive alternative. When coupled with an astronomic, programmable electronic time clock, an engineer can satisfy the basic requirements of the IECC.
Problems with retrofitting controls
Overcoming the greatest obstacle to the installation of automatic lighting controls requires and engineer to work with fixtures that are already installed and circuited to existing switches and branch circuits. Since the entire lighting system and lighting branch circuits already are installed, any changes to incorporate an automatic lighting control system requires selective demolition of selected portions of the lighting and its distribution. This involves intercepting conduits, installing additional junction boxes, finding space for contactors, and other problems—all while keeping the lighting operational so that the occupied area may remain in operation during working hours.
For smaller offices and utility spaces, replacement of the existing light switch with the appropriate wall-mounted occupancy sensor provides a simple solution. This type of installation will disrupt only a single area at a time, so the engineer should coordinate this with the occupants. For larger office areas such as those that use the low, demountable partitions, a choice must made whether to attempt to cover the area with a grid of occupancy sensors that can detect the presence of an occupant anywhere within the area controlled by the sensors, so the false “turn-offs” are minimized, or to provide some type of schedule-based control system. For the larger areas, most systems are best installed during evening hours, over weekends, or during holiday periods to limit disruption of the working environment.
The easiest lighting control to implement in existing buildings is a contactor, multi-pole lighting relay, or group of contactors that would be controlled by a timer that turns off all of the lights on the same programmed sequence. While most of the work for this installation is performed outside of the typical work environment, the impact of installing a main lighting contactor is spread over the largest area, thus impacting the greatest number of people. Therefore, installation of a main lighting contactor also should be performed after normal working hours since there could be a three- to four-hour lighting outage while the contactor is being installed.
If there are multiple zones that require different schedules, the use of a central, programmable lighting controller can provide the needed flexibility and minimize the installation complexity. While most of the central system may be installed during normal work hours without any work environment disruptions, control of the specific lighting circuits will use the same components as previously described and the installation will have the same impact on the building occupants. So the contactors and relays should be installed at times that do not affect operation of the office.
The inclusion of lighting controls in an office that previously had none creates some interesting interactions between the building owner, the architect, the engineer, and, most importantly, the office occupant. While the engineer has direct responsibility for the design of the control retrofit, the architect may have some objections because the varying control zones can impact the appearance of the building from the exterior. As long as the building owner has “bought into” the addition of lighting controls as a means of saving him utility operating dollars, he will be fully behind the effect that the automatic lighting controls have on his facility. However, if the engineer cannot provide the return on investment in terms that the building owner understands, then the project could be in jeopardy because the owner does not see where there is any benefit in his funding the controls addition.
The major problems begin when the office occupants do not fully understand the function of the lighting controls and attempt to manually control the lighting with no regard to the day-lighting contributions and the energy conservative aspects. For example, when the lighting is circuited to permit the perimeter fixtures to be turned off when the day-lighting contribution to the office space exceeds the design lighting level, the typical office occupant will turn on both light switches, irrespective of there being no need for the perimeter zone fixtures, so he or she will attempt to energize these fixtures in spite of there being adequate lighting throughout the area.
Utility rebates and incentives
Several years ago, there were quite a few programs to encourage the use of automatic lighting controls in office spaces that were motivated by various groups for differing reasons, but they all had some type of rebate or other incentive.
Now that the use of occupancy sensors has become an acceptable way to meet IECC lighting control requirements, the incentive programs have been discontinued. It should be noted that in rooms that have more than 200 W and are in use less than six hours a day, the occupancy sensor can pay for itself in less than three years in most electrical utility service areas.
Inclusion of automatic lighting control systems for both new and existing installations is becoming much more common. While much of this activity is driven by the new codes and laws governing energy conservation, building owners have found that they can benefit from significant savings in their utility costs by retrofitting their buildings with these lighting controls, and the return on their investment is typically within the criteria of virtually any building owner or manager.
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Lovorn is president and chief engineer with editorial advisory board.
During the early 1980s and prior to occupancy sensors being common in buildings, the building owner of a relatively large architectural-engineering firm understood that automatic control of lighting in large rooms that were used infrequently had the potential of significant electrical energy savings by automatically turning off the lights when the areas were not in use.
One of the first areas to which occupancy controls (ultrasonic-type motion sensors) were added was a large conference room where all major presentations and management meetings were held. After the first week or so of operation, it was reported that the lights were not being turned off when the room was unoccupied. An investigation found that all four of the sensors had been aimed upward, and one of them was aimed toward an exposed air supply duct that had a slight vibration which, to the sensor, was telling the system that the room was occupied.
The sensors were re-aimed correctly and the same problem occurred again the next week. After some investigation, it was found that some of the users of the room thought that the sensors were audio or video monitors and were placed there to monitor the actions in the room.