Consulting-Specifying Engineer - February 2009 - (Page 26)

Sensor mishap 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. 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. Cooperation 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 26 Consulting-Specifying Engineer • FEBRUARY 2009

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - February 2009

Consulting-Specifying Engineer - February 2009 Contents Viewpoint News M/E Roundtable Codes & Standards Electrical Modernization: A Tale of Two Hospitals Retrofitting Office Lighting Controls Case Study New Products Equipment Lifecycles Advertiser Index Green Space

Consulting-Specifying Engineer - February 2009

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