Field performance of daylight-linked lighting controls
Galasiu, A.D.; Atif, M.R.; MacDonald, R.A.
NRCC-44744
A version of this paper is published in / Une version de ce document se trouve dans : IES Conference Proceedings, Ottawa, Ontario, Aug. 5-8, 2001, pp. 207-215
www.nrc.ca/irc/ircpubs
FIELD PERFORMANCE OF DAYLIGHT-LINKED LIGHTING CONTROLS A D Galasiu, M R Atif and R A MacDonald Indoor Environment Research Program, Institute for Research in Construction, National Research Council Canada, 1200 Montreal Road, Ottawa, Ontario, K1A 0R6, Canada E-mail:
[email protected];
[email protected]
INTRODUCTION Research has shown that daylight-linked electrical lighting systems – such as automatic on/off and continuous dimming - have the potential to reduce the electrical energy consumption in office buildings by as much as 50%. Research has also shown that building occupants tend to favor daylighting over electrical lighting, especially in Canada where very cold winters make them spend most of their active time indoors. Most Canadian climatic regions favor the application of daylightlinked technologies in buildings due to the annual high sunshine availability. However, in spite of all these amenities, daylighting application in Canadian buildings has not advanced sufficiently and the real performance and limitations of these type of systems are not well known. In spite of promising laboratory test results and computer predictions, most daylight-linked systems do not provide the anticipated energy savings when installed in real buildings. There is a lack of information about how these systems perform in buildings with real occupancy, and there is a lack of commissioning procedures for proper operation and optimization for energy savings. Further, these procedures do not consider the impact of movable shading devices - such as blinds - on the lighting energy consumption, despite the fact that they are widely used by occupants for sunshading and glare control. This study aims at developing a systematic evaluation of real daylight-linked system performance in occupied spaces. Performance includes the lighting energy savings as a function of movable manual and automated shading devices and the effect of blind angle and retraction area on the energy consumption and the space illumination. This work will not only provide information on real performance of daylight-linked lighting control systems, but will also provide the basis for guidelines for proper installation, calibration and operation of this type of systems. OBJECTIVES The objectives of this study are: • to evaluate the lighting energy savings from daylighting in four individual daylit office spaces equipped with two types of commercial daylight-linked lighting systems: automatic on/off and continuous dimming; • to evaluate the impact of two types of movable shading devices, manually-operated and photocontrolled venetian blinds, on the performance of the daylight-linked lighting systems and their associated energy savings. TEST-SITE DESCRIPTION The testbed consists of four real side-by-side private offices situated in the southern wing of a research facility located in Ottawa, Canada. Figures 1 and 2 show an exterior and an interior view of the office spaces. The building is not obstructed by other constructions from the south but is facing a small hill on this side, which is mostly covered by green grass for about 8 months a year, and by 2 clean snow during the remaining months. Each office has a floor area of 14 m and a height of 3 m. All offices are used for about 8 hours/day. The regular working schedule is from 8 AM to 5 PM during weekdays, with a one hour break at noontime.
The fenestration system in each office consists of six double glazed, low-E, “view” window panes and three double glazed, low-E, “clerestory” window panes placed high in the walls to allow for deep daylight penetration. The overall opening of each window pane is 0.9 x 0.6 m. The “view” windows are clear and have a visible transmittance of 75%. The “clerestory” windows are gray-tinted and have a visible transmittance of 36%. This choice of glazing contradicts the general concept of using hightransmittance glazing for the upper windows to increase the daylight contribution away from the windows, and low-transmittance glazing for the lower windows to decrease glare and brightness ratios. On the exterior façade, the “view” windows are separated from the “clerestory” windows by a continuous and highly-reflective aluminum light-shelf. The daylight penetration into the offices is also increased by an interior, highly reflective, white-colored window mullion, 0.40 m deep, which acts as an interior light-shelf. All windows have aluminum frames and are equipped with white-colored, manually-operated, aluminum venetian blinds. Ambient lighting is provided in each office by two energy efficient recessed fluorescent lighting fixtures arranged in the space as shown in Figure 3. Each fixture incorporates two, 32-watt, T8 2 fluorescent lamps. The average lighting power density in each office is about 9 W/m and the average space design illuminance measured on the workplane at night under full electric lighting is 570 lux. The walls and ceilings are painted off-white and have an estimated reflectance of 70%. The floor is covered with a light-brown carpet with an estimated reflectance of 30%. All four offices are furnished with similar brown-colored furniture. The furniture layout, however, is different in each office and was maintained during the tests as originally set by the occupants. Daylight-linked Electrical Lighting Controls In two side-by-side offices the ballasts of the lighting fixtures were replaced with electronic dimming ballasts which adjust the power flowing to the lamps based on a signal received through a controller from a light photosensor located in the ceiling at a distance of 0.50 m from the upper window pane. The photosensor ensures an open-loop feedback to the lighting controller (photosensor does not see electric light and detects daylight only) and according to the manufacturer, the ballast dimming range is between 100% to 1% illuminance level. In the other two offices, the lighting fixtures were equipped with electronic on/off ballasts operated based on a signal received through a controller from a light photosensor located in the ceiling at a distance of 0.50 m from the upper window pane. The automatic on/off lighting system was calibrated to turn the lights off when the average illuminance from daylighting on the workplane exceeded 570 lux, the design illuminance at night under full electric lighting. In order to avoid the “passing-cloud” effect, the time delay between the on and off states of the lighting system was set to 3-minutes. Characteristics of the Motorized Shading System To investigate the impact of automatic blinds on the performance of the on/off and continuous dimming lighting control systems, all four windows in one “on/off” office and in one “dimming” office were provided with photo-controlled motorized blinds. The blinds are not retractable and cover the entire window. The position of the blind slats is controlled based on a signal received from a light photosensor mounted in the window frame, facing outdoors, which monitors the external daylight levels. The angle of the slats gradually adjust in tiny increments throughout the day to maintain a constant preset level of illumination, and close completely at night. In both offices, the blinds were synchronized to provide the same tilt angle.
Figure 1 Exterior view of the south-facing facade
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Figure 2 Interior view of a typical office space
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METHODOLOGY The field monitoring work consisted of the following: •
Calibration and commissioning of the daylight-linked lighting control systems
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Investigation of the effect that various positions of manually-operated venetian blinds have on the performance of the automatic on/off and continuous dimming lighting control systems;
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Investigation of the effect that automatic motorized venetian blinds have on the performance of the automatic on/off and continuous dimming lighting control systems.
During all tests, one “on/off” office and one “dimming” office was used as a base case (reference rooms) to which the performance of the “modified” offices (test rooms) having a similar type of electrical lighting control system was compared. Each test identified by how much each blind setting affected the lighting energy consumption of each type of lighting control system. System calibration tests were conducted periodically to determine the relative deviation between each pair of rooms (test rooms versus reference rooms) resulting from instrumental error, the room’s relative position to the exterior environment, and the system components and operation. For example, monitoring was conducted at night to determine the maximum light levels in the absence of daylight and to verify the similarity between the electrical lighting system of each pair of rooms. Several system calibration tests were also conducted during daytime under clear and overcast sky and determined the relative
deviation between each set of rooms under these two sky conditions. During these calibration tests all blinds were fully-retracted, simulating spaces without blinds in which an automatic lighting control system would provide the maximum lighting energy savings. Table 1 presents an overview of the variables tested. For the manually operated blinds, the performance of the lighting control systems for each blind setting was monitored for at least 3 days with clear sky and one day with overcast sky, from September to December 2000. The monitoring of the photo-controlled automatic blinds took place during January and February 2001. The blinds control system and the lighting control system worked independently of each other, each system having its own control photosensor and routine algorithm. The automatic lighting control system worked in parallel with the automatic blinds system, based on the interior daylight levels that the motorized blinds allowed it to "see". Table 1
Overview of variables in the test rooms
Lighting control system Automatic On/Off
Type of venetian blinds Manually operated
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Blind Retraction Area 100% Retracted
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Notes: § Blinds horizontal means slats tilt angle 0°. § Blinds at 45° upward: exterior edge of the slats goes upward (means a view of the sky from the interior). § Blinds at 45° downward: exterior edge of the slats goes downward (means a view of the ground from the interior). § Blinds closed means slats squeezed downward to their mechanical limit. Horizontal indoor illuminance measurements were automatically collected in each office at two testpoints, one located at the ceiling level just beside the photosensor operating the automatic lighting control system and the second located at the desktop height (0.85 m from the floor, and 2.75 m from the windows). The on/off state and the dimming percentage of the electrical lighting system were monitored by a data acquisition system installed at the breaker panel serving the lighting circuits. The power demand profile was monitored independently for each office, and the daily lighting energy consumption was calculated for 12-hour intervals, from 6 AM to 6 PM. The angular position of the blinds (tilt angle) was monitored along with the space illuminance and electrical lighting power consumption. The four blinds in each office were synchronized to provide the same angle, measured from the horizontal plane. An reading of about 10 V corresponds to a horizontal tilt angle. A reading lower than 1 V corresponds to the blinds being squeezed downward to their mechanical limit. Any reading between these two positions corresponds to a downward angle (a view of the ground from the interior).
EXAMPLE RESULTS Field data are still being collected and analyzed. Example data illustrating the calibration of the continuous dimming lighting control system and the effect of window blind position on the lighting energy consumption and the space illuminance are shown in Figures 4 and 5. For example, over a 12-hour period at night, from 6 PM to 6 AM, the continuous dimming used 1.66 kWh to provide an average illuminance of 570 lux on the desktop. Over a 12-hour period during several daytime calibration tests, from 6 AM to 6 PM, the continuous dimming control system varied the electrical lighting according to the available daylight and the difference in lighting energy consumption between the reference room and the test room in the “no blinds” configuration was less than 2% regardless of the sky condition. This confirmed an almost perfect match between this pair of offices. Figure 5 shows the effect of the blind slats positioned at a 45°upward angle on the performance of the automatic on/off and the continuous dimming lighting systems under a clear sky. Due to the presence of the window blinds, the illuminance at the ceiling photosensor was reduced on average by 50%. The daylight illuminance on the desktop decreased by about 50% and remained above the space design illuminance of 570 lux only before noon. The lighting energy consumption increased by about 40 to 45% for the automatic on/off system, and by 30 to 35% for the continuous dimming system. Figure 6 shows a typical performance of the photosensor controlled automatic blinds and the electric lighting systems under a clear winter sky. In both test-rooms, the motorized blinds closed at night and turned fully open (slats horizontal) at about 7:30 AM. When the daylight levels on the desktop exceeded 400 lux, the blind slats switched to a angle of about 30° and remained in this position until 3 PM, when the daylight illuminance on the desktop dropped to about 100 lux. At this point the blinds opened to a horizontal position until about 5 PM, when they closed completely for the night. At the ceiling photosensor the light levels were not significantly affected by the position of the automated blinds and this has reflected in the lighting energy consumption, which increased by less than 10% over a 12-hour period. This paper presents an update of an on-going research that aims to characterize the impact of various configurations of manually operated and photocontrolled motorized blinds on the lighting energy consumption of two types of commercially available lighting control systems. This work is directed towards the development of improved calibration and commissioning procedures for automatic lighting and blind control systems, based on a better understanding of how these systems influence one another in real-world installations. Detailed results will be presented in future publications.
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COMMENTS: • • •
The illuminance at the ceiling photosensor was reduced on average by 50%; The daylight illuminance on the desktop decreased by about 50% for the “blinds at 45°upward” configuration and remained above the space design illuminance of 570 lux only before noon; Lighting energy consumption increased by about 40 to 45% for the automatic on/off system, and by 30 to 35% for the continuous dimming system over a 12-hour period under clear sky.
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ACKNOWLEDGEMENT This work was conducted as part of a project partly funded by PERD (Panel on Energy Research and Development).
REFERENCES Foster, M., Oreszczyn, T., “Occupant control of passive systems: the use of venetian blinds”, Building and Environment Journal, vol. 36, 2001, pp. 149-155. Lee, E., DiBartolomeo, D., Selkowitz, S., “ The Effect of Venetian Blinds and Daylight Photoelectric Control Performance", Journal of the Illuminating Engineering Society, Vol. 28, No. 2, 1999. Lee, E., DiBartolomeo, D., Selkowitz, S., “Thermal and Daylighting Performance of an Automated Venetian Blind and Lighting System in a Full-scale private office”, Energy and Buildings no. 29, pp. 47-63, 1998. Swinton, M.C., “Assessment of the energy performance of a photocell-activated blind control system at the Canadian Centre for Housing Technology”, National Research Council Canada, Institute for Research in Construction, Report B6002.1, 2001 Ullah, M.B., Lefebvre, G., “Estimation of annual energy-saving contribution of an automated blind system”, ASHRAE Transactions, 2000. Vine, E., Lee, E., Clear, R., DiBartolomeo, S., Selkowitz, S., “Office worker response to an automated venetian blind and electric lighting system: a pilot study”, Energy and Buildings Journal, vol. 28, 1998, pp. 205-218.
