Sustainable Building Technical Manual - Etn-presco.net

Innovative Core Daylighting Systems❑ Consider light-pipe distribution.Light-pipe distribution has been commercialized for use with high-output luminairesin commercial buildings where special security requirements, difficulty of access, orexplosive or corrosive environmental conditions are present. The efficiency of lightpipedistribution is approximately 50 percent from source to delivered illumination. 12Available systems include those where the light transfer is internal only, or where thepipe itself is a continuous light source. 13 Daylighting applications using this technologyfor light distribution use concentrating collectors or heliostats as high-intensitylight sources.Control Strategies❑ Integrate lighting controls to respond to available daylight.To capitalize on the potential energy savings associated with daylighting strategies, itis usually necessary to automate the reduction of electrical lighting operation. This canbe accomplished in a variety of ways; however, hardware complexity, cost, wiringcomplexity, and types of lighting systems are all affected by desired control strategies.In addition, the subtlety of the lighting change actuated by the control systems isaffected by the mode of controls selected (see Chapter 12, “HVAC, Electrical, andPlumbing Systems”).❑ Ensure good control-system design.The chief failure of daylighting systems lies in the faulty design or installation of lightingcontrols. Several factors are critical to the correct functioning of daylighting controlsystems. Consider these practices to improve lighting control:– Properly locate and calibrate the photosensors. Correct location and calibration ofthe photosensor for all daylighting control systems is critical. Ordinarily, a singlephotosensor will control a group or zone of light fixtures in order to reduce systemcost. The sensor should “see” a mixture of both natural and electrical light andshould not be located so as to be “fooled” by movement of occupants or objectsin the space.– Use proper zoning. Daylight levels vary greatly within a building depending onmany factors. Typically, at least two zones—perimeter and core—should be establishedin a sidelighting situation. Toplighting situations usually require at least twoor three zones. Where more sophisticated controls systems are used, calibrate andcontrol each fixture individually based on a common reference photosensor.❑ Integrate daylight controls with other control strategies.In addition to controlling lighting to respond to levels of daylight, other lighting-controlstrategies are typically cost-effective in reducing lighting needs and thus reducinglighting and cooling energy consumption. These may include:– Time or scheduling controls;– Occupancy-sensor controls; and– Lumen-maintenance control programs.Some manufacturers of lighting-control and building energy systems allow daylighting-controlstrategies to be integrated with these additional control features in a singlesystem with a central control and program terminal.Emerging Glazing Technologies❑ Consider spectrally selective glazings.Specifying glazings with high visible-light transmittance is necessary for optimal energysavings. On the other hand, a low shading coefficient reduces relative heat gain throughthe glass, which lowers cooling loads. The daylight factor is the ratio of visible lighttransmittance to total solar transmittance; therefore, the higher the daylight factor, thebetter the choice for daylighting applications in general. Another measure is the luminousefficacy value (k-factor) which is the visible-light transmittance divided by the