Consulting Specifying Engineer April 2015-CSE : Page 66

Integration: Lighting and HVAC systems glowing arc of gaseous metals replacing sufficient heat generated by the diodes to as cool as possible. We are still in an era filaments as the primary light source, prevent overheating. In low-power linear or of learning to design with, modularize, electrodes can be more robust and long-planar LED fixtures with diodes distributed standardize, and maintain this new LED lasting, instead of thin enough to radiate along larger circuit boards, the circuit board lighting technology, and at the same time itself may be substantial enough to conduct it is evolving to be more efficient and notable light output themselves. So the gases and phosphors of fluores-and dissipate sufficient heat from dispersed more cost-effective with less waste heat. cent and other discharge lamps have been low-power diodes. In LED systems with Opportunities to ingrain heat mitigation more efficient at creating more light and power and intensity concentrated to a small for the benefit of LED into the next para-less heat, compared to incandescent. These intense light source, the circuit board must digm of building systems design are ripe arc lamp technologies also require ballast be assisted with a heat-sink to further con-for implementation. components to modulate the electrical cur-duct heat away, and to better dissipate this With appropriate management of solar rent to strike and maintain the glowing arc heat to the surroundings through increased radiation (and without the electrical ener-between electrodes. So some waste heat is surface area, or even through fan-like sys-gy expenditure of manmade lighting), moved to a ballast. At the lamp itself, with tems and airflow design. Also, instead of a daylight can be tailored to direct useful more of the electrical energy illumination where and when converted to light (and UV), it is required, while mitigating The designer’s challenge is to less infrared radiation is gener-solar gains through spectral, determine the best combination ated directly, and more of the angular, or temporal selectiv-waste heat is convected away ity—just as the thermal char-of design implementations from the lamp and ballast. acteristics of LED systems that holistically address the needs of Now with LEDs, the norm make heat a critical risk to be is changing again. Generat-mitigated, but with potential to both lighting and HVAC for buildings ing light through electrical more carefully accommodate excitation and interaction of or embrace these characteris-that fulfill occupant needs. electrons across semicon-tics through building design. ductor diodes, most LEDs used for illu-ballast controlling electrical arc, a combina-With these principles in mind, the mination emit almost no infrared or UV tion of driver and transformer (also known designer’s challenge is to determine the radiation. They are still not 100% efficient, as power supply) operate LEDs, and gener-best combination of design implementa-however, and so waste heat is generated ate a portion of the heat from the system. tions that holistically address the needs Keep in mind however, that although of both lighting and HVAC for buildings directly within the diode (and electronic components), which must be conducted LEDs are not directly radiating infrared that fulfill occupant needs, bring people heat into the room, the visible radiation joy or make life comfortable, and avoid and convected away. Critically, LED semiconductors are is still eventually being absorbed into the or at least limit detrimental impacts to the extremely sensitive to heat and tempera-room surfaces (after some inter-reflec-Earth. Some open-source tools that can ture. Just as computer components would tion and useful illumination). LEDs are help to assess and quantify the benefits of overheat without fans or heat-sink strate-decreasing internal heat gains from light-various design solutions include software gies, LED light output will fade severely ing within buildings only by the small like OpenStudio, Ladybug and Honey-and electrical components could fail if margin that they can be more efficient than bee modeling software plug-ins, and all not protected from the heat they gener-whatever they are replacing (currently a the other work behind the scenes of these ate. This is a new concern for lighting, as small but beneficial gain compared to lin-software packages such as Radiance, Ener-incandescence is practically insensitive ear fluorescent, and quickly improving). gyPlus, or Daysim. to temperature, and fluorescent lamps Whether it is convected from a heat-sink are more sensitive to cold temperatures or radiated from a filament, all electrical Chris Rush is senior lighting consul-impacting gas pressures within bulbs. energy used in a lighting system becomes tant at Arup, responsible for design, Ballasts may have been sensitive to internal energy gain to be accounted for in consultancy, and management for light-extreme high temperatures, but only with building HVAC design. ing projects throughout the U.S. and But we are now in an age of LED light-internationally, including all aspects of LEDs do we have a source that can cook itself to the point of failure even in room ing systems that essentially radiate only electric lighting, daylight, and lighting visible light into the direction of intend-controls. He focuses on detailed coordi-temperature conditioned space. Similar to computers, LEDs are typically ed usefulness. Heat is concentrated at nation of daylight analysis and electric laid out on circuit boards of some form, the source of the light, and these LED light and control designs with Arup’s whether small or large. Various strategies light sources will be very happy (with whole building energy models, HVAC are taken for these circuit boards, but in all increased lifespan and efficiency) if the design loads, and building automation cases, the circuit board must conduct away heat is dissipated quickly to keep them systems. 66 Consulting-Specifying Engineer • APRIL 2015

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