Consulting Specifying Engineer April 2015-CSE : Page 62

Integration: Lighting and HVAC systems the building that faces away from the earth’s equator. If every building was constructed in an anecdotal “vacuum,” then every building could be a long floor plate, with circula-tion spaces tolerant of temperature varia-tions along the south façade, fire stairs on the east and west ends of the building with no need for daylight, and a long façade variation be located where the sun is most problematic? Can the spaces that require the least light—that can have the smallest windows and use the least energy when blinds are closed—be located to the east and west where blinds will be closed daily at sunrise and sunset? After we assume the building has at least partially non-ideal orientation of low-e coating to limit infrared transmis-sion into a building, while still allowing proportionally more visible light indoors. Even when additional solar design tech-niques are employed, the benefits of coat-ings to tailor wavelength transmission can be valuable. Filtering wavelengths of light can improve the HVAC situation by limit-ing sun, but it can’t improve the issues of glare and requirements for window blinds. Selecting times of day also could be considered part of the status quo in many cases, although there is quite a range of methods by which solar impact on build-ings can be filtered temporally—running the gamut from user-operated interior window blinds to computer-controlled and motor-operated exterior louver sys-tems. The fallback lowest risk option is manually operated window blinds: people can always lower the blinds when needed, the cost and complexity of installation is basic, and if the shades are left down by occupants, the mechani-cal system doesn’t suffer, though electric lighting stays energized to compensate and counteracts much of the intention for the glass in the first place. If interior window blinds can be motor-ized and automated, it is a marginal improvement that the blinds are opened at least once a day, and admit useful vis-ible radiation (daylight) for most of the day until a person or an automated sensor closes the blinds—at the times that blinds must be down to prevent glare for work-place comfort and productivity. When simple blinds are internal, they might reflect a bit of infrared energy back through the glass outward to the exterior, but some of the heat has already been absorbed into the fabric or venetian blinds and transmitted through them to the building interior. If an automated motor-ized shading system can be moved to the building exterior, it can block as much infrared heat from the building at some times as it can block the visible glare at other times, and serve a more useful dual purpose. A more advanced and complex step is to combine automation for various times of day and seasons, with angular solar selectivity. Figure 4: At the Sacramento International Airport Terminal B, photographed by John Swain Photography, an external horizontal shading system reduces solar heat gains while also tempering direct sunlight for visual comfort in the ticketing hall. of windows for occupied spaces facing away from the equator. These theoretical buildings would also need to have all the beautiful landscape features and distant city skyline views in the same direction that the occupied spaces are getting their diffuse daylight from—if we want to avoid disrupting this idealized scenario. In the real world, buildings are limited to particular sites, with street frontage and size of lots impacting building shape; desirable views to natural or manmade landmarks in various directions (or avoid-ing undesirable views); and resulting in windows facing east, south, west, and north. Still, early design considerations prevail over engineering solutions. For example, can cafes, break rooms, lounges, lobbies, and other transient spaces with easier acceptance of glare and temperature 62 occupied spaces, how can we accom-modate daylight in a way that considers the best outcome for both lighting and thermal concerns? It becomes necessary to be selective about what portions of the sun’s radiation are admitted to the building. A building can select what wavelengths of sun to admit, at what times sun is admitted to each window, and what angles of sun to admit. Glazing and shading Selecting wavelengths could be con-sidered a part of the status quo approach. It is typical that in climates requiring multi-pane insulated glazing, the glazing is likely to have a low-emissivity coat-ing. In milder climates, a film or interlayer with particular reflectance and transmit-tance properties may take the place of Consulting-Specifying Engineer • APRIL 2015

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