{"id":7331,"date":"2015-03-02T14:26:02","date_gmt":"2015-03-02T19:26:02","guid":{"rendered":"http:\/\/www.constructionspecifier.com\/?p=7331"},"modified":"2016-12-22T14:37:10","modified_gmt":"2016-12-22T19:37:10","slug":"planning-for-effective-daylighting","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/planning-for-effective-daylighting\/","title":{"rendered":"Planning for effective daylighting"},"content":{"rendered":"
\"NYTimes_2\"<\/a>
Photos \u00a9 Carlos Rivera. Photos courtesy MechoSystems<\/strong><\/figcaption><\/figure>\n

by William L. Maiman
\n<\/strong>Building owners, architects, lighting designers, and engineers must work together so a project\u2019s design can be maximized to bring in as much light without causing excessive glare or heat gain. While skylights work for a building\u2019s top floor, most of the daylight in commercial building comes through windows.<\/p>\n

Architectural lighting design consultant Matthew Tanteri, principal of Tanteri + Associates (Austin, Texas), explained a climate analysis is conducted using typical meteorological data when creating a design.<\/p>\n

\u201cTwo primary parameters we look at are global horizontal illumination and cloud cover,\u201d he said. \u201cThat gives us an understanding of the predominant sky condition, whether it is clear, overcast, or partly cloudy.\u201d<\/p>\n

Once that information is available patterns of the key conditions over the day and the year is observed. This provides an understanding of the frequency and intensity of illumination values for the area. Solar angles are also studied and these directly relate to the site\u2019s latitude and the orientation of the building surfaces.<\/p>\n

A property\u2019s location is also factored into the equation. Design teams should look at what is nearby the building\u2014including obstructions such as other buildings or trees\u2014as well as the structure’s surrounding atmosphere.<\/p>\n

\u201cThe surroundings can obstruct the solar path, but it is also a source of reflected light\u2014a valuable resource, especially in dense, urban settings,\u201d Tanteri explained. \u201cPutting location and climate information together determines what daylight is available to the site.\u201d<\/p>\n

Daylighting analysis
\n<\/strong>If a building is already standing, how the sun and shadow plays on it will be analyzed to see if the fenestration is adequately shaded. The geospatial position of all fa\u00e7ades will be analyzed for the desired solar penetration and to select proper shading to match existing glazing and the building\u2019s orientation, especially to the east\/west orientation. The goal is to maximize the building\u2019s day-lit floor area from a half-hour after sunrise to a half-hour before sunset. The goal is to turn electric lights off as much as possible, while providing occupants with a view of the outdoor scenery, and meet and maintain expectations of visual and thermal comfort. Therefore, a key goal is also to keep shades up as often as possible, while still allowing for mitigation of glare and solar radiation.<\/p>\n

Some systems work with predictive modeling and different sensors, including radiometers. The radiometers measure Btus and are then used in the building\u2019s immediate area to determine the clear sky or cloudy conditions requiring shades to be lowered to predetermined positions to intercept direct solar radiation or to manage excessive glare. An algorithm is used that interprets the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) clear-sky model based on predetermined analysis of the building, it ensures the shades move to minimize solar radiation and improve occupant comfort.<\/p>\n

From a daylighting designer\u2019s perspective, of first order are the building\u2019s siting, massing, fenestration, and orientation. Glazing selection, interior finishes, and the whole physical nature of the interior (including furnishings and the room geometry) are the next part of the equation. Following this, the lighting control system (i.e.<\/em> sensors, controllers, control gear, and the intelligence linking them) must come together. Lastly, the system needs to be commissioned and verified by a third party and maintained on a periodic basis. Compliance with building codes and local laws also must be taken into consideration.<\/p>\n

\u201cAs envelope components, windows have traditionally been prescribed energy performance parameters akin to a wall, with the most important factor being a low U-value,\u201d Tanteri said.<\/p>\n

\"Clark_1\"<\/a>
Automated shades adorn the 3957-m2 (42,600-sf) Clark Center Art Museum, designed by Pritzker Prize-winning architect Tadao Ando of Osaka, Japan.<\/figcaption><\/figure>\n

\u201cOn the light-delivery side, a window\u2019s solar heat gain coefficient (SHGC) trumps visual light transmittance (VLT), giving daylight a back seat. This conservative approach may have reduced energy exchange through the building envelope, but failed to address other critical functions of the window, namely daylight and view and all their non-energetic benefits (i.e.<\/em> improved health, learning, or productivity).\u201d<\/p>\n

The design team and engineers associated with the building need to determine the criteria for installation of an automated shading system. Questions to consider include: Is the goal to minimize solar radiation or to maximize daylight integration? Is the entire building using automated shading or only a subtenant space?<\/p>\n

Certainly, if the building is wired to provide sub-metering or demand-response on their power consumption, an automated shading system that reduces solar heat is desirable, as less HVAC will be needed.<\/p>\n

While commercial office buildings of any size will gain from automated shading systems, managing glare and minimizing solar heat gain will have more impact in areas with bright sky conditions and strong sunlight. Building occupancy rates, hours of use, local utility energy rates, and Leadership in Energy and Environmental Design (LEED) certification, are some factors that must be considered when determining the return on investment (ROI) for a particular system.<\/p>\n

Improving codes and evolving metrics
\n<\/strong>Spatial daylight autonomy (sDA) can help achieve maximum daylighted floor area. The building and climate data is combined, and a simulation is conducted. If 55 percent of the building hits the target daylight level, it is sufficient\u2014however, the target preferred by designers is 75 percent. Then, a co-metric called annual solar exposure (ASE) is conducted that intends to determine whether illuminance levels are high enough that shading will be needed, or low enough they will be considered acceptable.<\/p>\n

\u201cIf too high, we redesign and re-run both metrics to achieve the best balance between shading and daylight,\u201d explained Tanteri. \u201cIt is a means to optimize performance.\u201d<\/p>\n

\u201cTrying to combine a glare-controlled environment with flexibility is what most clients want,\u201d said George Loisos, LEED AP, and principal of Loisos + Ubbelohde (Alameda, California).<\/p>\n

Controlling light through the window is the ultimate challenge; in addition to integrating electric lighting with daylighting as day time transitions to night time. How do these elements work together? Implementing a proper control system is the key to how electrical lighting responds to daylight.<\/p>\n

In the U.S. Green Building Council\u2019s (USGBC\u2019s) LEED program, view is considered nearly as much as daylight. Therefore, to take advantage of both, lighting designers may use a simple approach often referred to as a \u2018dual-function\u2019 window. The top of the window is for daylight and the bottom of the window\u2014up to about 2.1 m (7 ft)\u2014is for view. Considering shading from the outset is critical to both daylight and view function. Generally, it is difficult to create a shade-free environment without numerous design elements.<\/p>\n

\"NYTimes_1\"<\/a>
Shade positions on the window\u2014correlated to the sun’s position in the sky, the building location, orientation, and geometry\u2014are automatically raised and lowered at New York Times<\/em> building in New York City. The system contributes up to 70 per cent in energy savings. Photo \u00a9 PDK Commercial Photographers<\/strong><\/figcaption><\/figure>\n

Additionally, there are code aspects. Certainly, energy and building codes have great influence
\non the design process and the authority having jurisdiction (AHJ) will be scrutinizing plans for adherence to the regulations. In addition to LEED, many regulations<\/a> will be relevant, such as:<\/p>\n