Glass & Metals 501: The Architect's Guide
A Look at LBNL's COMFEN Software
Building orientation plays a tremendous role in energy performance and occupant productivity. Solar heat gain and daylighting can vary greatly depending on the path of the sun, creating a unique set of considerations for each face of the building. However, orientation is often overlooked during the design phase, resulting in excessive heat gain or glare issues that compromise energy performance and human comfort. In part five of Glass Magazine’s “All About Glass and Metals: A Guide for Architects and Specifiers” series, we look at the importance of building orientation when specifying glass and glazing. The guide addresses the performance measurements of glass and how each is affected by orientation; the impact of location and site on design; potential glass and glazing solutions for each façade elevation; and tools and resources for specifiers.
“All too often I find that façade orientation is not considered at all,” says Mic Patterson, vice president of strategic development at the Advanced Technology Studio for Enclos Corp. “Survey for yourself the crop of recent high-rise buildings and observe how many display the same façade at each building elevation. This is nothing less than an obvious admission that climate considerations have been ignored in the building design.”
“This is not a new concept, that orientation matters,” says Stephen Selkowitz, senior advisor for Building Science, and leader of the Windows and Envelope Materials Group at the Lawrence Berkeley National Laboratory. “The challenge is to get people to pay attention to orientation and then to make design decisions based on it.”
The impact of glass and glazing on a building’s energy performance relies on four factors: energy gain or loss due to temperature difference, driven by U-value; heat transfer by ventilation or air leakage; solar radiation transfer, driven by solar heat gain coefficient; and daylighting, driven by the optical properties of the façade (visible light transmission: VLT, VT or Tv), Selkowitz explains. “Of these, orientation has almost no impact on the first, with U-value. It has a modest impact on ventilation: think prevailing winds. But the biggest effect [of orientation] is on solar loads in summer or winter, and the associated variation in daylighting transmission,” he says.
Photo by Benjamin Benscheider
Of all building envelope materials, glass is perhaps the most influential in controlling solar heat gain and daylighting. “Glass is one of the products you can tune based on climate—where you are in terms of solar-control needs,” says Christopher Meek, research assistant professor, Department of Architecture, University of Washington. Choosing the right glazing products and employing them appropriately on each face of the building is critical in terms of building performance.
“The right glass will optimize energy performance (the right U-value and SHGC); provide the right amount of light for the occupancy without creating glare (the right VLT); and provide a direct connection to the outside through proper sizing, VLT, and minimal interior reflection,” says Bill Coady, architectural design manager, Northwest Region, Guardian Industries Corp.
Ideally, a façade tuned for orientation not only prevents problems such as excessive heat gain and glare, but also provides an energy benefit to the building through passive means: daylighting that reduces electric lighting loads, beneficial heat gain in heating-dominated climates, and natural cooling through ventilation that can reduce air conditioning costs, etc. “Good designers have always known that orientation matters but there are still not enough architects who take advantage of the fact that each orientation is different,” Selkowitz says.
Purpose and location, then orientation
Building orientation can’t be divorced from building purpose and location considerations. Before any direction-based tuning of the façade can take place, designers need to look at the use of the building, the climate and the building’s immediate site location, Meek says.
A designer should first ask what level of temperature control, glare control, visual control and comfort is required based on the activities planned for the building, Meek says. The requirements of one type of building may vary greatly from requirements of another.
Coady agrees. “Offices facing west will have different issues than a manufacturing space,” he says. “Likewise for common spaces, lobbies, classrooms, labs, etc.”
Designers should then look to building location, both in terms of the geographic climate and the local building site. Climate zones play an important role in tuning the glass for orientation. For example, solar heat gain can provide a benefit in the Northern climates, while SHGC should be minimized in the South.
“A lot of glazing solutions revolve around the specific climate that you're dealing with,” says Jack Williams, director of product marketing, EFCO Corp. “In cold climates, you may want a system that allows passive solar heat gain to ease the load required for temperature control of the building.” In cooling climates, “you want to avoid solar contribution and ensure you get a very low SHGC. Almost all direct-beam sunlight is bad in places like Florida or Georgia that can get very hot and humid,” Meek adds.
Building site also plays an important role in the design. Adjacent buildings, site restrictions and environmental surroundings can all affect the performance of glass and glazing. “A west-facing elevation has many similar conditions regardless of where it is located in the world,” Coady says. However, “a west elevation in Seattle on the water with unobstructed exposure is different than one in downtown New York where perhaps another building across the street provides shading at key times of the day/year.”
“Surrounding buildings and landscapes need to be considered,” says Lance Lawrence, architectural design associate for Viracon. “Will the building’s surroundings provide any shading throughout the day? Do reflections off existing buildings or bodies of water create intense conditions of lighting?”
Bill Strait, direct of commercial sales for View Inc., agrees, adding, “another often overlooked factor is nearby water. This can cause a reflection problem from below, instead of above.”
Proper product selection
Architects may be restricted by site location and unable to alter the axis of the building, or the location of elements such as the lobby, based on optimal orientation. In these instances, product choice can be used to determine performance solutions, sources say.
Once purpose and location requirements are assessed, an architect can begin to tune a building for orientation. “Each elevation will experience its own, unique climate, at any given time of day,” Strait says. In general in North America, buildings experience: all-day indirect sunlight on the north face; solar exposure throughout the day on the south face; direct light at low angles during morning hours on the east face; and direct light at low angles during the afternoon hours on the west face.
|The DaVita World Headquarters in Denver, designed by George Feathers of MOA Architecture, features several types of high performance, energy- control glass from Viracon: VE13-2M, VRE26-59 and VRE13-46. “Energy efficiency and daylighting are both very important on a project. You want to make sure you don’t get daylighting too high inside a building where you deal with issues like glare,” Feathers says. For the DaVita project, “we found the best balance to be somewhere in the 28 percent to 35 percent visible light transmittance range. That VT allowed us to create a good balance with energy consumption in the building.” The glazing contractor was Metropolitan Glass Inc.|
It is in this orientation “tuning” process that specific glass and glazing solutions come into play. All-glass, northfacing façades can be used to maximize natural daylighting on the north-facing elevation. On the east and west facades, where low-angle sun becomes an issue, shading controls such as sunshades or fritted glass, and dynamic products such as electrochromics, thermochromics, automatic blinds or shades can provide good solutions that maximize daylight during off-angle hours and prevent glare and heat gain during periods of direct sunlight. The south façade is subject to the most solar exposure throughout the day, though at a more consistent level. Low-E glass will provide benefits for the south face, and shading devices might be required. The south façade can also offer light-redirecting benefits through systems such as light shelves.
“The use of high performance solar coatings, tinted glass, and ceramic frit silkscreening are all techniques that can be used to provide an appropriate glass type,” Lawrence says. “More and more projects are using some, or all, of these techniques to reduce the visible light and heat gain into a building. … The direct low angles of the sun early and later in the day may require the east and west facades to use higher amounts of fritting than the south façade, while the north façade may not need any ceramic frit at all.”
However, Lawrence notes, “Any time there are conditions of direct sunlight, there is a potential for glare no matter how low the visible light of the glass may be. These techniques will reduce the potential for glare related to too much indirect natural light.”
As architects continue to seek higherperforming facades that consider orientation, dynamic products will become more in demand, sources say, pointing to solutions like dynamic windows, blinds and shades that can be used in conjunction with automatic lighting and temperature controls to maximize building and system performance. “Dynamic systems allow the properties of windows to be tuned on an hour-by-hour, season-byseason basis,” Selkowitz says. Architects can specify a “one-size-fits-all system if it is dynamic and can respond to different conditions.”
The basic rules of thumb for glass specification seem fairly straightforward—“ as low a U-factor as affordable, especially in climates with very hot and/or cold temperatures; a low SHGC in hot climates, but not so low as to yield a visible transmittance that compromises daylight quality; a higher SHGC in cold climates,” Patterson says. However, variables such as location quickly complicate the specification process.
“There are highly location-dependent considerations for south- and westfacing facades, presenting opportunities for beneficial solar gain in heatingdominated climates, and the threat of unwanted heat gain in cooling-dominated climates,” he says. “The designer quickly steps into escalating complexity. Layer on the façade considerations of air and moisture permeability, natural ventilation, glare control, daylighting, condensation resistance, acoustical performance, durability, structural integrity, security, resilience and environmental impact, and what could possibly present more of a challenge in the building arts?”
Managing the complexity requires ever-increasing modeling and support from the industry.
Missteps and hurdles
Prioritizing aesthetics, focusing on costcutting, or simply lacking product and system performance knowledge can all lead to inefficient façades.
“Hands down, the biggest mistake [we see is a lack of true] understanding of glare concerns while selecting glazing,” says Jason Wesely, architectural design manager, Pacific Region, Guardian Industries Corp.
“Many times this leads to issues with glare and heat gain,” adds Viracon’s Lawrence. “This in turn causes the occupants to use the blinds or shading devices, turn on the lights, and minimize or eliminate the benefits of natural daylight through glass facades.”
This issue is driven by a recent aesthetic trend toward high VLT in the form of clear glass walls. “The trend in architecture has been to increase natural lighting. Artificial lighting consumes energy and adds interior heat sources,” says Michael Johnson, regional sales and marketing manager for Pilkington north America. However, oftentimes the “glass specified provides too much light, and as a result, glare becomes an issue. … Some higher performance low-E products may fit the needs from a U-factor and SHGC standpoint, but provide too much light. As a result, we are seeing a renewed interest in good light-to-SHGC-ratio tinted substrates to control glare, while still allowing decent light transmittance.”
Measures to maximize daylighting, particularly within the Leadership in Energy and Environmental Design program, have also elevated the problem, leading to designs that “focus too much on LEED daylighting credits,” Coady says.
Another common mistake in glazing specification is “assuming the entire envelope should be treated the same,” Johnson says. This is often driven by a desire for a uniform “look” across all faces of a building, sources say.
“Using different types of glass on various facades sometimes concerns owners/developers regarding a building’s ‘look,’” Wesely says. “Often clarity is still king, and changing glass types tends not to get past some design review meetings.”
“There is often the expressed design intent to achieve a uniform appearance at each building elevation, thus an identical glass specification is applied to the facade regardless of orientation,” Patterson agrees. “This is a misguided strategy, however, as the appearance of glass is a product of the light reflected from its surface, and this varies dramatically for each elevation.”
Some in the building community also assume that the sun on all faces of a building can be controlled solely through the use of low-E glass. “There is a surprisingly prevalent assumption among building designers that performance concerns with the highly glazed façade can be dealt with simply by slathering low-E coatings on the glass,” Patterson. “The glass specification is often applied to each building elevation regardless of exposure, with the low-E properties largely wasted on the north facade and inadequate on the south.”
Glass industry’s role
The glass industry plays a crucial rule in assisting the design community in designing and specifying building glazing that maximizes performance according to building orientation. Education, collaboration, product development, and the availability of detailed product performance data and improved simulation tools are all key, sources say.
“At minimum, companies should be sure to have accurately labeled product data available,” Selkowitz says.
“Glass is an indispensable material in achieving optimal building performance, and the glass industry continues to do a remarkable job in delivering increasingly high-performance materials to facilitate the implementation of highly performing facades,” Patterson adds. There is an opportunity for the glass industry to educate "the design community as to the appropriate use of glass in a given application," he says. "This requires stepping beyond simply addressing the use of glass itself, and rather confronting the performance of the entire facade system and how the glass is used within that system.”