High-Performance Glass Solutions

A systems approach to efficient building envelopes
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Sponsored by National Glass Association
By Jessica Jarrard

Performance Perks for Occupants

When comprehensive high-performance glass solutions are specified and installed, occupants also enjoy the benefits of proper daylighting, thermal comfort, security, and safety from intrusions and blasts. When occupants are comfortable, they are healthier, happier, and more productive.

Building occupants are healthier and perform better when they are granted access to views and are comfortable in terms of daylighting levels and temperature. Studies on occupant comfort show increased healing times for patients, improved test scores among students, and decreased absenteeism and increased productivity among office workers. “We cannot underestimate the importance of daylighting and its ability to improve health and happiness within the workplace,” Wignall says. “People cannot sit in a brick box with no light.”

Because people in healthier buildings miss fewer days of work, perform tasks more efficiently, and stay in their jobs longer, owners and employers can see notable paybacks. Employers see productivity improvements and building owners can charge higher lease rates.

Too often, building managers and owners do not factor people into the building performance equation. However, it is the people who represent the costliest aspect of running a building, says Stephen Selkowitz, former senior advisor for building science, and former group leader of the Windows and Envelope Materials Group in the Building Technology and Urban Systems Division of Lawrence Berkeley Lab. He estimates that occupancy costs reach about 100 times the cost of energy.

Although building occupants need access to daylighting and views, too much daylight leads to glare and heat gain, which negates the potential occupant comfort benefits. “One of the biggest misconceptions I see is the automatic, if not subconscious, assumption that all-glass facades lead to better daylight and views,” says Galen Burrell, director of lighting design at View Inc. “However, the reality is that there can be too much of a good thing, and so we should focus on optimizing daylight rather than maximizing it. Unchecked sunlight can create various comfort issues associated with excessive glare and heat. As a result, blinds get closed and generally remain closed, and the entire value proposition of daylight and views get lost.”

Taking a "Systems" Approach When Specifying Glass, Glazing, and the Rest of the Facade

While high-performance glass and glazing can help reduce long-term heating, cooling, and lighting costs, it is important to recognize that specified glass is part of a larger system that includes the framing, the facade, and even the mechanical and lighting systems. When specifying glass, the system must be viewed as a whole to ensure that glass and glazing solutions not only provide proper daylighting and lower energy costs but are also aesthetically pleasing and designed to work with new or existing mechanical and lighting systems.

The biggest misconception in glazing system performance is that it is all about the glass. Performance values for the glass must be considered in concert with values for the framing system to develop whole-system performance values. “To many, glass seems to be the most obvious factor in performance, but the opposite is true,” says Anthony Intintoli, architectural sales representatives for YKK AP. “You have to find the right glazing system and framing system to achieve the desired high performance.”

At times, performance and aesthetic goals are at odds on projects. In recent years, this has been the case with trends toward ultra-clear, less-reflective glasses that can create challenges with solar heat gain and glare. “This is a big hurdle when it comes to glass performance,” says Viracon's Schmidt. “It is important to work with glass suppliers to find a compromise. How much are you willing to sacrifice in terms of appearance to achieve performance goals? We can come up with solutions for a building that meets renderings but still performs.”

Thermal Protection Through Glazing and Framing

Center-of-glass (COG) thermal performance values, U-factors, cannot be used alone to determine the performance of a complete glazing system. “The COG U-factor makes up only part of a window’s performance,” says Technoform’s Sanders. “It is necessary to look more broadly at the window system, including the edges: the frame and edge of glass. You can have a great center of glass value, but if you do not match that with thermal performance in the framing or edge of glass, you are going to have other performance issues, such as condensation or thermal discomfort.”

Framing systems are designed to meet different structural, water, and air performance requirements depending on their application. These differences translate to varying high-performance methods and thermal performance targets. For example, curtain wall systems can be made wider, thus allowing for improved thermal elements such as multi-cavity insulating glass units, or larger and more complex thermal breaks. “With a storefront, you are typically not going to achieve the performance as you would with a curtain wall,” says EFCO’s Wignall. “You usually see pour and debridge thermal breaks in storefront; you will typically have fewer opportunities for glass in terms of thickness.”

Misconceptions about glass and glazing performance, lack of high-quality modeling, and a siloed approach to design and construction all impede performance goals. To meet and exceed expectations, industry experts recommend project teams clearly understand the various performance values of glass, consider the relationship between the glazing and the rest of the facade, ensure correct modeling from the start, and more.

A project can feature the highest-performing glazing system options, but if thermal performance does not carry over to the connection points, the facade will not meet its goals. “We see big issues around the interfaces,” says Sanders. “This is where the thermal bridging happens.”

To tackle the problem, Sanders recommends project teams review the details of, and if possible model, the interfaces. “The models have to be well detailed—3D modeling rather than 2D modeling is needed for appropriate accuracy. And, we have to measure the performance—for example, take infrared pictures of the buildings,” she says.

Glass and Glazing Performance as Part of the Facade

Next-level facade and building performance comes when glazing systems are integrated into the full building. “Every building, every facade is going to be different,” says Tom Culp, code consultant for the National Glass Association (NGA) and owner of Birch Point Consulting. “You have to look at everything together—the glazing with the shading. Are you going to incorporate sun shades? Automated blinds? Are you going to do things with a double wall? Are you going to tie in daylighting controls? We have to think more broadly, beyond just two lites of glass.”

Considering Occupants and HVAC Systems

Occupants often stand in the way of performance goals. “On day one, building performance might be perfect. But that can change quickly if people in the building do not understand how it should be used—that is, if they are not operating windows, shading, etc. at the right times,” says Selkowitz. Automated systems that control shading, lighting, HVAC, and more ensure the building performs as it should. However, facility managers as well as occupants should be educated on why the automated systems are working as they are, Selkowitz says.

When calculating system performance values, seek assistance of suppliers. “Many manufac-turers offer advanced thermal analysis to help demonstrate the performance of framing systems,” says YKK AP’s Intintoli.

When completing performance calculations, it is essential to make calculations based on the specific products chosen for the system. Not all systems, despite the similarities, perform alike. “You need to be careful that you are doing good modeling and the actual modeling is featuring the products you are using,” Selkowitz says.


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Originally published in Architectural Record
Originally published in June 2020