This new tool helps architects design façades with comfort in mind
Our firm, The Miller Hull Partnership, has designed a highly successful net zero energy (NZE) office building; energy use is low, allowing for net-positive operation, and thermal comfort is very good. Large glazed openings and tall ceilings allow for ample daylighting, and building occupants report an overall high level of satisfaction with how the spaces feel and how connected they are with the outside.
This high level of satisfaction validates the “performance-driven” approach to the design of the building skin. In design, our team was constantly iterating the daylighting, ventilation, and energy models to achieve the right balance for window and opaque wall system performance. Once occupied, the building has operated so far beyond net zero that some have suggested we could have saved money with lesser-performing window and wall systems (e.g. going to double-insulated glass instead of triple-insulated, or less exterior insulation on the walls) while still achieving the energy goals. It seems that doing that, however, would have fundamentally changed the nature of the building. We suspected that this change would impact occupant comfort, but we didn’t really have the tools at our disposal to explain why.
When I first learned of Payette’s Glazing and Winter Comfort Tool, I realized that this might be the tool we needed. This easy-to-use software—which Payette has made available to other designers through a web interface—models thermal comfort as it relates to glazing design. It evaluates both radiant discomfort and the downdraft of air, both of which are caused by the cool surfaces of glazing elements.
How the tool benefits design
The main intent of the tool’s developers was to allow architects to design façades that didn’t require perimeter heating systems to address thermal losses at the window face. These perimeter systems are costly and difficult to detail in many design conditions, in addition to being inefficient means of providing thermal comfort. The tool can be used to study façade performance as it relates to occupant comfort by modifying a wide range of parameters about glazing configuration, glazing performance, and the impacts of other conditions such as exterior design temperature, indoor temperature and relative humidity, and more advanced comfort concepts.
Architects need to address comfort; simple as that.
With this tool, I eagerly modeled our NZE building and it showed what I expected: the high-performance window and wall systems helped it achieve comfort standards at low ambient temperature conditions for office building occupants (at the 10 percent dissatisfied level) within work station range of the façade, whereas modeling lesser performing systems showed it would fall out of the acceptable range. Since publication of the tool, we have studied several new projects in design and used it to analyze alternatives and then justify design decisions. The tool is simple enough to do several studies in only a few minutes.
The need to consider comfort
Architects need to address comfort; simple as that. Energy performance and heating and cooling loads control is important, but what we are really trying to provide for building occupants is a high level of thermal and visual comfort within other constraints of the project. To that end, fenestration and façade design is not just about energy performance; these façades are essentially a part of the comfort system. As we move beyond traditional HVAC systems and try to deliver truly integrated buildings, we need to work alongside engineers and contribute architecturally. The comfort tool allows us as designers to study what we have control over. We can use it to reassert our role and deliver façades that work better for users while also supporting cost-effective mechanical design and ultimately reducing energy use.
We are grateful to Payette for making this tool available to us: a quick, iterative option that allows comparisons and gives useful feedback. This tool allows us to back up our decisions with data, based on state-of-the art concepts in building science. Comfort science is evolving as designers and researchers continue to ask questions about how people can be made comfortable, but the science is improving and supplements other understandings we have developed through our own personal experience and the experience of others.
Tools like this also help members of our profession become better communicators. They allow us to better share why we make design decisions with other members of the design team, with our clients, and with contractors. In the case of the Glazing and Winter Comfort Tool, it helps us become conversant in metabolic rate, clo units, and mean radiant temperature. These are things that only HVAC engineers have talked about in the past but are essential for architects to understand to move toward truly high-performing buildings.
In the end, tools like these allow design professionals to bring value to our built work but also to better communicate the value of design to our clients and the public.
Jim Hanford, AIA, is a principal with the Miller Hull Partnership in Seattle, Washington.