Launch Slideshow

Double Skin Facade Modes

Double Skin Facade Modes

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    The façade diagram for the Tower at PNC Plaza in Pittsburgh shocases three modes. Shown here is the double-skin façade in passive mode or ideal mode on a net-zero day.

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    Here is the double-skin façade in active mode for mechanical cooling in the summer.

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    Finally, here is the double-skin façade in active mode for mechanical heating in the winter.

Quick, think of the starting point for the design of a high-performance building. Chances are, you pictured the building’s orientation or the façade of the building. As designers, we have been taught to work from the outside in to create a high-performing buildings. We review the site, orient the building to south, locate windows judiciously, apply overhangs to protect them, and insulate all remaining opaque surfaces. When following this process, the project team can create a smaller load profile to get close to a net-zero energy goal.

Unfortunately, this approach costs money. While a net-zero-energy goal sounds great and the standard approach appears logical, the return on investment typically does not pencil out. Energy savings alone rarely cover the additional costs of exterior skin elements, advanced HVAC systems, or renewable technologies that are needed even when you do everything as you should. And we also know that we can’t wait for the time when energy rates will make these advanced systems financially attractive or for energy codes to make them mandatory.

We need a new approach: We must learn to work from the inside out.

Staring from the inside means beginning with the building program and defining the user experience beyond a list of functional uses, footage, and space agencies. What will people be doing? What will they be wearing? How long will they be there? What environmental design criteria support these factors? Answering these questions changes the energy discussion to be about program needs, versus the application of technology needed to solve the energy equation.

At the Pearl Harbor Visitor Center at the World War II Valor in the Pacific National Monument in Hawaii, the project team, including Paladino, where I am the director of the building science practice, challenged the notion that a museum programmed to display rare artifacts from Dec. 7, 1941, had to be fully conditioned. Not only was there not enough budget to install high-performance HVAC systems, but also the 1.8 million annual visitor load meant that there was a constant flow of heat and humidity into the space, exacerbating the energy challenge of the project. Instead, the team modified the program by electing to condition only the artifact cases, and let visitors free flow freely through a passively ventilated museum. With steady trade winds at the site and visitors dressed in shorts and Hawaiian shirts, a naturally ventilated museum made sense. This programing decision cut the load of the museum building by roughly two-thirds and cut first costs nearly in half.

For the Evergreen State College Seminar II building in Olympia, Wash., our design team looked at two different design scenarios to meet the same space program, albeit by defining the use case differently. In the standard option, students and faculty were presented with a typical classroom space with a dropped ceiling, interior blinds, and fully conditioned space. In the low-energy case, they were presented with an increased floor-to-floor height, exposed ceilings with thermal massing, operable windows, and exterior sunshades, but no air conditioning. A detailed cost analysis showed that both options required equal capital expenditure. When asked to pick between the two options, students and faculty overwhelmingly selected the low-energy case, fully aware that they would need to learn to use the building differently.

For the Tower at PNC Plaza, a 33-story skyrise tower currently under construction in Pittsburgh, our project team enhanced the building program by defining four different space types, from low- to high-energy demand. Type I space is defined as protected outdoor space; Type II is interior tempered space, 65 F to 80 F with no humidity control; Type III is interior conditioned space, 68 F to 78 F at 30 to 60 percent relative humidity; and Type IV was reserved for the tightest temperature- and humidity-control band. By applying each of the four space types to program areas, the design team was able to show that the more Type I, II, and III spaces that were applied, the less systems and their accompanying energy use were needed to meet their environmental demand. The end result was a cost shift from HVAC systems to that of user amenities, such as interior porches within an occupiable double skin, operable windows, and user controls that create a healthier and more productive environment.

Ultimately, using the inside-out approach creates opportunities to use the building program as a design tool. With the user experience clearly defined, project teams will be free to challenge base conventions on how a high-performance green building should be designed and to discover innovative, low-energy solutions that benefit the environment, the occupants, and the owner.

Brad Pease, AIA, is the director of building science practice at Paladino in Seattle.