The M Files

Let’s use the sun to naturally heat the building in the cold winter months, and then find ways to shield it during the hot summer. What sounds like a common sense approach to commercial green building design is actually outside the industry norm. Passive solar elements, which absorb and redistribute the sun’s energy without the use of mechanical or electrical devices, can be difficult to find in our modern building environment. So when Chip Cargas, President of Cargas Systems, Inc. wanted to incorporate passive solar Trombe walls* in his company’s new facility, he had no idea that he was on the leading edge of the green building movement.

Thanks to a decades-long run of cheap electricity, natural gas, and oil we’ve been able to arbitrarily orient new buildings onto project sites, regardless of the energy consequences. It’s been an easy plug-and-play with our taken-for-granted energy infrastructure, letting modern heating and air conditioning systems overcome demands induced by the natural environment. Using naturally occurring solar, wind, and water patterns to influence commercial building design was once a necessity, but is now mostly a lost art. But this sort of thinking is migrating back toward the mainstream.

The Trombe walls at Cargas Systems's new facility. Photo courtesy of MM Architects, Inc.

Designed by MM Architects and installed by Wohlsen Construction, @WohlsenWorks and @LEED_Resource on Twitter, the Trombe walls consist of strategically positioned 18-inch thick slabs of concrete. They absorb solar radiation during the winter months, when the sun traces at low angles across the horizon. That heat is then radiated back into the occupied space throughout the day. At night, blinds are closed to retain heat within the building. Shading devices and the positioning of the walls prevent solar penetration into the building during the summer, when the sun shines at higher angles.

It all sounds simple enough, but designers were concerned that too much winter radiation might actually cause the building to overheat, leading to occupant discomfort and unwanted use of the air conditioning systems. The saying goes, ?ó?é¼?ôThe more passive the building, the more active the occupants.  In other words, regulating heat gain from passive solar elements requires people to actively engage in the operation of the building; in this case learning when and how to adjust the window shades. Could they count on that level of personal interaction in a commercial building?

When it comes to passive solar elements, the commercial building industry can probably learn some lessons from thoughtful residential builders. Michael Anschel (@MichaelAnschel on Twitter), Principal of Minnesota based Otogawa-Anschel Design Build, says that not paying attention to the potential for solar-induced temperature swings actually destroyed homes in the 1970s. Today his firm uses several modeling tools to optimize their passive solar designs. When asked if residential passive solar design is more art or science, he quickly responded “Science: 100% analysis.”

Peter Larson, Principal of Ashley McGraw Architects in Syracuse, NY, and @PeterLarson3 on Twitter is a bit of a pioneer in commercial building Trombe wall design. He agrees with the need for significant analysis. In his words, “We have found the design of Trombe walls to be an intricate thing, as they must be carefully matched to the spaces they serve, and to the sizing of the heating and cooling systems. These intricacies include thickness of mass and thermal lag, color, degree of shading, etc. I would not advocate using them without doing detailed modeling first, at least in a commercial or institutional building. We model them in DesignBuilder (Energy+), which seems to do a particularly good job assessing passive solar strategies.”

In Chip Carga’s case, the analysis seems to have paid off. Watch as he describes his first winter of managing the Trombe walls:

The design of the window-wall system has the added benefit of introducing glare-free daylight deep into the work space. After visiting their completed offices, I can attest that the walls do create an appealing work space. According to architect Donald Main, “We view the walls as a functional element with aesthetic opportunity. The walls are interesting due to their size and monolithic nature. The back sides of the walls are envisioned as a programming opportunity, a location to showcase Cargas’s company history.”

This unique design element will probably be a showcase for plenty of curious green building professionals for years to come. What do you think? Do systems like these belong in the commercial building industry?