Innovative Technologies for Sustainable Building Envelopes
CASE STUDY: LE MOYNE COLLEGE, SYRACUSE, NEW YORK
A transpired solar-collector system was specified for this science center to reduce the cost of heating and meet strict ventilation air standards required for laboratories.
The Project: When Le Moyne College in Syracuse, New York, was ready to begin the largest on-campus construction project in its 65-year history, the campus community was enthusiastic to push the boundaries of sustainability. The project consisted of a 48,000-square-foot addition to the Coyne Science Center.
Sustainable design was at the top of students’ priorities for campus development and, as an important tenet of Jesuit thinking regarding social and environmental justice, also held an important place for the faculty and administration.
In the upstate New York climate, heating is more of a concern than cooling and is a major expense. Design firm Ashley McGraw in Syracuse chose to incorporate a transpired solar collector on the south side of the addition with dual objectives:
- Substantially reduce the cost of heating fresh air.
- Meet stringent ventilation air requirements for laboratories.
The overall aesthetics of the wall was also a primary consideration given the prominence of the building on campus. Ashley McGraw worked closely with the manufacturer to specify a wall panel that had never been previously used for a transpired solar-collector wall system.
The Challenge: Ashley McGraw challenged the conventional wisdom regarding design for modern labs. “People tend to disregard opportunities for solar energy to heat the large volume of outside air that is required in college lab buildings,” says Matthew Broderick, principal of Ashley McGraw’s College and University Studio. “We wanted to prove that architecture-based strategies do make a difference.”
The Design: As Ashley McGraw designed the addition, it became clear that the project would bring both a fresh architectural vocabulary and new focus on sustainability. It would also occupy a central space in the entrance to campus, which the firm recognized as an excellent canvas for demonstrating sustainable design.
The team discovered that by keeping the perimeter (the north and west sides) orthogonal with the existing courtyard but angling the southern plane off the grid to face true south as closely as possible, the building could make best use of two key design strategies: active solar air heating and natural daylighting.
Furthermore, when the design team learned that the transpired solar-collector system would be more economical to install than a traditional masonry wall, it was a no-brainer. A multipurpose metal wall panel with a concealed fastening system was selected for its aesthetic appeal, giving the building a contemporary look and feel appropriate for a modern science lab.
The Results: Upon completion, the Coyne Science Center was awarded LEED Gold certification based on expected energy performance improvement compared to ASHRAE 90.1-2007 base model.
Additionally, the building has received two design awards, one for Outstanding Design in the post-secondary category of the 2012 American School and University Architectural Portfolio, and the other from the Central New York Chapter of the American Institute of Architects. The building earned accolades for both its sustainable measures and its design.
CASE STUDY: WAREHOUSE, ALLENTOWN, PENNSYLVANIA
The transpired solar-collector system has resulted in an average annual energy savings of $6,400.
The Project: The design objectives for this 60,000-square-foot warehouse in Allentown, Pennsylvania, included heating energy savings, comfortable air ventilation year-round, and positive air pressure. Being a light manufacturing plant, the set point temperature in the building is 55 degrees.
The Design: To meet these design objectives, dark bonze solar-collector panels with a solar absorptivity of 0.91 were installed 16 degrees toward southwest. The collector panel area is 221⁄2 feet high by 160 feet wide, totaling 3,600 square feet. Perforated ducts provide air distribution by destratifying overheated air at the ceiling.
Perforated fabric ducts provide distribution of heated air at the ceiling.
Two inlet fans (9,000 cfm capacity each) are programed to bring air from the transpired wall into the building only when needed. On a sunny winter day, the fans run consistently during the day. However, when clouds pass overhead, inlet fans run intermittently.
The Results: Since installing the system in 2006, the plant’s primary heat source is used minimally, resulting in approximately $150 total annual heating costs. This translates to average annual energy savings of $6,400 or 30 percent (annual energy savings $1.78 per square foot of collector wall). The total projected energy savings over a 30-year project life is roughly $305,000.
In addition, installation of the system has resulted in greenhouse gas reductions of 37,600 pounds per year. The total cost of the system was $112,500, with a $78,750 net cost after a 30 percent federal tax credit.
It is likely the use of transpired solar collectors will eventually be a common building system feature. According to the NREL report, “The future will likely see increased use of transpired collectors in the federal and private sectors. The biggest hurdle the technology must overcome is user acceptance. Many solar technologies have been stigmatized by the rapid expansion of solar markets in the 1970s, when many poorly designed and poorly performing systems were deployed. Many potential users are reluctant to commit to a solar technology if a proven conventional option is available. Transpired collector technology has been proven to be valid and reliable for reducing energy use and saving money, and the body of scientific data proving its effectiveness continues to grow.”
The report continues: “Transpired collectors are among the most efficient solar collectors available, converting 65–75 percent of the available solar energy. “
Cutting-Edge Cool Roof and Wall Technologies for Cooling Climates
Benefits and features of cool metal roofing include:
- Energy efficiency
- Sustainability
- Low life-cycle costs
- Durability
- Fire and wind resistance
- Light weight
Science Behind Cool Roofs: Solar Reflectance, Absorption, and Emittance
When sunlight strikes a surface, in terms of energy, there are three outcomes as follows.
The science behind cool roofs must begin with a discussion on solar reflectance, absorption, and thermal emittance.
Solar reflectance: Some solar energy will immediately reflect off of the surface. This is expressed as a decimal, 0.65, meaning that 65 percent of solar radiation is immediately reflected.
Absorption: The energy that is not reflected will be absorbed by the material, causing it to heat up. Some heat can be removed by airflow over the surface, as with the use of above-sheathing ventilation (discussed later in the article). Some heat will be conducted through the roof surface into the building.
Thermal emittance: This is expressed as a decimal, such as 0.90. Thermal emittance refers to the percent of absorbed energy that is emitted as thermal infrared (IR) energy into the night air. Materials with high thermal emittance cool down faster than those with low thermal emittance.
Solar Reflectance Index
It is the combination of solar reflectance and thermal emittance that determines the surface temperature of a roof and its ability to be a “cool roof.”
The solar reflectance index (SRI) is calculated using values for solar reflectance and emissivity. The SRI allows us to compare the ability of a material to reject solar heat. Here are the calculations:
- Standard black with a reflectance of 0.05 and emittance of 0.90 = 0 SRI
- Standard white with a reflectance of 0.80 and emittance of 0.90 = 100 SRI
The SRI can be calculated by interpolating between the values for white and black. Materials with the highest SRI values are the coolest choices for a metal roof.
Painted Metal Roofs/Unpainted Metal Roofs
Roofs that are highly reflective and highly emissive, such as pre-painted metal with appropriate colors, offer a system that significantly reduces heat gain into the building.
When evaluating the cooling potential for painted metal, reflectance depends on two factors: color and pigmentation.
- Color: Light colors reflect more heat than dark colors; dark colors absorb more heat than light colors.
- Pigmentation: This refers to the chemistry of the paint itself. Today’s pigments are designed to be highly reflective, and that applies to dark colors as well as light colors.
In warmer climates where cooling requirements dominate, a high reflectance and emittance is desirable, which can be met with a pre-painted metal roof using lighter colors and/or reflective pigmentation. For every 1 percent increment in roof reflectance, the surface temperature decreases 1 degree Fahrenheit. For every 10 percent increase in roof reflectance, heating and cooling costs drop 2 cents per square foot per year.
In cooler climates where heating dominates, it may still be desirable to reduce peak energy demands during the summer months with cool roofing technology. Heating penalties may be offset through above sheathing ventilation, to be discussed later in the article.
