Improved Simulation Tools Help Users Optimize Energy Efficiency

Tools to evaluate facade design, such as

Kumar spoke at a National Fenestration Rating Council (NFRC) presentation, Key Tools for Commercial Window Energy Performance, on December 6, at Ecobuild America in the Washington Convention Center, Washington, D.C.

“Nonresidential buildings consume 15.5 quadrillion  BTU of primary energy or 16 percent of all energy used in the U.S.,” said Nils Petermann, project manager of Efficient Windows Collaborative in Washington, D.C. “Fenestration consumes 32 percent of that primary energy. On average, only 30 percent of all nonresidential buildings use high-performance windows.”

Ray McGowan, senior program manager at NFRC, discussed the different NFRC tools to determine fenestration energy properties. There are three kinds of tools, he said, fundamental, intermediate and advanced. Fundamental tools, such as

“The Therm and Window tools, used for residential products, have seen 95 percent manufacturer participation,” McGowan said, however, “CMAST, used for commercial products, has had almost no certification and only 85 users in two years.”

Kumar elaborated on COMFEN, developed by the Lawrence Berkeley National Laboratory (LBNL) in Berkeley, Calif. “Fundamental performance indices of fenestration products, for example, U-value, solar heat gain coefficient (SHGC), visible transmittance (VT), condensation resistance (CR), air-leakage etc., are good for comparing products, but they do not provide information about the extent of impact on the building’s annual energy, peak loads, daylighting, or thermal and visual comforts. Building designers need these information in order to select the most energy-efficient and cost-effective fenestration solution for their application.”

COMFEN has come a long way since its initial versions, Kumar said. “This tool is being continuously improved by LBNL,” he said. “Some of the impressive features of COMFEN are the daylighting and comfort evaluations built-in COMFEN. It does daylight illuminance calculation to show the illuminance level in the façade boundary areas for a specific date and time. It takes into the account the effect of any overhand, fins, shading, or attachments on daylighting, besides energy. Daylighting calculation used Radiance as an engine, a ray tracing tool, developed by LBNL. It prepares the daylight illuminance map rendition.”

Thermal and visual comfort indices also are calculated for various design options, Kumar said. The COMFEN library has expanded with predefined façade component library -- such as glazing, frame, wall, shading systems, spandrel -- which allows users to accurately build the façade.

“I see increasing use of tools like COMFEN by design community to select appropriate fenestration system for their application and optimize their façade design,” Kumar said.