Volume 46, Issue 9 - October 2011


New Tools Influence Window Design
Design Resources Facilitate Efficient Choices
By Nils Petermann and Kerry Haglund

Façade design begins in the early concept phase, in which it may be difficult to conduct detailed engineering analyses of the impacts on heating, cooling and lighting systems. But even rough early assessments can help designers take steps toward balancing daylighting, thermal performance and comfort considerations. To facilitate such assessments, Lawrence Berkeley National Laboratory (LBNL) and the University of Minnesota have developed online resources that designers can use to identify promising façade designs and quantify the energy and comfort impacts quickly. These resources include the Façade Design Tool (FDT) and the Commercial Fenestration (COMFEN) energy simulation software.

The FDT is available free of charge on the recently updated Windows for High-Performance Commercial Buildings website, www.commercialwindows.org. This website, hosted by LBNL and the University of Minnesota, is a comprehensive resource for performance data on the energy-efficiency, interior environment and technical considerations that influence window design decisions. The FDT gives designers the means to compare design strategies for glazing, window area and shading quickly without the need for detailed input. Annual energy use, peak demand, daylight illuminance, glare and thermal comfort impacts are based on pre-simulated performance data specific to the climate and façade orientation. This pre-simulated data assumes a typical perimeter zone oriented in one of the cardinal directions. This allows for a rough assessment, based on which designers can quickly narrow down their options to the more promising ones and take note of likely impacts on energy use, lighting strategies and HVAC design. To supplement the quantitative assessments, the website also offers qualitative background information on relevant performance considerations, design guidance, codes and standards, as well as case studies.

Getting The Data
The FDT uses pre-simulated data for 17 cities that has been generated with the COMFEN schematic design and simulation tool, available for free download on http://windows.lbl.gov/software/comfen/comfen.html. COMFEN is more versatile than the FDT.
It provides in-depth data and thus supplements the quick insights that designers can gain by starting their analysis with the online tool. COMFEN enables the architect or designer to do “what-if” scenarios on specific façade, lighting and shading designs with the EnergyPlus simulation engine. Because COMFEN focuses on a specific zone within a building, it requires only limited input and allows its users to focus on the energy, daylighting and comfort impact of fenestration options without having to model entire buildings.

COMFEN also offers glazing contractors a tool for communicating the impact of glazing choices to their customers. It presents the simulation results in easily accessible graphics that help to visualize the benefits of glazing and shading choices.

Early Insight
The FDT and COMFEN provide early information on how different façade and daylighting choices may impact energy use and occupants. Even though these early insights do not substitute for in-depth modeling, they allow early assessments of façade performance and facilitate integrated design considerations during conceptual design and design development.

Nils Petermann is a program manager at the Alliance to Save Energy and a partner in the Efficient Windows Collaborative.

Kerry Haglund is a senior research fellow at the Center for Sustainable Building Research at the University of Minnesota.

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