Project Title:

Evaluating Facade Performance in Terms of Occupant Comfort

Creating new industry standards for window manufacturers, designers, and specifiers.

Status: Complete

Funding sources: CBE Industry Consortium, Research Grants

Project Objective

Develop tools and criteria for evaluating facade performance with respect to occupant comfort and energy efficiency, and propose an analytical method for evaluating this impact. Create a method that may form the basis for a future National Fenestration Rating Council (NFRC) window comfort rating method, useful to both designers, manufacturers, and consumers.

Significance to Industry

High performance glazing products now available that allow architects to design facades with large areas of relatively transparent glass. As glazing areas expand, providing comfort within the glazed facade often becomes more problematic, as perimeter zones in buildings are subject to numerous thermal influences resulting in greater fluctuation of temperatures. Although available energy software tools may be adequate for predicting the effect of glazing on building energy performance, current tools are not useful for predicting comfort implications of facade designs. Consequently, design teams may not fully understand the full implications of facade design decisions.

Research Approach

This project concentrates on the development of a method for building designers to make best use of the Advanced Thermal Comfort Model to assess thermal comfort in perimeter zones which experience thermal asymmetry due to the building envelope. Such a method would provide a standardized approach to quantify daily, monthly and/or yearly comfort in transient conditions under a variety of activity levels, clothing levels and environmental conditions. We have placed special emphasis on the way performance data is graphically represented to enable the user to understand the trade-offs they may be making in their design choice.

CBE researchers are developing a number of comfort metrics for possible inclusion into the future comfort standard. These metrics include a number of annual and point-in-time indices. Options include average comfort indices, number of hours inside and/or outside the comfort zone, and percentage of room floor area inside and/or outside the comfort zone.

As part of the development of this method, we upgraded the Advanced Thermal Comfort Model with enhancements that will improve its capability to model perimeter zone performance. The latest version of the Lawrence Berkeley National Laboratory (LBNL) Window software is capable of analyzing the thermal and optical properties of a wide variety of high performance glass types (including spectrally selective glass) and shading devices (including interior, exterior or between-glass venetian blinds). We will connect the modeling capabilities of Window with the CBE comfort model to accurately model facade interior surface temperatures and solar gain to enable the analysis of their impact on thermal comfort.

Publications and Reports

Huizenga, C., H. Zhang, P. Mattelaer, T. Yu, E. Arens and P. Lyons, 2006. Window Performance for Human Thermal Comfort. Final Report to the NFRC, Center for the Built Environment, University of California, Berkeley, CA, 91 pp. February.


Huizenga, C.,et. al., 2005. Window Performance for Human Thermal Comfort. Final Presentation to the NFRC, Center for the Built Environment, University of California, Berkeley, November.

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Wurster Hall facade

Comfort in perimeter zones is affected by many factors including air and surface temperatures, glazing types, and solar radiation.

Wurster Hall thermal model

The Advanced Comfort Model‘s sophisticated room modeler allows users to define facades and indoor environments in detail.

Themal model output for comfort

Output from the model can determine the comfort implications for a given facade design.