Energy modeling valuable architectural tool

Energy modeling valuable architectural tool

Photo by U.S. Department of Energy

Have you ever wondered how buildings are designed for energy-efficiency, when there are so many requirements, technologies and systems to consider? Building energy modeling (BEM) is a tool that helps architects solve many of the complex problems they face during the design process.

Energy-efficient buildings share many architectural characteristics: long east-west axes that maximize daylight; reduced glazing, especially to the east, west and south; and southern exterior shading. These features help reduce load on a building’s heating, cooling and lighting systems by increasing natural light and optimizing solar heat gain. While these design principles can result somewhat “paint by numbers” designs, individual buildings vary significantly, according to the U.S. Department of Energy.

BEM is used to inform project-specific decisions by quantifying energy-efficiency trade-offs between systems and between energy-related operating and up-front construction costs. In building vernacular, BEM is said to support “integrated design.”

Contrary to common perception, energy-efficient buildings are not significantly more expensive to build than their conventional counterparts. Some are slightly (e.g., 1-2 percent) more expensive, while others have no cost premium at all and can even be cheaper to build. BEM and integrated design help identify and realize these savings.


Most building projects face physical constraints. The lot may not accommodate a long east-west axis. Nearby buildings may block light. Local regulations may limit height or restrict the choice of façade elements. The project may retrofit an existing building, whose basic form and construction are fixed. The client may place requirements that counter energy-efficiency such as a large window-to-wall ratio.

BEM helps maximize efficiency opportunities in areas where design flexibility exists. In some cases — notably in the case of a large window-to-wall ratio — BEM is required to demonstrate that the building meets energy code despite possessing some inefficient energy characteristics.

More significantly, energy-efficiency is rarely the only project goal. Even projects that prioritize it and the resulting operating cost savings balance those benefits against up-front construction costs. BEM helps designers minimize construction costs and make construction/operating cost trade-offs, at both the component and whole-building level.


BEM is useful throughout the design process, but it is especially important at the beginning and the end. High-level architectural aspects including orientation, height, floor plans and major façade elements that have significant impact on energy-efficiency are usually settled upon early in the design process, sometimes as early as the project “bidding” stage. Using BEM early helps architects maximize energy-efficiency, or at least avoid designs that undermine it later on.


Electric lighting accounts for more than 20 percent of commercial building energy use. Lighting design — which includes daylight harvesting, electric lighting and the use of static and dynamic shading — is an important component of energy-efficient building design. Another important aspect is façade design — commercial buildings have custom, complex façades that often include metal components that act as thermal bridges, inadvertently channeling heat into and out of the building — making it more difficult to heat and cool the interior, reducing occupant comfort and increase operating costs.

In addition to BEM tools, the Department of Energy (DOE) develops tools that model lighting and façades in greater detail. Radiance is a state-of-the-art open-source lighting engine that is widely used in lighting design. THERM is a state-of-the-art engine — soon to be re-released under an open-source license — façade modeling engine. They support design, product ratings and codes and standards. Because they are computationally intensive and have specialized use cases, their capabilities interoperate with BEM tools rather than being embedded in them.


BEM has many uses, but building design contributes most directly to energy efficiency. Various estimates place BEM as being used for design in 20 percent of commercial new construction projects, with lower use in commercial interior, retrofit and residential projects. Increasing these numbers is a major goal for the DOE.

DOE is working toward increasing awareness of BEM and its benefits among architects and their clients by documenting the return on investment (ROI) associated with BEM — BEM is typically a small part of overall project budget and can disproportionately improve both construction and operating costs. DOE also supports the AIA 2030 Commitment, which promotes the use of BEM in design. 

Although BEM is already cost-effective, DOE is working to further reduce the associated effort and cost by promoting integration of advanced BEM, lighting and façade analysis capabilities with the design tools that architects already use. 

Topics: Architectural Firms, Associations / Organizations, Building Owners and Managers, Construction Firms, Engineering Firms, Great Commercial Buildings, Sustainable Communities, Urban Planning and Design

Companies: U.S. Department of Energy

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