COMFEN4 was used for all the simulations and analyses for this web site.

A general list of tools offered by the U.S. Department of Energy are available at:
Building Energy Software Tools Directory


COMFEN is a tool designed to support the systematic evaluation of alternative fenestration systems for project-specific commercial building applications. COMFEN provides a simplified user interface that focuses attention on key variables in fenestration design. Under the hood is Energy Plus, a sophisticated analysis engine that dynamically simulates the effects of these key fenestration variables on energy consumption, peak energy demand, and thermal and visual comfort. The results from the Energy Plus simulations are presented in graphical and tabular format within the simplified user interface for comparative fenestration design cases to help users move toward optimal fenestration design choices for their project.


The DOE-2 program for building energy use analysis provides the building construction and research communities with an up-to-date, unbiased, well documented public-domain computer program for building energy analysis. DOE-2 is a portable FORTRAN program that can be used on a large variety of computers, including PC's. Using DOE-2, designers can quickly determine the choice of building parameters which improve energy efficiency while maintaining thermal comfort. A user can provide a simple or increasingly detailed description of a building design or alternative design options and obtain an accurate estimate of the proposed building's energy consumption, interior environmental conditions and energy operation cost. DOE-2 has been used by national labs, universities, and industry for hundreds of studies of products and strategies for energy efficiency and electric demand limiting. Examples include advanced insulating materials, evaporative cooling, low-E windows, switchable glazing, daylighting, desiccant cooling, cogeneration, gas-engine-driven cooling, cool storage, effect of increased ventilation, sizing of thermal energy storage systems, gas heat pumps, thermal bridges, thermal mass, variable exterior solar and IR absorptance, and window performance labeling.

Energy Plus

EnergyPlus is a new-generation building energy simulation program based on DOE-2 and BLAST, with numerous added capabilities. The initial version of the program, EnergyPlus 1.0, was released in April 2001. EnergyPlus includes a number of innovative simulation features - such as sub-hour time steps, built-in template and external modular systems that are integrated with a heat balance-based zone simulation - and input and output data structures tailored to facilitate third party module and interface development. Other capabilities include multi-zone airflow, moisture adsorption/desorption in building materials, radiant heating and cooling, and photovoltaic simulation.


Optics allows the user to view and modify glazing data in many new and powerful ways. Optical and radiative properties of glazing materials are primary inputs for determination of energy performance in buildings. Properties of composite systems such as flexible films applied to rigid glazing and laminated glazing can be predicted from measurements on isolated components in air or other gas. Properties of a series of structures can be generated from those of a base structure. For example, the measured properties of a coated or uncoated substrate can be extended to a range of available substrate thickness without the need to measure each thickness. Similarly, a coating type could be transferred by calculation to any other substrate.

This tool is accepted by NFRC for rating window systems. In some cases, this tool can be applied by NFRC-certified simulators, test labs and inspection agencies to determine ratings for non-standard products.


Radiance is a suite of programs for the analysis and visualization of lighting in design. Input files specify the scene geometry, materials, luminaires,time, date and sky conditions (for daylight calculations). Calculated values include spectral radiance (ie. luminance + color), irradiance (illuminance + color) and glare indices. Simulation results may be displayed as color images, numerical values and contour plots. The primary advantage of Radiance over simpler lighting calculation and rendering tools is that there are no limitations on the geometry or the materials that may be simulated. Radiance is used by architects and engineers to predict illumination, visual quality and appearance of innovative design spaces, and by researchers to evaluate new lighting and daylighting technologies.


THERM is a state-of-the-art, Microsoft Windows™-based computer program developed at Lawrence Berkeley National Laboratory (LBNL) for use by building component manufacturers, engineers, educators, students, architects, and others interested in heat transfer. Using THERM, you can model two-dimensional heat-transfer effects in building components such as windows, walls, foundations, roofs, and doors; appliances; and other products where thermal bridges are of concern. THERM's heat-transfer analysis allows you to evaluate a product's energy efficiency and local temperature patterns, which may relate directly to problems with condensation, moisture damage, and structural integrity.

This tool is accepted by NFRC for rating window systems. In some cases, this tool can be applied by NFRC-certified simulators, test labs and inspection agencies to determine ratings for non-standard products.


WINDOW is a publicly available computer program for calculating total window thermal performance indices (i.e. U-values, solar heat gain coefficients, shading coefficients, and visible transmittances). WINDOW provides a versatile heat transfer analysis method consistent with the updated rating procedure developed by the National Fenestration Rating Council (NFRC) that is consistent with the ISO 15099 standard. The program can be used to design and develop new products, to assist educators in teaching heat transfer through windows, and to help public officials in developing building energy codes.

This tool is accepted by NFRC for rating window systems. In some cases, this tool can be applied by NFRC-certified simulators, test labs and inspection agencies to determine ratings for non-standard products.


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