Software Tools

LBNL has developed software tools that assist in the development of AERC’s certification process.


RESFEN is a PC program for calculating the heating and cooling energy use of windows in residential buildings.This computer tool can help consumers and builders pick the most energy-efficient and cost-effective window for a given residential application, whether it is a new home, an addition, or a window replacement. It calculates heating and cooling energy use and associated costs as well as peak heating and cooling demand for specific window products. Users define a specific “scenario” by specifying house type (single-story or two-story), geographic location, orientation, electricity and gas cost, and building configuration details (such as wall, floor, and HVAC system type). Users also specify size, shading, and thermal properties of the window they wish to investigate. The thermal properties that RESFEN requires are: U-factor, Solar Heat Gain Coefficient, and air leakage rate. RESFEN calculates the energy and cost implications of the window compared to an insulated wall. The relative energy and cost impacts of two different windows can be compared.


COMFEN is a PC Program for calculating the heating and cooling energy use, and visual and thermal comfort, of commercial building facades. This computer tool is 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 fps dormant within the simplified user interface for comparative fenestration design cases to help users move toward optimal fenestration design choices for their project.


WINDOW is a tool for analyzing window thermal and optical performance. This software enables analysis of products made from any combination glazing layers, gas layers, frames, spacers, and dividers under any environmental conditions and at any tilt, and can model complex glazing systems such as venetian blinds and roller shades.


THERM is software for analyzing two-dimensional heat transfer through building products. LBNL developed THERM 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.