RESFEN can help consumers and builders pick the most energy-efficient and cost-effective window for a given 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.


THERM is a state-of-the-art 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.


The Optics computer program is designed for work with optical data for glass and glazing layers. Integration with the International Glazing Database (IGDB) makes it easy to build stacks of multiple glass layers and calculate the resulting optical properties. The program works transmittance and reflectance as a function of wavelength. This allows for calculation of integrated values, such as visible transmittance, according to a range of standards.


BETTER is software toolkit that enables building operators to quickly, easily identify the most cost-saving energy efficiency measures in buildings and portfolios using readily available building and energy data. With minimal data entry, BETTER benchmarks a building’s or portfolio’s energy use against peers; quantifies energy, cost, and greenhouse gas (GHG) reduction potential; and recommends energy efficiency measures (technological and operational) for individual buildings or portfolios, targeting specific energy savings levels. The toolkit consists of a web application, application programming interface (API), and analytical engine source code.

Building Controls Virtual Test Bed (BCVTB)

A software environment that allows users to couple different simulation programs for co-simulation, and to couple simulation programs with actual hardware. For example, the BCVTB allows to simulate a building in EnergyPlus and the HVAC and control system in Modelica, while exchanging data between the software as they simulate.

Berkeley Lab WINDOW

Calculates performance of window and shading systems. It can be used to design and develop new products, teach about heat transfer through windows, and help develop building energy codes. It calculates total window thermal performance indices (i.e. U-values, solar heat gain coefficients, shading coefficients, and visible transmittances) for glazing and framing, as well as thermal and solar optical effects of a wide range of interior, between glass, and exterior shading systems.