New Models for Analyzing the Thermal and Daylighting Performance of Fenestration

Accurate determination of the energy impact of fenestration in nonresidential buildings requires daylighting prediction as well as thermal modeling. Despite the computational power of hour-by-hour simulation programs, they involve trade-offs in accuracy, cost, and flexibility. This paper describes new daylighting and thermal modeling capabilities in DOE-2.1B and planned additions. DOE-2.1B now contains a preprocessor-based daylighting model that is sensitive to daylight availability, site conditions, room and glazing parameters, window management for glare and solar control, and lighting controls. To model more complex designs, the next version of the DOE-2.1 program will have a daylighting model based on stored or user-input coefficients of utilization. A lighting program, named SUPERLITE, provides detailed data on illuminance and luminance distribution throughout interior spaces. Because the solar gains through sophisticated daylighting designs are not now adequately calculated, a procedure based on a library of new heat-gain coefficients is being developed. Using sun and sky simulators, these coefficients will be determined from direct measurements of solar optical properties of architectural devices.

The major experimental procedures and analytical models, along with validation studies of DOE-2.1B and SUPERLITE and sample results ban these new modeling tools, are described.