Beem: a simplifield procedure to calculate daylighting and other impacts of fenestration

A simplified procedure is described, to model daylighting, cooling, and heating impacts of vertical glazing in commercial buildings. Both annual and peak impacts are calculated, as well as cooling-equipment -sizing impacts. Simple economic analyses (present worth and simple payback) are included. The name BEEM is used, for Building Energy Estimation Module. The public domain procedure is implemented in spread-sheet software, available at nominal charge for materials and handling. The spread-sheet format was chosen to allow easy graphing, analysis, printing, saving, and customization of results. A help telephone number is provided for free assistance. The work was sponsored by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), the Empire State Electric Energy Research Corporation (ESEERCO), and ten other sponsors over a period of eight years. The paper presents a summary of derivation methodologies and sample applications, e.g., optimizing glass and shading with daylighting, economics of lighting controls for daylighting. Earlier papers on basic derivation and validation are referenced and briefly described. The fenestration treated may include glazing, overhangs and fins, fixed shading devices, automatic retraction of shading devices for all or part of the time that direct sun is not on the facade, and automated-angle louvers. Other inputs include: city, exposure, illumination required, installed lighting density, occupancy information, unit fuel costs, unit first costs (fenestration, lighting controls, cooling), and years of energy cost to treat as present worth (present worth factor). Outputs include workplace daylighting levels, fractional lighting savings, annual and peak energy impacts (lighting, cooling, and heating), cooling sizing impact, present worth of energy cost impacts, first costs (fenestration, cooling, lighting control), and total economic impact. Thus, intermediate results are readily available and further development of the calculation is practical. The analysis is applicable to new or retrofit construction. Derivation was based on a 'first principles' approach, starting with ASHRAE, Illuminating Engineering Society of North America (IESNA), and standard physical formulae.