Submitted for Publication to Energy and Buildings on January 30, 2007 Empirical validations of solar gain models for a glazing unit with exterior and interior blind assemblies Peter G. Loutzenhiser 1 , Heinrich Manz 1 , Stephan Carl 1 , Hans Simmler 1 , Gregory M. Maxwell 2 1 Swiss Federal Laboratories for Materials Testing and Research (EMPA), Laboratory for Building Technologies, CH-8600 Duebendorf, Switzerland 2 Iowa State University, Department of Mechanical Engineering, Ames, Iowa 50011 USA ABSTRACT Experiments performed at the Swiss Federal Laboratories for Materials Testing and Research (EMPA) test cell located in Duebendorf, Switzerland were used for empirical validations of building energy simulation programs. Four solar gain experiments were run with either an exterior Venetian blind or an interior mini-blind mounted over a glazing unit with the blind slats in the horizontal position and with the outer slat edge toward the ground tilted downward 45°. Models of the test cell setup were constructed in two distinctive building energy simulation programs, EnergyPlus and HELIOS, and the measured cooling power in the test cell was compared with the simulated cooling powers. For these experiments, the mean percentage of the absolute mean differences for EnergyPlus and HELIOS were all within 6.1% and 7.1%, respectively. 1. Introduction Modern commercial buildings are being designed to link occupants to their environments and provide daylight on the work planes by using highly glazed façades. Shading devices enable control to office dwellers to manage the extent of their interactions with the outside world. Blinds are very popular shading devices that are used in office spaces around the world and play an integral role in reducing solar gains in the summer and transmitting solar energy to the space in the winter through windows to offset of heating requirements. They also provide flexibility to the occupants for eliminating beam radiation into the space and prevent glare while still allowing diffuse natural light to enter. When exterior blinds are installed over the windows, the energy absorbed by the blind, for the most part, remains outside of the office space, which is highly advantageous in order to reduce overheating of the building. Quantifying the impact of both interior and exterior blinds has been the focus of prior research. A great deal of experimental work has been undertaken to examine various permutations of blind assemblies and windows in order to better understand and model the solar optical behavior and different heat transfer mechanisms (longwave radiation, air flow patterns and convective heat transfer) [1-8]. Using some of these experiments, validated models have been constructed for simulating the impact of blinds outside of the laboratory for practical analysis of actual window/blind assemblies for construction buildings [9-17]. Implementing models like these into building energy simulation programs increases the potency of the software—making them powerful tools for designing modern buildings optimized for energy efficiency and user comfort. Building energy simulation programs can be employed to evaluate different window/shading combinations prior to constructing a building and provide valuable information for assessing annual energy performance and sizing heating, ventilation, and air-conditioning equipment. There are different levels of