Determining the Solar Optical Properties of Windows with Shading Devices- New Measurement and Modeling Techniques

October 5, 2009 - 12:00pm

The global interest to reduce energy use in buildings has focussed new efforts to more aggressively reduce energy used by all major building components, such as window systems. Although good progress has been made in reducing heat loss, the contribution of windows to heat gain, peak cooling loads and cooling energy consumption is increasingly viewed globally as a problem. While glass coatings provide some control, shading devices on windows have the potential to do an even better job to reduce peak cooling load and annual energy consumption because there are more design parameters that can be used to control solar gain. Thus, the ability to accurate characterize performance of a wide range of window shading devices as part of a broader fenestration system is important to building scientists, manufacturers, building owners and policy makers. This talk provides an overview of recent research to develop new measurement techniques and new analysis models to characterize solar optical properties of windows with several different types of shading devices. It also addresses longwave radiative properties of shading devices via model development and experimentation. The energy performance of windows with shading devices was modeled using a two step procedure. A new multi-layer solar optical model was developed for glazing/shading systems that includes the effect of layers that scatter radiation in reflection and/or transmission. The effective solar optical properties of materials like fabrics, roller blinds and screens were obtained by developing a new laboratory measurement technique. The multi-layer solar optical model estimates the system solar transmission and absorbed solar components, which are then used in the second step, the overall heat transfer analysis. The final energy balance equations yield the temperature as well as the desired energy fluxes. The newly developed models were validated using the National Solar Test Facility (NSTF) solar simulator and solar calorimeter. The work provides building designers and engineers with more accurate models to optimize energy performance and provides manufacturers with new tools to create more energy efficient products. For more information about this seminar, please contact: Steve Selkowitz(510) 486-5064

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