A method for determining the effective longwave radiative properties of pleated draperies

Abstract

Draperies, attached to fenestration, offer a cost-effective strategy in controlling solar gain since draperies have the potential to reduce building peak load and annual energy consumption. The performance of a drapery is dependent on its solar optical and longwave radiative properties. The current study considers the determination of spatially averaged (effective) longwave radiative properties of draperies. As a first step, the longwave properties of fabrics were obtained by taking measurements with an infrared reflectometer using two backing surfaces. The measurement results enabled simple equations to be developed relating emittance and longwave transmittance to openness, emittance, and longwave transmittance of the fabric structure. In turn, the effective longwave properties of a pleated drapery are modeled using a net radiation scheme with fabric longwave properties as input. The model approximates a drapery as a series of uniformly arranged rectangular pleats. The effective longwave properties of the pleated drapery are calculated by considering an enclosure that is representative of the entire series of pleats. The longwave properties of the drapery are functions of only pleat geometry and openness of the fabric. The model compares favorably with expected trends and limits. The effect of pleating (folding ratio) is also examined.