Title

Suggested Methodologies for Determining the SHGC of Complex Fenestration Systems for NFRC Ratings

Report Number

FSEC-PF-422-02

URL

http://publications.energyresearch.ucf.edu/wp-content/uploads/2018/06/FSEC-PF-422-02.pdf

Keywords

Windows; Buildings

Abstract

Simple fenestration systems, for the purpose of this paper, are those whose solar heat gain and visible transmittance performances can be accurately simulated using the Window 4 or 5 programs developed at Lawrence Berkeley National Laboratory (LBNL). Complex fenestrations are everything else, including obscure or "privacy" glazing, corrugated or otherwise complex patterned glazing, curved, bent, or domed glazing, fritted glazing, glass blocks, glass fiber reinforced plastic daylighting panels, and glazings with internal or attached shading systems of a variety of types. The latter include exterior awnings and overhangs, attached exterior shade screens and shutters (including roll-up shutters), between-the-panes shades, including miniblinds, and interior shades which are vertical planar, horizontal blinds and vertical blinds. Also included are flux-directing and light-piped daylighting systems such as tubular skylights. As more building codes and governmental building requirements specify compliance with NFRC rules for rating, certification, and labeling of fenestration products for energy efficiency, and as these rules are extended to complex fenestration systems (CFS), the NFRC as well as manufacturers of these products are facing serious difficulties in getting such systems rated in the NFRC system. It is the complex nature of the optical performances of these systems which poses most of the problems. The purpose of this paper is to describe the optical qualities of complex fenestration systems which prevent them from being simulated accurately using the methods of Window 4 or Window 5 (ISO standard 15099). It is also to survey a variety of measurement and calculational techniques which might be able to determine the solar heat gain coefficients (SHGCs) and visible transmittances (VTs) of these systems more simply than the most general of methodologies. To do this, a general calculational methodology thought to be applicable to any complex fenestration system will be described first. In many cases, this may be the only method available for cost-effectively approximating the solar heat gain and visible transmittance properties of such systems. A further purpose is to offer suggestions in some of the cases for simplifying the optical problems involved, sufficiently to permit relatively easy and practical methods for determining the needed values, through computation alone, or a combination of computation and minimal measurement. Providing a detailed technical description of each different approach is beyond the scope of the present effort. Instead a general survey of some possible approaches is offered.

Date Published

2-27-2002

Subjects

Buildings - Windows

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