Renewable Ener#y Vol. 3, No. 6/7, pp, 683-690, 1993 0960- 1481/93 $6.00+.00 Printed in Great Britain. i~ 1993 Pergamon Press Lid THERMAL PERFORMANCE OF AN ARCHITECTURAL WINDOW WITH CHEMICALLY DEPOSITED SnS-Cu~S SOLAR CONTROL COATING C. A. ESTRADA-GASCA,* G. ALVAREZ-GARC1A~" and P. K. NAIR* * Laboratorio de Energia Solar, Universidad Nacional Autonoma de Mexico, 62580 Temixco, Morelos, Mexico ; t CENIDET, DGIT-SEP, AP 4-224, 62431 Cuernavaca, Morelos, Mexico (Received 8 April 1992 ; accepted 9 July 1992) Abstract--A mathematical model enabling the prediction of the thermal performance of solar control glazings employing chemically deposited solar control coatings with or without a transparent protective polymer coating is presented. Differential energy balance for the glazing is set up assuming one-dimensional steady state case for normal incidence of air mass 2 solar radiation and by considering conductive heat transfer within the glazing and convective and radiative heat transfer into the interior and exterior of the building. Using the specific example of the optical properties of the already reported SnS Cu~S solar control coatings, the redistribution of the absorbed component of the solar radiation is evaluated for constant convective heat transfer coefficient and temperature in the interior and for exterior temperatures in the (~ 50~C range. The results yield shading coefficient versus exterior temperature curves for two specific SnS Cu,S coatings without and with a protective transparent varnish and offering transmittance in the visible region of 27 and 21%. 1. INTRODUCTION Solar control coatings refer to single or multiple layer thin film coatings of metals or semiconductors applied to the inner side of architectural windows, offering reduced space conditioning cost and improved com- fort level in buildings located in regions with a warm climate. The energy saving achieved in this manner can add up to an enormous amount and hence can lead to notable energy saving at national level. The prospects for wide spread use of appropriate solar control glazings along with energy-efficient wall and ceiling materials for achieving energy conservation in buildings are demonstrated by the fact that in an average American home, 50-70% of the energy con- sumption is lbr space conditioning, amounting to 25- 35 kMJ per capita [1]. However, since the technology of solar control coatings is of recent origin [2], many buildings are devoid ofglazings incorporating them. Commercially available solar control coatings are mostly based on magnetron sputtered coatings on 4~6 mm sheet glass and have found their way into a few of the recent buildings, particularly in high rise construction [3-5]. Adhesive plastic sheets carrying metallic coatings have been offered as a short term solution in improving the energy efficiency of existing buildings with clear sheet glass windows, but their optical and thermal per- formance leave much to be desired. Ideally, solar control glazings must possess an inte- grated transmittance, T,*~, in the visible region (0.4-- 0.7/tin) of ~ 10-30% to permit adequate day lighting inside the buildings, a low integrated transmittance in the infrared region (0.7 2.5 #m), T~* of < I0%, to reduce the heating up of the interior under solar radi- ation and an integrated infrared reflectance, R*, of 50% combined with a low thermal emittance, e,, of - 0.1 for the interior side of the glazing [6]. The low e requirement is to inhibit the re-radiation of the ther- mal energy dissipated in the glazing to the interior of the building as well as to reduce thermal losses through the glazing from the heated interior during winter. Most of the above characteristics are met by chem- ically deposited solar control coatings of Cu,S [7, 8], PbS [9], PbS-Cu~S [10] and SnS-Cu,S [11] thin films reported from our laboratory in recent years. These coatings are deposited on sheet glass from dilute chemical solutions containing the constituent ions of the semiconductor film. The choice of the thin film combination offers a wide range of solar control characteristics to suit the solar availability and the ambient conditions of different locations. Considering the fact that many urban buildings exist without solar control coatings, this new possibility of applying the coatings on existing glazings as well as on fresh sheet glass for new buildings with a capital input at the lcvel of micro industries appears to be very attractive. The 683