ESTIMATION OF THE PERFORMANCE OF SUNSHADES USING OUTDOOR MEASUREMENTS AND

Solar shading devices can significantly reduce cooling loads, improve thermal comfort and reduce potential glare problems in commercial buildings. However, measured data or tools to facilitate a comparison among various shading devices have previously not been available to designers. The Solar Shading Project at Lund University was initiated in 1997 to increase the knowledge on shading devices. This paper describes results from an extensive measurement program and recent developments of the software tool ParaSol v 2.0. The total solar energy transmittance (g-value) of various shading devices has been estimated by means of measurements in a real climate using a double hot-box arrangement. Monitored results are shown for external products (awnings, Italian awnings, venetian blinds, horizontal slatted baffle, fabric screens, solar control films), interpane (between panes) and internal products (pleated curtains, roller blinds, venetian blinds, solar control films). The software tool ParaSol has been further developed to include all these types of products. In general, external shading devices are the best in reducing cooling loads, internal products are the worst, while interpane products fall between these two. Further, internal products must have a high reflectance in order to yield a low g-value. The monitored average g-value within each group (g-sunshade) was 0.3 for external products, 0.5 for interpane products and 0.6 for internal products. On average, external products are twice as good as internal products in reducing peak cooling loads. With the software tool ParaSol, it is possible to estimate the effective g-value of shading devices for various orientations in combination with an arbitrary glazing system. Further, effects on heating and cooling (both peak loads and annual energy demands) and operative temperatures of an office room can also be simulated

Description of ParaSol v3.0 and comparison with measurements

Parasol is a computer program for calculating the solar and thermal properties of windows with sunshades and the energy demands of a room with a window/shading system. The program has three main features. One of them is a calculation of g, T and U for normal incidence of beam irradiation, which is performed as soon as a window or an internal/interpane sunshade is selected. The other two are based on yearly simulations, using DEROB-LTH, a building energy simulation program on which ParaSol is based. One of the applications gives the monthly average of g and T for the window glazing and the glazing/sunshade system. The other application gives the heating and cooling demands for a room with a window, with and without a sunshade, where input data are given for the internal heat, ventilation settings, shading control and temperature set-points. Version 3.0 of Parasol, which has some new and improved models, is described in this paper. The g-values obtained with this program version are compared with measurements on windows with internal/interpane screens/venetian blinds. The absolute deviation is less than 0.03 for the venetian blinds. The measured values of dark internal screens with closed air gaps exceed those simulated by Parasol, but are lower than the ones simulated with open air gaps. (C) 2006 Elsevier B.V. All rights reserved