Establishment and Validation of Solar Irradiance and Daylight Illuminance Prediction Approaches and The Implications to Energy-Efficient Building Designs

Description

In Hong Kong, electricity consumption is mainly for air conditioning and electrical lighting in an effort to create a thermally and visually comfortable built-environment. Solar radiation and outdoor illuminance are essential climatic parameters for active solar energy system assessments, cooling load determinations and daylighting designs. One of active solar energy applications is photovoltaic (PV) system which holds great promise for electricity generation. In subtropical Hong Kong, the principal objectives of fenestration designs include eliminating direct beam radiation and reducing cooling energy. The solar heat that radiates through glass windows is by far the largest component of overall thermal transfer value (OTTV) calculations. Daylighting is an effective and sustainable development strategy for enhancing visual comforts and energy-efficiency building developments. There are great demands for obtaining solar radiation and daylight illuminance on a vertical surface for building energy and daylighting designs. The first step towards such proposes is to acquire information on the availabilities of solar radiation and daylight illuminance. In Hong Kong, only hourly horizontal global solar radiation data have been systematically recording by the Hong Kong Observatory for a long period. Hong Kong features many urban and suburban building projects that are squeezed into limited land areas. In this environment, it is common for the quantity of daylight and solar heat falling on the facades and penetrating into building interiors to be substantially restricted by shading effects caused by the proximity of surrounding buildings. However, the solar radiation received by building-integrated solar panels and solar heat through window glazing are often estimated under unobstructed skies and the required solar radiation and daylight illuminance data cannot be accurately obtained using such prediction approaches. Daylight is simply the visible portion of solar radiation. Computer simulations that allow for solar radiation and daylight illuminance on obstructed vertical facades to be calculated under a variety of overcast and non-overcast conditions may be quite time demanding for a full-scale analysis. The proposed project will aim to provide an overview of daylight prediction models and extend research into the modification of these models to assess solar heat gain in heavily obstructed buildings. Solar factors/OTTV, cooling energy requirements and duration of direct sunlight, shadowing for heavily obstructed buildings and visual aspects including uniformity and glare index under overcast and non-overcast skies will subsequently be computed. The findings would be useful to architects and building engineers engaged in building facade studies, building energy calculations and daylighting investigations.