Influence of solar radiation on the energy consumption of large buildings on a university campus

Abstract

This paper reports the numerical study on the influence of solar radiation on the energy consumption of large buildings on a university campus. The actual campus is located in the south of Portugal, in a Mediterranean type environment, and consists of 6 educational buildings. These six buildings have a total area of 27,599 m2 and 595 compartments, where 6,529 opaque surfaces (doors, walls, etc.) and 983 transparent ones (windows) were identified. This study aims to assess numerically how solar radiation transmitted on windows affects the energy consumption of the Heating, Ventilation, and Air-Conditioning (HVAC) systems, controlled by the PMV (Predicted Mean Vote) index, of each of these buildings, and the thermal comfort level of the occupants. Software developed by the authors is used to simulate the thermal behavior of buildings with complex topology. This software evaluates indoor air quality inside the spaces, thermal comfort of the occupants, thermal energy consumption of the HVAC system, and solar radiation distribution outside the buildings and inside the compartments, among others. The HVAC control system based on the PMV index applied in this work was designed to maintain the PMV comfort index within category C of ISO 7730, with a maximum of 15% of people dissatisfied. In order to evaluate the indoor comfort level of the occupants, the totals of cold and warm uncomfortable hours were calculated. Two different weather conditions, typical of the region, were set as inputs for the simulation performed in this study: a typical winter day, and a typical summer day. The outputs obtained were the daily evolution of total solar radiation transmitted on windows, total uncomfortable hours for the occupants, and total HVAC system energy consumption for each building. The results obtained show that, for typical winter conditions, an increase in the transmitted solar radiation on windows causes a decrease in HVAC system energy consumption, and also in the number of uncomfortable hours, which is a favorable situation. On the other hand, for typical summer conditions, it is observed that when transmitted solar radiation on windows increases, HVAC system energy consumption, and the total number of uncomfortable hours increase as well, configuring an unfavorable situation. It is also found that the values of solar radiation transmitted on windows are higher in winter than in summer conditions. In summer, the lowest values of solar radiation transmitted on windows occur at noon. The last two observations lead to the conclusion that, overall, these buildings have correctly positioned passive shading elements, a technique that contributes to an adequate solar passive architectural design.