Thermal performance of double-shell systems in hot-humid and hot-dry climates

Abstract

The double-shell system is a passive cooling concept that addresses the problem of excessive solar radiation heat gain in the hot-humid and the hot-arid regions of the world. The outer secondary shell provides shading for both the glazed and the opaque parts of the roof and the walls. The mathematical model in this dissertation establishes an efficiency factor for rating the performance of the double-shell system as compared with other means of reducing solar radiation impact on buildings. The output of the mathematical model is given in a form of condensed tables that incorporate all the variables that affect the efficiency of the system. Full scale modules of the double-shell systems have been constructed and tested. The test results correlate well with the mathematical model, and the efficiency factors in many cases approached 1.0. This indicates that the solar radiation part of the external heat load can totally be eliminated by the outer secondary shell, which results in a substantial saving on air conditioning load. The tests have been conducted in College Station, Texas, which is characterized by a hot-humid climate. The results, however, are applicable to both the hot-humid and the hot-arid climates all over the world, since the tests are related to the secondary shells only. The findings of this research should be of interest to a wide range of users. With this in mind, most of the theoretical development of the mathematical model has been placed in the Appendices. Designers interested in a quick estimate of the performance of various double-shell systems will find the summary tables particularly convenient.