Ratios of Siding Depth to Cavity Depth in Mixed Convection of Air Cavity behind Vinyl Siding for Building Envelopes

AbstractProviding an air cavity behind vinyl siding within a building envelope is an approach to mitigating building moisture-related issues, which also improves the building’s thermal performance. Previous studies commonly assume the cavity air as still and thus neglect the influence of mixed convection on the performance of the building envelope. Additionally, the air cavity is usually considered uniformly rectangular, neglecting the effects of its geometric irregularity and complexity. Therefore, to comprehensively investigate the effects of air cavities, this study analyzes ratios of siding depth to cavity depth in the mixed convection of air cavities, through rigorously formulating the problem and solving it using the perturbation method. The results show that increasing the ratio of the vinyl siding depth to the air cavity depth amplifies the metrics directly related to the energy performance of the building envelope, including the cavity air’s velocity, temperature, and mass fraction; the skin friction at cavity walls; as well as heat and mass transfer across the cavity. The effects of other critical parameters are also investigated, including the Reynolds number and temperature of the irregular cavity wall. This study provides guidance for comprehensively evaluating the thermal performance of an air cavity behind vinyl siding and improving the design of vinyl siding.