Thermal resistance of the ventilated air-spaces behind external claddings; theoretical definition and a parametric study

M Rahiminejad,D Khovalyg

doi:10.1088/1742-6596/2069/1/012197

M Rahiminejad, D Khovalyg

Open Access

https://doi.org/10.1088/1742-6596/2069/1/012197

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Abstract

The presence of a ventilated air cavity between the external cladding and the wall core of a wall assembly can have a varying contribution to the thermal performance of the building envelope. In particular, the thermal resistance of a ventilated air-space is a dynamic parameter that is influenced by various thermo-physical parameters. In this study, a theoretical definition of the thermal resistance of a ventilated air-space behind an external cladding is introduced, employing a non-linear network of thermal resistances in the air-space. A numerical code is developed for the steady-state condition and verified with data from hot box tests available in the literature. Thereafter, a parametric analysis is performed based on the air change rate in the cavity (0 to 1000 1/h), type of the external cladding (brick and vinyl siding), seasonal variation (summer and winter conditions), and presence of the reflective insulation. The results are compared with a closed cavity to see the efficiency of the ventilation in the air-space. The results confirm that the theoretical thermal resistance of the ventilated air-space is a function of multiple factors, and its magnitude varies under different conditions.

Highlights

Based on the analytical solution using the energy balance in the ventilated wall assembly at a steadystate condition, a MATLAB® code is developed to calculate temperatures and heat flow across the wall
The external cladding type has no significant effect on the theoretical thermal resistance of the cavity
The presence of reflective insulation on the cavity wall adjacent to the wall core affects the radiation between cavity walls and increases the thermal resistance of the air gap

Summary

Introduction

Based on the analytical solution using the energy balance in the ventilated wall assembly at a steadystate condition, a MATLAB® code is developed to calculate temperatures and heat flow across the wall. The presence of a ventilated air cavity between the external cladding and the wall core of a wall assembly can have a varying contribution to the thermal performance of the building envelope. The results are compared with a closed cavity to see the efficiency of the ventilation in the air-space.

Objectives

Results

Conclusion