Effective R-value approach to comprehend the essence of integrated opaque passive substrate properties

Abstract

<p>The concept of ‘effective’ <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/thermal-resistance" title="Learn more about thermal resistance from ScienceDirect's AI-generated Topic Pages">thermal resistance</a> could facilitate in-depth understanding of the impact of passive substrate properties such as surface radiative and thermo-physical (which are not directly measurable using instrumentations in terms of <em>R</em>-value). A simple to-use and concise single performance factor has been formulated in this study to comprehend the effective <a href="https://www.sciencedirect.com/topics/engineering/thermal-resistance" title="Learn more about thermal resistance from ScienceDirect's AI-generated Topic Pages">thermal resistance</a> provided by the enhanced surface radiative and thermo-physical properties of passive envelope materials. The derived expression is validated against measurements in real residential apartments located in Singapore. The derived effective <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/thermal-resistance" title="Learn more about thermal resistance from ScienceDirect's AI-generated Topic Pages">thermal resistance</a> expression is function of solar radiative properties, thermo-physical properties and weather parameters, and hence contains much more information than the traditionally estimated R-value. The effective <a href="https://www.sciencedirect.com/topics/engineering/thermal-resistance" title="Learn more about thermal resistance from ScienceDirect's AI-generated Topic Pages">thermal resistance</a> is found to be dynamic in behavior i.e., thermal resistance (or heat flow character) of the envelope material varies with transient weather conditions. Increasing roof surface radiative properties i.e., <a href="https://www.sciencedirect.com/topics/engineering/solar-reflectance" title="Learn more about solar reflectance from ScienceDirect's AI-generated Topic Pages">solar reflectance</a> (from 0.1 to 0.8) alone has advantages during both daytime and nighttime with daily integrated-heat gain reduction by 60–68%. Whereas increasing the other thermo-physical properties of the envelope i.e., <a href="https://www.sciencedirect.com/topics/engineering/adding-insulation" title="Learn more about adding insulation from ScienceDirect's AI-generated Topic Pages">adding insulation</a> or thermal mass (with a layer of phase change material-modified skim coat) has advantage only during daytime, but penalty during nighttime for the hot climates. The effect of increasing the <a href="https://www.sciencedirect.com/topics/engineering/solar-reflectance" title="Learn more about solar reflectance from ScienceDirect's AI-generated Topic Pages">solar reflectance</a> by 0.7 for an insulated gray <a href="https://www.sciencedirect.com/topics/materials-science/aluminum" title="Learn more about aluminum from ScienceDirect's AI-generated Topic Pages">aluminum</a> metal roof (with 20-mm polystyrene) is almost equivalent to effectively further adding 40-mm thick <a href="https://www.sciencedirect.com/topics/materials-science/polystyrene" title="Learn more about polystyrene from ScienceDirect's AI-generated Topic Pages">polystyrene</a>. The application of proposed approach has been demonstrated by investigating the effect of passive envelope properties for different roof assemblies under four different climates. Using this approach, the accuracy of estimation of heat flux through roof, an indicator of the roof <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/thermodynamic-efficiency" title="Learn more about thermal efficiency from ScienceDirect's AI-generated Topic Pages">thermal efficiency</a>, was found to have improved by up to 78%.</p>