Abstract
Attic design has a significant impact on buildings’ energy performance thus making investigation of its thermal performance characteristics imperative. Raised-ceiling is among the common complex attic configuration found in pitched-roof buildings. In this study, natural convection inside a raised-ceiling rooftop heated isothermally from the base wall (ceiling) is numerically investigated at a certain pitch angle range while keeping the enclosure base-length unchanged. The results show that the roof pitch and the kinks on the ceiling have a strong influence on the heat and fluid flow patterns. At low roof pitch, high heat transfer rate between the cold and hot walls leads to a multi-cellular flow structure. The number, size and strength of the counter-rotating cells change with the pitch angle. The kinks caused air velocity to double for every 15° increase in the roof pitch. The rate of convective heat transfer is enhanced with decreasing value of the aspect ratio.
Highlights
The study of thermal performance characteristics in enclosed surfaces is very important due to its wide application in engineering fields such as solar energy systems, cooling of electronic circuits, air conditioning, heat exchangers, roof designs, and many others
Critical observation of the air flow pattern shows that the aspect ratio, AR, which is proportional to the pitch angle, φ, has a strong influence on the flow behaviour
The practical significance of the results is that when the aim is to minimize heat loss from heated space below the ceiling into the attic, the roof pitch should be made high enough
Summary
The study of thermal performance characteristics in enclosed surfaces is very important due to its wide application in engineering fields such as solar energy systems, cooling of electronic circuits, air conditioning, heat exchangers, roof designs, and many others. A review of past studies shows that the flow fields and heat transfer mechanism in the attic of rooftops has received considerable attention by several investigations. With the foundational works of Flack (1980) and Akinsete and Coleman (1982) on the experiment and simulation of rooftop models respectively, many more investigations on pitched roofs in form of triangular enclosures have been considered. Moftakhari et al (2017) used natural element method to study convective and radiative heat transfer analysis of fluid flow inside a triangular cavity. Flow field and natural convective heat transfer in a trapezoidal cavity having a flexible partition is studied by Mehryan et al (2020) using Arbitrary Lagrangian–Eulerian finite element method.
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