Thermal environment in different types of covering, lining and undercovering with recycled and low-cost materials in reduced-scale models

Abstract

The roof greatly influences the thermal environment of a facility, either by radiating heat to its interior or losing to the external environment. The use of alternative materials and techniques in these structures is a way to integrate affordable materials and, in some cases, to mitigate problems related to the thermal comfort of the occupants and the disposal of waste in the environment. The objective of the present study was to assess the behaviours of different roofs, ceilings, sub-roofs, and reflective paintings in reduced-scale distorted models in summer conditions. The work was divided into two stages. The first one tested the following materials: ceramic tiles, galvanized steel tiles, galvanized steel tiles with Tetra Pak® packaging sub-roof, galvanized steel tiles with Tetra Pak® packaging liner, galvanized steel with thatch grass lining, and galvanized steel tiles with thatch grass sub-roof. In the second stage, the roofs tested were ceramic tiles, aluminium tiles, galvanized steel tiles, corrugated fibre cement roofing tiles, galvanized steel tiles painted white, and corrugated fibre cement tiles painted white. The side faces were closed with aviary tarpaulins, in order to simulate the real conditions of a commercial aviary. Data were collected during the summer, from 9 a.m. to 5 p.m., at 15 minutes of intervals. The measurement instruments used were air temperature, relative humidity, and black globe temperature sensors coupled to a Hobo® U12-013 datalogger, with ± 0.35°C from 0 to 50°C, ± 2.5% relative humidity from 10% to 90% precision; and an Extech hot wire thermoanemometer, model Sdl350, with ± 0.01 ms-1 precision. The reuse of Tetra Pak® packaging as a lining or undercoating material resulted in a significant improvement in the thermal comfort indexes. Therefore, the use of alternative materials provided a significant reduction in the heat transfer from the tiles to the interior of the dwelling, showing that they are viable materials in economically vulnerable regions and under conditions of high solar radiation. Using the data collected in the second stage of this study, the black globe humidity index (BGHI), temperature and humidity index (THI), enthalpy (H), and effectiveness (ε) of each roofing material were calculated. The painting of fibre cement tiles white showed the lowest values of the thermal comfort indexes. The galvanized steel tiles painted white did not improve the indexes of the thermal environment. Thermal comfort is achieved by controlling heat fluxes localy or throughout the environment, therefore, we can conclude that the use of alternative materials with properties of thermal isolation like Tetra pak packaging or thatch grass for lining and undercovering improves the heat insulation, in addition, the use of reflective painting on fiber cement tiles can be an option for improving the thermal comfort of buildings.