The traditional forms of building insulation and their role in energy savings are well recognized in cold climates, while energy performance optimization of the building envelope in hot climates is often misunderstood. Solar reflectance of roof surface, traditional insulation and thermal mass are widespread methods for reducing heat transfer inside buildings. Nevertheless, there are also alternative strategies for improving thermal performance of building envelope, such as the opportunity to have a ventilation layer in pitched roofs. This constructive technology provides thermal benefits thank to an air-flow which move along an air layer usually present at the intrados of the waterproof roof surface. This feature is commonly referred as: Above Sheathing Ventilation (ASV) and it is as an eaves-ridge open cavity present under the waterproof layer, thank to the laying of the tiles over a batten and/or counter-batten support system. Air enters both at eaves section and through the air-permeability of the overlapping tiles, and flows to the ridge, sinking the heat transfer generated by the solar radiation. Several studies have demonstrated the performance of a pitched roof, but it is not well yet investigated the impact of air-permeability of the external waterproof surface over the chimney effect occurring inside the ASV duct, because several factors contribute to the complexity of the problem, such as the increasing mass flow rate and the Buoyancy-driven forces. This document presents the methodology and the results of a preliminary study about the summer behaviour of a light-structure pitched-roof building in which varies the air-permeability between the elements of the waterproof covering layer (tiles), compared to a concrete flat roof building. The analysis has been approached by means of a numerical model, solving the fluid-dynamic and the heat transfer problems in unsteady state. Time series for wind, solar radiation and indoor space cooling were introduced to simulate realistic boundary conditions, taking into account different air-permeability of the waterproof surface and ASV thickness of the pitched roof.
Design of pitched roofs with discontinuous waterproof layer in middle-eastern geoclimatic conditions, evaluation of the performance, functionality and architectural image and comparison with other types of roof
ZANNONI, Giovanni;BOTTARELLI, Michele
2013
Abstract
The traditional forms of building insulation and their role in energy savings are well recognized in cold climates, while energy performance optimization of the building envelope in hot climates is often misunderstood. Solar reflectance of roof surface, traditional insulation and thermal mass are widespread methods for reducing heat transfer inside buildings. Nevertheless, there are also alternative strategies for improving thermal performance of building envelope, such as the opportunity to have a ventilation layer in pitched roofs. This constructive technology provides thermal benefits thank to an air-flow which move along an air layer usually present at the intrados of the waterproof roof surface. This feature is commonly referred as: Above Sheathing Ventilation (ASV) and it is as an eaves-ridge open cavity present under the waterproof layer, thank to the laying of the tiles over a batten and/or counter-batten support system. Air enters both at eaves section and through the air-permeability of the overlapping tiles, and flows to the ridge, sinking the heat transfer generated by the solar radiation. Several studies have demonstrated the performance of a pitched roof, but it is not well yet investigated the impact of air-permeability of the external waterproof surface over the chimney effect occurring inside the ASV duct, because several factors contribute to the complexity of the problem, such as the increasing mass flow rate and the Buoyancy-driven forces. This document presents the methodology and the results of a preliminary study about the summer behaviour of a light-structure pitched-roof building in which varies the air-permeability between the elements of the waterproof covering layer (tiles), compared to a concrete flat roof building. The analysis has been approached by means of a numerical model, solving the fluid-dynamic and the heat transfer problems in unsteady state. Time series for wind, solar radiation and indoor space cooling were introduced to simulate realistic boundary conditions, taking into account different air-permeability of the waterproof surface and ASV thickness of the pitched roof.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
