Si indaga il comportamento termico estivo di un edificio a falde a confronto con uno a tetto piano, mediante un modello ad elementi finiti. A parità di condizioni rispetto alla copertura piana quella a falde ventilata necessita di una potenza inferiore del 60% con conseguente risparmio energetico 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, such as the opportunity to have a ventilation layer in pitched roofs. This feature is commonly referred as: Above Sheathing Ventilation (ASV), 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. This study surveys the thermal behaviour during the summer season of a building in which varies the air-permeability between tiles, compared to a concrete flat roof building. 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, because several factors contribute to the complexity of the problem, such as the increasing mass flow rate and the Buoyancy-driven forces. 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.
Prestazioni termiche estive: confronto fra tetti a falda e coperture piane
ZANNONI, Giovanni;BOTTARELLI, Michele;BORTOLONI, Marco
2014
Abstract
Si indaga il comportamento termico estivo di un edificio a falde a confronto con uno a tetto piano, mediante un modello ad elementi finiti. A parità di condizioni rispetto alla copertura piana quella a falde ventilata necessita di una potenza inferiore del 60% con conseguente risparmio energetico 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, such as the opportunity to have a ventilation layer in pitched roofs. This feature is commonly referred as: Above Sheathing Ventilation (ASV), 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. This study surveys the thermal behaviour during the summer season of a building in which varies the air-permeability between tiles, compared to a concrete flat roof building. 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, because several factors contribute to the complexity of the problem, such as the increasing mass flow rate and the Buoyancy-driven forces. 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.
