Passive Design Strategies for the Improvement of Summer Indoor Comfort Conditions in Lightweight Steel-Framed Buildings

The market for lightweight construction systems is growing rapidly due to their potential in terms of prefabrication, ease of transportation and assembly. However, given their thermophysical properties, these types of structures present a limited thermal capacity that may reduce their performance in terms of comfort and energy consumption during the hot seasons. The present paper, through a series of computational fluid dynamics (CFD) simulations, offers a numerical assessment of the performance of an existing lightweight steel-framed building selected as a case study. The data required to perform the simulations are collected with a deep monitoring campaign and the building is analysed in its current state (actual conditions of use) and after the application of simulated passive cooling strategies. The role of natural ventilation, both day and night, is explored by investigating different opening/closing configurations of external windows and internal doors. Moreover, the positive effects of surface thermal mass and shading systems are numerically validated. The results, although limited to a specific context of analysis, show that, with appropriate adaptation strategies, even in lightweight buildings, occupants can achieve adequate levels of comfort, thus reducing the need for cooling. A combined and weighted use of passive solutions results in a reduction of about 3 °C in the average daily indoor temperature. Ventilation at night and solar shading during the day make a steelframed building as comfortable as a massive one, both with regard to the internal surface temperature of the building components and to the discomfort indices. Changing the mass of the interior cladding of a wall, ceiling or floor, for example, from plasterboard to cement board, is another effective cooling strategy.