Modelling natural ventilation for summer thermal comfort in Mediterranean dwellings

Abstract

There is an urgent need for adequate natural ventilation in apartment dwellers in densely built regions that could improve occupants' summer thermal comfort and reduce the rapidly increasing energy demand for cooling. The aim of the research reported here was to identify natural ventilation strategies that could offer energy efficient refurbishment solutions for domestic buildings whilst maintaining thermal comfort of occupants. An urban multi-storey apartment building in the city of Athens was selected for this study, which is representative of over four-million Greek domestic buildings. Four retrofit strategies were tested with the aim of offering indoor air temperature reductions and increased ventilation rates relative to the existing single-sided ventilation strategy of the building, using computational fluid dynamics (CFD) simulations. The ventilation performance of all strategies varied with wind speed and direction due to the proposed design configurations. During buoyancy driven flows, acceptable ventilation rates for comfort could be achieved with the implementation of a wind-catcher and a dynamic façade. Under wind-driven ventilation, these strategies delivered significant increases in ventilation rate (up to 7 times) and contributed to reductions in indoor air temperatures of up to 2 o C, relative to the existing ventilation strategy. Cooling by water evaporation enhanced the cooling performance of the wind-catcher providing up to 4 o C temperature reductions. The successful performance of the proposed strategies highlights the potential significance of reducing energy consumption and improving thermal comfort.

Low-energy cooling and ventilation refurbishments for buildings in a Mediterranean climate

“…Figure 21 provides a comparison of their expected performance. Empirical relationships were extrapolated and interpolated from a range of steady-state CFD results; these were in agreement with expected trends and could thus be used to predict ventilation performance behaviours under conditions that were not simulated (Spentzou et al, 2019). Higher wind speeds enhance the cooling performance of the cross-ventilation, wind-catcher, and dynamic façade strategies.…”

“…Steady-state simulations investigated the typical dry-bulb temperature (26°C), under low-average-highest wind speeds (buoyancy, 3.6 and 7 m/ s) and three wind directions, in response to a climate study performed. Further CFD modelling details are described in Spentzou et al (2019), including internal/external domains, mesh sensitivity studies, turbulence model, convergence criteria used and validation of the code. Further, the performance of low-energy retrofits in the case study using dynamic thermal modelling (DTM) was investigated, in order to predict the temporal changes in indoor air quality within specific zones over cooling period in a typical year (i.e.…”

“…Extensive CFD of the outdoor environment (i.e. air flow at neighbourhood scale) under all prevailing wind directions and speeds enabled derivation of pressure input parameters for the openings of the indoor building environment CFD models, which determined indoor ventilation characteristics, in (Spentzou, Cook, & Emmitt, 2019). DTM was used to evaluate thermal comfort and passive cooling performance over annual cycles at one-hour intervals, presented in (Spentzou, Cook, & Emmitt, 2018).…”

Natural ventilation strategies for indoor thermal comfort in Mediterranean apartments

“…Based on the work by Spentzou et al (2017), exploratory thermal modelling simulations performed identified the most suitable wind-catcher design and operation of its openings. Windcatcher tower height increments of 0.5m and up to 2m above and below were investigated; the taller towers delivered higher ventilation rates, although to a small degree.…”

“…Cross-partitions on 'X' arrangement (5m length) facilitate simultaneous inflow and upwards escape of stale air. A four-sided wind-catcher design with a top horizontal covering surface (see Figure 3), was favoured because it could utilise all available wind directions and mitigate against any negative impact of the surrounding buildings on the ventilation performance of the wind-catcher (Spentzou et al, 2017).…”