Ceiling and attic ventilation to improve the indoor thermal environment of residential buildings in hot-humid climates

Buildings are known as major energy consumers. The buildings sector accounts for about 36% of the world’s final energy consumption. Furthermore, nearly 56% - 67% of the electricity consumed within residential buildings is attributed to air conditioning. Cooling energy demand of residential buildings is predicted to increase to 750% in 2050. Furthermore, building overheating remains a significant challenge in residential buildings in hot-humid climates. In the absence of passive measures, the dependence on active cooling will continue to grow, resulting in a continuous rise in cooling energy demand. On the other hand, a study by SEfor ALL (Sustainable Energy for All) across 77 countries found that at least 4.02 billion lower-middle-income people in 2023, including both rural and urban poor, faced a high or medium risk of lacking access to cooling for thermal comfort. Therefore, it is necessary to consider effective passive cooling techniques for residential buildings to reduce the risk of overheating. Natural ventilation, particularly cross-ventilation through window openings on the windward and leeward walls, can effectively dissipate indoor heat. However, in certain conditions, such as in terraced houses, cross-ventilation may not be optimal. Additionally, its effectiveness decreases when the outdoor air temperature exceeds the indoor temperature. To the best knowledge of the author, only a limited number of studies have investigated the combined effects of buoyancy and inertial (wind) forces on the indoor airflow and heat release through a ventilated attic in residential buildings in hot-humid climates, either experimentally or numerically. Incorporating ceiling and attic ventilation, in addition to window ventilation, as a buoyancy and wind combined ventilation method may be important for optimizing indoor airflow and heat release in single-story residential buildings by improving air movement through the upper part of the building. The goal of this dissertation is to assess the effectiveness of a perforated ceiling in combination with attic ventilation for partitioned and unpartitioned building to optimize indoor airflow and heat removal from residential buildings in a tropical climate during night-time. In general, this dissertation consists of four stages which are meant to understand the airflow in partitioned and unpartitioned buildings, perform a CFD validation study using data from wind-tunnel experiments, subsequently assess the airflow and heat release in detail using CFD, and finally assess the impact of natural ventilation on yearly overheating hours using a multizone modeling approach. The first stage is wind tunnel measurements in closed-circuit atmospheric boundary layer wind tunnel (ABLWT) facility to investigate the effect of internal partitions and varying incident flow directions (α = 0° and α = 30°) on the natural cross-ventilation flow in a realistic typical single-story residential building. The horizontal velocities in and around the building model were measured using a non-intrusive optical measurement technique laser Doppler anemometry (LDA) at a geometric scale 1:40. The result indicated that the presence of the internal partition has relatively minor impact on the airflow distribution in the unpartitioned region. Conversely, it significantly influences airflow within the partitioned region. The second stage is the computational fluid dynamics (CFD) validation study under isothermal conditions. 3D steady Reynolds-averaged Navier-Stokes (RANS), scale-adaptive simulations (SAS) and large eddy simulations LES of cross-ventilation flow in a realistic building geometry, partitioned and unpartitioned, were validated using the results from WT experiments. The findings indicate that both SAS and LES exhibit equally well agreement in terms of mean streamwise velocities. The next stage involves CFD simulations under non-isothermal conditions that systematically assess the effectiveness of perforated ceilings in combination with attic ventilation as a buoyancy and wind combined ventilation strategy to efficiently optimize the indoor airflow and heat release from buildings during night-time. The building geometry is a full-scale version of the reduced-scale building model used in wind tunnel experiments. CFD simulations were conducted using boundary conditions that closely represent real-life scenarios, with the air velocity and temperature based on the weather station and field measurement data of Makassar, Indonesia. Three building configurations with 40% porosity were evaluated: the reference case with cross-ventilation through windows (C1), cross-ventilation through windows combined with perforated ceiling and attic ventilation (C2), and single-sided ventilation combined with a perforated ceiling and attic ventilation (C3). Simulations were performed for five wind directions (α = -60°, α = -30°, α = 0°, α = 30° and α = 60°). In general, C2 outperformed both C1 and C3, particularly in maintaining the lower indoor air temperature within the occupied zone. Finally, the annual overheating hours of the building equipped with perforated ceiling ventilation (C2) pairing with other passive design strategies (e.g. daytime and nighttime ventilation, window glazing, lightweight external wall material and the coating of the building envelope), were investigated using building energy simulations (BES). Similar to the finding from Stage 3, the building with perforated ceiling and attic ventilation (C2), outperformed the reference case (C1), effectively reduce overheating hours by approximately 60%. This research contributes to the knowledge on cross ventilation flow, provides database for CFD validation study under isothermal conditions, proposes an affordable building construction as a design recommendation for residential buildings and offers valuable insights for science and practice to optimize the building ventilation design in hot-humid climate.