Natural Ventilation Performance Research Articles

Optimizing air inlet designs for enhanced natural ventilation in indoor substations: A numerical modelling and CFD simulation study

This paper investigates the ventilation and heat dissipation performance of a 110 kV indoor substation under natural ventilation conditions using computational fluid dynamics (CFD). The objectives are to evaluate the influences of air inlet design parameters including location and size, and transformer load, on the airflow distribution, temperature field, and cooling efficiency. The study finds that staggered opposite inlets optimize cooling uniformity without airflow attenuation. Compared to a single inlet, the maximum transformer temperature is reduced by 1.3 °C and energy utilization increases by 9.1 % with staggered inlets. Increasing the inlet length ratio initially improves cooling until an optimal point (The length ratio is 1.10), while reducing the inlet height ratio decreases airflow and efficiency. With load increasing, the intake airflow rises but at a reduced rate, and the temperature difference can exceed 15 °C under high loads. In summary, optimizing inlet design enhances natural ventilation performance in indoor substations, but limitations exist at high loads, indicating supplemental mechanical ventilation may be required.

A theoretical and numerical analysis of solar chimney in multi-storey atrium building

Current research efforts on solar chimney are much on those configurations with single space or single vent, hampering its applications in complex buildings. To expand its implementation, the viability of solar chimney in multi-storey atrium buildings was explored numerically and theoretically. It was known that its natural ventilation performance can fulfil the WHO requirements (i.e., 6 air change per hour, ACH) even under low solar radiation of 200 W/m2 if it is appropriately designed, such as cavity gap (d), cavity height (Hc), solar radiation (Q), and window width (W). Its natural ventilation rate was found to be positively linear to the exponential form of the analyzed factors in this study, including cavity gap (d0.63∼0.69), cavity height (Hc0.59∼0.60), solar radiation (Q0.42∼0.43), and window width (W0.14∼0.20). The impacts of cavity gap and solar radiation are relatively weaker for big space such as atrium than those scenarios with single-space ventilation in the literature. The volume of the connected space was found to affect its natural ventilation performance, where the obtained ventilation rate of 4-storey is averagely 5.1 % lower than those of 3-storey buildings. A theoretical model was developed and experimentally validated, for the first time, to predict the natural ventilation rate of solar chimney when it is applied to the atrium with multiple air inlets. It was also noticed that the same theoretical model can be applied to the atrium buildings with odd and even storeys, but the area coefficients are different. The research outcomes of this study confirm the viability of solar chimney in complex buildings and offer a theoretical foundation for its implementation.

Balcony design to improve natural ventilation and energy performance in high-rise mixed-mode office buildings

Balconies have the potential to promote airflow and regulate solar heat gain, which can reduce energy usage for cooling in buildings. However, designing these elements can be challenging due to complex trade-offs for natural ventilation and energy performance, highlighting the need for advanced simulation tools to guide balcony design decisions. This study aims to evaluate the impacts of balcony design on natural ventilation and thermal and energy performance in high-rise mixed-mode office buildings in São Paulo, Brazil. To this end, an integrated method that involves computational fluid dynamics (CFD) and building performance simulations (BPS) is developed to identify optimal solutions. Through this method, the performance of 40 balcony designs is studied, comprising diverse alternatives for three balcony design parameters (width, depth, and location on the façade). Furthermore, the research is performed considering the balcony effects on two façade orientations (north and south), two wind incidences (windward and leeward), and three floor levels (upper, medium, and lower floors). Results are analysed through a sensitivity analysis, percentage of change and cross-analysis. The findings indicate that narrow and shallow balconies (2 m x 0.5 m) are the best design option for the south façade; they enhance natural ventilation and reduce energy consumption for cooling across all floor levels and balcony locations. Conversely, for the north, sun-facing façade, it is recommended to use wide and deep balconies (5 m x 2 m) to reduce solar gains and associated energy consumption for cooling, despite potential limitations in natural ventilation.

Study on the optimal layout of roof vents and rooftop photovoltaic of the industrial workshop

Roof vents are crucial for facilitating natural ventilation within industrial workshops. However, their substantial size and height can limit available roof space and create extensive shadow areas, thereby impeding the installation of photovoltaic (PV) systems on industrial roofs. This study quantitatively assesses the influence of roof vent positioning, morphology, and roof architecture on the natural ventilation efficiency of workshops with varying indoor heat sources. Subsequently, the study evaluates how different vent configurations affect the installable area for rooftop solar panels. Findings suggest that shifting from traditional roof ridge vents directly above a heat source to north-side vents inclined towards the roof can marginally decrease the ventilation flow rate by approximately 5%, translating to a minor temperature rise of around 0.46°C within the occupied zone. Nonetheless, the Predicted Mean Vote (PMV) thermal comfort indices remain consistent across scenarios. Notably, adopting north-side vents, either flush with the roof or inclined, can enhance the annual energy yield of the rooftop PV system by 15.49% and 22.67%, respectively, under equivalent solar irradiation. Thus, strategic adjustments to vent positioning, form, and roof design can substantially boost the photovoltaic system's power output without compromising the workshop's natural ventilation performance.

Erratum to: Research on the influence of outdoor trees on natural ventilation performance of an academic building

Erratum to: Research on the influence of outdoor trees on natural ventilation performance of an academic building

Experimental Study of Wind Pressures on Low-Rise H-Shaped Buildings

Recognizing the urgent need for mitigating global warming, natural ventilation presents a potential strategy to reduce cooling energy demands, enhance thermal comfort, and contribute to indoor air quality. H-shaped buildings are prevalent worldwide, and they constitute the majority of the social housing construction in Brazil. Research suggests that the inadequate design of these buildings can result in poor ventilation; however, investigations about their natural ventilation performance are limited. Thus, the present contribution aims to determine the impact of the geometric characteristics of H-shaped buildings on the pressure distribution through wind tunnel experiments. Three models were tested in the wind tunnel experiments, representing different proportions. Their scales were configured to comply with the 5% obstruction limit allowed for wind tunnel testing, which was performed for 20 wind attack angles. Moreover, a scour test was carried out to allow a better understanding of the wind flow. Python scripting was developed to automate data processing, which is openly available in this paper. The results indicate that the proportion of the model influences the pressure distribution on roofs and leeward walls. Additionally, the depth of the recessed cavity affects its side surfaces and can result in a mirrored behavior on the frontal face of deep cavities (i.e., the wind direction is 45°). The model height influences the windward surfaces in its lower portion, since taller models present a recirculation vortex that modifies the pressure near the ground.

Opening configurations and natural cross ventilation performance in a double-loaded multi-level apartment building: A CFD analysis

This study investigates the impact of varied opening configurations on natural cross ventilation of a double-loaded multi-level apartment. Using computational fluid dynamics (CFD) simulations, twenty-five building models with combinations of top-top (TT), top-bottom (TB), center-center (CC), bottom-bottom (BB), and bottom-top (BT) opening configurations were analyzed in both windward and leeward building blocks. In the windward block, the BB configuration yielded the highest dimensionless flow rate (DFR) for levels 1–3, and BT was highest for levels 5 and 6. Air Exchange Efficiency (AEE) was optimal at 45–55% for TB configurations on levels 1–3, and for CC and BT on levels 4–6. Factor optimization (α) was introduced to balance DFR and AEE, favoring TB configurations for level 1–3 and BT configurations for levels 4–6. Additionally, the leeward block's ventilation was slightly influenced (±3.5%) by the windward block's configurations. Notably, the TT configuration achieved the highest α score at level 1 and TB at level 2, even with the lowest DFR. Conversely, the CC configuration, while having the lowest AEE for the first two levels, yielded the highest DFR values. Bottom inlet configurations recorded the lowest α scores for levels 3–6. The research suggests that the TT and CC configurations are the most effective for ventilation in the leeward block. The results indicate that building design can be optimized for ventilation performance at each level without significant impact to adjacent structures. This informs improved ventilation strategies in high-rise buildings, emphasizing design adaptability to enhance indoor air quality.

Natural Ventilation and Indoor Air Quality in Domestic School Building: CFD Simulation and Improvement Strategies

Natural ventilation is a process of replenishing used air from the interior environment with fresh outer air without the use of mechanical equipment. This project aims to investigate the feasibility and performance of implementing natural ventilation in dilapidated classroom designs of actual geometry. Computer models of an existing classroom were created using SOLIDWORKS based on real-scale building floor plans, while the same software was applied to compute flow simulation studies to visualise the airflow pattern, temperature distribution, relative humidity, and the thermal comfort level of occupants in the classrooms. Estimated climate parameters were input in the simulation process to illustrate better the effect of hot and humid climate conditions in Malaysia towards the thermal comfort level of occupants. In this project, a visualised wind tunnel was created to simulate the prevailing wind source that supplies wind to the designed classroom, and the airflow pattern across the designed building was analysed. From the initial simulation results, it was discovered that the airflow into the classroom is uneven, whereby some locations in the building are experiencing extremely low wind breeze, which eventually affects the comfort level of occupants in the room. On the other hand, an internal analysis focusing on the interior comfortability of the classrooms was applied to examine the thermal comfort condition while using the naturally ventilated classrooms. Recommendation optimisation approaches such as the louvre angle and introduction of a windcatcher was presented in this project to improve the natural ventilation performance of the designed classroom.

Comparative study on the performance of a solar photocatalytic Trombe wall with different types of collectors: Copper/Thermoelectric/PV plate

Solar photocatalytic Trombe wall (SPTW) is a technology that can help to improve the indoor environmental quality and simultaneously enhance solar energy utilization, which receives lots of attention recently. Nevertheless, current research predominantly emphasizes the heat and mass transfer analysis of a single envelope system, with limited exploration of energy and performance comparison of multi-physics systems. For this, flow, heat and mass transfer analysis of SPTW with four different types of collectors: SPTW with copper plate, SPTW with photovoltaic plate (PV-SPTW), SPTW with thermoelectric plate (TE-SPTW) and SPTW with hybrid PV-TE plate (PV-TE-SPTW), are theoretically proposed to reveal the energy flow distributions among these systems. Based on the coupled analysis, parameter characteristics have been conducted to investigate the effects of solar radiation intensity, system channel width and system channel height together with ambient temperature on the heating Q, purification CADR and power generation Z performance of various SPTWs. Furthermore, a comparison of the energy and exergy performance among these four systems is clarified through the energy, exergy flow and equivalent energy saving. From the obtained results, it can be indicated that the reverse flow has a strong impact on the performance of natural ventilation and further varies the indexes of Q, CADR and Z when the solar radiation intensity is inferior to a threshold value from 100 to 300 W/m2. With the changing channel height and width, the maximum Q and CADR are both appears in TE-SPTW system, respectively reaching by 4.64 MJ/h and 136.56 m3/h as the structure of 0.05 m channel width and 3.0 m channel height, which show 39.7 % and 5.9 % respectively compared to the SPTW model. Conducting energy and exergy analyses on the four systems reveal their remarkable potential, sacrificing a minimal 0.032 MJ or less in purification performance in exchange for substantial energy savings of at least 0.314 MJ. This work will establish a foundational contribution to advancing energy-efficient building technologies.

Performance of Lower Ventilation Opening to Improve Air Change per Hour in Classroom at Tropical Humid Region (Case Study: Palembang City)

Fresh air circulation in a room had an impact on indoor air quality. In today’s pandemic, good fresh air circulation is one of the main strategies to prevent viruses from spreading through air molecules. A good ventilation opening design influences indoor air exchange. This research conducts a test on lower ventilation opening design that can maximize natural ventilation performance in a classroom. This test aimed at a recommendation for schools in the tropical humid region so they can hold offline learning with low virus spreads. Natural ventilation optimization should be a solution because not everyone can afford mechanical air filters or virus killers. This research used an experimental method. Computer simulation test variables were classroom openings consisting of existing openings, new outlets/openings, and lower ventilation opening. Parameters of observation are wind velocity, air circulation pattern, and air change per hour. This evaluation compares the experiment result to Air Change per Hour (ACH) threshold limit provision required in Indonesia. The result of the experiment shows outlet/opening addition provides a better impact on ACH escalation than with only existing classroom opening. And when the existing opening is closed, lower ventilation opening had good performance in achieving the ACH threshold limit provision requirements which were 9,8 ACH.

Study of Natural Ventilation Strategies in the São Cristóvão Church in Lisbon Using a Multizone Airflow Model

Visitors have a significant impact on the indoor climate of buildings housing works of art, and the relationship between the number of visitors, the indoor air quality and the protection of exposed works of art is an important factor in the overall study of the indoor climate of heritage buildings without mechanical ventilation and/or air-conditioning systems. In view of these concerns and the lack of studies on natural ventilation in heritage buildings, this study aims to analyse the performance of natural ventilation in the São Cristóvão Church in Lisbon, Portugal. For the preparation of this study, an analysis of the natural ventilation of this church was carried out by creating a model in the CONTAM software, and the indoor air quality was analysed based on different international standards and guidelines for carbon dioxide levels and air flow rates (ACH). Estimating the current ventilation strategy, an average ACH of 0.75 h−1 was estimated during the time the church is open, and an ACH of 0.15 h−1 was estimated during the time the doors were closed. In a yearly analysis, an average ACH of 0.30 h−1 was obtained. These air exchange values guarantee EN 16798-1 category I air quality for 72% of the year and category II air quality for 18% of the year. Different natural ventilation strategies were analysed: (a) three scenarios exploring different cross ventilation scenarios; (b) a scenario assuming that the church is closed all year round; and (c) a scenario estimating an increase in the number of visitors, giving an idea of the variations in human pollutants and possible consequences. Taking into account the air infiltration and the fact that masses, an occasional situation with a high number of visitors, are always held just before the church closes, it is guaranteed that carbon dioxide levels will never exceed the limit of 350 ppm above the outdoor values imposed by EN-13779, registering a maximum of 291 ppm.

Impacts of horizontal and vertical louvers on the natural cross-ventilation performance of a generic building

Wind-based natural cross-ventilation is defined as a process in which fresh air is injected into a building via a high-pressure windward window and exhausts into the atmosphere through a low-pressure leeward window. There are several parameters that affect the natural ventilation performance, which should be considered in detail to reach the maximum air quality inside the buildings. In the present study, the effects of horizontal and vertical louvers on the wind-driven natural cross-ventilation performance of a generic building are assessed using computational fluid dynamics. In this regard, horizontal and vertical louvers with installation louver angles of 15°, 30°, and 45° are compared with each other and corresponding non-louver cases. Computations are carried out for three different free-wind speeds of 1, 2, and 3 m/s to show the impact of the external conditions on the natural ventilation of louvered cases. The obtained results revealed that under a low free-wind speed of 1 m/s, the minimum age of air and maximum air exchange efficiency occur for vertical louvers with an installation angle of 15°, while at moderate and high free-wind speeds of 2 and 3 m/s, the horizontal louvers with an installation angle of 15° provide the best condition for a generic building. Highlights Effects of horizontal and vertical louvers on the wind-driven cross-ventilation were studied. At a free-wind speed of 1 m/s, the minimum age of air and maximum air exchange efficiency occur for vertical louver with α = 15°. At U H = 2 and 3 m/s, horizontal louver with α = 15° provides the best condition for a generic building.

Buoyancy-driven natural ventilation performance of a multi-story building with vertical shaft designed by using dimensionless design approach

Components with a tall vertical space attached to multi-story buildings are used to assist natural ventilation, which however unavoidably results in different buoyant forces on different stories. To achieve equal flow rates on all stories, a dimensionless design approach was developed in literature. This study aims to examine the reliability of the dimensionless approach for designing the buoyancy-driven ventilation of multi-story buildings. Moreover, it validates the application of the approach to scenarios where the heat source strengths on stories vary. The experimental and numerical results confirm the reliability of the dimensionless approach for designing naturally ventilated buildings with uniform airflow rates and air temperatures on each story. In the case of a story with flexible heat flux, changing the heat flux affects the ventilation rates on all the stories. In particular, when the heat flux on this story is zero, buoyant ventilation continues and may even be observed on the third story. Furthermore, an increase in the heat flux on the first or second story enhances stack ventilation, whereas increasing the heat flux on the third story has a damping effect on ventilation in the other stories. Additionally, stories with identical heat fluxes had similar ventilation rates and indoor temperatures.

Impact of planar area ratio and opening positions on natural cross ventilation performance in sheltered high-rise buildings: A simulation study

This paper studies the impact of planar area ratio (λP) and opening positions on natural cross ventilation performance of a sheltered three-level high-rise building through numerical simulations. Three building clusters of different λP and five different opening configurations each were assessed. To improve the accuracy of the numerical simulations, a novel calibration method utilizing 2k full-factorial design of experiment (DoE) approach was proposed to determine the closure coefficients of the Standard k−ε (SKE) turbulence model. Various parameters such as velocity profile (U/UH), pressure difference (ΔCp), turbulence kinetic energy (TKE), dimensionless flow rate (DFR), age of air (AOA) and air exchange efficiency (AEE) were examined. On level 1, distinct variations in DFR, AEE and AOA were observed for different λP values. Maximum DFR and AEE and maximum AOA are achieved when λP=0.25 for all opening configurations. Conversely, the impact of λP is minor for levels 2 and 3. Specific opening configurations, such as top-bottom and top-top on levels 1 and 2, and center-center and bottom-top on level 3, demonstrate favorable AEE of about 45–50%. The trade-off between AEE and DFR suggests that the bottom-bottom configuration performs best on level 1, while top-top and top-bottom configurations work best on level 2, and the center-center configuration is the best on level 3. The presence or absence of openings on levels 1 and 3 do not significantly affect the indoor airflow on level 2. The insights and recommendations derived from this study have practical implications for sustainable high-rise building design.

Effect of outdoor wind on the hybrid natural ventilation performance of monitor roofs

The monitor roof of a building has a raised structure running along the gable ridge, with its smaller roof parallel to the lower main roof. As a common building ventilation design, monitor roofs are expected to induce indoor airflow through thermal buoyancy and/or wind; however, studies on the design details and the induced natural ventilation performance are limited. In this study, how outdoor wind affects the efficiency of induced hybrid natural ventilation of monitor roofs was analyzed through computational fluid dynamics (CFD). Based on engineering practice and weather conditions, the Grashof number (Gr) was 2.11x1011-5.67x1011, and the Reynolds number (Re) was 2.5x105-1.7x106. The results indicated that for a larger monitor roof (width = 3 m, height = 1.2 m), the presence of outdoor wind combined with thermal buoyancy increased the ventilation rate to 1.5–3.5 times that found when only buoyancy was present. For a smaller monitor roof (width = 1.2 m, height = 0.3 m), Gr/Re2 = 0.45–3.2 was the transition range over which the presence of outdoor wind decreased the ventilation rate below that found when only buoyancy was present. Therefore, attention should be given to this disadvantage in ventilation design.

Simulation Study on Natural Ventilation Performance in a Low-Carbon Large-Space Public Building in Hot-Summer and Cold-Winter Region of China

Recently, climate governance has entered a new phase of accelerating decarbonization. In order to achieve low-carbon buildings, natural ventilation has been widely used as it requires no fan power. However, there are great challenges for achieving effective natural ventilation in large-space public buildings especially in areas characterized by hot-summer and cold-winter climatic regions, due to empirically unsuitable ambient temperatures and theoretically complex joint effect of wind pressure and thermal buoyancy. Therefore, this numerical study was conducted on the performance of a natural ventilation strategy in a large-space public building in a hot-summer and cold-winter region by using computational fluid dynamics (CFD) methods. Simulations were performed by applying FLUENT software for obtaining airflow distributions within and around a typical low-carbon public building. The temperature distribution in the atrium of the building was simulated particularly for analyzing the natural ventilation performance in a large-space area. Results demonstrated that thermal pressure was dominant for the large-space building in the case study. The average indoor airflow velocities on different floors ranged from 0.43 m/s to 0.47 m/s on the windward side which met indoor ventilation requirements. Most areas of wind velocities could meet ventilation requirements. The natural ventilation performance could be improved by increasing the relative height difference between the air inlets and air outlets. These findings could help provide references and solutions for realizing natural ventilation in low-carbon large-space public buildings in hot-summer and cold-winter regions.

Comparative assessment of night ventilation performance in a nearly zero-energy office building during heat waves in Brussels

With increasing urbanization, overheating intensifies, resulting in a greater risk of indoor overheating in commercial buildings, which already have high internal gains. The impact of urban climate on the cooling energy needs of buildings has been extensively researched. However, the building performance during extreme heat events needs further investigation to reduce the energy demand from the grid during critical events and to ensure an acceptable indoor thermal environment. Here, a comparative assessment approach for natural and mechanical night ventilation performance to reduce indoor overheating and energy needs of a nearly zero-energy office building in Brussels, Belgium, was evaluated for the heat wave and non-heat wave periods in urban and rural microclimates, using calibrated thermal-energy simulations. The analysis indicated that active cooling with natural night ventilation was more effective during heat waves than other cooling strategies. In addition, natural night ventilation was also effective in maintaining safer levels of heat index values in the reference office compared to other strategies. Natural night ventilation reduced overheating by 0.39 °C in the urban microclimate and 0.50 °C in the rural microclimate relative to the Baseline. Considering the cooling energy use, natural night ventilation had no significant impact. In contrast, mechanical night ventilation increased energy use by 0.54 kWh/m2 in urban microclimate and 0.40 kWh/m2 in rural microclimate due to prolonged ventilation fan operation in the reference office building. The presented findings in the paper lead to the formulation of design guidelines, recommendations for future practices and identifying needs for further research.

The effect of domed and hip roof coverings on mosque design in case of fire

The architectural design seeks solutions to many problems, one of which is designing buildings that can quickly and safely evacuate people. Mosques, which are places of worship and multifunctional gathering centers for Muslims, are significant buildings in terms of fire research because they often host many people at the same time. However, there is a lack of research on fire safety in mosques. This study focuses on the consequences of different scenarios and types of mosque roof design, with a capacity of 500 people, as produced by the Turkiye Presidency of Religious Affairs. The examined scenarios are Scenario 1 (500 kW fire size) and Scenario 2 (1000 kW fire size), and the investigated roof types of mosques are Type 1 (hip roof) and Type 2 (dome). In the analyzed scenarios, it was observed that the dome roof type in the examined mosque design extended the evacuation time by around 10–35%. The dome creates a space for storing smoke, which reduces the spread of smoke in the main room and raises the ASET. This study recommends expanding the scope of future research by incorporating a greater variety of fire scenarios and roof covering types in mosques, while also investigating the impact of natural ventilation openings on evacuation times.

Estimation of Natural Ventilation Rates in an Office Room with 145 mm-Diameter Circular Openings Using the Occupant-Generated Tracer-Gas Method

Natural ventilation in a building is an effective way to achieve acceptable indoor air quality. Ventilation dilutes contaminants such as bioeffluents generated by occupants, substances emitted from building materials, and the water vapor generated by occupants’ activities. In a building that requires heating and cooling, adequate ventilation is crucial to minimize energy consumption while maintaining healthy indoor air quality. However, measuring the actual magnitude of the natural ventilation rate, including infiltration through the building envelope and airflow through the building openings, is not always feasible. Although international and national standards suggested the required ventilation rates to maintain acceptable indoor air quality in buildings, they did not offer action plans to achieve or evaluate those design ventilation rates in buildings in use. In this study, the occupant-generated carbon dioxide (CO2) tracer gas decay method was applied to estimate the ventilation rates in an office room in Seoul, South Korea, from summer to winter. Using the method, real-time ventilation rates can be calculated by monitoring indoor and outdoor CO2 concentrations without injecting a tracer gas. For natural ventilation in the test room, 145 mm-diameter circular openings on the fixed glass were used. As a result, first, the indoor CO2 concentrations were used as an indicator to evaluate how much the indoor air quality deteriorated when all the windows were closed in an occupied office room compared to the international standards for indoor air quality. Moreover, we found out that the estimated ventilation rates varied depending on various environmental conditions, even with the same openings for natural ventilation. Considering the indoor and outdoor temperature differences and outdoor wind speeds as the main factors influencing the ventilation rates, we analyzed how they affected the ventilation rates in the different seasons of South Korea. When the wind speeds were calm, less than 2 m/s, the temperature difference played as a factor that influenced the estimated ventilation rates. On the other hand, when the temperature differences were low, less than 3 °C, the wind speed was the primary factor. This study raises awareness about the risk of poor indoor air quality in office rooms that could lead to health problems or unpleasant working environments. This study presents an example of estimating the ventilation rates in an existing building. By using the presented method, the ventilation rate in an existing building can be simply estimated while using the building as usual, and appropriate ventilation strategies for the building can be determined to maintain the desired indoor air quality.

Research on the influence of outdoor trees on natural ventilation performance of an academic building

Research on the influence of outdoor trees on natural ventilation performance of an academic building