Natural Ventilation Efficiency Research Articles

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.

Effectiveness of natural ventilation through single-sided window opening in air-conditioning rooms

Since many buildings are not equipped with fresh air systems, many people open windows to allow for natural ventilation while the air conditioner is running. However, prolonged window opening may cause unnecessary energy consumption. Additionally, the diverse ways of window opening lead to significant variations in indoor airflow distribution, consequently impacting ventilation efficiency. Therefore, this study used field experiments and computational fluid dynamics (CFD) to determine the air exchange efficiency and air change rate of single-sided natural ventilation in air-conditioning rooms by fitting the decay curves of tracer gas. CFD simulation was performed using the unsteady Reynolds-averaged Navier-Stokes (RANS) model to examine how window openings affect the room’s air distribution, and the computed indoor CO2 concentration was compared to the corresponding field experiment data. The results show that natural ventilation through the window opening induced constant heat and mass exchange between indoor and outdoor air, which caused extra cooling losses but was globally effective in eliminating indoor contaminants. The air exchange efficiency is influenced to varying degrees by factors such as the air supply register’s position, window opening percentage, and window opening position. The air supply register’s position exerted the most significant impact at 46.45%. Efficient indoor-outdoor air exchange can be achieved by opening windows intermittently. When the window is opened from one side and the opening percentage is 100%, the indoor environment can be improved by opening the window for about 10 min every 39 min for X-direction air supply and about 7 min every 39 min for Y-direction.

Utilizing periodic boundary conditions to save computational resources for assessing building natural ventilation in urban areas

For the first time in literature, we innovatively conducted CFD simulations with periodic boundary conditions to predict coupled indoor-outdoor airflows for a full-scale 3D six-floor residential building unit in urban areas with uniformly building clusters. A few influencing parameters on building ventilation performance are comprehensively analyzed, including the impacts of the surrounding buildings, wind incident angle (θ), external opening designs, cross or single-sided ventilation modes, and indoor facilities. Ventilation evaluation is contingent on factors including air change rate per hour (ACH), the corresponding ACH of purging flow rate (ACHPFR), and age of air (τ).Results show that the efficiency of natural ventilation on each floor differs from previous research conclusions after considering the impacts of surrounding buildings. Single-sided ventilation is significantly less effective than cross-ventilation in all scenarios. Most cross-ventilation cases have one-order greater ACH and ACHPFR values compared to those with single-sided ventilation. The window-to-wall ratio on the windward and leeward sides can affect the natural ventilation rate of the corresponding rooms. A large leeward opening helps to increase the ventilation rate, especially for the rooms on the upper floor, but it decreases the ventilation for the rooms near the ground. Indoor furniture has an insignificant impact on outdoor airflow and natural ventilation efficiency.

CFD Analysis and Optimization of a Plastic Greenhouse with a Semi-Open Roof in a Tropical Area

A numerical simulation model of a natural ventilation greenhouse is helpful for improving the production and quality of greenhouse crops in tropical areas. Field experiments show that the mean coefficient of variation of indoor light intensity in four seasons was lower than 10.0%. The highest indoor temperature reached 39.3 °C during summer, while the average indoor temperature ranged from 24 °C to 26 °C in the other three seasons. The average relative humidity in the greenhouse ranged from 76% to 87% annually, which was higher and more stable than that in the external environment. A three-dimensional steady-state numerical model of the greenhouse was established based on computational fluid dynamics. Under natural ventilation conditions, the maximum error between the simulated value and the measured value of the temperature in each measuring point was 5.90%. And the average relative error between the simulated and measured values was 3.0% in the range of 0.7−1.5 m of crop cultivation height. Finally, a numerical simulation of adding side windows and expanding the vents was carried out. The results show that these methods can homogenize the airflow distribution in the greenhouse and improve the utilization efficiency of natural ventilation without more mechanical system operations.

A study on natural ventilation of dormitories for college students in northeast China during spring: A case of linear-shaped dormitory buildings

This study employed computational fluid dynamics to investigate the natural ventilation efficiency and indoor air temperature changes in different rooms of a linear-shaped dormitory building at a university in northeastern China during the spring season. Using a four-student dormitory in Jilin City as a physical model. Volume ratio of air age curves, depicting indoor air quality, are constructed based on air age values. Due to the dormitory building's symmetry, five wind angles, averaged from 0° to 90° (N - E), are chosen as typical. The results indicate that, following adequate ventilation, the average indoor air temperature (Temstabilize) can be stabilized above 11 °C in rooms located on the leeward side of the dormitory building. Specifically, rooms located on the upwind area at wind angles of 22.5° and 45°, as well as rooms near the environmental air inlets and outlets at wind angles of 67.5° and 90°, can maintain an average air temperature above 15 °C. However, the minimum continuous ventilation time (Tmin) required for these rooms exceeds 1200 s. On the windward side of the dormitory building, rooms near the environmental air inlets and outlets exhibit high ventilation efficiency, but the air temperature in these rooms decreases more rapidly. When the wind angle is 45°, 67.5°, or 90°, the average indoor temperature in these rooms falls below 11 °C. Through normalization analysis, a significant linear relationship is observed between Tmin and Temstabilize data, represented by the numerical relationship Tminnorm=1.0134×Temstabilizenorm. The findings of this study are valuable for assisting students in developing ventilation plans and can also serve as a reference for architects designing dormitory buildings based on prevailing wind directions in the area.

Combined wind catchers and side windows for cross ventilation in row houses

Purpose This paper aims to explore the efficiency of natural ventilation in the bedrooms of typical two-storeyed row houses with newly reconfigured design that incorporate rooftop wind catchers and side windows to create cross ventilation. Design/methodology/approach A CFD program was used to assess average air velocity coefficient (Cv) in 32 airflow cases. Parameters include location of openings with respect to wind direction, inlet-to-outlet area ratio (IOR) and opening-to-floor area ratio (OFR). Findings The results reveal that indoor air velocities in the cases of air entering wind catchers are generally higher than those in the cases of air entering side windows while air velocities at the openings are the opposite. The IOR of 1:2 provides best results in terms of both velocities of the indoor air and velocities at the openings. Increasing the OFR from 20% to 50% generally improves indoor air velocities and airflow rates. Originality/value This study proved that the new solution of combining one-sided wind catchers and side windows can effectively solve the problem of ventilation uniquely existing in the conditions of typical row houses by catching prevailing wind from two opposite directions into multiple rooms. The results are given as non-dimensional air velocities, which can be interpreted with any climatic data, and therefore can be applied to row houses in any locations and climatic conditions. The findings can create a new and efficient design of row houses that benefits building industry.

Evaluation of photovoltaic-based solar chimney–assisted stack ventilation within a large space hall: A case study

Photovoltaic (PV)-based solar chimneys could assist stack ventilation within a large space hall. This study considered a comprehensive office building with a PV-based solar chimney as a case study to explore measures for enhancing stack ventilation. A computational fluid dynamics (CFD) model was established, and the influences of the inner heat source, chimney inlet position, solar heat gain and photovoltaic (PV) arrangement on the ventilation rate were investigated. The results revealed that PV-based solar chimneys could assist stack ventilation and would effectively provide a suitable indoor environment for occupied areas during the transitional season. Raising the chimney inlet position is conducive to improving the ventilation rate and cooling performance. The increase in the inlet position from a height of 0.2 m to 3.8 m would increase the ventilation rate up to 5%. The heat gain from the PV backside is an important method of enhancing the ventilation rate. A 200 W/m2 heat gain can lead to a 16.4% increase in ventilation. Moreover, the lower the heat source location, the higher the ventilation efficiency. This study provides basic strategies for optimising design schemes to improve natural ventilation efficiency.

Residential Unit Design for Natural Ventilation in Tropical Multi-Family High-Rises With a Double-Loaded Corridor

This research investigates practical methods to improve the efficiency of natural ventilation in residential units of multi-family high-rises without additional areas. Typical studio- and one-bedroom-types of small units were redesigned using: 1) air post, 2) transom window, 3) buffer space with one corridor opening and 4) buffer space with two corridor openings. The simulation study using a CFD program to reveal that the indoor average air velocity coefficient (Cv ) in the best redesigned case (0.46) significantly improves from the base case (0.01). The paper demonstrates an example of application to an actual climate in Bangkok, Thailand. It was found that the proposed redesign using buffer spaces can considerably help upgrade the living conditions of the occupants in terms of both thermal comfort (24 hours vs. 0 hours in the comfort zone per day) and indoor air quality (24 hours vs. 8–17 hours that pass the minimum ventilation requirement per day) in the transitional month of February.

Design and Construction of Energy Saving Buildings in Varied Climates: Bioclimatic Approach and Sustainability

The research will explore how the design and construction of nearly zero-energy buildings can be addressed from a bioclimatic perspective, considering factors such as orientation, natural ventilation, sustainable materials, and energy efficiency strategies. Some case studies in different climates and regions are presented to understand how bioclimatic principles adapt to various environmental and geographical conditions. The documentary methodology focuses on reviewing articles published in Scopus database journals, mainly from recent years. The main results show that sustainable constructions are necessary for conserving the environment but also favor human life and the reuse of biodegradable raw materials.

Measurement and large-eddy simulation of single-sided natural ventilation in urban building groups

Natural ventilation is a highly respected and effective way to improve indoor air quality, and single-sided natural ventilation is easily formed in residential buildings. The site experiments were carried out, and the unsteady characteristics of the airflow were analyzed based on 3D wind speed series. With the experimental verification, large-eddy simulation was successfully applied to calculate the indoor–outdoor flow field of urban building groups. When the entrance boundary was constant, the flow field of the window varied all the time, and outflow was irregular. The natural ventilation efficiency was 42% with the incoming flow almost parallel to the window. The discrete wind speed inlet boundary is more suitable for the natural ventilation simulation of buildings in a real environment than the average wind speed boundary and the average wind speed superposition ±10% disturbance.

Numerical Analysis of Natural Ventilation on One Side of a Room with Two Different Opening Configurations

Single-side natural ventilation is a commonly used means of ventilation to effectively regulate the thermal environment in building interiors without any fossil energy consumption. To achieve most of the potential for the efficiency of single-side natural ventilation, research needs to be undertaken into the forces that drive single-side natural ventilation. This paper examines the single-side natural ventilation of a single vertical single opening (SSO) and a vertical double opening (SDO) in a freestanding building under wind and thermal pressure. The change in the trajectory of vortex shedding when the building is leeward as well as the frequency of vortex shedding in square buildings was investigated by large eddy simulation (LES), and computational fluid dynamics was used to analyze the difference in the air exchange rate of single-side natural ventilation of SSO and SDO in the windward and leeward conditions of the building. Both of these methods were used in conjunction with one another. According to the findings, the creation of vortices at SSO and SDO in the presence of low wind speeds reduces the ventilation effect of thermal pressure under windward circumstances. Consequently, the influence of thermal stress and wind stress ultimately cancel each other out, and this phenomenon finally disappears as the wind blowing from the outside of the structure increases. The shedding of vortices in the leeward state accomplishes a form of air supply pumping with a particular periodicity of airflow fluctuations in the lateral direction. The Strouhal number computed using the LES simulation acts in a manner consistent with the experimental findings.

Radon (222Rn) as a tracer in natural ventilation efficiency assessment in underground workings – an example of „St John Mine” tourist complex in Krobica (the Sudetes, SW Poland)

The authors characterize the use of 222Rn as an effective tracer of natural ventilation of an underground site where air circulates within a whole system of workings and ventilation intensity (the number of air exchanges in the space) is determined by atmospheric factors. A radon-related database containing results of measurements conducted at various intervals and at different stages of site accessibility was compiled.During 8 months of the calendar year 222Rn activity concentration exceeds the mean annual reference value established by Polish law (300 Bq/m3). These months correspond to periods with low intensity of natural ventilation of the workings and reduced efficiency of air exchange between the site and the atmosphere. They occur in autumn – in the second half of September, in October and November, and in May in spring, and persist for 7 to even 14 days. During these periods, the time spent inside the facility which is considered safe in terms of radiation protection is limited to an average of 6–8 h a day, i.e. from 6 a.m. to 6 p.m. in October, from 11 a.m. to 6 p.m. in November and from 11 a.m. to 5 p.m. in May. The length of a safe stay in the facility is determined by atmospheric factors, mainly the air and ground temperature.The concentrations of other gases in the atmosphere inside the facility comply with Polish mining regulations.

Limited ventilation of the central Baltic Sea due to elevated oxygen consumption

The Baltic Sea is known as the world’s largest marine system suffering from accelerating, man-made hypoxia. Notably, despite the nutrient load reduction policy adopted in the 1980s, the oxygen conditions of the Baltic Sea’s deep waters are still worsening. This study disentangles oxygen and hydrogen sulfide sources and sinks using the results from the 3-dimensional coupled MOM-ERGOM numerical model and investigates ventilation of the deep central Baltic Sea by the 29 biggest oxygen inflows from 1948 to 2018 utilizing the element tagging technic. Everywhere across the central Baltic Sea, except in the Bornholm Basin, a shift in oxygen consumption from sediments to water column and a significant positive trend in hydrogen sulfide content were observed. The most notable changes happened in the northern and western Gotland basins. Mineralization of organic matter, both in the water column and sediments, was identified as the primary driver of the observed changes. A significant negative trend in the lifetime of inflowing oxygen was found everywhere in the central Baltic Sea. It leads to the reduced efficiency of natural ventilation of the central Baltic Sea via the saltwater inflows, especially in the northern and western Gotland basins.

Post Occupancy Evaluation of Ventilation Coefficient Desired for Thermal Comfort in Educational Facilities

In tropical regions, one sustainable measure identified to attain thermal comfort and energy savings for interior spaces is natural ventilation. However, the ventilation coefficient as a factor for effective passive ventilation required for thermal comfort in educational facilities in warm, humid climates has not been adequately investigated. This study is a post-occupancy evaluation aimed at investigating the ventilation coefficient as a parameter for effective passive ventilation efficiency for good thermal comfort in the classrooms of public primary school buildings in Enugu Metropolis, Nigeria. Among the data collection instruments are two data logging devices (thermo-anemometers -AZ 9871) used to measure air velocity, humidity levels, and temperature outside and inside the classrooms of 60 government primary school buildings in the study area. This selection was based on stratified random sampling techniques. For data analysis, the global ventilation coefficient and linear regression analysis were used. The findings demonstrate that the average natural ventilation efficiency was 80%, which is higher than the global ventilation efficiency standard of 60%. The research results further highlight that colonial classroom prototype buildings have a lower temperature value and ventilation coefficient of 83%, which in turn influenced the thermal comfort conditions of the classrooms investigated. The significance of this study is that the findings contribute to the existing knowledge base that would advance strategic policy formation towards acceleration of the uptake of sustainable and energy-efficient building designs for educational facilities in warm, humid tropical environments. Doi: 10.28991/HEF-2023-04-01-07 Full Text: PDF

Statistical Analysis Approach of Single-sided Ventilation Based on Particle Track Technique Using Large Eddy Simulation

The main objective of this study is to investigate the airflow characteristics in single-sided ventilation. A CFD method of large eddy simulation (LES) using particle track technique was conducted in this study, and the simulation results are validated by experiment results. The mostly used ventilation efficiency indicators of natural ventilation are Air Flow Rate (AFR) and Purging Flow Rate (PFR). AFR is the volumetric airflow exchange rate through the openings and PFR is the effective airflow rate that removes indoor air pollutants. The ventilation efficiency (εν) of natural ventilation, which is defined as the ratio of PFR and AFR, is not well investigated in previous research, therefore, this study discusses the case of the εν of single-sided ventilation and tries to explain the distinction between AFR and PFR by statistical analysis approach based on particle movements. Particles are emitted from the opening and the particles’ movements are tracked by tracing their locations at different time steps. The residence time measures the time between the time that particles enter the room and the time that particles leave the room, and indoor travel distance indicates the sum of the displacement when the particle travels in the room. The Probability Density Function (PDF) of the residence time and indoor travel distance is used to depict airflow characteristics of the ventilation path of single-sided ventilation. The analysis method of study might be another useful approach to studying natural ventilation in detail.

Numerical Analysis of Ventilation Efficiency of a Korean Venlo-Type Greenhouse with Continuous Roof Vents

A Venlo-type greenhouse with a continuous roof vent (CR-Venlo greenhouse) was proposed by the Ministry of Agriculture, Food and Rural Affairs, South Korea (2019) for natural ventilation even during summers. It is ventilated through the buoyancy effect of the heated air using the high eave elevation. However, the CR-Venlo greenhouse was not distributed domestically, and its ventilation efficiency was not quantitatively evaluated. We aimed to analyze the natural ventilation efficiency of the greenhouse according to the eave height, using computational-fluid-dynamics. The simulation model was analyzed for hot summer conditions. The target greenhouse is ventilated only through the roof vent with all roof windows open; therefore, the air introduced through the roof window is easily exhausted. To evaluate the efficiency of ventilation, the external air entering through the roof window was calculated and evaluated. The amount of incoming air varied greatly with the location of the span and average temperature of the greenhouse; The temperature of the crop zone decreased lognormally with increasing height of the eave. Moreover, the ventilation efficiency of CR-Venlo greenhouse could be increased by improving the ventilation structure such as a shape, position or combination of roof window.

Natural Ventilation and Aerosol Particles Dispersion Indoors

Aerosol pollutant particles indoors significantly affect public health. The conventional wisdom is that natural ventilation will alleviate the dispersion of airborne or aerosol particles. However, we show that the problem is far more complex and that natural ventilation should be applied under specific conditions to be effective. We performed several simulations of a simplified (and easily reproducible) room with a window opening and aerosol particles stratified layers. Opening a window can scatter particles present in stratified layers indoors and potentially contribute to the degradation of indoor air quality for a significant period of time. Moreover, we show that thermal instabilities arising from the temperature gradients due to temperature differences between the indoor and outdoor environment spread the particles randomly indoors, adversely affecting air quality and architectural design. Recommendations for more efficient natural ventilation minimizing aerosol pollutant particles dispersed indoors are provided.

Оценка влияния температурных условий на естественную вентиляцию глубоких карьеров Арктической зоны

The Arctic zone of Russia is a territory where such minerals as gold and other precious metals are concentrated. Most often, the development of such deposits is carried out by an open method. The conditions hindering its use should be considered: the depth of distribution of permafrost and significant amplitude of changes in atmospheric air temperature during the year, month and day. The consequence of the alternation in depth of temperature zones may be the formation of recirculation zones in which harmful substances accumulate. Purpose of work. Study of the formation of velocity and temperature fields in a quarry under natural ventilation, taking into account the complex dynamics of atmospheric air temperature. Research methods. Systematization, generalization and analysis of theoretical and experimental studies in this area, including those carried out at the considered fields. Analysis of the results of mathematical modeling of aerodynamic processes in a quarry. Results. It is noted that to assess the peculiarities of formation of the mine atmosphere parameters it is sufficient to carry out only mathematical modeling of aerodynamic processes allowing to define the conditions of temperature inversions formation and dimensions of recirculation zones being potentially dangerous for accumulation of pollutants. The methodology of aerodynamic processes modeling taking into account the geometry of the pit space, temperature gradient, speed and direction of the wind flow is proposed. It is shown that at positive and negative temperature differences for the two investigated air media the development of recirculation movement zones of air masses that assure the accumulation of pollutants which in turn leads to reduced efficiency of natural ventilation in the pit, is characteristic. The conclusion has been made on the necessity to apply additional engineering measures during the period of inversion formation with negative temperature gradient in order to normalize the pit air parameters.

Thermal Perception in Naturally Ventilated University Buildings in Spain during the Cold Season

The indoor thermal environment has become a critical factor, due to its impact on the energy efficiency of a building and the health and performance of its occupants. It is particularly important for educational buildings, where students and teachers are exposed to these thermal conditions. This study assessed the impact of natural ventilation efficiency and university students’ thermal perception during the cold season. A field monitoring campaign and a questionnaire survey were conducted. A total of 989 students participated in this study. The results show that, although the CO2 concentration in 90% of the evaluated classrooms was below the European recommended value (i.e., 800 ppm), only 18% of the classrooms were within the thermal comfort zone defined by national regulations. These thermal conditions caused 55% of the students surveyed to report that they were dissatisfied, and that this environment interfered with their academic performance. Significant differences were found between thermal sensation votes from female and male students (p < 0.001). The obtained neutral temperature was one degree higher for female students than for males. Our results suggest that ventilation protocols need to be modified by adjusting the window opening strategy, and these findings should be used as guidelines during their redesign.

An Assessment of Orientation on Effective Natural Ventilation for Thermal Comfort in Primary School Classrooms in Enugu City, Nigeria

The current harsh climatic and high thermal conditions observed across the globe due to climate change is a challenge for indoor thermal comfort in buildings. In most developing nation, educational buildings where formal teaching and learning is conducted are designed to function without mechanical ventilation in an attempt to save energy costs hence relying solely on Natural ventilation. However, the effects of orientation on effective natural ventilation in educational buildings in the hot-humid tropical environments have not been adequately explored. The aim of this study was to investigate the effect of orientation of the classroom buildings with respect to cardinal and wind directions on effective natural ventilation desired for thermal comfort in buildings of public primary schools in the city of Enugu, Nigeria. It adopted a combination of experimental and descriptive survey research design. Instruments for data collection were two thermo-anemometer data logging device (AZ 9871) for determining both indoor and outdoor temperatures, wind velocities and relative humidity of classrooms of selected 60 public primary school building in the metropolis based on stratified sampling technique. Data analysis was done using linear regression analysis, the global coefficient of ventilation and building orientation standards. The research results showed that there was a correlation between classroom building orientations and effective natural ventilation coefficient and that the mean natural ventilation efficiency of 80% above the 60% global ventilation efficiency standard was achieved. In addition, orientation of classroom buildings in terms of inlet window planes to the dominant wind direction had positive significant effect on natural ventilation efficiency, invariably influencing the thermal comfort conditions of the investigated classrooms. The research concludes that adequate attention should be given to the orientation in classroom buildings especially in the hot humid tropical environments by architects and building designers to ensure thermal comfort is achieved for effective teaching and learning.
 Keywords: Building orientation, Natural ventilation, Tropical environment, Classroom buildings, Thermal comfort