Single-sided Natural Ventilation Research Articles

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.

Periodic approaching flows and pollutant dispersion of a single-sided generic building with natural ventilation

In real urban environments, wind velocities often exhibit significant time-dependent variations. However, the impact of these fluctuations on ventilation performance is not frequently addressed in the literature. To accurately predict the building ventilation performance, this paper intends to elucidate the influence of the unsteady approaching flow. Four distinct inflows, characterized by periodic sinusoidal fluctuations, are evaluated using large-eddy simulation (LES). A single-sided building model with natural ventilation is constructed and validated through a wind tunnel experiment. Four periodic inflows consist of combinations of two frequencies (f = 0.1 and 0.3 Hz) and two amplitudes (A = 0.06 and 0.09). This paper mainly compares the results of airflow patterns and ventilation performance with those of stable inflows. The results indicate that periodic inflows cause greater fluctuations in the velocity fields on the leeward side. At higher frequencies and lower amplitudes, the vertical distribution of indoor bottom vortices is relatively dispersed. It shows that periodic flows lead to noticeable changes in the ventilation rate, with a deviation between instantaneous and average Q* ranging from 13.8% to 16.5%. Compared to the stable inflow, the impacts of periodic inflows on ventilation performance vary over time; 6% and 9% variations in incoming velocities result in deviations of up to 17.5% in ventilation rates. The frequencies and amplitudes of the periodic inflows do not exhibit a linear relation with ventilation rate. Therefore, it is prudent to be cautious about adopting averaged incoming wind velocities in predicting ventilation performance. This study helps in the more accurate prediction of single-sided natural ventilation.

The Numerical Simulation Study of Pumping Airflow Driven by Wind Pressure for Single- and Multi-Room Buildings

Pumping airflow occurs in single-sided natural ventilation buildings when the openings are located on the leeward side; the direction of airflow through the building then changes periodicity. In order to propose a calculation method of the ventilation rates for single-room buildings and analyze the pumping ventilation for multi-room buildings, the CFD method with an SST k-ω turbulence model was used to conduct numerical simulation in this study, which is verified by other experimental results. Firstly, the qualitative and quantitative characteristics of pumping ventilation were investigated for a single-room building with two openings. The results show that the steady-state method underestimates the ventilation flow rates, and the unsteady-state method captures the microstructures of the flow better. Secondly, the vortex-shedding and indoor airflow oscillation frequencies were analyzed based on transient simulation for a single-room building. It was found that both of them increase with air speed. Then, the factors affecting ventilation flow rates were analyzed. A calculation method for dimensionless ventilation rates is proposed. Finally, the pumping ventilation for a multi-room building was numerically simulated. The ventilation rate for a middle room is greater than that for a corner room, and the ventilation rate for any room in a multi-room building is greater than the single-room building given the same room size and the same incoming wind speed. The findings of this paper are helpful for the design and evaluation of natural ventilation.

Experimental evaluation of airflow guiding components for wind-driven single-sided natural ventilation: A comparative study in a test chamber

Single-sided ventilation is a frequently employed ventilation strategy in contemporary structures, yet its effectiveness is often mediocre, underscoring the need for solutions to enhance its performance. To evaluate the effect of louvres and guide vanes on the effective ventilation rate, 21 different louvre configurations and four guide vane designs were compared with a plain opening for single-sided ventilation in a full-scale experimental test chamber under three different magnitudes of local wind velocity. Ventilation rates were measured using the tracer gas decay method with 12 NDIR CO2 sensors. The findings, obtained under specific test conditions, indicate that deeper openings result in a decline in ventilation rate performance. It was observed that wider guide vanes lead to higher ventilation rates, suggesting their potential to enhance SSV performance. The results reveal that, in most cases, louvres contribute to a decline in the system's performance. However, the ventilation rate is influenced by the angle and number of louvres, with optimal performance observed at specific angles and fewer louvres. These findings provide valuable insights for optimizing the design of airflow-guiding components in wind-driven single-sided ventilation systems, enabling the development of more efficient and customized solutions for natural ventilation in buildings.

The effect of geometry and location of balconies on single-sided natural ventilation in high-rise buildings

The demand for housing and the expansion of urbanization have increased the price of land and vertical growth of buildings, resulting in converting the courtyard and porch to balconies. Nowadays, semi-open spaces, which play a critical role in providing optimal indoor air and thermal conditions, are neglected. In addition, the area of such spaces is regarded as limited and sometimes even the balcony is eliminated, leading to improper thermal behavior and increased energy consumption, while such elements can be used for better natural ventilation of spaces and utilization of natural energy, resulting in reducing energy consumption in addition to controlling the pressure created by the wind in the case of correct design. The purpose of the current paper is to evaluate the performance of balconies on the high-rise buildings using single-sided ventilation in the harsh hot-arid climate of Hamdan in Iran, which there has not been studied already A general basic model is presented according to field studies and criteria. Field survey indicates that most of the high-rise buildings in Hamedan have single-sided natural ventilation, as well as are located on the south side, have a rectangular shape, are enclosed on three sides, and have recessed balconies. Based on the climate data of Hamedan, July is considered the hottest month of the year, during which natural ventilation should be applied. Simulation is conducted by computational fluid dynamics (CFD) method and ANSYS software. Based on the results, 4.5 m width and 1.5 m depth are regarded as the best geometry of the balcony for Hamedan providing a mass flow rate up to 1.38 kg/s. In addition, the position of the balcony in the wall of the building should not be symmetrical. The usage of a balcony in the middle of the façade could provide higher ventilation rate and reduce cooling energy up to 7% compared with the base case. Through a meticulous balcony design, wind could path through the larger spaces then it is led towards the opposite window, and finally exits the building in a single-sided ventilation mode. This causes the air to flow in most of the interior spaces, leading to better ventilation than other methods.

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.

A New Correlation for Single-Sided Natural Ventilation Rate Based on Full-Scale Experimental Study in Mogao Grottoes, Dunhuang, China

Although research on the natural ventilation of single-sided buildings is progressing, research on the natural ventilation of the Mogao Grottoes, which have special shapes and structures, is relatively limited. The purpose of this paper is to develop a correlation for calculating the natural ventilation rates of such grottoes. Field experiments were carried out on two typical caves to measure their meteorological parameters and natural ventilation rates to verify the validity of the proposed correlation. The results show that our correlation has good reliability and stability when predicting the natural ventilation rates of the caves. First, the new correlation has a small average deviation of 16.35%. The average deviations in the natural ventilation rates predicted by seven established correlations are as low as 17.85% and as high as 59.39%, revealing a large gap compared with the correlation proposed herein. Second, the maximum deviation in the outputs of the proposed correlation is only 7.70% between each case. Finally, a comparison between the calculated results and the values measured in Cave 328 shows that the correlation is also suitable for large-volume caves. The developed correlation provides theoretical support and a scientific method for preventive protection and a quantitative analysis method for the study of natural ventilation in caves.

Model predictive control of short-term winter natural ventilation in a smart building using machine learning algorithms

Natural ventilation in buildings has the potential to reduce building energy consumption and the incidence of sick building syndrome. However, controlling natural ventilation is often challenging. For instance, natural ventilation through operable windows may cause cold draughts for the occupants in winter. This paper presents the key findings of a novel machine learning-based model predicted control of single-sided natural ventilation in a retrofitted four-story smart building in Cambridge, Massachusetts, in the northeast region of the United States. A data-driven methodology is used to realize this natural ventilation modeling, including data collection, system dynamics identification, and control formulation. The prediction model of indoor CO2 and room air temperature is built through a learning process. The model predictive control (MPC) formulation step combines thermal comfort and indoor air quality requirements. Finally, the natural ventilation MPC is tested in the real building, and the results showed that indoor air quality and thermal comfort are maintained successfully, without increasing significantly the heating energy consumption in winter. This scalable data-driven methodology can potentially be applied to natural ventilation in smart buildings.

The role of near-façade flow in wind-dominant single-sided natural ventilation for an isolated three-storey building: An LES study

Wind-driven single-sided ventilation is present in many existing buildings globally, and its performance can be unreliable and challenging to improve. To address these performance challenges, a better understanding of the interconnected relationship between the external and internal flows is required. Therefore, a detailed assessment of this type of natural ventilation is vital. A detailed CFD analysis of wind-dominant single-sided natural ventilation is presented by adopting the Large Eddy Simulation method, validated using previous wind tunnel studies. An isolated cube, representing a three-storey building, was used to investigate four case studies with different opening positions on the building façade. The presence of parallel flow near the building façade and the effect this has, both on the structure of the flow at the opening and the internal secondary flow, is investigated. Results demonstrate that a mixing layer jet of air is the main structure of the flow at the opening. The flow characteristics of this jet are a function of how the external near-façade flow interacts with the building. It can be deflected or attenuated by the near-façade fluctuating pressure and vortex structures close to the opening. Tracer gas decay results show that only 3/5 of the flow at the opening contributes to effective ventilation in this type of natural ventilation. Comparisons between the ventilation rates for openings at different positions on the building façade demonstrate the importance of the pressure role at the opening in single-sided natural ventilation.

Inverse identification of source location in a single-sided natural ventilation building

Natural ventilation is a common way of ventilation for urban residents, which is simple and energy-efficient. However, this ventilation not only introduces fresh air from outdoors into the indoor environment but also brings various pollutants from outdoors into the indoor environment, thus reducing indoor air quality and causing a series of human respiratory diseases in severe cases, such as asthma, pneumonia, bronchitis, etc. In a high-density urban environment, the proximity of rooms within a building can easily lead to cross-infection between occupants in the event of a public health emergency. Therefore, it is of great significance to quickly and accurately find the source of viruses or pollutants. The objective of this study is to accurately locate pollutant source which spread between units by wind effect. A model with three-storey building of wind-driven single-sided ventilation was built. Carbon dioxide (CO2) was used as a tracer of indoor pollutants. Computational Fluid Dynamics (CFD) is used to accurately simulate and predict airflow and concentration fields in and around the building. The results indicated that the location of the predicted pollution source is close to the position where the pollutant is released. The results of this paper can provide vital information for preventing the spread of contaminants in buildings.

Experimental analysis of single-sided natural ventilation and interunit dispersion in scaled 2D street canyons

Interunit dispersion problems have been studied previously mainly through on-site measurements, wind tunnel tests, and CFD simulations. In this study, a scaled outdoor experiment was conducted to examine the interunit dispersion characteristics in consecutive two-dimensional street canyons. Tracer gas (CO2) was continuously released to simulate the pollutant dispersion routes between the rooms in street canyons. The reentry ratio was analyzed to reveal the interunit dispersion of the rooms in the street canyons. This study provides authentic airflow and pollutant dispersion information in the street canyons in an urban environment.

Dynamic compartmentalization of double-skin façade for an office building with single-sided ventilation

In this study, a compartmentalized double-skin façade (DSF) is developed for an office room with single-sided ventilation to enhance the performance of the passive design strategy. We designed a DSF that has both an inlet and an outlet to ensure compatibility with single-sided natural ventilation, increased the air cavity heights to overcome the effects of limited ventilation rate, and compartmentalized to suit seasonal conditions. The performance of the dynamically compartmentalized DSF was evaluated using four key parameters: cavity height, cavity depth, opening-to-glazing ratio (O/G ratio), and solar heat gain coefficient (SHGC). Two different seasons, namely summer and winter, were targeted. The results revealed the interdependency of each parameter and indicated the potential energy savings in terms of both cooling and heating. In summer, a greater cavity depth with a higher O/G ratio was helpful when the cavity height was increased. A higher SHGC increased the airflow rate, but it increased the room temperature because the solar heat gain was more influential than the increased airflow rate. In winter, the interdependency between the parameters increased with the SHGC. When airflow rate was restricted to fulfill the minimum ventilation requirement, a higher inlet cavity height helped increase the room temperature by 2 °C on average in winter.

Scaled outdoor experimental analysis of ventilation and interunit dispersion with wind and buoyancy effects in street canyons

Driven by wind and buoyancy effects in the urban environment, ventilation performance and pollutant transmission are highly related to human health. In order to investigate characteristics of the single-sided natural ventilation and interunit dispersion problem, this study conducted scaled outdoor experiments in summer and winter periods in two-dimensional street canyons. Tracer gas method was adopted to predict the ventilation rate and simulate the pollutant dispersion. It was found the ventilation performance of windward and leeward rooms showed different trends with wind velocities. Archimedes number Ar was used to examine the interactions of the buoyancy and the wind forces. It revealed that the non-dimensional ventilation rates of all rooms were generally smaller than the results of buoyancy effect only. It indicates that interactions between the buoyancy and wind effects were destructive, which reduced the ventilation rates. The interunit dispersion characteristics with the wind effect were highly dependent on source locations. The results of the tracer gas concentrations of the reentered rooms were not showing simple increasing or decreasing trends. This study provides authentic and instant airflow and pollutant dispersion information in an urban environment. The dataset of this experiment can offer validations for further numerical simulations.

Effects of Pivot Windows and Wing Walls on Single Sided Natural Ventilation in Rumah Susun (Walk Up Flat)

Rumah susun (walk up flat) are one of the buildings that rely on natural ventilation. However, the application of natural ventilation in rumah susun (walk up flat) in urban areas is influenced by tropical climate problems such as high temperatures and low wind speeds. The design of the openings in the facade has not been able to distribute air into rooms properly. In addition, the layout design makes single-sided natural ventilation the only strategy possible for double loaded corridor type flat. This study aimed to determine the effect of a combination of pivot window designs and wing walls in directing and distribute air into room. The study was conducted in two stages, that was field measurements and experimental with Computational Fluids Dynamics simulations. Simulations were conducted on a combination designs of wing walls and pivot window with 45o and 90o opening angles to determine their effects on the distribution and indoor air velocity. The combination design of wing walls and pivot window created a pressure difference so that it could increase indoor air velocity under both oblique and parallel to the opening. In the direction of the wind that was not oriented to the openings, the combination of wing walls and vertical pivot windows with 90o opening angles increased indoor air velocity up to five times in the corner room. While the 45o opening angle increased the indoor air velocity up to seven times than base case condition in a middle room.

A projection an-isotropic spectrum method for inflow turbulence of Large Eddy Simulation in natural ventilation of buildings

The inflow boundary turbulence generation procedure is a critical topic for Large-Eddy Simulations (LES) in accurately simulating natural ventilation. The present study focuses on the turbulence energy spectrum, generated by the synthetic spectrum method for the fluctuating inflow velocity of LES. A projection algorithm is proposed for modifying the previous spectrum method to sustain the target turbulence spectrum, which is then validated by channel flow，airflow around the building and cross ventilation. The results show better performance in comparison with the previous spectrum methods. This validated procedure is then also applied to the LES calculations for building single-sided natural ventilation with two openings. Results indicate that the instantaneous flow change rate around two openings was specifically shown to have back and forth oscillation between positive and negative values, a valuable finding for future building natural ventilation designs.

How to quantify natural ventilation rate of single-sided ventilation with trickle ventilator?

This study quantifies the natural ventilation rate in single-sided natural ventilation with a trickle ventilator, inserted in a window frame or a shutter box. The seasonal characteristics of natural ventilation in actual residential conditions were examined by long-term field measurements in a multi-residential building during spring and summer seasons. The wind velocities and pressure differences between indoors and outdoors in the summer season, which are the driving forces of natural ventilation, were relatively lower compared to the spring season. The turbulence intensity was greater in summer when the outdoor wind velocity was lower.During this study about 90% of the outdoor wind velocity was less than 2.5 m/s, and the wind speed and wind direction constantly fluctuated. The ventilation rate of the trickle ventilator was quantified by four methods: the tracer gas method, inlet air velocity-based, pressure difference-based, and reference wind velocity-based. The tracer gas method was considered the reference to which the other three methods were compared. The calculation method based on the indoor/outdoor pressure difference, which is widely used for calculating the natural ventilation rate, failed in this case to capture the actual natural ventilation rate; only 63% of the ventilation rate quantified by the tracer gas method could be explained by this method. In addition, the reference wind velocity-based quantification showed the worst agreement, with an error rate around 54%. The inlet air velocity-based quantification of the ventilation rate showed the best agreement with the results of the tracer gas method in the trickle ventilator.

Study on Design Strategies About Single-sided Natural Ventilation in Residential Buildings

Natural ventilation is an effective measure to reduce energy consumption and improve indoor environment. The enlargement of the depth of high-rise residential buildings allows only single-sided natural ventilation, which makes the problem of poor natural ventilation itself more serious. In this study, CFD numerical analysis was used to verify the optimal design strategy of one-sided ventilation residence in a practical case, and the results showed that the design strategy could improve the ventilation effect of one-sided ventilation houses [1].

A numerical investigation of balcony geometry impact on single-sided natural ventilation and thermal comfort

Balconies could enhance natural ventilation (NV) and reduce reliance on mechanical ventilation in cooling dominant climates. Indoor environment and thermal comfort under NV mode are usually less predictable than Mechanical Ventilation (MV), and balcony geometry's impacts on these parameters have not yet been classified. This study aims to investigate the effects of balcony depth and door opening scale on the NV performance and thermal comfort of the attached Livingroom. The present article conducted a 3D – steady-state Computational Fluid Dynamics (CFD) simulations using ANSYS Fluent. The simulation results were validated against measured data in a residential high-rise building in subtropical Brisbane, Australia. Five different openings and nine depth scenarios are defined as configuration tests. The simulation results reveal that both the opening and depth sizes affected the Indoor Air Distribution (IAD), mean Indoor Air Velocity (IAV) and temperature, while these effects are not identical in the defined scenarios and opening size had more significant effects. The smaller openings, including the case study, led to a better thermal comfort than other scenarios. Contrary, the smaller depth sizes (less than 2 m) led to a non-uniform and unstable IAD at the attached Livingroom. The best thermal comfort and the highest IAV also occurred, respectively, in the deeper balconies with 35 and 30% depth ratio. Finally, a comparison between the findings and literature reveals the balcony's depth scale effects on mean IAV significantly depends on the orientation of buildings.

Numerical simulation of single-sided natural ventilation: Impacts of balconies opening and depth scale on indoor environment

Heating Ventilation and Air Conditioning (HVAC), including, Mechanical ventilation (MV) in the building sector accounts for around 40% of electricity consumption and a large percentage of Greenhouse Gas (GHG) emissions. Natural ventilation (NV), as an alternative method, assist in decreasing energy consumption as well as harmful emissions. Balconies, a common architectural element in high rise residential buildings, could enhance NV and reduce reliance on mechanical ventilation in cooling dominant climates. Indoor air velocity and distribution, IAV and IAD, due to NV is less predictable than MV, and the impacts of balcony geometry on IAV and IAD profile have not yet been classified. This study, focusing on single-sided ventilation apartments, seeks to determine to what extent balcony depth and door opening area impacts on the indoor environment of the attached living area. For this, 3D – steady-state Computational Fluid Dynamics (CFD) simulations were conducted using ANSYS Fluent. The simulation results were validated against measured data in a full-scale experimental study in a residential building in subtropical Brisbane, Australia. Five different openings and nine depth scenarios were modelled, with results showing variances in indoor mean air velocity and temperature. The outcomes reveal the impacts of opening and depth scales on IAD profile, as well as IAV and temperature magnitude at the attached indoor area. Although the defined scenarios could not reach a firm conclusion, the findings of simulation reject the shallowest balcony scenario (depth less than 2 m) due to weak IAD. Besides, the results show that a small opening could lead to an acceptable IAV at the attached indoor area. Results also suggest that further research on the indoor distribution of temperature and air velocity, consequently neutrality based on thermal comfort model, may provide further clarity on the effect of geometric factors on occupant comfort through NV.

Numerical investigation of gaseous pollutant cross-transmission for single-sided natural ventilation driven by buoyancy and wind

Single-sided natural ventilation was numerically investigated to determine the impact of buoyancy and wind on the cross-transmission of pollution by considering six window types commonly found in multistory buildings. The goal of this study was to predict the gaseous pollutant transmission using computational fluid dynamics based on the Reynolds-averaged Navier-Stokes equations and baseline k-ω turbulence equations. The results indicated that ventilation rates generally increased with increasing wind speeds if the effects of buoyancy and wind were not suppressed; however, the re-entry ratio representing the proportion of expelled air re-entering other floors and the corresponding risk of infection decreased. If the source of the virus was on a central floor, the risk of infection was the highest on the floors closest to the source. Different window types were also considered for determining their effectiveness in controlling cross-transmission and infection risk, depending on the source location and driving force (e.g., buoyancy and wind).