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Abstract Indoor air environment inside operating room (OR) is crucial for the success of surgical operation. The opening and closing process of sliding door is very common in OR. In this case, the designed positive pressure will disappear. Since the air exchange characteristic at the interface of the sliding door will influence the Surgical Site Infection risk, the combined effects of temperature and pressure differences on interface airflow along with the air infiltration volume and intruding particles caused by the airflow are studied by theoretical and numerical methods. Two different cases are compared, where the temperature of OR is lower or higher than that of anteroom, respectively. Results show that the contaminants accumulate in the upper space of the OR due to the airflow pattern between two rooms when the temperature of OR is lower than the anteroom. This will increase the possibility that airflow carrying contaminants intrudes into OR. On the contrary, the contaminants are controlled in the lower space of the OR when the temperature of OR is higher than that of anteroom. On average, the particle intrusion ratio of the second case decreases by 55% compared with that of the first case. So, it is helpful to protect the clean environment of OR when the temperature of OR is higher than that of the anteroom. Moreover, the air infiltration volume of the closing phase is found unequal to that of the opening phase. This study provides the useful information for maintaining a clean indoor environment under operational condition. Highlights • Interface airflow of sliding door with temperature/pressure differences is studied. • Theoretical model was established for interface flow under the coupled effect. • Air infiltration rate of the closing phase is more than that of the opening phase. [ABSTRACT FROM AUTHOR]

Flammable gases and vapours are widely used in industrial field, which brings up the explosion risk in the large premises. In this paper, several transient experiments have been conducted in a newly built large space chamber. Sulfur hexafluoride (SF 6 ) was released in a specific place in each experiment while the space was ventilated throughout each experiment. The concentrations were measured and recorded at several points. Several parameters have been changed, namely air distribution pattern, air change rate, contaminant gas emission rate and contaminant source releasing method. The approximate accessibility of contaminant source (ACS) in different experiment conditions have been yielded with experimental data and compared. The dimensionless number ( g ' q V / D ) 1 / 3 / U i n l e t has been proposed on the basis of the passive gas criterion of ( g ' q V / D ) 1 / 3 / U to represent the magnitude of the gas gravity effect. The experiment results show obvious correlations between ACS and ( g ' q V / D ) 1 / 3 / U i n l e t at different locations. [ABSTRACT FROM AUTHOR]

The flow interactions between the personalized air and the thermal boundary layer (TBL) may play an important role to the inhaled air quality and energy efficiency performance of a personalized ventilation (PV) system. This paper aims to investigate these interactions and their impacts on the performance of a PV system. Schlieren imaging technique, Laser Doppler Anemometry (LDA) and tracer gas measurements are employed to identify the airflow patterns in the breathing zone (BZ) and the effect of the interactions on ventilation effectiveness. Although it has always been considered that it is difficult for a PV jet of low flow rate to penetrate the TBL, it is found in this study that the TBL is penetrable even at invading velocities lower than the normally recognized value of 0.3 m/s. The advantage of the reduced blockage effect allows for a more effective delivery of fresh air to the BZ. It is also shown that the airflow interactions alter the airflow distributions in the BZ and affect the inhaled air quality. This interaction depends on the positioning and direction of the non-uniform invading flow from the nozzle, which should be carefully considered for optimal ventilation design to enhance the effectiveness of ventilation at relatively low energy consumptions. [ABSTRACT FROM AUTHOR]

Natural ventilation enables personal control, and occupant behaviors in window opening play a decisive role on natural ventilation performance, indoor air quality (IAQ), and/or airborne infection risk in a hospital setting. The occupant behaviors differ significantly from different building types with different functions and living habits. Based on a one-year field measurement in two general hospital wards in Nanjing, China, the effects of air quality (i.e. indoor CO 2 concentration and outdoor PM 2.5 concentration) and the climatic parameters (i.e. indoor/outdoor temperature, relative humidity, and outdoor wind speed, wind direction and rainfall) on window opening/closing behaviors are analyzed. Indoor air temperature or relative humidity is found to be a dominant factor for window opening behaviors. Seasonal differences are observed for the different influences of physical factors. The outdoor temperature is found to be associated with the window opening probability negatively during the cooling season, but positively during the transition and heating seasons. The indoor relative humidity positively affects the window opening probability during the transition season while a negative impact appears during the cooling and heating seasons. Based on the seasonal variation of window opening behaviors, Logistic regression models in different seasons (cooling, transition and heating seasons) are developed to predict the window opening/closing state and are verified to be promisingly adaptable with results of accuracy bigger than 70%. [ABSTRACT FROM AUTHOR]

Precision ventilation is used in open-plan offices to establish micro-climate zones according to the metabolic requirements of its occupants. The aim of this study is to determine design criteria and highlight the opportunities and limitations for precision ventilation in large-scale offices. The simulations and experiments were conducted under steady state conditions with fixed airflow from all active chilled beams (ACBs) and constant room temperatures. A temperature difference of 3.5K was maintained between supply and room air in all cases with and without occupants. Results showed that precision ventilation can simultaneously establish low-level (<0.15 m/s), medium-level (<0.45 m/s), and high-level (<0.65 m/s) air velocity zones in the same shared office space such that occupants with different metabolic rates had Predicted Mean Vote (PMV) values maintained within the acceptable limit. The establishment of a single air velocity zone in an open-plan office layout without influencing air velocities of other zones was achieved by lowering the airflow rates of two ACBs by 35%. The vertical and horizontal temperature uniformity was maintained with this precision ventilation system with draught rates of less than 20% for occupants with normal metabolic rates. Comparative analysis using precision ventilation with and without occupants showed that targeted air velocity distribution in the room can be negatively influenced by the absence of any heat sources in any zone. An annual energy saving of up to 15% was achieved by raising the cooling setpoint temperature from 23 °C to 25 °C. • Precision ventilation strategy is applied to the large-scale open-plan officeto establish design criteria for multiple ACBs working. • Experimental and simulation results showed more stable targeted airflow distribution in the case of occupants in the room compared to without occupants. • The Draught Rate and Vertical Temperature Difference for occupants in all zones remain within acceptable limits even with the formation of high air velocity zones. • An annual energy saving of up to 15% was achieved by raising the cooling setpoint temperature from 23 °C to 25 °C. [ABSTRACT FROM AUTHOR]

Expiratory flows of an infected individual can spread diseases in indoor environment. This probably explains why there have been many studies of how exhaled flow disperses and interacts with ventilation. A number of experimental studies have found that the exhaled flows can be locked up in the stratified layer in a room ventilated by displacement; however, its mechanism has not been explored so far. A non-dimensional theoretical buoyant jet dispersion model was developed here to compare the dispersion characteristics of the exhaled flow in a thermally stratified environment with those in a thermally uniform environment. Our results show that the exhaled flow can freely float upward in a uniform environment while it exhibits an oscillatory trajectory at a certain height in a thermally stratified environment. The terminal temperature of exhaled jet flow is equal to the ambient temperature. The latter is the so-called lock-up phenomenon as observed in some early studies. In displacement ventilation, the location of the lock-up layer is lower than the stratification height. A smaller Ar number and a steeper temperature gradient lead to a lower lock-up height in a thermally stratified environment. The variation of the lock-up height with different temperature gradients is found to follow a power law relation. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to determine the dispersion and distribution characteristics of exhaled airflow for accurate prediction of disease transmission. The development of airflow dynamics of human exhalation was characterized using nonhazardous schlieren photography technique, providing a visualization and quantification of turbulent exhaled airflow from 18 healthy human subjects whilst standing and lying. The flow shape of each breathing pattern was characterized by two angles and averaged values of 18 subjects. Two exhaled air velocities, u m and u p , were measured and compared. The mean peak centerline velocity, u m was found to decay correspondingly with increasing horizontal distance x in a form of power function. The mean propagation velocity, u p was found to correlate with physiological parameters of human subjects. This was always lower than u m at the mouth/nose opening, due to a vortex like airflow in front of a single exhalation cycle. When examining the talking and breathing process between two persons, the potential infectious risk was found to depend on their breathing patterns and spatial distribution of their exhaled air. Our study when combined with information on generation and distributions of pathogens could provide a prediction method and control strategy to minimize infection risk between persons in indoor environments. [ABSTRACT FROM AUTHOR]

Airborne particles released from surgical team members are major sources of surgical site infections. To reduce the risk of such infections, ultraclean-zoned ventilation systems have been widely applied, as a complement to the ventilation of the main operating theatre. The function of ventilation in an operating theatre is usually determined without considering the influence of the staff members' posture and movements. The question of whether the surgeon's posture during an on-going operation will influence particle distribution within the surgical area has not yet been explored in depth or well documented. In the present study we analysed data from investigation of two positions (bending and straightened up), which represent the most common surgeon and staff-member postures. The investigation was performed by applying the computational fluid dynamics methodology to solve the governing equations for airflow and airborne particle dispersion. Ultraclean-zoned ventilation systems were examined as an addition to the conventional operating theatre. We examined three distinct source strengths (mean value of pathogens emitted from one person per second) due to the variety of staff clothing systems. In the upright posture, the screen units reduced the mean air counts of bacteria and the mean counts of sedimenting bacteria to a standard level for infection-prone surgeries in the surgical area. However, the performance of this system could be reduced drastically by improper work experience. Surgical garments with a high protective capacity result in lower source strength and thus reduces the particle concentration within the surgical area. These results are useful for developing best practices to prevent or at least reduce the infection rate during a surgical intervention. [ABSTRACT FROM AUTHOR]

Pollutants generated from cooking process are detrimental to occupant's health. For conventional residential kitchen in hot summer and cold winter region of China, range hood is installed to exhaust oil fume and other pollutants. In typical kitchen, air is supplied through the insect screen. However, this kind of air supply and exhaust system is not capable of providing air distribution for good indoor air quality in kitchen. In order to solve this problem, the combined scheme with air supply through slot air curtain and air exhaust through range hood is proposed, which is termed as the push-pull ventilation system. Both numerical simulation and field test were carried out to investigate the air velocity, temperature and pollutant distributions. Orthogonal study was performed during numerical simulation. Air curtain velocity (A), air curtain angle (B, C, D, E) and exhaust velocity (F) were chosen as six factors during the L 25 (5 6 ) orthogonal test. The average CO 2 concentration of the 25 cases in breathing region was compared. It is shown that by using the range hood alone, oil fume generated by cooking cannot be effectively exhausted out of the kitchen. With application of the push-pull ventilation system, the air temperature can be reduced during the summer scenario, which may improve occupant thermal comfort. Meanwhile, the pollutant concentration can be reduced with the improved air distribution. Moreover, the sequence for effect of influencing factors on the pollutant concentration distribution is A>B>C>E>D>F. This proposal provides a scientific support to reduce the indoor pollutant concentration in kitchen. [ABSTRACT FROM AUTHOR]

A modified backward-facing step flow with a large expansion ratio of five (5) was modeled by 19 teams without benchmark solutions or experimental data for validation in an ISHVAC-COBEE July 2015 Tianjin Workshop, entitled as “to predict low turbulent flow”. Different computational fluid dynamics (CFD) codes/software, turbulence models, boundary conditions, numerical schemes and convergent criteria were adopted based on the own CFD experience of each participating team. The largest coefficient of variation is larger than 50% and the largest relative maximum difference of penetration length is larger than 150%. The predicted non-dimensional penetration lengths as a function of the Reynolds number (1–10,000) are found to be significantly diverse among different teams. Even when the same turbulence model or even the laminar model is used, the difference in the predicted results is still notable among different teams. It indicates that the combined effects of a lack of general turbulence model, and possible errors in multiple decisions based on users' experience may have caused the observed significant difference. Prediction of transitional flows, as often observed in building ventilation, is shown to be still a very challenging task. This calls for a solid approach of validation and uncertainty assessment in CFD “experiments”. The users are recommended to follow an existing guideline of uncertainty assessment of CFD predictions to minimize the errors and uncertainties in the future. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) was first introduced in the ventilation industry in the 1970s. CFD has been increasingly used since then, as testified by the number of peer-reviewed articles, which was less than 10 per year in the 1990s, and which is now 60 to 70 per year. This article discusses the principle behind CFD, the development in numerical schemes, turbulence models and the importance of the increased computer size since the 1970s. Special attention is given to the selection of the correct governing equations, to the understanding of low turbulent flow, to the selection of turbulence models, and to addressing situations with more steady-state solutions. The article finishes with a number of different case studies such as design of air supply openings, smoke management in buildings, cross-infection risks from the exhalation of particles and calculation of people moving in a room. The use of benchmark tests is also addressed. [ABSTRACT FROM AUTHOR]

Local ventilation systems are widely used in industrial production processes to capture heat release and/or gaseous/particulate contaminants. The primary objective of this study was to determine important empirical factors on local pollutant capture efficiency and characteristics of thermal stratification in the working areas of industrial plants. Investigated factors were confined airflow boundaries, flow rates of the exhaust hoods, source strengths, airflow obstacles and distances between sources and exhaust hoods. Reduced-scale experiments were conducted with a geometric scale of 1:15 corresponding to a portion of the blast furnace workshop of a steel plant. The dependency of capture efficiency on Archimedes numbers was established. The results showed that confined airflow boundaries, flow rates of the exhaust hoods and source strengths were important empirical factors on pollutant capture efficiency. Hood performance was also evaluated by thermal stratification heights in the plants. This study could help improve the capture efficiency of local ventilation systems used in industrial plants. Safe operation heights are recommended in the upper space of industrial plants based on the thermal stratification in the plants. [ABSTRACT FROM AUTHOR]

Abstract: The distribution of particles in a room is of great interest because of the effect of particles on human health. Using computational fluid dynamics, it is possible to study the behaviour of particles in a room. In this study, the commercial software STAR-CCM+ was used to simulate the dispersion of passive particles in a room with displacement ventilation system. In addition, some experiments are performed to verify the accuracy of the simulation results. According to the comparison of the experiment and the simulations in front of supply opening, the k–ε model seems to give better results than the k–ω model. It is shown that, in order to have an accurate result, the simulation of radiation effect is essential. Furthermore, the results of particle simulations show that when the passive particle source is in the height of 1.5 m and the heater is at the height of 0.5 m, the average concentration in the room is the lowest. Depending on the particle source height and heater location, the average particle concentration profile will change. In remote areas, the concentration profile does not show any significant difference between upper zone and lower zone. [Copyright &y& Elsevier]

In order to control the spread of Covid-19, authorities provide various prevention guidelines and recommendations for health workers and the public. Personal protection equipment (PPE) and physical barrier are the most widely applied prevention measures in practice due to their affordability and ease of implementation. This study aims to investigate the effect of PPE and physical barriers on mitigating the short-range airborne transmission between two people in a ventilated environment. Four types of PPE (surgical mask, two types of face shield, and mouth visor), and two different sizes of the physical barrier were tested in a controlled environment with two life-size breathing thermal manikins. The PPE was worn by the source manikin to test the efficiency of source control. The measurement results revealed that the principles of PPE on preventing short-range droplet and airborne transmission are different. Instead of filtering the fine droplet nuclei, they mainly redirect the virus-laden exhalation jet and avoid the exhaled flow entering the target's inhalation region. Physical barriers can block the spreading of droplet nuclei and create a good micro environment at short distances between persons. However, special attention should be paid to arranging the physical barrier and operating the ventilation system to avoid the stagnant zone where the contaminant accumulates. • The principles of PPE on preventing droplet and airborne transmission are different. • PPE redirects the exhalation jet and avoids the exhalation flow to enter the target's inhalation region. • Physical barriers block the spreading of fine droplet nuclei and create a good macro environment. • Ventilation shows significant impacts on the exposure risk in the scenario without PPE or physical barriers. [ABSTRACT FROM AUTHOR]

• Three phases of probable aerosol transmission of SARS-CoV-2 from source to receptor are comprehensively reviewed. • Key parameters of two models for SARS-CoV-2 risk assessment are analyzed. • Ventilation plays an important role in mitigating infection risk by intervening both dispersion and inhalation phases. • Novel personalized, intelligent and resilient ventilation strategies should be developed for clear objective of epidemic control. Global spread of COVID-19 has seriously threatened human life and health. The aerosol transmission route of SARS-CoV-2 is observed often associated with infection clusters under poorly ventilated environment. In the context of COVID-19 pandemic, significant transformation and optimization of traditional ventilation systems are needed. This paper is aimed to offer better understanding and insights into effective ventilation design to maximize its ability in airborne risk control, for particularly the COVID-19. Comprehensive reviews of each phase of aerosol transmission of SARS-CoV-2 from source to receptor are conducted, so as to provide a theoretical basis for risk prediction and control. Infection risk models and their key parameters for risk assessment of SARS-CoV-2 are analyzed. Special focus is given on the efficacy of different ventilation strategies in mitigating airborne transmission. Ventilation interventions are found mainly impacting on the dispersion and inhalation phases of aerosol transmission. The airflow patterns become a key factor in controlling the aerosol diffusion and distribution. Novel and personalized ventilation design, effective integration with other environmental control techniques and resilient HVAC system design to adapt both common and epidemic conditions are still remaining challenging, which need to be solved with the aid of multidisciplinary research and intelligent technologies. [ABSTRACT FROM AUTHOR]

Abstract: A two-bed hospital ward with one standing healthcare person and a ceiling-mounted lowimpulse semicircular inlet diffuser is simulated in a full-scale room. Tracer gas is used for simulating gaseous contaminants, and the concentration is measured at different air change rates and different postures of the patients. A textile partition between the beds, which is typical in a hospital ward, is used for protection of the patients in some of the experiments. Three different layouts of return openings are tested. One layout with one opening at the ceiling, another with four openings at the wall opposite to the inlet diffuser, and one with a high location of these four openings. The downward recirculating flow is on average parallel with the partition, and in most cases the partition does not decrease cross-infection. A high location of the four return openings decreases the risk of cross-infection. [Copyright &y& Elsevier]

Abstract: The present study performed a series of experiments in a wind tunnel to investigate the impact of velocity, turbulence intensity and liquid–air temperature difference on ammonia emission rates. Decreasing velocity, turbulence intensity and liquid temperature are shown to reduce the ammonia emission rates. The emission rates are more sensitive to the change of velocity at a low velocity compared to change of velocity at a higher velocity range, which corresponds with the conclusion that the boundary layer thickness of velocity increases sharply when velocity is changed from 0.2m/s to 0.1m/s. In addition, the emission rates are more sensitive to the change of temperature at a higher temperature than at a lower liquid temperature range. The influence of velocity and liquid–air temperature difference on boundary layer thickness is also analyzed. The relationship between the emission rate and boundary layer thickness is presented. [Copyright &y& Elsevier]

Abstract: The classical Wells–Riley model for predicting risk of airborne transmission of diseases assumes a uniform spatial distribution of the infected cases in an enclosed space. A new mathematical model is developed here for predicting the spatial distribution of infection risk of airborne transmitted diseases by integrating the Wells–Riley equation into computational fluid dynamics. We applied our new integrated model to analyze a large nosocomial SARS outbreak in Hong Kong during the 2003 SARS epidemics, which was studied in the literature with regard to the association between airflow and SARS infection. The predicted numbers of infected cases of medical students in the same cubicle, the adjacent cubicle and the distant cubicle were 6.39, 0.78 and 0.2 respectively while the observed numbers of infected medical students in the three cubicles were 7, 0 and 0 respectively during the morning of March 6th, which was the highest attack period. The predicted numbers of infected cases of inpatients during the morning of March 6th in the same cubicle, the adjacent cubic and the distance cubicle were 7.8, 5.1, and 4.8 respectively which also agree well with the observed distribution of the infected inpatients during the entire infection period. The new developed model provides a new modelling tool for investigating the airborne transmission of diseases in enclosed spaces. The model is applicable when the susceptible stays mostly at the same location in an enclosed space during the infectious period, such as inpatients in a hospital ward, passengers in an airplane etc. [Copyright &y& Elsevier]

Abstract: The Centers for Disease Control and Prevention has recommended the use of downward ventilation systems in isolation rooms to reduce the risk of cross-infection from airborne transmissible diseases. The expected airflow pattern of a downward ventilation design would supply cooler and slightly heavier clean air from a ceiling diffuser to push down contaminants, which would then be removed via outlets at floor level. A “laminar” (strictly speaking, unidirectional) flow is expected to be produced to avoid flow mixing and thus reduce cross-infection risk. Experiments were carried out in a full-scale experimental hospital ward with a downward ventilation system to investigate the possibility of applying downward ventilation in a general hospital ward. Two life-sized breathing thermal manikins were used to simulate a source patient and a receiving patient. Computation fluid dynamics was also used to investigate the airflow pattern and pollutant dispersion in the test ward. Based on both experimental and numerical results, the laminar airflow pattern was shown to be impossible to achieve due to turbulent flow mixing and flow entrainment into the supply air stream. The thermal plumes produced above people were found to induce flow mixing. We also studied the effects of the locations of the supply and extraction openings on both the flow pattern and pollutant exposure level in the occupied zone. A number of practical recommendations are suggested. [Copyright &y& Elsevier]

The interaction between ambient airflow and human thermal plume may affect airflow distribution in human micro-environment and then personal exposure. This study aims to investigate this interaction and to determine what dominates personal exposure: ambient airflow pattern or local human thermal plume. A computational fluid dynamics (CFD) method was employed in a downward ventilated room with a standing person below the supply grill. The research has taken into consideration the effects of room height, supply air opening area on the interaction. Results showed that the airflow was dominated by the downward jet from supply grill when the downward jet velocity was higher than high turning point of 0.275 m/s, but was dominated by the upward human thermal plume when the downward jet velocity was lower than low turning point of 0.075 m/s in the Case where room height is 2.7 m and supply air opening size is 0.6 m × 0.6 m. Dual steady flows were found when the downward jet velocity was between low and high turning point in the same case, indicating that the airflow pattern was determined by initialized airflow field with same boundary conditions. Besides, a higher downward jet velocity, larger air supply opening area and lower height were more likely to produce downward airflow pattern. This study may help to develop appropriate ventilation strategies to reduce personal exposure and save energy. [Display omitted] • Supply air velocity higher than high turning point downward jet dominates airflow. • Supply air velocity lower than low turning point thermal plume dominates airflow. • Supply air velocity between low and high turning points, dual solutions were found. • Both room height and supply area had significant impacts on multiple solutions. [ABSTRACT FROM AUTHOR]

The role of personalized ventilation (PV) in protecting against airborne disease transmission between occupants was evaluated by considering two scenarios with different PV alignments. The possibility that PV may facilitate the transport of exhaled pathogens was explored by performing experiments with droplets and applying PV to a source or/and a target manikin. The risk of direct and indirect exposure to droplets in the inhalation zone of the target was estimated, with these exposure types defined according to their different origins. The infection risk of influenza A, a typical disease transmitted via air, was predicted based on a dose-response model. Results showed that the flow interactions between PV and the infectious exhaled flow would facilitate airborne transmission between occupants in two ways. First, application of PV to the source caused more than 90% of indirect exposure of the target. Second, entrainment of the PV jet directly from the infectious exhalation increased direct exposure of the target by more than 50%. Thus, these scenarios for different PV application modes indicated that continuous exposure to exhaled influenza A virus particles for 2 h would correspond with an infection probability ranging from 0.28 to 0.85. These results imply that PV may protect against infection only when it is maintained with a high ventilation efficiency at the inhalation zone, which can be realized by reduced entrainment of infectious flow and higher clean air volume. Improved PV design methods that could maximize the positive effects of PV on disease control in the human microenvironment are discussed. • Role of personalized ventilation (PV) against airborne disease transmission is evaluated using droplets. • Interactions between PV and infectious exhalation can facilitate the transport of exhaled pathogens. • PV used for the infector increases indirect exposure to the exposed occupant. • Direct entrainment of an infectious exhaled flow by PV should be strictly avoided. • Infection risk is lowered when PV delivers clean air to inhalation without direct entrainment from infectious exhalation. [ABSTRACT FROM AUTHOR]

Highlights: [•] We carried out full-scale tests in a partly underground metro tunnel with one opening portal in Chongqing, China. [•] The maximum temperature and temperature distribution under the metro tunnel ceiling were investigated during the tests. [•] We conducted CFD simulations in the full-scale metro tunnel. [•] The smoke movement characteristic was analyzed under mechanical ventilation situations. [•] The evacuation routes decided by the operation modes of the emergency vents on the top of the tunnel were analyzed. [ABSTRACT FROM AUTHOR]

Abstract: Naturally ventilated dairy cattle buildings are a major source of ammonia and greenhouse gas emissions. Accurate estimation in gas emissions constitutes the first step towards reducing the negative impact of emissions on the local environment. The greatest uncertainty in the emission estimation from a naturally ventilated livestock building with large openings is the determination of the air exchange rate (AER) and the choice of the gas sampling positions for representative outlet gas concentration. To reduce the uncertainties in the emission estimation, the performances of three techniques – integrating volume flow rates (VFR), tracer gas decay (TGD) and constant tracer gas (CTG) for determination of ventilation rates were assessed in this paper by Computational fluid dynamics (CFD). In the developed CFD model, the animal occupied zone (AOZ) was treated as porous media and the resistance coefficient of porous zone was derived by pressure drops across AOZ using a sub-CFD model. The results showed that AERs predicted by VFR and TGD were in good agreement with each other within a large range of wind speeds. The large difference in AER estimation using CTG and VFR indicates that the mean CO2 concentration of the entire room may not represent the concentration at the air exit. It may be not suitable to calculate AER using mean concentration of internal sampling positions. When wind became stronger, the accuracy of CTG decreased. The gas sampling positions should be close to the openings or even in the openings; the gas sampling positions should be located adjacent to the openings or even in the openings. To reduce the uncertain introduced by wind direction, all the openings especially of different azimuths should possess sampling tubes. The maximum gas concentrations in the different openings could be the optimum value to represent the concentration in the exit air. [Copyright &y& Elsevier]