Stratum Ventilation Research Articles

Dynamic modelling of air temperature in breathing zone with stratum ventilation using a pulsating air supply

Transient thermal conditions in the breathing zone created by pulsating air supply, can improve thermal comfort compared with steady air supply under stratum ventilation. This study proposes a dynamic physical-empirical hybrid model for the transient air temperature in a stratum-ventilated classroom, concerning specific locations and dynamics in the breathing zone, accuracy to the second. The model is validated through experiments of four cases and twelve measurement points at the height of 1.1 m each case. The raw air temperature signal is divided into an approximation component maintaining the major fluctuations and a detail component representing the stochastic volatility, by a validated denoising structure using wavelet decomposition. Firstly, the dynamic model can accurately predict the raw air temperature, with the root mean square errors (RMSE) of 0.04–0.07 °C. Secondly, the rate of air temperature variation positively correlates to the air velocity variation between the idle/duty period and the steady state, as well as the supply air velocity deviation, with the Pearson correlation coefficient value of about 0.7 (p < 0.01). Thirdly, the dynamic models for the approximation component are consistent with that for the raw air temperature signal, with an improved coefficient of determination of 0.91–0.97, and the RMSE of 0.02–0.05 °C. The decomposition level is the key hyperparameter to denoise the air temperature signal for approaching the modelled value. Lastly, the first 20% of the approximation component is used to model the entire period, reducing measurement costs. The model performs well on accuracy, simplicity and robustness.

Evaluation of sidewall air supply with the stratified indoor environment in a consultation room

To take advantage of both stratum ventilation and displacement ventilation, while breaking some of their limitations, the sidewall air supply is introduced. Computational fluid dynamics simulations of 16 cases are conducted, to assess the application of the sidewall air supply in a consultation room, referring to thermal comfort, indoor air quality and energy utilization. Two supply air terminal layouts of the sidewall air supply (i.e., single-side supply and double-side supply), four supply air temperatures within 20–26°C, and five air change rates within 2.9–14.7 air changes per hour are applied. The results indicate that the sidewall air supply can provide satisfactory thermal comfort levels up to Category A in ISO 7730, with proper design. Using double-side supply reduces the draft rate by up to 25%, and improves the energy utilization coefficient and contaminant removal efficiency by up to 3.3 and 1.83, compared with the single-side supply. Additionally, for the single-side supply which achieves stratum ventilation, the closer the supply air jet center to the breathing zone, the higher the energy utilization coefficient and contaminant removal efficiency at the breathing zone are. Finally, the energy utilization coefficient and contaminant removal efficiency show a positive relationship for the sidewall air supply. This may be valid for the air distribution methods that provide stratified indoor environments. This study expands the application scenario of displacement ventilation and stratum ventilation, guides to obtain the best thermal comfort, energy utilization and contaminant removal performances simultaneously, while saving the measuring costs of indoor air quality.

Coughed droplet dispersion pattern in hospital ward under stratum ventilation

This study aims to investigate the characteristics of coughed droplet dispersion in hospital wards under stratum ventilation (SV). The dynamic dispersion process of the coughed droplets and the spatial distribution of the droplets in a two-bed ward under SV are investigated, considering the initial size and evaporation of the droplets. For SV, the supply air grilles are on the wall opposite the patients with the centre height at 1.5 m above the floor, the exhaust diffusers are on the lower part of the wall near the patients, and the air change rate is 12 ACH. For comparison, displacement ventilation (DV) and mixing ventilation (MV) are also discussed. The RANS-based RNG k-ε model is applied to solve the flow field. The Lagrangian approach is applied to solve the droplet motion. The exposure risk in the ward is less under SV because (a) The horizontal airflow leads to a strong deposition at the initial dispersion stage that decreases droplet concentration. With the infector in the supine and sitting positions, 68% and 49% of the coughed droplets are deposited on indoor surfaces in 10 s, respectively. (b) The air jet directly supplied to the breathing zone dilutes local droplet concentration. Compared with DV and MV, SV has better control over the 50 μm diameter droplet because the higher airflow velocity under SV could increase the deposition of the 50 μm diameter droplet. Controlling the droplet dispersion in the initial stage is more efficient to improve the infection control performance of SV.

Pollutant and heat removal of a small fire in a cinema hall by different ventilation systems

This paper investigates the effects of chair burning on the concentration of toxic gases and heat exhaust in a cinema hall. Different ventilation systems, including displacement ventilation (DV), impingement jets ventilation (IJV), stratum ventilation (SV), and hybrid ventilation (combination of displacement and stratum ventilation) were considered in this study. Large Eddy Simulation (LES) of the turbulent flows was performed using Pyrosim software. Concentrations of the toxic gases (CO and CO2) and the heat generated by the fire in the exit doors have been discussed in detail. Concentrations of the generated toxic gases from the fire in all three systems were within the permissible safe ranges. However, among the tested systems, displacement ventilation and impingement jet had better results. Displacement ventilation could decrease the concentrations of soot by 31%, CO by 16%, and CO2 by 11% rather than stratum ventilation. The maximum concentrations of CO and CO2 were 6.35 ppm and 335 ppm, respectively, in the displacement ventilation system. For the stratum ventilation, the concentrations of CO and CO2 were reported 7.5 ppm and 370 ppm, respectively. Using the displacement and the impingement jet ventilation systems, the heat exhaust from door #1 and door #2 are, respectively, 66.6%, and 96% lower than those obtained by the stratum ventilation system.

Energy performance index of air distribution: Thermal utilization effectiveness

The energy performance index is crucial for the energy-efficient design and operation of air distribution. Heat Removal Efficiency (HRE) is a widely used energy performance index, and Energy Utilization Coefficient (EUC) and Effectiveness of Heat Removal (EHR) are alternatives to HRE. This study justifies that these existing indices are unreasonable and incompetent as energy performance indices. This study also proposes a new index called Thermal Utilization Effectiveness (TUE) and verifies its efficacy as an energy performance index via theoretical analyses and experiments on stratum ventilation, displacement ventilation, and underfloor air distribution. EUC is not a suitable energy performance index since it does not consider the relative contributions of the occupied and unoccupied zones to the energy performance of air distribution. EHR cannot qualitatively distinguish the energy performance of air distribution because of its floating benchmark point. HRE cannot quantitatively distinguish the energy performance of air distribution because it unequally weighs the thermal energy of the air temperature of the occupied zone. TUE accounts for the relative contributions of the occupied and unoccupied zones to the energy performance with the help of the exit air temperature, qualitatively distinguishes the energy performance because of its two fixed benchmark points, and quantitatively distinguishes the energy performance by equally weighing the thermal energy of the air temperature of the occupied zone. Therefore, TUE overcomes the drawbacks of EUC, EHR, and HRE, and is a reasonable and competent energy performance index of air distribution.

Modelling indoor environment indicators using artificial neural network in the stratified environments

Ventilation methods that create stratified environments, e.g., stratum ventilation and displacement ventilation, can achieve a satisfactory indoor environment and energy saving. The indoor environment indicators in a stratified environment vary along the heights of a room, making it difficult to monitor and adjust the conditions around the occupants. This study selects the back-propagation (BP) model from artificial neural network (ANN) models to predict the energy performance presented by the energy utilization coefficient, thermal comfort presented by predicted mean vote (PMV) and draft rate (DR), and indoor air quality (IAQ) presented by air age and air change efficiency (ACE), using the air supply and exhaust temperatures. The prediction performances under both heating and cooling conditions are considered and compared. Forty cases by computational fluid dynamics (CFD) with different supply air parameters are conducted to collect data for ANN development. The results show that, the BP neural network model can predict the indoor environment indicators with high accuracy, while the linear regression model is not capable of it. The air velocity information is statistically redundant as input for indoor environment predictions under cooling operation, indicating internal relationships with other inputs. In contrast, it is statistically useful for improving the thermal comfort prediction accuracy under heating. Adding the genetic algorithm brings a small improvement for the indoor air quality prediction under heating. Validation using experimental data shows the robustness and generality for applying the developed ANN models in stratum ventilation and displacement ventilation with varied heat loads and room geometries.

Infection probability under different air distribution patterns

Infectious diseases have caused significant physical harm to humans as well as enormous economic losses over the years. Effective ventilation and distribution of fresh air could help to reduce indoor cross-infection. The computational fluid dynamics (CFD) method was used in this paper to investigate airborne transmission with seven different air distribution methods. The revised Wells-Riley model, which took into account the non-uniform air distribution generated with the methods, was used to calculate the infection probability in an office room shared by ten occupants for 4 h. One of the occupants was an infector. The significance of the infector's location was studied. The obtained infection probability was compared to that obtained in the case of complete air mixing, which is uncommon in practice. Under specified conditions of this study, personalized ventilation (PV) performed the best in terms of preventing cross-infection, followed by displacement ventilation (DV), impinging jet ventilation (IJV), stratum ventilation (SV) and wall attachment ventilation (WAV). The number of infected occupants was reduced below the number obtained under the complete mixing assumption by using these air distribution methods. Mixing ventilation (MV) and diffuse ceiling ventilation (DCV) exhibited the worst performance. In comparison to the case of complete mixing the infection probability for seven out of nine susceptible occupants was higher with MV and for all occupants in the case of DCV. In SV, the position of the infector had a clear impact on the infection probability of susceptible individuals. WAV may perform better in practice if the system is well designed. The location of the exhaust outlets had a significant impact on the infection probability for DCV.

Study on the impact of parallel jet spacing on the performance of multi-jet stratum ventilation

With the wide spread of novel coronavirus SARS-CoV-2 pandemic around the word, high quality indoor environment and more efficient mechanical ventilation become the new focus of scholars' attention. Stratum ventilation refers to the ventilation mode that the air supply port on the side wall slightly higher than the height of the working area directly sends fresh air into the working breathing area. As an efficient mechanical ventilation mode, it can create a more healthy and comfortable indoor environment. However, the impact caused by airflow characteristic under stratum ventilation on the thermal performance and indoor comfort is noteworthy due to its supply air outlets are close to the occupied zone. It is widely known that parallel turbulent jets are important for the flow structure and air distribution. Hence, an optimum parallel jet spacing (PJS) between two jet centerlines can obviously enhance the fluid interaction and indoor thermal comfort with low energy consumption. Therefore, this study aims to investigate the impact of the PJS on the performance of multi-jet stratum ventilation. A validated Computational Fluid Dynamics (CFD) model was used to conduct the year-round multivariate analysis. A total of eight PJSs, four inlet locations and five climate zones were discussed synthetically. Air distribution performance index (ADPI), ventilation effectiveness (Et) and economic comfort coefficient were employed as the evaluation indicators to assess the thermal comfort and energy efficiency in various scenarios. Research results indicated that the PJS showed different influences on the indoor thermal comfort and energy utilization efficiency as a result of cooperative effect including energy dissipation, air short-circuit probability, air distribution uniformity and airflow path. Combining with building energy simulation method, the optimum PJSs of stratum ventilation with different air inlet positions in five climate zones were obtained, which can help provide a comfortable indoor thermal environment and improve energy efficiency in a low-cost way. The data and conclusions presented in this study can supplement the theoretical basis for the actual applications of multiple-jet stratum ventilation used in an office.

Experimental and numerical analysis of air temperature uniformity in occupied zone under stratum ventilation for heating mode

In warm air heating systems, a good indoor air temperature distribution can provide a comfortable indoor environment and reduce energy consumption. Few studies were conducted for the uniformity of air temperature distributions under stratum ventilation (SV) for heating. In this study, the horizontal and vertical air temperature uniformities in an occupied zone were evaluated under SV heating mode. Different indoor thermal environments were created using both experiments and computational fluid dynamics (CFD) simulations. Results showed that the horizontal air temperature uniformity is generally inferior to the vertical direction. Based on the experimental and simulation cases, the maximum horizontal and vertical air temperature gradient is 3.46 °C/m and 2.44 °C/m, respectively. The uniformity of the air temperature distribution can be significantly affected by supply air parameters. The maximum extremum air temperature difference is 6.26 °C at the height of 0.6 m. However, it can be reduced to less than 0.62 °C by varying the supply air velocity, temperature and angle. Appropriate supply air parameters can provide an energy utilization coefficient (EUC) higher than one, showing the potentials of energy saving. A grey relational analysis revealed that the relational degree of the supply air velocity and temperature on the air temperature uniformity is relatively high, followed by the outdoor temperature and then supply vane angle. The results derived from this study can contribute to better understand the characteristics of indoor air temperature distribution under SV heating mode.

Experimental study of thermal comfort in a field environment chamber with stratum ventilation system in winter

Stratum ventilation has potentials to be used for winter heating. Both local and overall thermal perceptions are essential for ensuring indoor satisfactory thermal environments. This study aimed to comprehensively investigate the subjective perceptions in a field environment chamber heated by stratum ventilation. The chamber was configured as a two-row classroom. Eleven cases were conducted with supply air velocities of 0.8–1.4 m/s and supply air temperatures of 23–30 °C. With room air temperatures of approximately 20–24 °C, thirty-six subjects were recruited to evaluate the thermal environments. The questionnaires concerned overall thermal sensation and comfort (OTS and OTC), local thermal sensation and comfort (LTS and LTC), draft sensation, and humidity sensation. The results showed that the OTS conformed to Category C in ISO 7730. The overall discomfort was related to the OTS cooler than thermal neutrality. The LTSs of body segments fluctuated within the range of −0.7 – 0.7. Among the body segments, the head had the most significant influence on OTC, and followed by the feet. The percentage of dissatisfied due to discomfort of warm head and/or cold feet (PD) might exceed 10%, which was mainly resulted from the discomfort risk of cold feet. The relationship between PD and LTS of the feet indicated that with LTS of the feet higher than −0.5, the PD could be below 10%. With stratum ventilation for winter heating, the air movement was acceptable with draft rate less than 20%. However, the humidity environment remained to be improved by additional measures.

Study on the performance of interactive cascade ventilation oriented to the non-uniform indoor environment requirement

With the targets to achieve carbon neutrality and carbon emissions peak, numerous energy-saving and emission-reduction measures have been studied. In this study, a novel ventilation system named Interactive Cascade Ventilation (ICV) was proposed to save building energy consumption along with indoor thermal comfort satisfaction. A comparative experiment was conducted to compare this novel ICV with traditional stratum ventilation (SV) and mixed ventilation (MV). Draught rate (DR), temperature drop per unit cooling capacity (TDCC) combined with local coefficient of cooling capacity utilization (LCU) were introduced as the indices to comprehensively evaluate the thermal comfort and energy utilization. The results show that ICV, could enhance the local thermal comfort by 72.5% as compared to SV; improve TDCC by 23% and 30% as compared to SV and MV respectively; the lowest LCU of ICV confirmed that ICV has the strongest ability to control the local environment and delivers the most relative cooling capacity in the occupied area. The findings of this study confirm that ICV performs excellent in both indoor comfort and energy saving.

Optimization of air supply parameters for stratum ventilation based on proper orthogonal decomposition.

Under the current COVID-19 epidemic conditions, stratum ventilation can provide treated fresh air directly into the human breathing zone, improving the air quality for inhalation. However, in the design of air supply parameters for stratum ventilation, the traditional trial-and-error and experimental methods are inefficient and time consuming, and they cannot be used to identify the optimal air supply parameters from a large number of parameters. Therefore, in this paper, the inverse design method based on proper orthogonal decomposition (POD) was applied to the design of ventilation parameters for a room with stratum ventilation. Predicted mean vote (PMV), predicted percentage dissatisfied (PPD) and droplet nuclei concentration in the human breathing zone were selected as design objectives to optimize air supply parameters. The transmission of COVID-19 was controlled by reducing the concentration of droplet nuclei in the respiratory area. The results show that, compared with the trial-and-error method, the inverse design method based on POD is more than 90% faster. POD method can greatly expand the sample size. Considering the dispersion of exhaled droplet nuclei in the room, the appropriate stratum ventilation parameters can reduce the concentration of fine droplet nuclei by more than 20% compared with the traditional design parameters.

Decision-making analysis of ventilation strategies under complex situations: A numerical study

Current buildings are facing different environmental demands, such as improving thermal comfort and energy efficiency and reducing exergy loss. However, conventional mixing ventilation (MV) cannot satisfy the different demands; therefore, advanced ventilation modes utilizing a non-uniform environment have gained attention. Multiple scenarios with different occupant activity levels cause difficulties in ventilation control. For these multi-factor and multi-objective oriented problems, two issues exist: 1) how to change the operational mode when the scenarios and demands change simultaneously, and 2) how to evaluate the overall ventilation performance under different scenarios and demand conditions. Therefore, this study proposes an approach for assisting in the decision making of ventilation strategies in different scenarios under single or multiple demand conditions. Using a typical office, three occupancy conditions were predesigned by combining MV, displacement ventilation (DV), and stratum ventilation (SV) solutions. Computational fluid dynamics simulations were performed to calculate the indicators for a single demand, namely, heat removal efficiency (HRE), contaminant removal efficiency (CRE), air diffusion performance index (ADPI), and modified index of mixing (IOM*). In the case of multiple demands, the Z-score was applied for standardization and ranking. The result showed that different scenarios with different demand orientations require different ventilation modes. Taking the HRE and IOM* as objectives, DV performed best for the scenario of independent working, whereas SV performed best for discussion and meeting. When considering four demands simultaneously, SV performed best in the scenario of meeting, while MV performed best in the remaining scenarios. This study has verified the effectiveness of using a multi-indicator evaluation method for ventilation strategy optimization under multi-factor and multi-scenario conditions.

Sustainable Ventilation Strategies for a Medium-Sized Space with Regional Effect

The analysis of ventilation strategies is fundamentally affected by regional climate conditions and local cost databases, in terms of energy consumption, CO2 emission and cost-effective analysis. A systematic approach is covered in this paper to estimate a local economic and environmental impact on a medium-sized space located in two regions during supply-and-installation and operation phases. Three ventilation strategies, including mixing ventilation (MV), displacement ventilation (DV) and stratum ventilation (SV) were applied to medium-sized air-conditioned space with this approach. The trend of the results for three ventilation systems in the life cycle assessment (LCA) and life cycle cost (LCC) analysis is SV &lt; DV &lt; MV. The result of CO2 emission and regional LCC shows that SV is the lowest one in both regional studies. In comparison with the Hong Kong Special Administrative Region (HKSAR) during 20 Service years, the case analysis demonstrates that the percentage differences in LCC analysis of MV, DV &amp; SV in Guangdong are less than 20.5%, 19.4% and 18.82% respectively. Their CO2 emission of MV, DV and SV in Guangdong are more than HKSAR in 10.69%, 11.22% and 12.05%, respectively. The present study could provide information about regional effects in the LCA and LCC analysis of three ventilation strategies emissions, and thereby help set up models for decision-making on high efficiency and cost-effective ventilation strategy plans.

Effects of Supply Parameters of Stratum Ventilation on Energy Utilization Efficiency and Indoor Thermal Comfort: A Computational Approach

Stratum ventilation shows the significant potential on energy conservation and indoor thermal comfort under cooling applications. Yet, only limited researches focus on the thermal performance of stratum ventilation under heating condition. The heating and cooling operation characteristic of stratum ventilation is different due to the distinct airflow characteristics. Therefore, this paper investigated the parameters that affect energy utilization efficiency and indoor thermal comfort under heating condition served by stratum ventilation via CFD simulations approach. The supply air parameters included temperature, airflow rate, angle, and return air outlet positions. The evaluation indicators adopt ventilation effectiveness and effective draft temperature (EDT) for assessing the energy utilization efficiency and indoor thermal comfort served by stratum ventilation under heating condition. The results demonstrated that, under the heating mode of stratum ventilation, different effects on the thermal performance were made by the mentioned parameters. The ventilation effectiveness was higher when the air supply temperature is 26°C, airflow rate is 7 air change per hour (ACH), and the air supply angle is 45°. The EDT range of the occupied zone is closest to zero K when the air supply temperature is 28°C, airflow rate is 12 (ACH), and the air supply angle is 60°. The related conclusions obtained from this study provide the theoretical basis for the stratum ventilation design and promote its heating application.

Determining optimal parameter ranges of warm supply air for stratum ventilation using Pareto-based MOPSO and cluster analysis

Energy-efficiently creating comfortable and healthy indoor environment is required as people spend the majority of their time indoors. As a novel air distribution method, stratum ventilation (SV) has been demonstrated to be potentials for winter heating. This study aimed to derive out the optimal ranges of supply air temperature and velocity so as to achieve both energy-efficient thermal comfort and stable operation of the environmental control system for the heating applications of SV. Experiments with six cases were firstly conducted in a field experimental chamber to examine the influence of warm supply air on indoor airflow pattern as well as indoor thermal environment. The results revealed that the supply air temperature and velocity affected thermal comfort and energy efficiency inconsistently, which were measured by predicted mean vote (PMV), vertical air temperature difference between head and ankle levels (ΔT), draft rate (DR), and energy utilization coefficient (EUC). Then, using numerical simulations validated through the experiments, 42 cases with combinations of six different supply air velocities and seven different supply air temperatures were analyzed. The supply air temperatures and velocities were optimized using Pareto-based multi-objective particle swarm optimization (MOPSO). The results revealed that the locations of the 25 Pareto optimal solutions got by MOPSO were isolated in their value spaces. Thus, cluster analysis was used to obtain the optimal ranges of the warm supply air. The optimal ranges of warm supply air temperature and velocity for SV were 28.2–28.5 °C and 1.54–1.66 m/s, respectively.

Energy and exergy analyze of different air distributions in a residential building

To improve the living and sleeping quality for human beings, air conditioning is widely applied to maintain a comfortable indoor environment in bedrooms. However, most current air conditioning methods in bedrooms are based on mixing ventilation, which is low efficiency due to the uniform environment created by this ventilation method. In this study, stratum ventilation is introduced applied in a sleeping environment to improve ventilation performance. To better analyze the application potential of stratum ventilation, three ventilation methods are compared, including mixing ventilation, displacement ventilation and stratum ventilation. Based on computational fluid dynamics technology, the energy and exergy efficiency of the three air distribution methods are conducted and compared. The results show that stratum ventilation provides a nonuniform environment both in the vertical and horizontal directions in a typical sleeping environment with a higher energy and exergy efficiency than the mixing ventilation and displacement ventilation. When the predicted mean vote value in the occupied zone equals zero, energy consumption and exergy loss of stratum ventilation reduce 10% and 15.6% in comparison with mixing ventilation respectively. The energy consumption difference of stratum ventilation and displacement ventilation is not significant, but the exergy loss reduces 6.2%, with the predicted mean vote equals zero in the occupied zone. In addition, the energy utilization coefficients of stratum ventilation, displacement ventilation and mixing ventilation are 1.3, 1.03 and 0.89 respectively. The results show that stratum ventilation has a high potential for energy-saving in a sleeping environment.

Experimental investigation of airflow pattern and turbulence characteristics of stratum ventilation in heating mode

Stratum ventilation (SV) is feasible for heating applications. Owing to the downward supply vane angle and positive thermal buoyancy, the airflow characteristics of SV for winter heating can be distinct from those for summer cooling. This study aimed to investigate the airflow pattern and turbulence characteristics in a field environment chamber heated by SV experimentally. Twelve cases were studied with the room air temperature controlled between 19.9 and 24.3 °C. Air velocities and temperatures in the occupied zone were measured. Based on the measurements, draft risk (DR) and vertical air temperature difference between head and ankle levels (ΔT) were evaluated. The results show that the warm supply air jets were initially delivered to the zone below 1.1 m, but gradually ascended to the upper zone owing to the effect of positive thermal buoyancy. Consequently, the heights where the highest air velocity and temperature were measured varied with the distance from the supply inlets. As a result of the airflow pattern, the re-separation phenomenon of velocity spectra at different heights was observed at the far field from the inlets. These characteristics were different from those of SV for summer cooling. The airflow pattern illustrated that SV could warm the occupied zone efficiently, especially when the Archimedes number was less than 0.045. An appropriate reduction in the supply air temperature is recommended to achieve satisfactory local thermal comfort with ΔT and DR values conforming to the comfortable ranges as stipulated in ISO 7730–2005.

Reducing the exposure risk in hospital wards by applying stratum ventilation system

In order to improve the ventilation design for hospital wards and protect the healthcare workers from respiratory infections, stratum ventilation is proposed to reduce the exposure risk. A numerical (CFD) approach is applied to investigate contaminant distribution in a two-bed hospital ward with two patients and one healthcare worker under stratum ventilation, mixing ventilation, downward ventilation and displacement ventilation. Tracer gas (CO2) is also applied to simulate the exhaled and coughed contaminants by patients. The patients are in positions of lying or sitting in bed. The contaminant concentration distributions and contaminant removal effectiveness under the different air distributions are compared. The results show that under stratum ventilation, with two patients breathing, the contaminant concentration in the breathing zone (1.3–1.7 m above the floor) is comparably lower, the contaminant removal effectiveness is relatively higher. The contaminant concentration at different moments after a patient's cough is also compared. The results show that the coughed contaminant is diluted quickly under stratum ventilation, and the high concentration spot is substantially reduced. The results show that stratum ventilation minimises the exposure risk of healthcare workers in hospital wards.

Multi-indicator evaluation on ventilation effectiveness of three ventilation methods: An experimental study

Enhancing ventilation effectiveness can improve indoor air quality (IAQ). Both contaminant removal effectiveness (CRE) and air change effectiveness (ACE) are widely used to evaluate ventilation effectiveness. They reflect two different aspects of IAQ, and an analysis based exclusively on ACE or CRE has important limitations. Firstly, this study is to evaluate the overall IAQ integrating ACE and CRE by using multi-indicator methods. Secondly, this study is to find out an indicator to best characterize the overall IAQ. Twenty-four experiments with different combinations of three ventilation methods (i.e. mixing ventilation (MV), displacement ventilation (DV) and stratum ventilation (SV)), four air exchange rates and two point pollutant source locations are conducted in a simulated office. Three multi-indicator methods are applied and compared, including Z-score method, Rank Sum Ratio method, and Technique for order preference by similarity to an ideal solution (TOPSIS). The results show that, for ACE, in the occupied zone, DV performs best with the values of 0.76–0.84; in the breathing zone, SV performs best with the values of 1.21–1.35. For the overall IAQ, in the occupied zone, DV performs best (ranking in the top 4–33%), followed by SV (ranking in the top 38–92%), and then MV (ranking in the top 50–100%); in the breathing zone, SV performs best (ranking in the top 8–54%), followed by DV (ranking in the top 4–79%), and then MV (ranking in the top 58–100%). All the three evaluation methods indicate that CRE is more representative than ACE for measuring overall IAQ.