The strong flow field in a hoistway will cause a significant piston effect during the operation of high-speed/ultra-high-speed elevator. Thus, studying the airflow in the hoistway and the reasonable ...opening of ventilation holes is important. First, a three-dimensional geometric model of the ventilation holes (VHs) and elevator car was established. Based on this model, a multi-region dynamic layering method was proposed. The movement of the unsteady airflow in hoistways with different numbers of VHs and the interaction between the VHs were then analyzed. The correctness of the numerical simulation method was verified by comparing the results of the simulation, experiments and theoretical calculations. Finally, the influence of the number, location and cross-sectional area of the VHs on the airflow movement was analyzed, and the optimal opening positions of one and two pairs of VHs were discussed. The results showed that the variations of the number, location and cross-sectional area of the VHs had a significant influence on the airflow movement. According to the quantitative analysis of the ventilation efficiency, the optimal positions of one and two pairs of VHs were located in the middle of the hoistway and the upper and lower sides of the middle position, respectively.
One of the major challenges in modern buildings is to guarantee healthy indoor air quality and excellent thermal comfort in an energy efficient manner. In this study, the performance of a ...micro-environment system combined radiant panel and convective flow was designed and compared to an all-air diffuse ceiling ventilation (DCV) system. In the analyzed micro-environment system of personalized ventilation and radiant panel (PVRP), two local personal air terminal devices supplied clean air directly to occupants. The radiant panels were used to satisfy the required cooling load. The results show that the air change efficiency with the PVRP was over 60% which was better than the fully mixing flow (50%). The mean age of air of personalized airflow system was smaller at the micro-environment near the workstation than the DCV despite the airflow rate was much lower. Furthermore, the air temperature near the workstation can be maintained at designed value with the PVRP and the draught rate can be kept at acceptable level. Furthermore, the vertical temperature difference did not cause thermal discomfort with the PVRP system near the workstation.
•Comparison of personal ventilation with radiant panel (PVRP) and all-air system.•The perimeter exhaust over window increases heat removal efficiency.•The air change efficiency with PVRP is over 60%, much higher than fully mixed flow.•The temperature difference between occupied and exhaust could be 0.6°C with PVRP.•The draught risk remains at acceptable level at occupied zone with PVRP.
Unsteady airflows lead to better mixing in ventilated enclosures, facilitating indoor pollutant dispersion and exhausting. In this study, an air jet ventilated enclosure and its flow characteristics ...were investigated using experimental measurements and computational fluid dynamics simulations, focusing on the quasi-periodic fluctuation of the airflow field and the advantages of such an oscillation pattern for the ventilation efficiency. Starting from a non-converged Reynolds-averaged Navier–Stokes (RANS) simulation, we then used the unsteady RANS method (URANS). As validated by sampling the high-frequency velocity data of representative positions in the jet-ventilated space, the URANS results reflected the unsteady flow characteristics more precisely than the RANS results, further confirming that the supply jet air swung up and down quasi-periodically. The ventilation performance of such an actual quasi-periodic airflow was evaluated by purging a gaseous pollutant from the enclosure, and the results were compared with those in the average steady-state airflow field to showcase the different performance of the unsteady ventilation system.
•Different ventilation methods were evaluated experimentally for road vehicles.•Ventilation efficiency was quantified through aerosol measurements.•The risk of infectious respiratory disease was ...estimated for various scenarios.•Moving vehicles with all windows open had the greatest infection risk reduction.
This study experimentally measured the ventilation efficiency in road vehicles. Two air circulation methods, air conditioning and opening windows, were considered and their ventilation efficiencies were measured for a sedan and a cutaway bus. The ventilation efficiencies have been evaluated by measuring the aerosol concentration parameter at different locations inside the vehicle. For both vehicles, any of the ventilation scenarios significantly increased the air exchange rate. The best performance was shown when all windows were open in a moving vehicle. As an illustration of using the obtained measurements, respiratory infection probability was calculated using the Wells-Riley model. Any of the ventilation cases significantly decreased the infection risk. The ventilation efficiency and infection probability were highly dependent on the air circulation method and vehicle type.
This paper deals with the numerical investigation of heat transfer by mixed convection inside ventilated cavities with supply and exhaust slots, and filled with air under a steady and turbulent flow ...regime. Four configurations, rated A, B, C and D are considered here, according to the position of the inlet and outlet air ports: A, the inlet is on the top of the left vertical wall, while the outlet is on the bottom of the right vertical wall; B, the inlet is on the bottom of the left vertical wall and the outlet at the top of the opposite wall; C, the two slots are on the same side, i.e. the inlet is at the bottom and the outlet at the top of the left vertical wall, and D, the inlet is at the top and the outlet at the bottom of the left vertical wall. The bottom of the cavity is kept at a temperature TH and other walls are fixed at a temperature TC, with TH>TC. The cavity is provided with two slots: an inlet slot for introducing fresh air, and an outlet slot to extract hot air. The main aim sought here is to analyze the ventilation efficiency for temperature distribution, and fix the best configuration providing the thermal comfort targeted. We also address the influence of heating on the behavior of flow and thermal comfort, while considering different Rayleigh numbers ranging from 6.4×108 to 3.2×109. Numerical studies have been yet devoted to these configurations, using RANS simulations. The RNG k-ε turbulence model has been adopted for the turbulence closure, and the set of governing equations was then numerically solved via the finite volume method. The SIMPLEC algorithm was associated to ensure the pressure-velocity coupling. In terms of results achieved, the configuration D provides a better ventilation effectiveness for temperature distribution εT and ensures an even temperature in the occupied zone. As for configurations A and C, they maintain an acceptable level of heat and can be used in winter period to ensure good indoor air quality, while configuration B provides an efficiency close to unity and can be used to insure indoor air quality in temperate climate zones.
•Intensity of mixed convection causes variations in the heat transfer and the ventilation effectiveness for the thermal field.•Rise of Rayleigh number speed up the flow and improves the homogenization of flow.•Input and output locations significantly influence heat transfer and ventilation efficiency.•Proven assessment of the numerical model to handle the mixed convection in ventilated cavities.
The transmission of coronavirus disease 2019 (COVID-19) has presented challenges for the control of the indoor environment of isolation wards. Scientific air distribution design and operation ...management are crucial to ensure the environmental safety of medical staff. This paper proposes the application of adaptive wall-based attachment ventilation and evaluates this air supply mode based on contaminants dispersion, removal efficiency, thermal comfort, and operating expense. Adaptive wall-based attachment ventilation provides a direct supply of fresh air to the occupied zone. In comparison with a ceiling air supply or upper sidewall air supply, adaptive wall-based attachment ventilation results in a 15%–47% lower average concentration of contaminants, for a continual release of contaminants at the same air changes per hour (ACH; 10 h−1). The contaminant removal efficiency of complete mixing ventilation cannot exceed 1. For adaptive wall-based attachment ventilation, the contaminant removal efficiency is an exponential function of the ACH. Compared with the ceiling air supply mode or upper sidewall air supply mode, adaptive wall-based attachment ventilation achieves a similar thermal comfort level (predicted mean vote (PMV) of −0.1–0.4; draught rate of 2.5%–6.7%) and a similar performance in removing contaminants, but has a lower ACH and uses less energy.
The total energy consumption of buildings in China has been increasing year by year, ventilation energy consumption accounts for more than 20% of the total building energy consumption. The ...optimisation of ventilation system design aiming at energy conservation is of great significance while keeping healthy indoor air quality. However, the current codes and standards are still lacking specification requirements for vents design, e.g. inlet size ratio or position, which can greatly impact on indoor airflow and ventilation efficiency. In this work, we investigated the aspect ratios of vent inlets and their locations on indoor air quality. Both experimental and numerical simulation methods were adopted. Ventilation efficiency is represented with the local average peak concentration 〈C ̅*〉A,max. Results showed that when vent inlet is in symmetric conditions (i.e. located in the middle of the sidewall) and the aspect ratio between the length and width of the vent inlet equals to 4, ventilation removal efficiency showed the best performance. These findings are of great importance to the engineering applicability and able to provide reference for future design standards.
•The transportation time of the inhaled chemical in airway model was investigated.•Two indexes were introduced to quantify the ventilation efficiency in upper airway.•The variation of the ventilation ...efficiency with the flow rate was discussed.•The long regional staying time of inhaled chemical suggests the high potential of the surface adsorption.•The transportation time could aid in assessing the potential impact of the inhaled chemicals on human health.
The present numerical study investigated the transportation time of the inhaled chemicals in three realistic human airway models by adopting a methodology from the field of the building ventilation. Two indexes including “scale of ventilation efficiency 3 (SVE3)” and “local purging flow rate (L-PFR)” were used to evaluate the respective arrival time and staying time under different inhalation flow rates. The general trend of the SVE3 was predicted as expected and the exceptions within the nasal cavities were attributed to the uneven allocation of the inhaled flow between the internal channels and the formation of the vortex circulation therein. The complicated situation of the L-PFR was also explained by the structure constrains. Moreover, the variation of the two indexes with the flow rate was sensitive to the inter-subjective differences but the distribution pattern was not changed significantly. By combining the SVE3 and L-PFR, it could help with assessing the potential effect of the inhaled chemicals on the human health for engineering applications to which the relative impacts are more interested than the absolute value. But for the precise evaluation regarding a specific chemical, comprehensive simulation is still necessary with the surface adsorption included under realistic respiration cycles.
This research attempts to probe into the correlation between the residential building layout and ventilation performance of various spaces in an operative level. To quantify the influence of design ...change on outdoor ventilation, numerical modeling technology is adopted with ANSYS-Fluent as the simulation tool. As to evaluate the ventilation efficiency of exterior space, local mean age of air (L-MAA), which is common used in recent urban form studies, is further discussed for local region's ventilation efficiency in residential neighborhoods. Using this ventilation index, several cases are calculated and three types of building layout changes (lateral spacing, building lengths and stagger of location) are discussed. The simulation results show that L-MAA is a useful ventilation index to access the design changes on urban space ventilation and these design changes have great effects on exterior space ventilation. Building length has great influence on ventilation efficiency of different spaces, while the influence of lateral spacing and stagger of location changes varies greatly in different local regions.
Heating, ventilating, and air‐conditioning (HVAC) systems usually supply air, which is a mixture of fresh air from the outdoor environment, and return air from rooms via the ventilation ductwork. ...This air reduces the heat load and cost impact of air conditioning using outdoor air. This recirculation of room air in air‐conditioning systems is reasonable in terms of energy saving; however, the deterioration of air quality might be a concern because of the recirculation of contaminated room air. Here, we numerically investigate the effect of pollutant recirculation/return on the formation of concentration distributions of local pollutants in indoor environments when the mixing ratio of recirculated air in the HVAC system changes. We discuss the detailed structure of the formation mechanism of local pollutant concentration distributions using various indices for indoor ventilation efficiency in simplified room models. Among the indices, visitation frequency and net escape probability are the ones that directly assist in evaluating the recirculation/return characteristics of indoor pollutants. As a result, when the proportion of air that is recirculated becomes large, the number of pollutants returning to a target local domain, the visitation frequency, increases exponentially, and the net escape probability—which directly expresses the probability of pollutant discharged from the target domain—is close to zero.
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