Air Diffusion Performance Index Research Articles

Numerical Study of Air Distribution and Thermal Environment in Attached Ventilation Mode in the Generator Layer of a Hydropower Station

Because they are in enclosed underground buildings, the generator layers of hydropower stations have limited ventilation. In order to reduce the influence of a hot and humid environment on equipment and staff health and create a good thermal environment with good air quality for underground buildings, in this paper, vertical wall-attached ventilation was combined with the generator layer of a hydropower station to replace traditional ventilation. The influence of air supply velocity, air supply outlet position, and the opening mode of the generator layer on indoor velocity and temperature field distribution were analyzed via numerical simulation, and the evaluation indices of different cases were also compared. In the single-sided vertical wall-attached ventilation mode, when the velocity was increased from 4 m/s to 8 m/s, the maximum increment in the energy utilization coefficient was 41%, and the maximum reduction in the velocity non-uniformity coefficient was 9.5%. The results show that the single-sided mode can offer a higher ventilation efficiency than the double-sided mode, with a higher energy efficiency and a more uniform air distribution. Based on the mean temperature and velocity, and the key evaluation indices (head-foot temperature difference, percentage of dissatisfaction, non-uniformity coefficient, energy utilization coefficient, and air diffusion performance index), it is suggested that the single-sided air supply mode should be adopted for this kind of tall building, with an air supply velocity of v = 6 m/s and two open air supply outlets at each interval.

Impact of Diffuser Location on Thermal Comfort Inside a Hospital Isolation Room

Thermal comfort is increasingly recognized as vital in healthcare facilities, where patients spend 80–90% of their time indoors. Sensing, controlling, and predicting indoor air quality should be monitored for thermal comfort. This study examines the effects of ventilation design on thermal comfort in hospital rooms, proposing four distinct ventilation configurations, each with three airflow rates of 9, 12, and 15 Air Changes per Hour (ACH). The study conducted various ventilation simulation scenarios for a hospital room. The objective is to determine the effect of airflow and the diffuser location distribution on thermal comfort. The Reynolds-Averaged Navier–Stokes (RANS) equations, along with the k–ε turbulence model, were used as the underlying mathematical representation for the airflow. The boundary conditions for the simulations were derived from the ventilation standards set by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) and insights from previous studies. Thermal comfort and temperature distribution were assessed using indices like Predicted Percentage Dissatisfaction (PPD), Predicted Mean Vote (PMV), and Air Diffusion Performance Index (ADPI). Although most of the twelve scenarios failed to attain thermal comfort, two of those instances were optimal in this simulation. Those instances involved the return diffuser behind the patient and airflow of 9 ACH, the minimum recommended by previous studies. It should be noted that the ADPI remained unmet in these cases, revealing complexities in achieving ideal thermal conditions in healthcare environments. This study extends the insights from our prior research, advancing our understanding of ventilation impacts on thermal comfort in healthcare facilities. It underscores the need for comprehensive approaches to environmental control, setting the stage for future research to refine these findings further.

Assessment of COVID-19 infection Risk, thermal Comfort, and energy efficiency in negative pressure isolation wards with varied ventilation modes

Negative pressure isolation wards (NPIWs) play a crucial role in providing care to COVID-19 patients during a pandemic. However, the exhalation of patients releases aerosols containing pathogens, posing a potential infection risk for healthcare workers (HCWs). While robust ventilation systems within NPIWs can help mitigate this risk, they may also lead to increased energy consumption and reduced thermal comfort for patients. Therefore, it is imperative to strike a delicate balance between HCW safety, patient comfort, and energy efficiency when optimizing airflow within NPIWs. This study introduces TARGETING, a novel index designed to assess the efficiency of aerosols removal of ventilation systems in NPIWs. The primary goal of TARGETING is to enhance the precision of ventilation systems, consequently reducing the required air changes per hour (ACH) and minimizing energy consumption. The research delves into the impact of various supply air parameters, including ACH and temperature, as well as different ventilation modes. Through a comprehensive evaluation utilizing an array of metrics such as the Air Diffusion Performance Index (ADPI), Predicted Mean Vote (PMV), TARGETING, infection risk assessment, and energy consumption estimation measured by cooling load (Lcool), this study employs an Analytic Hierarchy Process to assess the aforementioned indices. The findings highlight that air curtain ventilation (ACV) emerges as the most favorable choice, delivering comprehensive benefits, including an infection risk of less than 0.03%, an ADPI score of 90.2%, a PMV close to zero, TARGETING at 1.3, and energy savings ranging from 35.1% to 57.3%.

Experimental Study of Indoor Air Distribution and Thermal Environment in a Ceiling Cooling Room with Mixing Ventilation, Underfloor Air Distribution and Stratum Ventilation

A ceiling cooling system integrated with a mechanical ventilation system has been widely used in modern buildings with large sensible cooling loads due to the high thermal comfort level and large energy efficiency. However, there is a lack of systematic research on the influence factors such as ceiling surface temperature and cooling load on the indoor air distribution and thermal environment, and the impact of ventilation system type in the ceiling cooling room is still unclear. Therefore, this paper presented an experimental study of indoor air distribution and thermal environment in a ceiling cooling (CC) room with mixing ventilation (MV), underfloor air distribution (UFAD) and stratum ventilation (SV); the ceiling surface temperature was 17 °C–26 °C and the internal or external cooling load was 41.5 W/m2–69.5 W/m2. The results showed that the vertical air temperature difference and contaminant removal effectiveness were 0.2 °C–0.4 °C and 0.53–0.85 with CC + MV, 0 °C–1.2 °C and 0.68–1.25 with CC + UFAD and 0.3 °C–0.9 °C and 0.50–0.83 with CC + SV, and the corresponding heat removal effectiveness and air diffusion performance index were 0.96–1.11 and 96–100%, 0.9–1.5 and 57–100% and 1.11–1.34 and 71–100%, respectively. Moreover, the difference between mean radiant temperature and air temperature and the predicted mean vote of thermal sensation were from 0 °C to 0.9 °C and between 0 and 0.26 with CC + MV, from −0.1 °C to 2.2 °C and between −0.1 and 0.42 with CC + UFAD and from −0.1 °C to 0.9 °C and between −0.2 and 0.13 with CC + SV. Hence, the ventilation system type clearly affected the indoor air distribution and thermal environment in the ceiling cooling room, and the experimental results would be beneficial for the design and control of a ceiling cooling system combined with a mechanical ventilation system in practice.

Evaluation of heating performances of different ventilation methods in an office

In this study, 12 cases were investigated in an office-layout room using experiments and computational fluid dynamics (CFD) simulations. The heating performances of four ventilation methods (i.e. mixing ventilation (MV), stratum ventilation (SV), deflection ventilation (DeV) and impinging jet ventilation (IJV)) were comprehensively compared by various evaluation indexes (i.e. predicted mean vote (PMV), draught rate (DR), vertical air temperature difference (△T), air diffusion performance index (ADPI), energy utilization coefficient (EUC), air change efficiency (ACE) and contaminant removal efficiency (CRE)). Better thermal comfort was found in rooms heated by SV and DeV. The PMV, DR and △T under SV and DeV complied with Category B of ISO 7730:2005, and the ADPI was in full compliance with the stipulation of ANSI/ASHRAE 113-2022. For the energy-saving characteristic, the targeted-occupied-zone ventilation methods (i.e. SV, DeV and IJV) can effectively deliver warm air to the occupied zone, with the EUC values higher than unity and thus providing a good potential for energy saving. SV and IJV showed slightly higher ACEs in the breathing zone. The contaminant removal effectiveness of SV, DeV and IJV was comparable. Under the combined influence of occupant thermal plumes and locations of exhausts, MV showed a high CRE. However, the CRE under MV decreased significantly when the exhausts were not above occupants. In the case of supply air parameters in this study, the entropy-weight method indicated that DeV and SV had a better overall performance for winter heating, followed by IJV and then MV.

Sensitivity analysis of indoor air distribution performances in an office room with ceiling cooling and mechanical ventilation

A hybrid system with a ceiling cooling (CC) system and a mechanical ventilation system has been extensively applied in modern office buildings with large sensible cooling loads. Both the chilled ceiling and supply air may greatly influence indoor air distribution in the office room. Therefore in this paper, indoor air distribution performances in a ceiling cooling room with underfloor air distribution (UFAD) or mixing ventilation (MV) were sensitively analyzed by numerical simulation. Indoor air distribution performances, which were evaluated by the heat removal effectiveness, contamination removal effectiveness and air diffusion performance index, were quantitatively analyzed by using the orthogonal experiment method. The results showed that when the supply air temperature was 18 °C-24 °C for CC + UFAD and 16 °C-21 °C for CC + MV, the heat removal effectiveness changed by 0.01 with 1 °C increment of supply air temperature or ceiling surface temperature, and the contamination removal effectiveness increased by 0.001-0.002 with 1 W/m2 increment of external sensible cooling load. Moreover, the air diffusion performance index increased by 0.6%-1.1% with 1 °C increment of supply air temperature, and it decreased by 0.02% with 1 W/m2 increment of internal sensible cooling load. Finally, formulas of heat removal effectiveness, contamination removal effectiveness and air diffusion performance index for CC + UFAD and CC + MV were obtained by fitting, and they may provide guidance for the optimal design and control of a hybrid system with a ceiling cooling system and a mechanical ventilation system.

An active diffuser control method based on the constant jet throw for improving airflow distribution in variable air volume systems

The air supply of the variable air volume (VAV) system could decrease with indoor load, resulting in reduced indoor comfort. An active diffuser is a good solution, but its adjustment process is often neglected. In most cases, the diffuser maintains the air supply velocity constant by controlling the air supply area. This traditional control method based on constant velocity (CMV) often fails to reach jet throw expectation due to the continuous change of airflow diffusion performance during the adjustment process. In this study, a new control method based on constant jet throw length (CMT) is proposed and applied in two typical rooms (office and conference). The results show that the CMT could increase the throw length in the spreading zone and enhances the airflow at the wall zone and ground zone, providing a more uniform temperature and more comfortable indoor environment. In 40% air volume condition, the air diffusion performance index (ADPI) in the office using CMT has improved from 89.66% to 95.69% compared to CMV, while ADPI in the conference improved from 92.11% to 97.37%. This study can help designers determine the optimal adjustment scheme to improve the adaptability of the active diffuser to the VAV system.

Effect of Air Inlet Spacing on Air Distribution and Ventilation Performance of Stratum Ventilation Using Multiple Parallel Jets

An appropriate layout of air terminals can improve the thermal comfort and air quality for room occupants. Stratum ventilation (SV) can efficiently provide thermal comfort and quality of inhaled air. However, investigations into the impact of the supply air inlet spacing on performance under SV are lacking. This study conducted experimental measurements and numerical simulations to analyze the effect of the supply inlet spacing on the air distribution and ventilation performance of the SV. Six theoretical axial velocity attenuation formulas were verified using experimental results. The effective draft temperature for SV (EDTS), air diffusion performance index (ADPI), the local mean age of air (LMAA), and energy utilization coefficient (EUC) were used as the evaluation indexes. The results indicated that the modified Abramovich formula was the most suitable for predicting the attenuation of the axial velocity of multiple parallel jets under SV. At an air supply spacing of 650 mm, the position near the central air supply inlet experienced a cold thermal environment with high air velocity and low air temperature; the positions on both sides of the room were warmer owing to insufficient airflow. The air distribution at these positions improved with increasing air inlet spacing, but some areas could not be covered by the supply airflow. The optimal value of ADPI corresponded to an air inlet spacing of 800 mm, whereas optimal LMAA and EUC corresponded to a spacing of 950 mm. Analysis of a multi-objective optimization method indicated that an air inlet spacing of 800 mm provided optimal overall performance.

Experimental study of air distribution and heating performances of deflection ventilation

Deflection ventilation uses a purposely-designed deflector to divert supply air jet into the occupied zone directly. A few numerical studies have shown good indoor air quality with deflection ventilation. However, there was a lack of research on thermal comfort, which is also important to ensure human wellbeing. This study conducted experimental measurements when deflection ventilation was operated for winter heating. Eleven cases with different supply air velocities, supply air temperatures and deflection angles were carried out in an office-layout experimental chamber. As a comparison, another case with mixing ventilation was also measured. The predicted mean vote (PMV), draft rate (DR), air diffusion performance index (ADPI) and energy utilization coefficient (EUC) were adopted to evaluate the heating performances. The results showed that the deflection angle played a decisive role on air distribution. An inclined deflector (deflection angle: 35° downward) could elevate air temperature in the lower occupied zone as compared with a horizontal deflector (deflection angle: 0°), which provided efficient air distribution for winter heating. The average PMV values were in the range of −0.7 – 0.5, and the values of DR and ADPI in the occupied zone were typically less than 20% and higher than 80%, respectively. According to ISO 7730 and ASHRAE 113, deflection ventilation achieved satisfactory indoor environment with regard to thermal comfort. The EUC was typically greater than unity, indicating high energy efficiency of deflection ventilation, especially for the cases with deflection angle of 35°. In comparison with mixing ventilation, deflection ventilation can provide better thermal comfort as well as energy efficiency.

An investigation of a nonthermally insulated mixing ventilated office room for partitioning in hot and dry climate by simulation approach

AbstractDue to the recent situation, especially since the beginning of the spread of COVID‐19, work in administrative or service offices under conditions of social divergence and the working environment has become conditional on the ventilation system; thus, enhancing ventilation's function to minimize the spread of infections, and impurities to larger areas or limiting its transition from one employee to another who work in the same place for long hours. A nonisothermal office room, designed with a mixing ventilation system has been simulated by using AIRPAK3.0.16 software, and RNG k– as a turbulence model, where the adoption of partitions in such rooms was studied and its effect on thermal employee's comfort and quality of fresh air, by monitoring the air diffusion performance index, prediction of the mean vote, and percentage of predicted dissatisfied. The main findings were that partitions are seen as a technique of preventing and protecting against the spread of pollutants and illnesses since they prevent contaminants from reaching the breathing zones of the office's inhabitants. It was noted that the change in the height of the partition with an increase of 10% of the room's height as a gap, gives a more acceptance value of the heat removal efficiency and ventilation rate.

Decision-making analysis of air supply strategies for high rack cold stores

The thermal performance of a high rack cold store is related to the quality of fresh fruit and vegetable preservation. As the complex air supply strategies, a comprehensive evaluation of the thermal and airflow performance needs more than one demand. Therefore, the Z-score method was used to evaluate the thermal and airflow performance of the high rack cold store in this paper. The Z-score considered the energy utilization coefficient, non-uniformity coefficient and Air Diffusion Performance Index (ADPI). Firstly, a numerical simulation model of a high rack cold store was developed and validated. The effects of air supply form, air supply angle and air supply velocity on thermal performance and flow properties were then investigated. The velocity, temperature and pressure distribution were analyzed. Based on the previous data, the air supply strategies of the high rack cold store were evaluated with the proposed Z-score method, and the results proved that it could be utilized as the multi-indicator comprehensive analysis method for the high rack cold store. The cooling effect and the thermal uniformity of the vertical wall attached ventilation was excellent in a high rack cold store. When the air supply angle is −90°, the high rack cold store has a more uniform and reasonable temperature field. Considering the energy consumption of fans, the optimal air supply velocity was 11.7 m·s−1. Those results could provide a reference for the design of air supply form in the high rack cold store.

Ventilation impacts on infection risk mitigation, improvement of environmental quality and energy efficiency for subway carriages

Subway carriages are enclosed for extended periods of time, with a high density of passengers. Providing a safe, healthy, and comfortable cabin environment is a great challenge, particularly during the COVID-19 pandemic. An increase in ventilation rate can potentially reduce infection probability, which may result in worsening environmental quality (e.g., thermal comfort) and larger energy consumption. Thus, exploring the trade-off among infection risk, environmental quality (with regard to ventilation, thermal comfort, and air quality), and energy consumption is important to optimize ventilation systems for carriages. The effect of different supply air parameters (e.g., velocity and temperature) and ventilation modes of mixing ventilation (MV) & Supply air from the Floor and Return air from the Ceiling (SFRC) was studied. The questionnaires were analyzed to explore passenger dissatisfaction with the carriage environment using a MV system. Simulations were performed to predict the velocity, temperature, and CO2 concentration fields. In addition, the comprehensive benefit was evaluated by analytic hierarchy process (AHP), based on infection probability from the revisited Wells–Riley equation, Air Diffusion Performance Index (ADPI), Predicted Mean Vote (PMV), Pollutant Removal Effectiveness (PRE) and energy consumption estimated by cooling load (Lcool). Compared with MV, the optimized SFRC provided softer draft sensation and decreased CO2 concentration by 42%. The SFRC achieved better comprehensive benefits, with an infection risk reduced to 0.4%, ADPI of 80%, PMV approaching zero, PRE up to 16, and energy efficiency increased by 30%. This work contributes to the optimal design of subway carriage ventilation systems in the post-epidemic era.

Effect of the air supply angle of swirling diffusers on the air diffusion performance index in a vehicle assembly workshop

Airflow improvement in a large industrial building is one of the most effective ways to improve the thermal comfort of workers. Air Diffusion Performance Indices (ADPI) of an industrial workshop area under different air supply angles (15°, 30°, 45°, 60°, 75° and 90° in summer and 90° in winter) of the ceiling-mounted swirling diffusers were evaluated by on-site measurements and computational fluid dynamics (CFD) modelling. The measurement data was used to verify the CFD numerical model. The temperature and velocity field of the working area were simulated and analysed under seven operating conditions of swirling diffusers. The findings showed that in summer, the increase of the swirling air supply angle would increase the air velocity. When the air supply angle was larger than 75°, a draughty wind speed (>0.3 m/s) in the local working area, was produced. When the air supply angle was 30°–75°, the indoor design comfortable temperature range (26°C–28°C) was produced. The ADPIs of the workshop were 100% with the air supply angles of 45° and 60° in summer and 90° in winter, respectively. The research findings should provide a reference for improving the airflow organization in the working area of a tall factory building.

Thermal environment investigation of asymmetric radiation coupled with convection heating.

The couple of radiation with convection heating owned advantages of less energy utilization, healthier and more comfortable indoor environment. However, local thermal discomfort was often induced by large vertical temperature difference and radiation asymmetry temperature. This work studied indoor thermal environment characteristics under different coupling ways of radiation and convection heating terminals through experiments and CFD simulation. The studied five scenarios were denoted as: (I) lateral air supply + adjacent side wall radiation, (II) lateral air supply + opposite side wall radiation, (III) lateral air supply + floor radiation, (IV) lateral air supply + adjacent side wall radiation + floor radiation, and (V) lateral air supply + opposite side wall radiation + floor radiation. The overall thermal comfort indices (including air diffusion performance index (ADPI), predicted mean vote (PMV), and predicted percent of dissatisfaction (PPD)) and local thermal comfort indices under different scenarios were investigated. For Scenarios I–III, the local dissatisfaction rates caused by vertical air temperature difference were 0.4%, 0.1%, and 0.2%, respectively, which belonged to “A” class according to the ISO-7730 Standard. While the vertical asymmetric radiation temperature of Scenario I/II was about 6.5 °C lower than that of Scenario III/IV/V. The ADPI for Scenarios III–V were about respectively 5.7%, 16.7%, and 21.0% higher than that of Scenarios I–II, indicating that a large radiation area and radiation angle coefficient could reduce the discomfort caused by radiant temperature asymmetry. The coupling mode improved local discomfort by decreasing vertical temperature difference and radiation asymmetry temperature wherefore improving the PMV from −1.6 to −1. The lateral air supply coupled with asymmetric radiation heating could potentially improve the thermal comfort of occupied area, while the comprehensive effect of thermal environmental improvement, energy-saving, and cost-effectiveness needes to be further investigated.

Field Test on Performance of an Air Source Heat Pump System Using Novel Gravity-Driven Radiators as Indoor Heating Terminal

The simultaneous need for energy efficiency and indoor comfort may not be met by existing air source heat pump (ASHP) technology. The novelty of this study lies in the use of a new gravity-driven radiator as the indoor heating terminal of ASHPs, aiming to provide an acceptable indoor comfort with improved energy efficiency. To confirm and quantify the performance improvement due to the proposed system retrofit, a field test was conducted to examine the system performance under real conditions. In the tests, measurements were made on the refrigerant- and air-side of the system to characterize its operational characteristics. Results showed that the proposed radiator has a rapid thermal response, which ensures a fast heat output from the system. The proposed system can create a stable and uniform indoor environment with a measured air diffusion performance index of 80%. The energy efficiency of the proposed system was also assessed based on the test data. It was found that the system’s first law efficiency is 42.5% higher than the hydraulic-based ASHP system. In terms of the second law efficiency, the compressor contributes the most to the overall system exergy loss. The exergy efficiency of the proposed system increases with the outdoor temperature and varies between 35.02 and 38.93% in the test period. The research results and the analysis methodology reported in this study will be useful for promoting the technology in search of energy efficiency improvement in residential and commercial buildings.

Airflow deflectors of external windowsto induce ventilation: Towards COVID-19 prevention and control.

Since the Corona Virus Disease 2019 (COVID-19) outbreak, the normalization of the epidemic has posed great challenge to epidemic prevention and control in indoor environment. Ventilation systems are commonly used to prevent and control indoor transmission of disease. However, most naturally ventilated rooms are not efficient to prevent the spread of virus, i.e., classrooms. The goal of this work is to effectively adopt forced interference strategies (e.g., airflow deflector) applied to external windows to strengthen airflow diffusion performance (ADP) of natural ventilation. So far, no systematic study has been done to investigate the effectiveness of such airflow deflectors on its influence on natural ventilation and effectiveness of preventing the disease transmission in indoor environment. In this work, a case study was conducted based on cross-ventilated classrooms. Different settings of airflow deflectors (i.e., size and installation angle) were applied to the external windows. Air Diffusion Performance Index (ADPI) was utilized to evaluated airflow diffusion performance under different settings of the airflow deflectors. Then, the Wells-Riley model was applied to evaluate infection risk. According to the results, the infection risk can be reduced by 19.29% when infection source is located at the center of classroom and 17.47% when source is located near the side walls. This work would provide guidance for the design of classrooms ventilated with induced natural wind for epidemic prevention and control.

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.

Air distribution and thermal environment optimization on subway platform using an innovative attached ventilation mode

Subway systems are extensively used due to their safety and convenience. Scientific and reasonable air distribution is necessary for creating a comfortable environment on the subway platform. In the present study, three ventilation modes (four-side slot outlets of attached ventilation (FSOAV), both-side slot outlets of attached ventilation (BSOAV), and mixing ventilation (MV)) were investigated based on numerical methods. Visualization experiments were conducted to characterize the attached ventilation airflow. A series of evaluation indexes, including the air velocity, temperature, air diffusion performance index (ADPI), and relative warmth index (RWI), were utilized to assess the ventilation effects of the three modes. The average temperatures among the three modes were 29.09 °C, 29.85 °C, and 29.18 °C; the ADPI values were 81.28%, 84.78%, and 55.89%; and the RWI values were 0.236, 0.256, and 0.239, respectively. These results demonstrate that FSOAV outperforms BSOAV and MV in terms of air distribution and thermal environment. Thus, FSOAV is recommended for application on subway platforms. Considering the actual layout of the construction, the positional distribution and width of air outlets were discussed to optimize the ventilation performance of FSOAV. The thermal environment of attached ventilation with double-row air outlets is better than that with single-row air outlets, and the increase in velocity contributes to the uniform diffusion of airflow in attached ventilation. This research provides design references for ventilation design in subway stations.

Effect of inlet/outlet on thermal performance of naturally ventilated building

Abstract Ventilation is a way of improving the air quality of rooms by circulation. The position of the inlet and outlet greatly influences the thermal comfort. This attempt proposes to analyse the effect of the position of window openings for a room building with natural ventilation and the air flow and temperature distribution numerically using a commercial computational fluid dynamics (CFD) code. This proposed study consists of (i) approving the numerical model against experimental data gathered in an environment similar to the one used in simulations and (ii) applying the CFD model to explore the results of four varying configurations of ventilator on the natural ventilation system and thermal comfort. For the varying arrangements, the wind speed is 0.2 m⋅s−1 perpendicular to the openings for a wind, (iii) evaluating the comfort level utilizing the Air Diffusion Performance Index (ADPI) on the basis of ASHRAE 55-210 criteria. The obtained results show that the positions of outlet and inlet openings highly affect the performance in the thermal comfort while they have a trivial effect on the occupied zone mean velocity. The computational results showed that the two cases (a) and (b) present results very close to each other with a slight difference at the center of the chamber. Most of the calculated values (effective draft temperature, EDT) are between (−1.7 and 1.1). Then ADPI is over 70% for case (a) and over 75% for case (b), so all points they are located in the comfort zone. The results affirmed also that configuration with inlet openings set at 1.022 m above ground and an outlet opening set at 0.52 m brings about the most applicable solution ventilation efficiency and give the best EDT that fulfills the criteria of ASHRAE 55-210 with an ADPI of ~90%.

Computational study of natural ventilation in a sustainable building with complex geometry

We deploy a fully coupled thermo-fluidic finite element approach to simulating natural ventilation in a sustainably designed building with complex geometry. The ‘interlock house’ uses building design for climate control instead of mechanical means (such as air conditioning). Therefore, accurately modeling the natural ventilation flows is crucial to assess thermal comfort in such designs. A residual-based variational multiscale method (VMS) is employed, which is a Large Eddy Simulation (LES) type approach to turbulence modeling. The VMS formulation is further augmented with a weakly enforced boundary condition method to efficiently resolve the effect of boundary layers. We validate the framework using a canonical Rayleigh Bénard convection problem across different flow regimes. We deploy the framework to analyze thermal flows in the house under two natural ventilation configurations characterized by window opening strategies. Mesh convergence study using one of the configurations is performed to verify the framework. Comparisons of the flow fields and temperature distributions between the two scenarios are discussed. Air diffusion performance index (ADPI) and predicted mean vote (PMV) are computed to investigate thermal comfort in both configurations. This work illustrates the ability of the framework to comprehensively model and predict natural ventilation under various operating scenarios.