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![Figure 6: Layout of the two-person office used in Yuan et al. [52]...](profile/Mohamed_Lateb/publication/362875023/figure/fig3/AS:11431281083553457@1662646159330/Layout-of-the-two-person-office-used-in-Yuan-et-al-52-experiment-and-reproduced-for_Q320.jpg)
This study aims to investigate the mixing and displacement ventilation systems commonly used in buildings indoor ventilation by means of computational fluid mechanics (CFD). The study is carried out using steady-state methodology to examine the indoor air velocity and temperature distributions, which in turn, are used to estimate the draft risk wit...
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... dimensions of the mannequin are illustrated in Fig. 3. The height of the mannequin is 1.7 m, whereas the width is equal to 0.493 m. A square-shaped block of 0.05×0.05 m 2 is created on the head level of each mannequin to represent the mouth and nose ...
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... of the occupant face (Fig. 14b) resulted in low draft risk with a PD of 0 to 2%. The occupants in the cubicle are free from any dissatisfaction caused by the draft. The region of supply air traveling upward (near the lobby wall) has the highest PD, i.e. 15%. Hence, any occupant standing close to the lobby wall may encounter a little discomfort. (Fig. 30a), the supply air from the cubicle moves to the lobby, and then to the outlet. The occupants do not encounter any discomfort. The highest PD on this plane is in the lobby, which is around 14%. In the cubicle where the occupant stands, the PD is below 12%. The DV (Fig. 30b) showed a high draft in front of the occupant shoe/ankle. A ...
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... occupant standing close to the lobby wall may encounter a little discomfort. (Fig. 30a), the supply air from the cubicle moves to the lobby, and then to the outlet. The occupants do not encounter any discomfort. The highest PD on this plane is in the lobby, which is around 14%. In the cubicle where the occupant stands, the PD is below 12%. The DV (Fig. 30b) showed a high draft in front of the occupant shoe/ankle. A maximum PD of 34% is seen in this region. The discomfort will be sensed if the occupant stands in the path of supplied air. Whereas, a PD of 3% exists in the space away from the supply airflow. Therefore, the level of discomfort is negligible if the occupant stands away from ...
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... Therefore, a high draft risk in the cubicle is a cause of concern. The DV (Fig. 32b) showcased a PD of less than 10%. This may indicate a satisfactory comfort level to the occupant standing in the lobby. However, the cut-section is positioned above the inlet; the supply air is not captured on this cut-section plane. Plane z = 0.05 m (Fig. 30b) has illustrated a clear picture of the supply air PD distribution. The maximum PD of 25% was found in the supply air path (i.e. at the ankle level) in the lobby. The plane x = 0 m is helpful to precisely understand the PD% above the knee level. The cut-section revealed a low draft risk with PD below 6% in front of the occupant ...
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Site museum is a kind of special public building constructed at the original place where the historical sites were unearthed, in which the unearthed relics are preserved and exhibited. The environmental control of such buildings is usually face with the problems of high energy consumption and disturbance between relics and visitors since the relics...
Citations
... Compared with experimental research, computational fluid dynamics (CFD) shows unique advantages in studying the performance of ventilation systems 8 . A large number of studies based on CFD technology such as gas diffusion behavior [9][10][11] , comparison of ventilation mode applicability 12,13 , and analysis of influencing factors on ventilation system performance 14 have appeared. In terms of gas diffusion behavior, Schmidt et al. 15 investigated the diffusion behavior of hydrogen/air mixed clouds between buildings under meteorological conditions, release rate, release time, and release amount. ...
Nitrogen is widely used in various laboratories as a suppressive gas and a protective gas. Once nitrogen leaks and accumulates in a such confined space, it will bring serious threats to the experimental staff. Especially in underground tunnels or underground laboratories where there is no natural wind, the threat is more intense. In this work, the ventilation design factors and potential leakage factors are identified by taking the leakage and diffusion of a large liquid nitrogen tank in China Jinping Underground Laboratory (CJPL) as an example. Based on computational fluid dynamics (CFD) research, the effects of fresh air inlet position, fresh air velocity, exhaust outlet position, leakage hole position, leakage hole size, and leaked nitrogen mass flow rate on nitrogen diffusion behavior in specific environments are discussed in detail from the perspectives of nitrogen concentration field and nitrogen diffusion characteristics. The influencing factors are parameterized, and the Latin hypercube sampling (LHS) is used to uniformly sample within the specified range of each factor to obtain samples that can represent the whole sample space. The nitrogen concentration is measured by numerical value, and the nitrogen diffusion characteristics are measured by category. The GA-BP-ANN numerical regression and classification regression models for nitrogen concentration prediction and nitrogen diffusion characteristics prediction are established. By using various rating indicators to evaluate the performance of the trained model, it is found that models have high accuracy and recognition rate, indicating that it is effective in predicting and determining the concentration value and diffusion characteristics of nitrogen according to ventilation factors and potential leakage factors. The research results can provide a theoretical reference for the parametric design of the ventilation system.
... Generally, the energy consumption of HVAC systems is proportional to the outdoor airflow required, the environmental conditions, the number of occupants and the efficiency of the sub-sections. Based on the performance of HVAC systems that depends on indoor air quality which, in turn, ensures the occupant comfort, several indices have been proposed to compare the efficiency of HVAC systems in terms of energy [3][4][5][6][7][8], comfort [9][10][11][12][13][14], and performance [15][16][17][18][19]. ...
In the present work, a swirl diffuser with a new design is proposed to be applied in the ventilation of living rooms, aiming to improve thermal comfort in an occupied area with a lower cost. For that, the effects of geometric parameters on a swirl air diffuser performance are experimentally and numerically investigated. To use an appropriate turbulence model that best reproduces the complex character of the swirl diffuser airflow for investigation, three turbulence models from the large-eddy simulation (LES) class—i.e., the Smagorinsky–Lilly (LES/S–L), the wall-adapting local eddy-viscosity (LES/WALE), and the kinetic-energy transport (LES/K–ET) turbulence models—are selected and tested. It is found that the three turbulence models are not able to predict simultaneously the thermal evolution of the flow in the entire jet domain. However, the results obtained with the LES/K–ET turbulence model are highly consistent with the experimental results. It can be concluded that the new design of the swirl air diffuser improves the spatial temperature homogeneity by spreading a significant air quantity over the room which, in turn, permits to obtain homogenized temperature in large spaces. The character of this jet type appears important and useful for the applications of heating, ventilation, and air conditioning (HVAC) systems.
... Without a doubt, the prediction of indoor airflow by CFD has advanced HVAC system design (Awbi, 1989;Huo et al,. 2000;Zhao et al., 2003;Luo et al., 2004;Nielsen, 2015;Khan et al., 2022). Based on the turbulence models, the current computational methods for studying swirl diffusers may be loosely divided into two groups: (i) LES models (Tavakoli & Hosseini 2013) and (ii) RANS models (Aziz et al., 2012;Villafruela et al,. ...
When reducing the energy prerequisites of buildings, the correct distribution of fresh air flows injected into the living rooms poses a problem. If the problem of mixing the injected air in the ambient air is not effectively solved, there will be a strong deterioration in air quality and comfort. In this research, a new design of swirling diffuser is investigated experimentally and numerically using large eddy simulations. The influence of fins is studied for the improvement of air diffusion and jet mixing with ambient air. The study was carried out for a fins angle of 30° with the jet's axis and 60° with the blowing orifice's plane with the condition of uniform heat flux of the air. The working fluid used is air. It has been validated that using fins leads to a greater spreading of the jet and good air mixing compared to those obtained from smooth tubes (circular nozzle). To enhance the accuracy of the turbulence models' predictions, three turbulence models are tested: the wall-adapting local eddy-viscosity turbulence model (LES/WALEVM), Smagorinski-Lilly (LES/S-LM) model and the kinetic-energy transport model (LES/K-ETM). It is worth highlighting that the LES/K-ETM model is well established in the prediction of swirling flows, which have been successfully compared with experimental results. Article History
... The essence of this full-space environment control method is the dilution principle so as to maintain uniform parameters in the room. Based on this, some new ventilation strategies have been developed, such as displacement ventilation (DV) [5], underfloor air distribution (UFAD) [6], and stratified air conditioning [7]. These methods are designed to ensure the comfort of the space where the occupants are located and to send the airflow directly below the working plane. ...
... The above formula can be sorted into an expression about air exchange quantity Q (Equation (4)), which is irrelevant to the environmental parameter ∆P oi . It can be simplified into a more general form, Equation (5). By testing the air infiltration rates under different pressure differences, the parameters C and D can be fitted, and then the performance curve of a specific air curtain can be obtained. ...
... Equation (6) shows that the relationship between Q and √ ∆P oi is still linear and can be simplified as Equation (5). However, this relationship depends on the assumption of orifice. ...
Large public buildings (LPBs) are the main energy consumers in cities, and the air conditioning system contributes a large part. Supply air allocation by partition can avoid excessive regulation of the system. In spatially interconnected LPBs, thermal coupling relationships exist between different subzones. The convective heat transfer to the non-occupied zone increases the actual cooling/heating capacity of the air conditioning area. This paper applies the air curtain as an airflow barrier indoors, and the air curtain grid system (ACGS) is created by the combined operation of multiple air curtains, which aims to reduce the convective heat exchange between adjacent subzones. The computational fluid dynamics (CFD) model is established and simulated. The main conclusions are as follows: (1) For the scenarios addressed in this paper, the combination of a 60° diffuser air supply angle and 2 m/s air curtain velocity can reduce the convective load from the adjacent space by more than 50%. (2) It is recommended to install incomplete air curtains indoors, and a 50% air curtain coverage ratio can reduce 52% of the heat exchange. (3) The mathematical model of air infiltration/exfiltration under the combined operation of multiple air curtains is established and verified in ACGS. This paper provides a new approach to the air conditioning partition control of LPBs.
Advanced air distribution is essential for the energy-efficient provision of thermal comfort and indoor air quality. This study proposes a novel advanced air distribution, i.e., graded ventilation. The airflow pattern of graded ventilation is characterized by a bimodal distribution of vertical air velocity and a unimodal distribution of vertical air temperature. Graded ventilation possesses four mechanisms for high energy-efficient provision of thermal comfort and indoor air quality. First, graded ventilation has a high conditioned air supply efficiency into the occupied zone, particularly the head level, for both thermal comfort and indoor air quality, due to the push-down and pull-down forces of the internal airflow recycling. Second, graded ventilation decouples outdoor fresh air and return air, with high outdoor fresh air supply efficiency for indoor air quality. Third, graded ventilation utilizes higher-quality conditioned air for the zone, which is more critical to thermal comfort and indoor air quality. Fourth, graded ventilation only handles the cooling load of the outdoor fresh air without handling the cooling load of the return air. Case studies demonstrate that compared with mixing ventilation, Type-I stratum ventilation, Type-II stratum ventilation, and interactive cascade ventilation, graded ventilation improves energy efficiency by 49.7%–55.4%, 24.8%–29.1%, 16.3%–23.3%, and 8.4%–12.3% respectively for thermal comfort and indoor air quality. Therefore, this study advances air distribution for low-carbon, thermally comfortable, and healthy buildings.
Ventilation methods are widely used for creating livable indoor environments. The ventilation performance index of thermal comfort is indispensable for the provision of thermal comfort in indoor environments with ventilation methods. While the air temperature, air velocity, and relative humidity are three predominant environmental air parameters of ventilation methods affecting thermal comfort, existing ventilation performance indices, i.e., Effective Draft Temperature (EDT) and Effective Moisture Temperature (EMT), cannot account for these three parameters simultaneously for thermal comfort evaluation. This study proposes a novel ventilation performance index, i.e., Effective Draft – Moisture Temperature (EDMT) to simultaneously consider the abovementioned three environmental air parameters for the thermal comfort evaluation. The EDMT is proposed based on equivalent thermal comfort effect transfers of the air velocity and relative humidity to the air temperature. Two algorithms of cascaded equivalent thermal comfort transfers are developed, based on which the EDMT is quantified and tabulated for the practical convenience of different demands of thermal comfort under cooling and heating. The results based on Monte Carlo simulations and ASHRAE Thermal Comfort Database II show that the accuracies of thermal comfort evaluation by the EDT and EMT are 88.7% − 95.5% and 70.9% – 89.0% respectively, and those of the proposed EDMTs of Algorithms 1 and 2 are 97.3% − 99.3% and 97.7% − 99.3% respectively. The proposed EDMTs of Algorithms 1 and 2 are credible and convenient for practical applications and contribute to updating ventilation performance evaluation-related standards for developing thermally comfortable buildings.
In recent years, rapid urban development has led to capsule hotels, sleep pods, and other tiny sleeping spaces that adapt to people’s fast-paced lives, achieving maximum functionality with a very small footprint. However, due to the small space, human metabolic pollutant (such as CO2) is more likely to accumulate, and the air is not easily circulated. In this paper, a full-size experimental platform is set up with three types of ventilation modes to explore the exclusion efficiency of metabolic pollutants and the overall distribution of age of air under these ventilation modes. The conclusions showed that the mean values of metabolic pollutant exclusion rates for the different ventilation modalities varied very little across the spatial dimensions of the confined space but varied considerably in the area around the head. The double-side attached ventilation method was the most effective in removing human metabolic pollutants, especially in the head region (CN ≥ 0.92), while the single-wall attached ventilation method had the best air exchange efficiency (η ≥ 0.85). This suggests an inconsistent distribution of CO2 and age of air, which is contrary to general common sense. The conclusions of this paper can guide the design of ventilation for tiny sleeping spaces.
