Springer Science and Business Media LLC

As infectious respiratory diseases are highly transmissible through the air, researchers have improved traditional total volume air distribution systems to reduce infection risk. Multi-vent module-based adaptive ventilation (MAV) is a novel ventilation type that facilitates the switching of inlets and outlets to suit different indoor scenarios without changing ductwork layout. However, little research has evaluated MAV module sizing and air velocity selection, both related to MAV system efficiency in removing contaminants and the corresponding level of protection for occupants in the ventilated room. Therefore, the module-source offset ratio (MSOR) is proposed, based on the MAV module size and its distance from an infected occupant, to inform selection of optimal MAV module parameters. Computational fluid dynamics simulations illustrated contaminant distribution in a two-person MAV equipped office. Discrete phase particles modelled respiratory contaminants from the infected occupant, and contaminant concentration distributions were compared under four MAV air distribution layouts, three air velocities, and three module sizes considered using the MSOR. Results indicate that lower air velocities favour rising contaminant levels, provided the ventilation rate is met. Optimal contaminant discharge can be achieved when the line of outlets is located directly above the infected occupant. Using this parameter to guide MAV system design, 85.7% of contaminants may be rendered harmless to the human body within 120 s using the default air vent layout. A more appropriate supply air velocity and air vent layout increases this value to 91.4%. These results are expected to inform the deployment of MAV systems to reduce airborne infection risk.

Polyether polyurethane foam (PPUF) has been analyzed at various scales to determine its thermal decomposition characteristics. Analysis of its decomposition behavior was gathered through experiments of thermogravimetric analysis (TGA) and calorimetry. Material properties were extracted from micro-scale experiments. Observations of the macro-scale burning reveal the complexity of its behavior. Notable difficulties exist within the current CFD framework to accurately replicate such behavior. However the simplified description of traits of melting, change of density and liquid flows can allow for relatively accurate fire modeling. The purpose of this paper is to improve the ability of the polyurethane fire model in numerical simulations.

Despite the widespread assumption that outdoor environments provide sufficient ventilation and dilution capacity to mitigate the risk of COVID-19 infection, there is little understanding of airborne infection risk in outdoor urban areas with poor ventilation. To address this gap, we propose a modified Wells-Riley model based on the purging flow rate (QPFR), by using computational fluid dynamics (CFD) simulations. The model quantifies the outdoor risk in 2D street canyons with different approaching wind speeds, urban heating patterns and aspect ratios (building height to street width). We show that urban morphology plays a critical role in controlling airborne infectious disease transmission in outdoor environments, especially under calm winds; with deep street canyons (aspect ratio > 3) having a similar infection risk as typical indoor environments. While ground and leeward wall heating could reduce the risk, windward heating (e.g., windward wall ~10 K warmer than the ambient air) can increase the infection risk by up to 75%. Our research highlights the importance of considering outdoor infection risk and the critical role of urban morphology in mitigating airborne infection risk. By identifying and addressing these risks, we can inform measures that may enhance public health and safety, particularly in densely populated urban environments.

The low-oxygen environment restricts the exploitation of mineral resources on plateaus and affects miner’s safety. This paper proposes an oxygen-enrichment method using an annular air curtain. Through numerical simulation and experiments, it was confirmed that the proposed method improves the breathing environment in the single-head roadway of a plateau mine. Computational fluid dynamics (CFD) was used to investigate the oxygen-enriching effect and oxygen spatial distribution regularities after using the proposed oxygen-enrichment method in the single-head roadway of a plateau mine. The reliability of the CFD model was confirmed by experiment. Orthogonal testing was conducted to investigate the influence degree and optimal level combination of factors influencing oxygen enrichment. The results demonstrate that the annular air curtain effectively prevented oxygen loss, thus forming a local oxygen-rich space and improving the effective utilization rate of oxygen. Oxygen supply concentration and velocity are positively correlated with the oronasal oxygen mass fraction through a linear function, while the air curtain outlet wind velocity is negatively correlated with the oronasal oxygen mass fraction through a linear function. The annular air curtain diameter and oronasal oxygen mass fraction do not have an obvious functional relationship. When the annular air curtain diameter was greater than 0.9 m, the oronasal oxygen mass fraction was stable at approximately 25.30%. The influencing factors of the novel oxygen-enrichment method are, in descending order, as follows: oxygen supply concentration, annular air curtain diameter, air curtain outlet wind velocity, and oxygen supply velocity. The optimal level combination is oxygen supply concentration of 100%, oxygen supply velocity of 11 m/s, air curtain outlet wind velocity of 1.5 m/s, and annular air curtain diameter of 0.9 m.

The frosting is a critical phenomenon in building systems because it decreases the performance of exchangers and damages them. In this article, heat and mass transfer in a specified liquid-to-air membrane energy exchanger (LAMEE) and their effects on condensation and frost formation are simulated numerically using the 3D computational fluid dynamics (CFD) technique. The CFD model has been validated with experimental results for different design parameters, and the agreement is within ±2%. The developed CFD model provides the distribution of temperature and humidity ratio and MgCh concentration along the LAMEE. In the present study, effects of exchanger structure on producing viscosity and heat and mass transfer are studied. The selected LAMEE is a counter cross structure, therefore vortices appear in the inlet and outlet solution channel, and their influence can be seen on heat transfer in these parts. In addition, the diffusion of heat and mass transfer are studied on distributions of temperature and humidity ratio. Results show that the permeable membrane and moisture transfer make more regular temperature distribution along airflow direction in energy exchangers. This study provides an extended vision of heat and mass transfer. A 3-dimensional CFD model is developed to predict frost formation based on obtained temperature and humidity ratio. The CFD model is validated with an experimental study by calculating the frost limit. The developed model distinguishes condensed and frosted areas, and a new parameter is defined for this purpose namely as the frosted humidity ratio. Results show that frost and condensation distributions depend significantly on temperature and humidity ratio distributions. Adjusting temperature and humidity ratio to avoid air vapor to reach to saturation conditions is the better way to combat frosting.

The large-scale application of renewable energy is an important strategy to achieve the goal of carbon neutrality in the building sector. Energy flexibility is essential for ensuring balance between energy demand and supply when targeting the maximum penetration rate of renewable energy during the operation of regional integrated energy systems. Revealing the energy flexibility characteristics of centralized hot water systems, which are an important source of such flexibility, is of great significance to the optimal operation of regional integrated energy systems. Hence, in this study, based on the annual real-time monitoring data, the energy flexibility of the centralized hot water system in university dormitories is evaluated from the perspective of available storage capacity (CADR), recovery time (trecovery), and storage efficiency (ηADR), by the data-driven simulation method. The factors influencing the energy flexibility of the centralized hot water system are also analyzed. Available storage capacity has a strong positive correlation with daily water consumption and a strong negative correlation with daily mean outdoor temperature. These associations indicate that increased water use on the energy flexibility of the centralized hot water system is conducive to optimal dispatching. In contrast, higher outdoor temperature is unfavorable. The hourly mean value of the available storage capacity in spring and winter is found to be around 80 kWh in the daytime, and about twice that in summer and autumn. Recovery time is evenly distributed throughout the year, while trecovery/CADR in spring and winter is about half that in summer. The storage efficiency was significantly higher in spring, summer, and winter than in autumn. The hourly mean storage efficiency was found to be about 40% in the daytime. The benefits of activating energy flexibility in spring and winter are the best, because these two seasons have higher available storage capacity and storage efficiency, while the benefit of activating energy flexibility is the highest at 6:00 a.m., and very low from midnight to 3:00 a.m.

The fire ignited due to air conditioner (A/C) malfunctioning is studied numerically for a single room, two rooms with interconnection, two interconnected rooms with attached corridor and a two-storeyed building with stairs. Coupled finite difference and finite volume based open source solver, Fire Dynamics Simulator (FDS) is used for domain discretization and solution of governing equations. Heat release rate per unit area (HRRPUA) is varied in the single room case and temperature and visibility contours are studied to determine HRRPUA corresponding to maximum hazard, judged based on available safe evacuation time (ASET) calculation. Further, positions of air conditioners, at a prescribed HRRPUA, are varied in two interconnected rooms to obtain the case with maximum ASET. Evacuation strategy is discussed and the maximum number of persons who can be safely evacuated from the accident site is calculated followed by the variation in the position of doors in the case with inter-connected doors attached with a corridor. Soot flow pattern and flame contours are also observed for each of the above cases. At the end, fire breakout is simulated in a two-storeyed building with stairs and having the room configuration based on the maximum ASET value.

Recent advancements in the domain of modeling physical processes offer opportunities to use equation based modeling environments, such as Modelica, for the simulation of building heating, ventilation, and air-conditioning (HVAC) systems. The current work demonstrates Modelica capabilities in a case study of real building solar thermal system simulation. The simulated system is part of an innovative ENERGYbase building, designed according to the so called Passivhaus standard. Model calibration and validation procedure is developed to include optimization based parametric adjustments of component models using the monitoring data during a single week. The calibrated system adequately reproduces half a year of real system operation. Future work will concentrate on application of the developed calibration and validation methodology in the whole year overall building energy simulation.