Air Change Research Articles

Human exposure to respiratory aerosols: Impact of ventilation rates, mixing ventilation configuration, and breathing patterns

This study investigates airborne transmission dynamics between occupants in office rooms equipped with mixing ventilation (MV). The primary aim was to assess how different ventilation configurations, air change rates (ACH), breathing patterns, and supply air temperatures influence cross-exposure and infection risks. The experimental setup involved two thermal manikins simulating an infected and an exposed occupant within a climate chamber. The investigated parameters included four ACH levels (1.2, 2, 4 and 6.6 h⁻1, representing four EN 16798-1 ventilation categories), two MV configurations (near-ceiling and near-floor inlets), two breathing patterns (nose and mouth breathing), and two supply air temperatures (19°C and 21°C). Carbon dioxide (CO₂) was used as a tracer gas to simulate exhaled aerosols, enabling precise measurements of effectiveness (), intake fraction (IF), and infection probability (P). The findings indicate that higher ACH do not uniformly improve but are linked to reduced cross-exposure risk. The near-floor inlet MV configuration significantly outperformed the near-ceiling configuration in reducing IF and P by 15-41% under most investigated scenarios. Additionally, mouth breathing increased IF and P compared to nose breathing, especially at higher ACH (2, 4, and 6.6 h⁻1). The results also showed that lower supply temperatures do not always correlate with higher IF and P, as MV configuration and breathing patterns significantly influence outcomes. This research provides insights into optimizing ventilation strategies for safer indoor environments, emphasizing the importance of airflow dynamics, breathing patterns, and supply temperature in ventilation design.

Effect of natural ventilation on aerosol transmission and infection risk in a minibus

High passenger density, prolonged exposure, and close interpersonal distance create a high infection risk (IR) in minibuses. While improving natural ventilation induced by turbulent airflows is essential for controlling IR in minibuses, comprehensive studies on its effectiveness are lacking. To address this, we conducted computational fluid dynamics simulations studies coupling indoor–outdoor turbulent airflows to examine the impact of window opening locations, window opening sizes, and initial droplet diameters (dp) on the ventilation airflow and dispersion of pathogen-laden droplets. Results show that the surrounding turbulent flow patterns create higher surface pressure at bus rear than bus front, which is a key factor influencing bus ventilation. When all windows are closed, ventilation is primarily provided by skylights at bus rooftops. Ventilation through only two skylights resulted in an air change rate per hour (ACH) of 17.55 h−1, leading to high IR of passengers. In contrast, fully opening front and rear windows increases ACH by 27.28-fold to 478.79 h−1, significantly reducing IR by 1–2 orders of magnitude compared to skylight ventilation. Expanding window opening sizes can effectively enhance ventilation when both front and rear windows open (attributed to the pumping effect), while is ineffective when only front windows open. To reduce IR in minibuses, we recommend opening multiple windows at the bus front and rear. Even if the total opening area of the front and rear windows is only two-thirds of that of the front window, its ACH is 2.8 times more than only opening front windows.

Relating ten years of rock temperature monitoring to rockwall weathering processes in steep mountain valleys in western Norway

Most existing studies on rockwall frost regimes and frost weathering at rockwalls focus on permafrost-affected rockwalls. However, a high share of rockwall surface areas in Norway and in many other cold-climate environments is actually free of permafrost. It is therefore of interest how these permafrost-free rockwall systems will respond to future changes in air and rock temperatures. In this study, we report field measurements conducted at rockwalls beneath the current permafrost limit and investigate thermal regimes at rockwalls that include both rockwall areas with and without permafrost. We present a unique dataset of up to ten years of rockwall temperature measurements from ten temperatures sensors installed in two mountain valleys in western Norway. An analysis of the different rockwall thermal regimes with respect to rock weathering and associated rockfall supply for both, permafrost-affected and permafrost-free rockwalls is provided. The highest intensity of recent rockwall weathering including determined rockwall retreat rates and associated rockfall supply is detected for northeast-facing rockwalls followed by south-facing rockwalls in our study area. Frost cracking activity, probably in the form of segregation ice growth, seems to be an important factor particularly for the high weathering intensity on northeast-facing rockwalls whereas solar radiation-induced thermal stresses, which favour incremental subcritical crack growth, is assumed to play a relevant role in the moderate weathering intensity on south- and southwest-facing rockwalls. A mean annual and study area-wide rockwall retreat rate of 0.24 mm yr−1 is estimated for our ten-year investigation period (2010−2020) which is comparable to other published rates in similar lithologies and climates. As it can be assumed that seasonal frost regimes and permafrost will react differently to ongoing and future climate changes, more attention should be paid to analyse these two different thermal regimes with respect to possible varied implications for mechanical rockwall weathering and associated rockfall supply.

The effects of ventilation layout on cough droplet dynamics relating to seasonal influenza

The primary aim of this paper is to investigate airborne virus transmission in a typical meeting room relating to the heating, ventilation, and air conditioning (A.C.) systems. While the installation of 4-way cassette A.C. systems in offices and meeting rooms has become increasingly common, their efficiency in mitigating short-range airborne virus spread remains poorly understood. Addressing this gap is critical in the post-pandemic era, where understanding the limitations of various ventilation systems is paramount for public health. We systematically compare the performance of the 4-way cassette A.C., various configurations of mixing and displacement ventilation systems, and natural ventilation in controlling the spread of respiratory viruses. Our research uniquely integrates evaporation models to accurately simulate cough clouds' multiphase behavior under both quiescent and thermally influenced conditions. The study benchmarks these systems against two widely recognized ventilation standards (i.e., 5 air changes per hour and 10 l/s per person), offering evidence-based insights applicable across diverse indoor settings. Our findings reveal significant thermal effects in the quiescent case, resulting in 32.3%, 54.3%, and 8.0% changes in the axial, vertical, and lateral spread of the virus-laden droplets, respectively. Notably, the 0.5 m/s 4-way cassette A.C. system demonstrated superior performance, reducing the axial spread by 29.6% compared to other mechanical ventilation configurations. Furthermore, the role of exhaust outlets or doors was found to be critical in shaping the spread pattern in natural ventilation scenarios. This work can offer practical guidance to office workers, engineers, and public health officials on enhancing indoor airborne infection control.

Analysis of ventilation and infiltration rates using physics-informed neural networks: Impact of space operation and meteorological factors

This study presents the development and application of a Physics-Informed Neural Network (PINN) model to estimate ventilation and infiltration rates using long-term observation data, addressing the challenge of dynamically varying space operations and meteorological conditions. A central research equestion is: How can we accurately estimate ventilation rates while accounting for these time-varying factors? Traditional tracer gas methods require numerous measurements to accurately characterize air change rates (ACR) under dynamic space operations and varying meteorological conditions. Our PINN model integrates these fluctuating factors, providing a more precise analysis of their transient effects on ACR. We employed Shapley Additive Explanations (SHAP) to interpret the sensitivity and contributions of each influencing factor. Our findings indicate that the state of windows and doors significantly affects spatial operations, while wind speed and direction are the most impactful meteorological factors. The interaction between open windows and doors results in higher ventilation rates compared to their individual effects. Wind-related factors cause ACR variations exceeding 200 %, with the wind direction relative to the office window playing a crucial role. Additionally, external temperature and indoor-outdoor temperature differences show a strong correlation with ACR. However, limitations include the lack of outdoor CO2 measurements and the assumption of uniform indoor CO2 levels, which may affect accuracy. Generalizability is also limited due to the specificity of the space studied. Future work should incorporate outdoor CO2 data and multiple spaces to enhance model applicability. This study contributes to optimizing ventilation strategies for better indoor air quality and energy efficiency.

Experimental investigation on the application of cold-mist direct evaporative cooling in data centers

The rapid development of the internet era has driven the construction of numerous data centers worldwide. In hot climate, data centers consume significant energy for cooling. Cold-mist direct evaporative cooling offers a natural cooling solution that can help reduce this energy consumption. This study investigates the temperature and relative humidity changes of natural high-temperature air after being cooled using a cold-mist direct evaporative cooling test bench. The effects of several control factors such as spray angle, spray flow rate, and air speed on the cold-mist direct evaporative cooling performance was systematically examined. The findings revealed that: (1) the optimal spray angle for cold-mist direct evaporative cooling treatment air is 65°; (2) high-temperature air between 27 °C and 37 °C can be cooled to 23.57 °C – 25.58 °C after cold-mist direct evaporative cooling treatment, with relative humidity levels of 67.0 % – 78.8 %, meeting the air supply requirements for data centers; (3) the proposed approach could reduce the data center energy consumption by 14 % – 41 %, while extending the annual natural cooling period by 3.16 % – 20.45 %.

Evaluation of a Kirigami-inspired double-skin adaptive façade for natural ventilation and solar harvesting to enhance indoor environment and energy performance

A novel kirigami-inspired design concept for an environmentally responsive adaptive façade is presented and evaluated for the objectives of solar energy harvesting and adaptive ventilation through controllable surface orientation and opening. The concept is a double-skin façade where the outer skin includes a straight cut kirigami-inspired adaptive component. Controllable actuation of the kirigami-inspired section opens the outer skin for ventilation while also changing the orientation of the outer surface for solar tracking. The primary objective of this study is to evaluate the potential benefits for this concept integrated within a building façade for solar energy harvesting, air changes, and indoor temperature control. As such, a computational study is used to estimate the proposed facade concept's performance within various generalized building-environment scenarios. The methodology is detailed to computationally estimate the potential environmental performance of this concept with respect to solar harvesting with adhered solar panels, as well as air changes and HVAC cost for associated interior spaces. The example scenarios include various building components, from a single room to multiple building stories, and two geographic locations with significantly different environmental conditions, and both daily and yearly performance estimates are shown. The component is most effective when the outdoor temperature is near to the desired indoor temperature and wind speeds are mild, but can still reduce HVAC usage for more disparate temperatures. For example, in the scenarios shown the component can eliminate HVAC use for a 5°C difference between outdoor and indoor temperature and reduces HVAC usage for temperature differences up to 15°C. Moreover, the component has the potential to significantly increase net energy generation, with yearly performance estimated for the scenarios to be as much as 25% greater than that of a flat closed façade. However, the component cut parameters can have a significant impact on environmental performance, and thus require careful design consideration.

Twisted tapes in solar chimney-earth air heat exchangers for equipment downsizing and passive cooling

Harnessing solar and geothermal energy in hot and arid climates is an effective strategy to reduce building energy consumption. This research investigates integrating Twisted Tapes (TT) into Earth Air Heat Exchanger (EAHE) pipes within a Solar Chimney (SC)-EAHE system, aiming to reduce EAHE pipe length while meeting ventilation requirements and decreasing cooling demand. Two key innovations are introduced: first, this study pioneers the integration of TT into a SC-EAHE system; second, it comprehensively explores TT geometry optimization, analyzing the effects of width ratio and rotation rate across 77 configurations. Numerical simulations are conducted in ANSYS Fluent using the k-ε RNG turbulence model to investigate thermal performance and airflow characteristics. Findings reveal that TT integration results in a 153 % increase in Nusselt number. Additionally, it is shown that a 1 m SC diameter achieves ventilation of 4.8 Air Changes per Hour (ACH) using TT with a width ratio and rotation rate of 0.5, while reducing EAHE pipe length by 2.6 %. Increasing the SC diameter to 1.25 m, with a TT width ratio of 0.6 and rotation rate of 1.25, leads to a 13 % (35 m) reduction in EAHE pipe length while meeting a minimum outlet temperature of 290.15 K and ACH requirements. However, the benefit diminishes beyond a 1.25 m SC diameter. This study contributes to understanding of integrating TT into SC-EAHE systems, addressing the critical need for sustainable energy solutions and offering a novel and energy-efficient approach for passive cooling in extreme climates.

Assessment of a LPG hybrid solar dryer assisted with smart air circulation system for drying basil leaves

The fluctuation of solar radiation throughout the day presents a significant obstacle to the widespread adoption of solar dryers for the dehydration of agricultural products, particularly those that are sensitive to high temperatures, such as basil leaf drying during the winter season. Consequently, this recent study sought to address the limitations of solar-powered dryers by implementing a hybrid drying system that harnesses both solar energy and liquid petroleum gas (LPG). Furthermore, an innovative automatic electronic unit was integrated to facilitate the circulation of air between the drying chamber and the ambient environment. Considering the solar radiation status in Egypt, an LPG hybrid solar dryer has been developed to be suitable for both sunny and cloudy weather conditions. This hybrid solar dryer (HSD) uses indirect forced convection and a controlled auxiliary heating system (LPG) to regulate both temperature and relative humidity, resulting in increased drying rates, reduced energy consumption, and the production of high-quality dried products. The HSD was tested and evaluated for drying basil leaves at three different temperatures of50, 55, and 60 °C and three air changing rates of 70, 80, and 90%, during both summer and winter sessions. The obtained results showed that drying basil at a temperature of 60 °C and an air changing rate of 90% led to a decrease in the drying time by about 35.71% and 35.56% in summer and winter, respectively, where summer drying took 135–210 min and winter drying took 145–225 min to reach equilibrium moisture content (MC). Additionally, the effective moisture diffusivity ranged from 5.25 to 9.06 × 10− 9 m2/s, where higher values of effective moisture diffusivity (EMD) were increased with increasing both drying temperatures and air change rates. Furthermore, the activation energy decreased from 16.557 to 25.182 kJ/mol to 1.945–15.366 kJ/mol for the winter and summer sessions, respectively. On the other hand, the analysis of thin-layer kinetic showed that the Modified Midilli II model has a higher coefficient of determination R2, the lowest χ2, and the lowest root mean square error (RMSE) compared to the other models of both winter and summer sessions. Finally, the LPG hybrid solar dryer can be used for drying a wide range of agricultural products, and it is more efficient for drying medicinal plants. This innovative dryer utilizes a combination of LPG and solar energy, making it efficient and environmentally friendly.

Experimental and numerical investigation of the cooling performance of a solar chimney integrated with a humidification system

Solar chimneys are efficient systems for natural ventilation based on thermal principles. However, in regions with high temperatures it may not serve to ensure a comfortable indoor environment. To overcome this challenge, integrating air humidification into the ventilation process becomes necessary. The present study investigates the feasibility of integrating a solar chimney with a humidification setup for evaporative cooling in the climate of Kirkuk, Iraq. This investigation utilizes both experimental and numerical techniques. Numerical simulations carried out using a finite volume approach and validated against the experimental data. The experimental outcomes highlight the effectiveness of evaporative cooling in lowering outdoor air temperatures entering the room from months May to August in the range 5°C–10°C. A parametric analysis of the system indicates that increasing water supply can enhance the rate of evaporative cooling and lower the room temperature while elevating relative humidity. Additionally, higher humidity diminishes air buoyancy, leading to a significant decrease in air changes per hour (ACH) rate. The findings also show that both air changes per hour and water consumption reach their peak at a chimney height of 0.5 m. Moreover, a direct correlation is observed between chimney width and both ACH and water consumption. Expanding the chimney width results in higher ACH and increased water consumption for evaporative cooling. Artificial neural network (ANN) model demonstrates robust predictive accuracy, evidenced by high regression coefficients of 0.9566 for ACH and 0.9505 for room temperature correlated from computational fluid dynamics (CFD) results. This underscores ANN model effectiveness in forecasting system performance under varying input conditions, providing valuable insights for different scenarios and configurations of the system.

Effect of bedding application and air change rates on environmental ammonia concentrations for intensively housed beef cattle

Context Manure deposition during livestock export voyages contributes to air ammonia levels, potentially affecting human and animal health if not managed. Mitigation strategies may include increased air change rates and application of bedding. Aim This study examined the effect of bedding application rate (BAR) and air change rate (ACH) on air ammonia (NH3) concentrations and pad properties, including pad surface condition, pH, moisture, and pad ammonium (NH4+) concentrations, for intensively housed beef cattle. Methods Six 7-day runs were conducted with 72 Bos indicus cross steers (mean liveweight ± s.d. = 338 ± 32 kg) housed in respiration chambers by using a 3 × 3 factorial design. The BARs were set to 0%, 50%, and 100% of the Australian Standards for the Export of Livestock (ASEL), and ACH were varied at 20, 35, and 52. Air NH3 was measured twice daily at three heights. Pad surface condition was collected with the first air NH3 measurement. Video footage captured standing and lying behaviours for each steer. Pad samples were collected on the final day for pad chemical analysis. Key results The ACH of 20 changes per hour resulted in higher air NH3 concentration than ACH of 35 and 52. Higher BAR led to lower pad pH and moisture, with slightly lower pad NH4+ concentration in 100% and 50% BAR than 0% BAR. Although air NH3 concentration on Day 7 was positively correlated with pad NH4+ concentration, BAR had no marked effect on air NH3 concentration (within the temperature range of this experiment). Drier and firmer pad surfaces were associated with each high BAR and high ACH. Moreover, high BAR increased the frequency of lying behaviour in steers. Conclusions These findings indicated that NH3 can be mitigated by optimising air changes to minimise air NH3 concentration and utilising bedding to minimise pad NH4+. This offers practical solutions for intensively housed beef cattle, such as livestock export voyages to improve human and animal welfare onboard. Implications The study results emphasised the importance of optimising ACH to maintain low air NH3 concentrations in livestock export conditions. Although there was no evidence that BAR affects air NH3 directly, it reduced pad NH4+ and improved pad conditions for overall animal comfort and environmental quality in confined housing with sufficient air changes.

Estimating Air Change Rate in Mechanically Ventilated Classrooms Using a Single CO2 Sensor and Automated Data Segmentation.

With a growing emphasis on indoor air quality (IAQ) in educational environments, CO2 monitoring in classrooms has become commonplace. CO2 data can be used to estimate outdoor air change rate (ACH) based on the mass balance principle, which can be further linked to human health, performance, and building energy consumption. This study used a novel machine learning method to automatically segment CO2 concentration time series data into build-up, equilibrium, and decay periods, and then estimated classroom ACH using the corresponding CO2 mass balance equations. This method, applied to 40 classrooms in two mechanically ventilated K-6 schools, generated up to ten ACH estimates per day per classroom. A comparison with ACH calculated using the mechanical ventilation rates with 100% outdoor air reported by the building automation system during the study period reveals a slight underestimation by the decay and build-up methods, while the equilibrium method produced closer estimates. These differences may be attributed to uncertainties in occupancy, activity, CO2 emission rates, and air mixing. This research underscores the potential of leveraging CO2 data for more comprehensive IAQ assessments and highlights the challenges associated with accurately estimating ACH in real-world settings.

Ten questions concerning particle exposure in open electrosurgery and its control strategies

The increasing use of high-frequency electrosurgical pencils in open surgeries has heightened concerns about the adverse implications of electrosurgical smoke (ES) on perioperative personnel. Since 2015, there has been an increasing amount of research on electrosurgical smoke particles annually. Despite data discrepancies, nanoparticles (core particle size <200 nm) generally dominate in number distributions. Particulate matter (PM) concentration is closely related to the type of target tissue. Most studies show that ultrafine particle (UFP) concentrations near the main surgeon’s breathing zone inversely correlate with operating room air changes and positively correlate with the power of the electrosurgical pencil. Local smoke evacuation devices with negative ions, specialized filters and N95 respirators are more effective in protecting perioperative staff health, particularly against UFPs. The objective is to summarize particle exposure knowledge in open electrosurgery and establish a research agenda to protect medical personnel from ES exposure.

Assessing the impacts of air-sealing on the sizing, operation, and economic feasibility of ground-source heat pumps for electrifying single-family houses in the US

According to recent studies and reports, in single-family houses (SFHs), air-sealing can significantly lower the thermal loads for space heating and cooling. Thus, air-sealing in SFHs could reduce the required size and cost of ground source heat pump (GSHP) systems for electrifying SFHs. This study investigated the costs and benefits of integrating air-sealing with GSHPs for retrofitting existing SFHs when compared with air-source heat pumps. A whole building energy simulation tool integrated with an advanced design tool for modeling ground heat exchangers was used to calculate changes in required GSHP capacity, total borehole length, and building energy consumption with and without air-sealing in SFHs in 16 US climatic regions. The results from this study showed that reducing outdoor air infiltration from 0.8 air changes per hour (ACH) to the minimum ventilation requirement (0.35 ACH) can significantly reduce borehole length (up to 55%), GSHP capacity (up to 48%), and total heating electricity reduction, especially in cold climates (up to 44%). The results also showed that for airtight homes (0.03 ACH infiltration) with a direct outdoor air system, the minimum required borehole length, GSHP capacity, and total heating electricity consumption can be reduced up to 70%, 68%, and 67%, respectively, when compared with SFHs with 0.8 ACH infiltration. Moreover, the life cycle cost analysis showed that air-sealing in conjunction with a GSHP is more profitable than replacing the existing system with an air-source heat pump, even without any incentives for most climatic regions in the US (except for some hot regions).

Ventilation effectiveness and incomplete mixing in air distribution design for airborne transmission

How ventilation should be arranged to be effective at reasonable air change rates is one key question as ventilation criteria and standard airborne disease transmission models are based on the well-mixed assumption, but air distribution patterns lead to non-uniform spatial concentrations. In this study a new method for ventilation effectiveness application in ventilation design for airborne transmission was developed and tested with tracer gas measurements in 22 rooms. Contrary to existing ventilation effectiveness values measured with distributed source, the developed method uses a couple of point source locations corresponding to an infector to quantify infection risk for each occupant. Novelty of the method is new ventilation effectiveness indicator that makes it possible to describe the effect of spatial variation of concentration and risk with single parameter. Quanta were used as input data to calculate the ventilation rate supplied by air distribution system corresponding to a specified risk level, but the differences between studied cases do not significantly depend on the quanta values. Application of the method to measured rooms showed that simple ventilation effectiveness calculation from average concentration at the breathing height, not requiring quanta data, provided lower ventilation effectiveness and higher ventilation rate in all cases. In many cases the difference in required ventilation rates was only a few percent, but in some large spaces it exceeded 10% with maximum of 39% in large open plan office with high concentration differences. Measured ventilation effectiveness values ranging from 0.5 to 1.4 indicate a substantial improvement potential in many cases.

Study of patterns of PM2.5 and PM10 changes in the atmospheric air of Ivano-Frankivsk region

The purpose of this research is to analyse the temporal patterns of changes in concentrations of dust particles – aerosols, regression modeling of the interdependence of PM2.5 and PM10 at the level of instantaneous, average hourly, average daily and average weekly concentrations, and assessment of the impact of the anthropogenic component of dust pollution of atmospheric air in the Ivano-Frankivsk region on regularities of the temporal distribution of these shares.The database for the study included measurements of the concentration of PM10, PM2.5 every hour at four Ecocity public monitoring stations: in the central part of the city of Ivano-Frankivsk, in the village of Bovshiv within the influence of the Burshtyn TPP, in the village of Broshniv-Osada within the influence of the woodworking enterprise "SVISS KRONO" and within the recreational territory of the village of Mykulychyn, Nadvirnyan district. The general regularity of the temporal distribution of PM10, PM2.5 was established for all posts for daily fluctuations – the highest concentrations are observed at night, the lowest – during the period of maximum daily temperatures. It has been proven by actual data that the greater the level of atmospheric air pollution (the greater the anthropogenic component of PM), the higher the daily concentrations of PM10, PM2.5 and the more often the one-time standards of solid suspended particles are exceeded.According to the data of monitoring stations from the territories with different anthropogenic influence, functional dependences of PM2.5 content on PM10 content were obtained for instantaneous values, hourly average values, daily average values, and weekly average values. The scientific novelty of the conducted research consists in the establishment of identical functional interdependence of temporal changes in concentrations of PM2.5 and PM10 dust particles within a conditionally clean area and within the limits of the influence of stationary sources of pollution with a high level of direct regression dependence and a coefficient of determination greater than 0.9 in all cases. This allows us to conclude that the temporal patterns of changes in both PM2.5 and PM10 will not differ in clean and polluted air conditions for the Ivano-Frankivsk region. In conditions of incomplete data on the temporal distribution of the concentration of PM10, the obtained equations can be used to forecast the temporal distribution of the concentration of PM2.5.

MODELING THE ENTRY OF AIR CONTAMINANTS INTO A ROOM

A mathematical model of air contaminant (products of human activity) inflow into the isolated air space has been developed. On the basis of the formula modified by us the simulation of human respiration with carbon dioxide, water vapor and heat emission is implemented. The model also takes into account the heat input from the human body through clothing. Applying numerical modelling ANSYS CFD (Computational Fluid Dynamics) on the basis of continuity equations and Reynolds-Averaged Navier-Stokes equations "RANS" (Reynolds-Averaged Navier-Stokes) the following results on air medium state change in the isolated space were obtained: - the human respiratory cycle is modelled at simultaneous heat transfer from the body surface through clothes into the studied air space; - the exponential equation of the trend line of concentration to observation time was obtained; - monitoring and rendering (visualization) of changes in concentration, temperature and relative humidity in the space under study by time along the room height was performed. These results and regularities served as initial data for solving a number of model non-stationary problems on aerodynamics and heat and mass transfer in the room. The inverse problem of general exchange ventilation was to be solved. Changes in the state of the air environment initially contaminated with carbon dioxide, heat and water vapors were studied when people were in the studied space and the supply and exhaust ventilation was operating. Of the four air change schemes planned for the study, the results for one schemes are presented in this publication. The dynamics of assimilation of excess heat, humidity and carbon dioxide made it possible to assess the efficiency of ventilation systems and to predict improvements in their energy efficiency when air parameters are brought up to standard values.

Structural optimization and battery temperature prediction of battery thermal management system based on machine learning

Lithium-ion batteries significantly extend the driving range for electric motorcycles. The battery thermal management system (BTMS) is critical for achieving optimal battery performance. Moreover, precise battery temperature prediction is essential for efficient thermal management. Therefore, a battery thermal management system integrating air and phase change material (PCM) cooling is proposed. Initially, the impact of PCM height, PCM thickness, and air velocity on battery temperature is analyzed. Subsequently, with cost minimization as the objective and ensuring that the maximum battery temperature remains below a threshold, the Black Kite Algorithm (BKA) is employed to optimize the BTMS structure. Finally, a BKA-Convolutional Neural Network (CNN)-Self Attention (SA) model is introduced for battery temperature prediction. The results indicate that increasing the thickness of the PCM and air velocity facilitates battery heat dissipation but with diminishing marginal effects. An increase in PCM height enhances battery cooling at low air velocities but becomes detrimental at high air velocities. The optimized PCM height is 35 mm, resulting in a cost of 0.073 USD for the BTMS per battery. Additionally, the BKA-CNN-SA model achieved a maximum error of 0.45 °C on the validation set and accurately predicted battery temperature changes before and after PCM melting.

Assessment of Energy Recovery Potential in Urban Underground Utility Tunnels: A Case Study

Underground spaces contain abundant geothermal energy, which can be recovered for building ventilation, reducing energy consumption. However, current research lacks a comprehensive quantitative assessment of its energy recovery. This research evaluates the energy recovery potential of the Xingfu Forest Belt Urban Underground Utility Tunnels. Field experiments revealed a 7 °C temperature difference in winter and a 2.5 °C reduction during the summer-to-autumn transition. A computational fluid dynamics (CFD) model was developed to assess the impact of design and operational factors such as air exchange rates on outlet temperatures and heat exchange efficiency. The results indicate that at an air change rate of 0.5 h−1, the tunnel outlet temperature dropped by 10.5 °C. A 200 m tunnel transferred 8.7 × 1010 J of heat over 30 days, and a 6 m × 6 m cross-sectional area achieved 1.1 × 1011 J of total heat transfer. Increasing the air exchange rate and cross-sectional area reduces the inlet–outlet temperature difference while enhancing heat transfer capacity. However, the optimal buried depth should not exceed 8 m due to cost and safety considerations. This study demonstrates the potential of shallow geothermal energy as an eco-friendly and efficient solution for enhancing building ventilation systems.

The co-benefits of a low-carbon future for PM2.5 and O3 air pollution in Europe

Abstract. There is considerable academic interest in the potential for air quality improvement as a co-benefit of climate change mitigation. Few studies use regional air quality models for simulating future co-benefits, but many use global chemistry–climate model output. Using regional atmospheric chemistry could provide a better representation of air quality changes than global chemistry–climate models, especially by improving the representation of elevated urban concentrations. We use a detailed regional atmospheric-chemistry model (WRF-Chem v4.2) to model European air quality in 2050 compared to 2014 following three climate change mitigation scenarios. We represent different climate futures by using air pollutant emissions and chemical boundary conditions (from CESM2-WACCM output) for three shared socioeconomic pathways (SSP1-2.6, SSP2-4.5 and SSP3-7.0: high-, medium- and low-mitigation pathways respectively). We find that in 2050, following SSP1-2.6, mean population-weighted PM2.5 concentrations across European countries are reduced by 52 % compared to 2014. Under SSP2-4.5, this average reduction is 34%. The smallest average reduction is 18 %, achieved following SSP3-7.0. Maximum 6-monthly-mean daily-maximum 8 h (6mDM8h) ozone (O3) is reduced across Europe by 15 % following SSP1-2.6 and by 3 % following SSP2-4.5, but it increases by 13 % following SSP3-7.0. This demonstrates clear co-benefits of climate mitigation. The additional resolution allows us to analyse regional differences and identify key sectors. We find that the mitigation of agricultural emissions will be key for attaining meaningful co-benefits of mitigation policies, as evidenced by the importance of changes in NO3 aerosol mass to future PM2.5 air quality and changes in CH4 emissions to future O3 air quality.