Search Results (160)

High outdoor PM_2.5 levels in Chinese cities pose significant challenges to maintaining healthy indoor air quality in residential buildings, where mechanical ventilation systems are increasingly adopted for pollution control. In this paper, to control the indoor PM_2.5 concentration, a mass balance equation for the non-uniform mixing model has been established to calculate the filter efficiency. This study aims to optimize PM_2.5 pollution control in residential buildings through mechanical ventilation systems by evaluating the synergistic effects of filter efficiency and ventilation air flow rates under high outdoor PM_2.5 conditions. Field measurements and numerical calculations were conducted to monitor indoor and outdoor PM_2.5 concentrations. Results showed that, When outdoor PM_2.5 concentrations remain below 100 μg/m³, an air exchange rate of 3 h⁻¹ effectively maintains indoor PM_2.5 levels below 35 μg/m³ for M6-F8 air filters. Experimental data demonstrate that when a fresh air system equipped with H10 filters operates at an outdoor PM_2.5 concentration of 150 μg/m³, the corresponding optimal ventilation rate is 0.45 h⁻¹. Increasing the mechanical ventilation rate to 1 h⁻¹ enables the system to effectively handle higher outdoor concentrations up to 176 μg/m³. Under severe pollution scenarios with outdoor PM_2.5 concentrations reaching 250 μg/m³, the air exchange rate should be further increased to 1.65 h⁻¹ to maintain indoor PM_2.5 concentrations within acceptable limits. This study provides practical insights for improving residential indoor air quality under high outdoor PM_2.5 conditions in Chinese cities. Full article

Outdoor access, often referred to as pop holes, is widely used to improve the production and welfare of hens. Such cage-free environments present an opportunity for precision flock management via best environmental control practices. However, outdoor access disrupts the integrity of the indoor environment, including properly planned ventilation. Moreover, complaints exist that hens do not use the holes to access the outdoor environment due to the strong incoming airflow through the outdoor access, as they behave as uncontrolled air inlets in a negative pressure ventilation system. As the egg industry transitions to cage-free systems, there is an urgent need for validated computational fluid dynamics (CFD) models to optimize ventilation strategies that balance animal welfare, environmental control, and production efficiency. We developed and validated CFD models of a cage-free hen house with outdoor access by specifying real-world conditions, including two exhaust fans, sidewall ventilation inlets, wire-meshed pens, outdoor access, and plenum inlets. The simulations of four ventilation scenarios predict the measured air flow velocity with an error of less than 50% for three of the scenarios, and the simulations predict temperature with an error of less than 6% for all scenarios. Plenum-based systems outperformed sidewall systems by up to 136.3 air changes per hour, while positive pressure ventilation effectively mitigated disruptions to outdoor access. We expect that knowledge of improved ventilation strategy will help the egg industry improve the welfare of hens cost-effectively. Full article

This paper presents the airflow characteristics of humidity-sensitive air inlet. This type of air inlets and exhausts are often part of demand control ventilation, especially in dwellings where humidity is an important indicator of ventilation needs. Humidity-controlled ventilation is one of the simplest implementations of smart ventilation, even in the case of a natural ventilation system. This type of solution leads to decreased energy consumption and increases the indoor air quality. A description of airflow characteristics is crucial for resolving these issues. The presented characteristics are based on the measurements of the indoor/outdoor relative humidity, airflow, and pressure drop across the air inlet. The characteristics are described based on a general power law flow model (V = C·∆pⁿ), which is the most suitable, for example, for the CONTAM multizone indoor air quality and ventilation analysis computer program. The characteristics include relationships between the indoor and outdoor relative humidity, hysteresis, and dynamic changes in indoor relative humidity. The simplified and complex formulas are presented. The accuracy of the airflow calculation based on these formulas is discussed. Full article

Double skin facade (DSF) is an energy-efficient solution for glazing facades. However, previous studies have reported inconsistent findings regarding thermal comfort in naturally ventilated DSF buildings. To examine this issue, this study evaluated airflow velocities in naturally ventilated DSF buildings during transition seasons through a comparative study approach. A full-scale box-type DSF room and a traditional window-wall room were simultaneously monitored in a laboratory building under real climatic conditions, with indoor environmental parameters recorded for 10 days. Airflow sensation surveys complemented the physical measurements to evaluate perceived comfort. The results showed that the DSF room consistently exhibited lower air velocities (≤0.2 m/s) compared to the traditional room, demonstrating minimal response to wind conditions related to its small openings (opening ratio of 4.7%) and increased flow resistance from the dual-layer structure of the DSF. Under unfavorable wind conditions, the DSF room demonstrated higher ventilation rates due to the enhanced stack effect. However, this advantage had a negligible effect on the thermal comfort vote for the indoor temperature range (26 °C to 28 °C). These findings highlight the climate-dependent performance of DSFs: while advantageous for thermal comfort in cooler climates, they may lead to reduced thermal comfort in warm and hot climates due to low indoor airflow velocities. Future work could include the optimization of DSF opening configurations to enhance wind-driven ventilation while maintaining stack ventilation benefits. Full article

Porosity is the key factor affecting a medium’s tortuosity, effective evaporation area coefficient, and ventilation resistance, and further affects the drying efficiency, energy consumption, and drying uniformity in the drying process. To reveal the dynamic variation characteristics of porosity in paddy flow layer, an air convection drying apparatus was established and a mathematical porosity model was established based on response surface methodology. The reliability of the model was verified through EDEM–Fluent coupled digital simulation and experiments. The research results show that under different paddy flow rates v_d (0.01 m/s, 0.03 m/s, 0.05 m/s), different moisture contents M_c (14% w.b., 23% w.b., 32% w.b.), different wind speeds v_w (0.4 m/s, 0.6 m/s, 0.8 m/s), and different layer thicknesses L (100 mm, 150 mm, 200 mm), the porosity values obtained by the porosity measurement device range from 39.562% to 46.006%. The relative errors between the actual values (ε_r), the simulation values (ε_s), and the predicted values (ε_p) are all within ±1%. Moreover, the obtained mathematical porosity model has high reliability (R² = 0.968). The Conclusions provide an analysis method for dynamic change characteristic parameters and basic data for the dynamic change of porosity to reduce drying energy consumption, improve the drying power coefficient, and enhance drying quality. Full article

This study investigates the mechanism behind the cavitation-induced noise in an automotive heater core and proposes a structural solution to eliminate it. Abnormal noise during cold-start conditions in a compact passenger vehicle was traced to cavitation in the heater core of the heating, ventilation, and air conditioning (HVAC) system. Controlled bench tests, in-vehicle measurements, and computational fluid dynamics (CFD) simulations were conducted to analyze flow behavior and identify the precise location and conditions for cavitation onset. Results showed that high flow rates and low coolant pressure generated vapor bubbles near the junction of the upper tank and outlet pipe, producing distinctive impulsive noise and vibration signals. Flow visualization using a transparent pipe and accelerometer data confirmed cavitation collapse at this location. CFD analysis indicated that the original geometry created a high-velocity, low-pressure region conducive to cavitation. A redesigned outlet with a tapered transition and larger diameter significantly improved flow conditions, raising the cavitation index and eliminating cavitation events. Experimental validation confirmed the effectiveness of the modified design. These findings contribute to improving the acoustic performance and reliability of automotive HVAC systems and offer broader insights into cavitation mitigation in fluid systems. Full article

The building drainage system (BDS) is a critical building component and must be designed to protect public health by maintaining safe and hygienic conditions within the indoor environment. The recent COVID-19 pandemic and the emergence of other wastewater-related issues, such as the spread of anti-microbial resistance (AMR), place the BDS at the centre of the public health agenda. To understand the complex characteristics of the BDS and its performance, the numerical simulation model AIRNET was used to model whole system responses to discharging events. In this study, the model’s effectiveness and accuracy were evaluated through its application in a case study system representative of a real-world tall building. Data reflecting actual conditions were collected using the drainage test rig at the National Lift Tower (NLT) in Northampton. The data show a strong correlation between the measured and modelled air pressures in the system over time and along the drainage stack height. More importantly, a sample dataset representing various ventilation configurations, flow rates, and water usage combinations shows a strong linear relationship between the simulated and measured pressure values. These results confirm the accuracy and reliability of the AIRNET model in modelling the BDS, even when applied to high-rise buildings. This is crucial for addressing drainage challenges in high-rise building design. Full article

This study quantitatively analyzes the effects of various ventilation parameters on airflow stability in confined spaces ventilated by opposed jets, a common configuration in high-density settings. Using large eddy simulations (LES), we evaluate how changes in supply velocity, airflow configuration, enclosure geometry, and thermal gradients influence airflow dynamics. Findings show that higher supply velocities, up to 1.92 m/s, lead to a measurable increase in oscillation period (from 7.7 s to 11.3 s) and reduce small-scale flow disturbances. The free jet configuration exhibits higher oscillation amplitude and a more disordered structure compared to the attached jet, resulting in uneven airflow distribution. Aspect ratio has a pronounced effect, with increased ratios extending oscillation periods from 10.6 s to 18.1 s and intensifying turbulence. Thermal gradients, with floor temperatures rising from 15 °C to 35 °C, and the oscillation period are increased, further dispersing airflow and reducing stability. Phase space reconstruction and power spectral analysis provide quantitative benchmarks for oscillation frequencies and patterns, correlating velocity time series with airflow structural changes. The findings from this study can serve as a foundation for future research on thermal comfort and air quality management in enclosed environments. Full article

This work presents a study on the calculation of transmittance in an air handling unit (AHU) through three methods. A semi-empirical estimation based on simplified models of heat and mass transfer has been used. In addition, experimental tests were carried out in a real AHU under controlled conditions. The measured temperature inside and outside the AHU were used to calculate the transmittance. Finally, numerical simulations were performed on specific sections of the AHU and on a global model, with and without radiation. The simulations provided detailed results on the flow behavior and temperature distribution. The results were compared and analyzed to assess the accuracy and applicability of the three methods. The heat transfer obtained with the semi-empirical method is 38% larger than that obtained with the experimental measurement, in contrast with the 8% of difference observed with numerical simulations. It is revealed that radiation, and thus the emissivity of surfaces, plays an important role in heat transfer of the AHU. This research contributes to the knowledge and understanding of transmittance in AHUs, providing valuable information for the design and optimization of heating, ventilation, and air conditioning (HVAC) systems. Full article

This study evaluated housing designs and bedding systems to improve air quality in swine facilities, focusing on odor and particulate matter (PM) reduction. Three experimental animal house designs (M1, M2, M3) were tested: M1 used circulating airflow with negative pressure, M2 featured a plug flow air pattern with a perforated plastic bed, and M3 employed a sawdust bedding system with recirculating ventilation. Nine fattening swine were housed in each 12 m² house over 110 days (6 May to 26 August 2018). Appropriate air samples were collected, and odorous compounds, volatile organic acids (VOA), PM, and bacterial concentrations measured. Results showed that M3 had the lowest ammonia (NH₃) levels (5.9 ± 1.5 ppm) and undetectable hydrogen sulfide (H₂S), while M1 recorded the highest NH₃ (9.1 ± 2.2 ppm). VOA concentrations were significantly lower in M3 (75 ± 1.3 ppbv) compared to M1 (884 ± 15 ppbv) and M2 (605 ± 10.3 ppbv). PM10 levels were highest in M3 (312 ± 11 μg/m³) and lowest in M1 (115 ± 3 μg/m³), and thus bacterial counts were elevated in M3 (2117 ± 411 cfu/min), whereas M1 showed the lowest bacterial count of 1029 ± 297 cfu/min. The sawdust bedding system effectively reduced odorous compounds, highlighting its potential for odor control. However, higher PM levels in M3 emphasize the need to balance environmental management with animal welfare. These findings suggest that optimizing housing designs and bedding systems can enhance air quality in swine facilities while addressing sustainability and welfare concerns. Full article

Battery electric vehicles (BEVs) are one promising approach to mitigating local greenhouse gas emissions. However, they still lag behind conventional vehicles in terms of maximum driving range. Using the heating, ventilation, and air-conditioning (HVAC) system reduces the maximum driving range of the vehicle even further since the energy for the HVAC system must come from the battery. This work investigates the impact of (1) an air–air heat exchanger and (2) an improved thermal insulation of a truck cabin on the heating performance of the HVAC system. Additionally, the required fresh-air volume flow rate to keep the CO₂ level within the truck cabin below the critical value of 1000 ppm is factored in. The results show that the two simple measures proposed could increase the energy efficiency of the truck’s HVAC system by 22%. When two persons are present in the truck cabin, a fresh-air volume flow of around 100 m³/h is required to keep the CO₂ concentration around 1000 ppm. These results prove that, even with simple measures, the energy efficiency of vehicles’ subsystems can be increased. In the future, more research will be necessary to further improve the energy efficiency of other vehicular subsystems. Full article

The acoustic emissions of ventilation systems and their subcomponents contribute to the perceived overall comfort in indoor environments and are, therefore, the subject of research. In contrast to fans, there is little research on the aeroacoustic properties of air diffusers (often referred to as outlets). This study investigates a commercially available ceiling swirl diffuser. Using a hybrid approach, a detailed three-dimensional large-eddy simulation is coupled with a perturbed wave equation to capture the aeroacoustic processes within the diffuser. The flow model is validated for the investigated operating point of 470 m³/h using laser-optical and acoustic measurements. To identify the noise sources, the acoustic pressure is sampled with various receivers and on cut sections to evaluate the cross-power spectral density, and the sound-pressure level distribution on cut sections is evaluated. It is found that the plenum attenuates the noise near its acoustic eigenmodes and thus dominates other noise sources by several orders of magnitude. By implementing the plenum walls as sound-absorbing, the overall sound-pressure level is predicted to decrease by nearly 10 dB/Hz. Other relevant geometric features are the mounting beam and the guide elements, which are responsible for flow-borne noise emissions near 698 Hz and 2699 Hz, respectively. Full article

Determining the appropriate position of a positive pressure ventilator, where it exhibits the highest efficiency (measured by the achieved volumetric flow rate), can influence the success of rescue operations conducted by fire protection units. The aim of this article is to evaluate the possibility of using LES (Large Eddy Simulation) analyses to verify the positioning parameters of positive pressure ventilators in numerical simulation conditions, without the need for time-consuming experiments. The article presents a comparative analysis of full-scale experimental studies (conducted on a test setup to assess the velocity profile of the air jet in open flow) and CFD numerical analyses. The analysis confirmed the convergence of the flow rate parameter entering the surface of the door opening model installed on the test setup. Depending on the distance of the ventilator position (1–7 m), a convergence degree ranging from 1.6% to 3.8% was achieved for the volumetric flow rate. This publication demonstrates that the LES model is a suitable tool for effectively determining the working positions of positive pressure ventilators, as defined in real working conditions (open flow). The analysis may serve as a helpful tool for manufacturers of mobile ventilators, who can use the method for the technological testing of their units without conducting time-consuming experiments. Full article

Air pollution in urban street canyons presents a serious health risk, especially in densely populated areas. While previous research has explored airflow characteristics in these canyons, it often lacks detailed data on pollutant dispersion and the effects of wind speed on airflow patterns and vortex formation. This study uses Computational Fluid Dynamics (CFD) to deliver quantitative measurements of pollutant dispersion rates and qualitative insights into airflow patterns across various street canyon morphologies. The analysis examines a range of aspect ratios (ARs), from wide (AR = 0.75) to narrow (AR = 4.5), and different wind speeds to evaluate their effects on pollutant dispersion. Findings indicate that purging flow rates decline as the AR increases, with a more pronounced decrease at lower AR values. In narrower streets, airflow patterns are particularly sensitive to wind velocity, leading to unexpected vortices that hinder effective pollutant dispersion. By incorporating these insights into urban design strategies, cities can enhance street ventilation, thereby reducing pollutant concentrations and improving public health. This study also tests a specific street layout in Seville to predict pollutant accumulation under various conditions, assessing health risks based on World Health Organization guidelines. Ultimately, this research aids in developing healthier, more sustainable urban environments. Full article

Background: Chronic Obstructive Pulmonary Disease (COPD) is a disease with high morbidity and mortality globally. Exacerbations of COPD are major contributors to disease progression and a decline in health-related quality of life (HRQoL). High-flow nasal cannula (HFNC) oxygen therapy is an innovative therapy that provides humidified and heated blended air and oxygen through a nasal cannula. There is some preliminary evidence supporting the effectiveness of HFNC in managing COPD exacerbations, but there are limited data on its effectiveness when used at home for patients with stable, severe COPD. The aim of the present study is to test the hypothesis that home HFNC can decrease the COPD exacerbations rate and hospital admissions and improve HRQoL measures in severe COPD patients with frequent COPD exacerbations. Methods: In a prospective proof-of-concept interventional multicenter study, 40 GOLD stage III and IV COPD patients with a high disease burden (≥2 exacerbations treated with antibiotics and/or corticosteroids) and ≥1 hospital admission in the last year were included. Patients were given instructions on the usage of HFNC by a ventilation practitioner during a group session. The flow rate was 25–30 L/min and FiO₂ was 21–35%. Outcome measures included the COPD exacerbations rate, hospital admissions, in-hospital days, Medical Research Council dyspnea (MRC) score, Clinical COPD Questionnaire (CCQ) score, Hospital Anxiety Depression Scale (HADS) scores and capillary pCO₂. Repeated analysis of variance (ANOVA) was used to analyze the data. Significant effects identified in the ANOVA were further examined using Student’s t-tests. Results: After 1 year, 27 patients could be evaluated. The COPD exacerbations rate decreased by 1.40 (mean difference ± SD: 1.40 ± 2.09; p = 0.002), hospital admissions decreased by 0.96 admissions per year (0.96 ± 1.37; p = 0.001), and in-hospital days decreased by 7.22 days (7.22 ± 9.26; p = 0.001). Capillary pCO₂ decreased by 0.02 kPa (0.02 ± 0.52; p = 0.85). The CCQ score decreased by 0.06 (0.06 ± 0.96; p = 0.76). The MRC dyspnea score decreased by 0.04 (0.04 ± 0.80; p = 0.81). The HADS anxiety score decreased by 0.63 (0.63 ± 3.12; p = 0.31). And finally, the HADS depression score decreased by 0.32 (0.32 ± 3.48; p = 0.64). There was a significant difference between the normocapnic (capillary pCO₂ < 6.0 kPa) group and the hypercapnic group in terms of change in the CCQ score (−0.24 ± 0.55 and 0.49 ± 1.32 decrease, respectively, p = 0.05) and the HADS depression score (−0.76 ± 1.86 and 2.20 ± 4.75 decrease, respectively, p = 0.03) after 1 year of HFNC treatment. Conclusions: One-year-long HFNC therapy significantly decreased the COPD exacerbations rate, hospital admissions, and in-hospital days in severe COPD patients with a high disease burden and frequent COPD exacerbations irrespective of them having hypercapnia and with the HRQoL measures only improving in the hypercapnic group. This may imply that severe COPD patients with a high disease burden and frequent COPD exacerbations, irrespective being hypercapnic, are candidates for treatment with home HFNC oxygen therapy. Full article