In winter, greenhouses located in mid to high latitudes are required a function of dehumidification and warming due to the low outdoor temperature. Focusing on small spires greenhouses, this study ...regulates the low temperature and high humidity environment inside the greenhouse and proposes a new-type of greenhouse heat and humidity regulation system by combining composite solid desiccant dehumidification with ground heat exchange system. The greenhouse internal environment is warmed and dehumidified at night by utilizing the adsorption effect of the compound dehumidifier and the sensible heat exchange between the heat exchange system in the ground and the greenhouse. Solar thermal energy is collected during the day using multi-curved tank collector (MTC) for thermal storage in the geothermal system and desiccant desorption. The rationality of pipeline layout is verified through CFD simulation, and the indoor temperature and humidity distribution during the system operation is explored. The experimental results show that the moisture adsorption capacity of the composite desiccant SG-CaCl2 for 10h is 0.511 g/g. The optimal regeneration temperature is 80–100 °C. This system can reduce the nighttime relative humidity of the greenhouse in winter from 96.5 % to 83.6 %, and the average indoor air temperature after warming is 12.8 °C. The heat exchange efficiency of the underground heating exchange system is 0.38. During the desorption phase on daytime, the maximum outlet temperature of MTC is 103.8 °C, and the average heat collection efficiency is 0.42. The system can effectively regulate the air environment in the greenhouse to the appropriate zone for crop growth by combining solar thermal collector technology with recyclable solid dehumidification technology.
•A novel heat and humidity control system of solar greenhouse with composite desiccants was proposed.•The performance of the system is analyzed in detail through experiments and simulations.•The moisture adsorption capacity of the composite desiccant SG-CaCl2 for 10h is 0.511 g/g.•This system can reduce the nighttime relative humidity of the greenhouse in winter from 96.5 % to 83.6 %.
The air quality in a street canyon seriously affects the exposure level of pollutants for pedestrians and is directly related to the indoor air quality (IAQ) of surrounding buildings. In order to ...improve the street canyon environment, it is necessary to clarify the distribution and dispersion characteristics of pollutants. Through field tests, wind tunnel experiments, and numerical simulation, the current research studied the nature of pollutants in street canyons and provided some improvement measures. This paper comprehensively introduces the characteristics of pollutants in street canyons and reviews past studies on the following parts: (a) the dispersion principle and main impact factors of pollutants in street canyons, (b) the spatial and temporal distribution of pollutants in street canyons, (c) the relationship between pollutants in street canyons and indoor air quality, and (d) improvement measures of the street canyon environment. The dispersion of pollutants is dominated by the air exchange between the street canyon and the upper atmosphere, which is strengthened when the wind speed is high or when the temperature in the street canyon is obviously higher than the surrounding area. The heat island effect is beneficial for pollutant dispersion, while the inversion layer has a negative influence. Dense buildings mean lower pollutant diffusion capacity, which causes pollutants to easily gather. Pollutants tend to accumulate on the leeward side of buildings. The concentration of pollutants decreases with the increase of height and drops to the background level at a height of several hundred meters. The temporal distribution of pollutants in street canyons varies in diurnal, weekly, and annual periods, and the concentration peaks in the winter morning and summer evening. Besides, pollutants in street canyons have a significant influence on IAQ. To improve the street canyon environment, green belts and other facilities should be reasonably set up in the streets. Future research should pay attention to comprehensive test data, solving disagreement conclusions, and quantitative evaluation of the various impact factors on pollutants, etc.
The ventilation performance of air shafts is important to the air quality of subway tunnels, but there is no unified evaluation index of ventilation performance. In this paper, the air shafts at ...different locations in subway tunnels were taken as research objects, and the wind speed as well as the particulate matter concentration of each air shaft was tested. The effective ventilation volume and PM2.5 discharge efficiency of the air shafts were defined to evaluate the ventilation performance. It was found that on average, during the subway train service, the station air shaft on the train-arriving side can discharge 2050 m3 of dirty air in the tunnels and inhale 218 m3 of fresh air from the outside environment, while the station air shaft on the train-leaving side can absorb 2430 m3 of fresh air but can hardly effectively discharge dirty air; meanwhile, the middle air shaft can not only effectively exhaust 1519 m3 of dirty air but can also absorb 7572 m3 of fresh air. In addition, the middle air shaft has better ventilation performance if its inner opening is set on the top rather than on the side of the tunnel. The PM2.5 discharge efficiency of the station air shaft on the train-arriving side is 52.0~62.8%, higher than that of the middle air shaft of which the value is 26.8~40.7%. This research can provide guidance for ventilation performance evaluation of subway air shafts and provide a reference for subway tunnel air shaft location design.
The ventilation performance of air shaft is important to the air quality of subway tunnel, but there lacks of unified evaluation index of ventilation performance. In this paper, the air shafts at ...different locations in subway tunnel were taken as research objects, and the wind speed of each air shaft was tested. The effective ventilation volume of air shafts was defined to evaluate the ventilation performance. It was found that on average, during the subway train serve once, the station air shaft in train-arriving side can discharge 2050 m
3
dirty air in the tunnel and inhale 218 m
3
fresh air from the outside environment, while the station air shaft in train-leaving side can absorb 2430 m
3
fresh air, but can hardly effectively discharge dirty air; meanwhile, the middle air shaft can not only effectively exhaust 1519 m
3
dirty air, but also absorb 7572 m
3
fresh air. And the middle air shaft has better ventilation performance if its inner opening set on the top rather than on the side of the tunnel. This research can provide guidance for ventilation performance evaluation of subway air shafts and reference for the subway tunnel air shaft location design.
At present, the massive emissions of carbon dioxide and nitrogen oxides and other greenhouse gases caused by human activities have caused more and more serious negative effects on global climate ...change. In order to cope with global warming and achieve sustainable development, achieve “carbon neutrality” as soon as possible. In the refrigeration industry, it is necessary to reduce greenhouse gas emissions related to refrigerants, including the production, use, and recycling of refrigerants. This paper has carried out the calculation of greenhouse gas emissions during the refrigerant preparation process, and compared and analyzed the emission reductions of refrigerant recycling and reuse; the research based on the energy consumption of the refrigerant production process uses the greenhouse gas emission inventory analysis method to Taking refrigerant R134a as an example, the carbon emission accounting boundary of the production process is set, the emission source is determined, the emission is calculated based on the emission factor method, and the emission inventory is established; the carbon offset effect of the recycling and reuse of the refrigerant is analyzed. The research results show that if the entire refrigerant industry fully recycles waste refrigerants, it can reduce carbon emissions by about 29.7% compared to just producing new refrigerants.
Highway traffic increasingly extends to the mountainous area, requiring highway tunnels to be longer. Highway tunnel construction is risky and challenging, especially in the high ground temperature ...area of Western China. In this study, the Nige Tunnel of Yunnan Honghe Jian(ge) Yuan highway is the research object. By conducting numerous field temperature tests, geological surveys, water quality experiments, and other processes, the causes of high temperatures in the ground have been analyzed. The results show that the hot liquid or vapor from the earth's crust deep area carries various chemical materials, passing through various channels (faults and fissures) to the superficial area and forms the geothermal of the tunnel. The thermal anomaly bodies in the deep crust move upward through faults Fn1 and Fn2. Some heat sources are exposed to the surface and form hot springs, and others are distributed through secondary channels after being transmitted to the shallow part of the crust. Among them, the entrance section of the Nige Tunnel is limestone, and the groundwater infiltrating the fracture channel is mixed in the conduction process, resulting in the overall low water temperature, and the rock wall temperature is lower than the water body temperature. The exit section of the Nige Tunnel is granite, the heat source is mainly conducted through structural fractures or rock mass, resulting in high rock temperature at the exit. By analyzing the causes of high ground temperature, this study provides a theoretical basis for developing the tunnel scheme.
Wind tower is a traditional zero-energy natural ventilation device, which is capable of reducing building energy consumption and improving indoor environment. Many studies were conducted for its ...performance evaluation and design optimization, but most of them are more like underground applications. This paper aims to integrate the wind tower with single-sided natural ventilated house to arrange more desirable indoor air distribution. The ventilation behavior of the wind tower in a low-rise house was firstly compared with a common underground application. Then, effects of combining with different window configurations were investigated. CFD simulations were conducted using well validated numerical models. The results show that local wind environment must be well reproduced to accurately predict indoor airflow. Under the same incoming wind speed, the ventilation effectiveness of the wind tower in the low-rise house is 15%–40% lower than the underground application due to the effect of the separating flow above the roof. Optimizing the roof structure and slope to change the local flow field may improve the ventilation capability of the wind tower. When combining wind tower with different window configurations, setting a window on the windward wall is a more promising solution to improve cross-ventilation, since that the wind tower is in the negative pressure region above the roof. When the indoor temperature is higher than the outdoor, the exhaust wind tower will perform better due to the stack effect. The findings can provide practical implications for the performance evaluation and application of wind tower in contemporary house design.
•The wind tower is integrated with single-sided natural ventilated house.•CFD to accurately predict the ventilation behavior of the wind tower.•The application in low-rise house was compared with underground house.•Effect of combining with different window configurations were investigated.•Practical implications are provided for contemporary wind tower house design.
Airflow and traffic pollutant dispersion characteristics within street canyons are complicated due to buoyancy forces induced by uneven thermal environments. This study investigates the ...microenvironment within street canyons under the combined impacts of wind-thermal forces and the airflow driving mechanisms based on the Richardson number using Computational Fluid Dynamics. The buoyancy force drives airflow and pollutants to converge towards the central axis, forming a pair of large-scale counter-rotating vortices with the height of vortex centers exceeding 2.7H. This concentrates over 50% of total pollutants and 90% of total updraft in the central region. High-speed wind forms air curtains at junctions and generates multiple pairs of vortices with vortex center heights near 0.7H. Under low-speed wind conditions, the air exchange between the street canyon and the upper atmosphere can increase to 7 times when thermal effects are taken into account. These findings deepen the understanding of microenvironment characteristics within street canyons.
Natural ventilation in relatively enclosed underground spaces has aroused people’s interest due to the poor air quality and high energy consumption of mechanical ventilation. Small-scale experiments ...and numerical simulation are utilized to investigate the influence of thermal and wind conditions on the ventilation characteristics of underground corridors. The non-dimensional flow rate is calculated, which can be used to evaluate ventilation performance and predict airflow rate. The interaction of driving forces is quantitatively analyzed based on the Archimedes number and the critical non-dimensional flow rate. The results reveal that incoming wind counteracts buoyancy partly in shear ventilation, while the wind promotes buoyancy-driven ventilation in cross ventilation. The air change rate decreases under different driving force modes, from the purely buoyancy-driven to the combined-force-driven to the purely wind-driven, for shear ventilation with the wind speed of 1 ∼ 3 m/s. For cross ventilation, the descending order is the combined-force-driven, the purely wind-driven, and the purely buoyancy-driven. When driven by wind, non-dimensional flow rate remains constant with a value of 0.025 for shear ventilation and 0.68 for cross ventilation in the corridors with the opening ratio less than 12 %. When driven by combined force, Q* is not a constant value but rather varies with wind speed. Especially when the wind speed exceeds 1.5 m/s, the buoyancy can be ignored in cross ventilation. The findings of this study can serve as a basis for ventilation design and the prediction of ventilation rate in underground corridors.
Particles deposition on surfaces directly affects the transmittance of PV panels, which leads to the decrease of performance of PV modules. This paper introduces a kind of overlapping model proposed ...by NASA, analyses the effect of the shape and size distribution on transmittance, and verifies it by test data of relevant references. Then a computation model on different incident angles is studied, whose result is compared with another model's. It demonstrates that this computation model can accurately calculate the effect of particle deposition on transmission of photovoltaic panels.
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