学生公寓节能设计中自然通风的研究与实践

本文对自然通风技术在学生公寓中的应用进行了数值模拟分析,同时采用建筑热环境模拟软件DeST分析了自然通风对全年能耗的影响,研究表明自然通风对于改善宿舍室内热环境是非常有利的。     

公路隧道纵向射流通风数值模拟与分析

采用CFD方法,建立公路隧道纵向射流通风的物理数学模型,对某隧道内一组射流风机通风进行三维数值模拟,以隧道纵向射流通风基本理论为基础,分析了隧道内气流速度和压力分布特性,为进一步优化纵向射流通风设计提供参考。     

Analysis of air conditioning system impact on a fuel cell vehicle performance based on a realistic model under actual urban conditions

In this study, a practical fuel cell vehicle considering the Heating, Ventilation, and Air conditioning system is considered to analyze hydrogen consumption under different working conditions. As a prevalent hydrogen-fueled vehicle, Toyota Mirai has been meticulously modeled in Simecenter Amesim software. The simulated model covers all of the vehicle's components with a concentration on Heating, Ventilation, and Air conditioning system. Since the air temperature and ‘weather conditions can significantly impact the vehicle's overall performance, various environmental conditions, including temperature variations, humidity, and varied solar fluxes, are taken into account. Furthermore, New York City is chosen as a densely populated megacity to simulate the dynamic behavior of the fuel cell vehicle under actual driving circumstances. The results illustrate that the Heating, Ventilation, and Air conditioning system can notably alter hydrogen consumption under real driving conditions. In this regard, turning on the Heating, Ventilation, and Air Conditioning system results in a 19% increase in fuel consumption. Moreover, the degradation phenomenon, which is a typical result of using fuel cell vehicles under urban driving conditions, impacts the vehicle's mileage and hydrogen consumption. The simulation results indicate that a fresh fuel cell stack consumes 80 g of hydrogen, while for 2500 and 5500 working hours fuel cells, the stack consumes 89.6 and 107 g of hydrogen, respectively. Based on the obtained results, a 33.75% increase in fuel consumption occurs by implementing a degraded fuel cell stack under real driving conditions.     

煤矿智能局部通风监控系统

煤矿局部通风监控系统是为煤矿井下掘进工作面设计的专用通风监测监控系统。系统采用先进的计算机网络技术、变频驱动技术、传感技术、瓦斯涌出预测技术、智能通风技术、EMC抗干扰技术,实现掘进工作面通风设备的远程监控和无人值守、掘进工作面环境参数的远程监测、掘进工作面通风量的手动、自动调节。     

Removal of submicron particles using a carbon fiber ionizer-assisted medium air filter in a heating,ventilation, and air-conditioning (HVAC) system

Laboratory tests of particle removal were performed with a pair of carbon fiber ionizers installed upstream of a glass fiber air filter. For air flow face velocities of 0.4, 0.6, and 0.8 m/s, the overall particle removal efficiencies of the filter for all submicron particles were 17%, 16%, and 14%, respectively, when the ionizers were not turned on. These values increased to 27%, 23%, and 19%, respectively, when the ionizers were used to generate ions of 6.0 × 10⁹ ions/cm³ in concentration. The carbon fiber ionizers were then installed in front of a glass fiber air filter located in a heating, ventilation, and air-conditioning (HVAC) system. Field tests were performed in a test office room with a total indoor particle concentration of 2.2 × 10⁴ particles/cm³. When the flow rate was 75 cubic meters per hour (CMH), the steady-state values of the total indoor particle concentrations using the glass fiber air filter with and without ionizers decreased to 0.87 × 10⁴ particles/cm³ and 1.15 × 10⁴ particles/cm³, respectively, resulting in a 25% decrease of the ionizer effect. When the operation flow rate was increased to 115 and 150 CMH, the effect of the ionizer decreased to 19% and 17%, respectively. These experimental data match the results calculated using a mass-balance model whose parameters were determined from laboratory tests.     

Experimental investigation of thermal and ventilation performances of stratum ventilation

Stratum ventilation has been proposed to cope for elevated indoor temperatures. Air speed, temperature and CO₂ concentration of a stratum ventilated office are investigated experimentally. The data obtained under well defined conditions and therefore can be used for validating numerical models. Thermal comfort conditions and ventilation efficiency are studied based on the experimental results of four experimental cases. Thermal comfort indices, i.e. PMV, PPD and PD are calculated from measured data. The values of these indices are found to satisfy the requirements of ISO 7730, CR 1752-1998 and ASHRAE 55-2010. In terms of thermal comfort, the two cases with supply air temperature of 21 °C are found to perform better compared with the two cases with supply air temperature of 19 °C. For all the cases, the ventilation effectiveness is close to 1.5. This ventilation method could therefore be expected to provide indoor air quality in an efficient way.     

Three dimensional study for evaluating of air flow movements and thermal comfort in a model room: Experimental validation

This paper presents the results of a three dimensional study for evaluating the temperature profiles and air flow movement in a model room with a numerical model based on the Euler equations. Numerical results obtained for two scenarios of ventilation and air conditioning are compared with the predictions of a Navier-Stokes model. These numerical results are validated by experimental results measured in the model room. A comparison of the local thermal comfort indices PMV and PPD obtained experimentally and numerically is also presented. Results show that the Euler model is able to predict adequately total thermal comfort in the model room. Furthermore, the use of Euler equations allows a reduction of computational time in the order of 50% compared to the Navier-Stokes modeling.     

Thermal energy savings in buildings with PCM-enhanced envelope: Influence of occupancy pattern and ventilation

Integration of building materials incorporating PCMs into the building envelope can result in increased efficiency of the built environment. A PCM-enhanced wall system is proposed in this paper and a simplified model for the heat exchange between the indoor environment and ambient was developed. The objective of the study was to assess the effect of occupancy pattern and ventilation on the energy savings potential of the wall system. It was found that (1) the occupancy pattern influences the value of the PCM melting point for which maximum energy savings value was reached and (2) the ventilation and its pattern reduces the relative value of the energy savings.     

The maximum temperature of buoyancy-driven smoke flow beneath the ceiling in tunnel fires

In order to detect a fire and provide adequate fire protection to a tunnel structure, the maximum gas temperature beneath the ceiling to which the structure is exposed needs to be estimated. Theoretical analysis of maximum gas temperature beneath a tunnel ceiling based on a plume theory is given. The heat release rate, longitudinal ventilation velocity and tunnel geometry are taken into account. Two series of model-scale experimental tests were also carried out. The results of both analysis and experiments show that the maximum excess gas temperature beneath the ceiling can be divided into two regions. When the dimensionless ventilation velocity is greater than 0.19, the maximum excess gas temperature beneath the tunnel ceiling increases linearly with the heat release rate and decreases linearly with the longitudinal ventilation velocity. When the dimensionless ventilation velocity is less than 0.19, the maximum excess gas temperature beneath the ceiling varies as the two-thirds power of the dimensionless heat release rate, independent of the longitudinal ventilation velocity. In both regions, the maximum excess gas temperature varies as the −5/3 power of the vertical distance between the fire source bottom and tunnel ceiling. The investigation presented here considers only the cases when the continuous flame region is lower than the ceiling height.