Effects of Indoor Temperature and Air Movement on Perceived Air Quality in the Natural Ventilated Classrooms

Perceived air quality is an important aspect in current guidelines and standards for indoor environment. It represents occupants’ real feeling about indoor air and affected by almost all environmental parameters, such as the temperature, the relative humidity, the air movement, and et al. Studies were conducted mainly in controlled climate chambers or air-conditioned spaces, rarely in natural ventilated spaces. In this paper, the effects of temperature and air movement on perceived air quality in natural ventilated classrooms are investigated. The indoor environmental parameters in 7 classrooms for 35 lessons are continuously measured and the students in class are asked to report their perception on the temperature, air movement, and the air quality of classrooms by filling questionnaires at once after a lesson. The number of received validated questionnaires is 992. The correlation analysis is used to investigate the effects of temperature and air movement on the perceived air quality. Results show that in natural ventilation classrooms, which are warm at temperature and moderate at humidity with an air speed lower than 0.1m/s, it is the thermal sensation rather than the temperature, enthalpy, thermal acceptability, or CO2 concentration that affects the perception of occupants for air quality. The perception for air movement influences the air quality acceptability. Increasing air movement increases the air quality acceptability. Besides, it is found that the preference of air movement is related to the air quality acceptability. When participants feel that the air movement is just suitable, the acceptability of air quality reaches the highest. When participants feel the air movement need to be adjusted, the air quality acceptability decreases

Study on Thermal Comfort for University Classrooms in Pre- Heating Season in Xi\u27an

Thermal comfort of students in university classrooms during transition season in Xi\u27an, before heating, is studied. Indoor thermal environment parameters and outdoor weather parameters of seven typical classrooms in a university campus in Xi\u27an were measured. At the same time, the subjective questionnaires were used to know students\u27 satisfaction and expectation with various environmental factors. 992 valid questionnaires were received. Based on the data collected, the thermal comfort of occupants in classroom was discussed and a thermal comfort adaptive model was established. The results show that the range of thermal comfort acceptable to students is broader than that defined in the ASHARE standard, indicating that students have some adaptability to indoor air environment. The measured indoor thermal neutral temperature is lower than the theoretical one. There is difference between the thermal sensation vote (TSV) and the predicted mean vote (PMV). The slope of TSV cure vs. operative temperature is greater than that of PMV, indicating that under actual condition, students are more sensitive to air changes. The proposed adaptive model provided a reference for understanding the thermal comfort of university buildings under natural ventilation environment in Xi’an, helpful to improve the thermal comfort and save energy for university buildings in Xi’an

Energy Efficient Indirect Evaporative Air Cooling

An energy-saving and environmentally friendly air-conditioning method has been proposed. The key component is a novel indirect evaporative heat exchanger (IEHX) based on the M-cycle. In this design, the compact IEHX is able to produce sub-wet-bulb cooling and reduce the air temperature approaching dew-point temperature. This chapter aims to achieve a fundamental understanding of the novel IEHX. A numerical model has been developed and validated by comparing the simulated outlet air conditions against experimental data. The model showed a good agreement with the experimental findings. Employing the validated numerical model, we have theoretically investigated the heat and mass transfer behavior occurred in the IEHX. The detailed cooling process has been analyzed on the psychrometric chart. In addition, the effects of varying inlet conditions and airflow passage dimensions on the cooling efficiency have been studied. By analyzing the thermal performance of the IEHX, we have provided possible suggestions to improve the performance of the dew-point cooler and enable it to attain higher cooling effectiveness

Interference of Urban Morphological Parameters in the Spatiotemporal Distribution of PM₁₀ and NO₂, Taking Dalian as an Example

Recently, air quality has become a hot topic due to its profound impact on the quality of the human living environment. This paper selects the tourist city of Dalian as the research object. The concentration and spatial distribution of PM10 and NO2 in the main urban area were analyzed during the peak tourist seasons in summer and winter. Simulations were used to explore the spatial and temporal variation patterns of PM10 and NO2, combining building and road density at different scales to reveal the coupling relationship between individual pollutant components and urban parameters. The results show that the PM10 concentration is high in the center and NO2 is concentrated in the northern district of Dalian City. In an area with a radius of 100 m, the dilution ratio of building density and road density to the concentration of the PM10 pollutants is at least 43%. Still, the concentration of NO2 is only coupled with road density. This study reveals the spatial and temporal variation patterns of PM10 and NO2 in Dalian, and finds the coupling relationship between the two pollutants and building density and road density. This study provides a reference for preventing and controlling air pollution in urban planning

Research progress on marker-assisted selection pyramiding breeding of disease resistance genes in wheat

Marker-Assisted Selection (MAS) pyramiding breeding combined with traditional breeding techniques has become an important method for molecular breeding in wheat. In recent years, with the continuous discovery of disease-resistance genes and the development of molecular markers associated with related genes in wheat, the research of MAS pyramiding disease-resistance genes has made great progress. The progress on the study of MAS pyramiding resistance genes in wheat powdery mildew, rust, and Fusarium head blight (Fhb) was reviewed. The aims of pyramiding breeding were discussed in order to promote the research on MAS pyramiding breeding in wheat

Thermo-Economic Assessments on a Heat Storage Tank Filled with Graded Metal Foam

To save and better deploy waste heat, the use of a mobilized heat storage system (MHSS) with phase change enhancement means is developed. In this paper, three kinds of gradient structures (positive gradient, negative gradient, and non-gradient) are designed in the MHSS system. The uniform porosity is 94% in the non-gradient structure, and the gradient porosities are 86%, 93%, and 98% in the gradient structure, respectively. Numerical models are developed to explore the contribution of the graded metal foam structure to the heat storage and release process. An economic analysis and comparison of MHSS systems with different heat transfer models are carried out. The results show that the positive gradient case can promote the thermal cycle of the melting and solidification process, while the negative gradient case inhibits the thermal cycle. The positive gradient case can reduce the melting time by 9.7% and the solidification time by 4.4%, while the negative gradient can prolong the melting time by 31.4% and the solidification time by 35.9%. Although graded metal foam increases the initial investment by 76.09%, the 1 KW·h heat cost of graded metal foam is reduced by 10.63% compared to pure phase change material (PCM). It is cost-effective in the long run of thermal cycles

Visualization study of co-existing boiling and condensation heat transfer in a confined flat thermosyphon

Flat thermosyphon (FTS) has gained wide attention in solving heat dissipation problems of data centers. The miniaturization of densely packed electronics has led to a demand for compact heat sinks. In this paper, a confined FTS consisting of an evaporator, condenser and customized quartz-glass chamber was developed. Bubble behaviors were investigated by the visualization approach under vacuum conditions. Effects of the space height, nominal heating power, and liquid filling ratio on the thermal characteristics were involved. Experimental results found that the bubble behaviors with 10 mm height are different from others. For 10 mm height, bubble contacts the condensation surface and then bounces back to the evaporator. The quantitative analysis shows that the boiling heat transfer coefficient with 10 mm height is 65.5 % of that with 25 mm height, and a condensation heat transfer coefficient with 10 mm height is 58.9 % of that with 20 mm height. Increasing heating power deteriorates the condensation heat transfer via forming a bubble film on the condensation surface. A small filling ratio (30 %) with 10 mm height is beneficial for the phase change heat transfer. It is hoped that these results can offer guidance for designing effective cooling devices.The authors are grateful for the support of the National Natural Science Foundation of China (52376073), and the Key Research and Development Program of Shaanxi (2023-GHZD-54)

Review of enhancing boiling and condensation heat transfer: surface modification

Data centers have tended to develop towards large scale and high density, with overall power consumption reaching up to 3 % of the total national electricity consumption. It is vital to establish energy-efficient electronic cooling devices for data center improvement. Phase-change heat transfer has emerged as a highly efficient method for addressing the heat dissipation problem. As the demand for micro-electronic cooling devices grows, enhancing the phase-change heat transfer has been a key focus of engineering research for several decades. Surface modification can effectively facilitate heat transfer favored by the surface area expansion and free energy transition. This review delved into the multiple processes involved in phase-change heat transfer, containing boiling and condensation. Considering the surface roughness and free energy, the wettability theories and manipulations of hydrophilic and hydrophobic surfaces were presented. The fabrication techniques available for modified surfaces mainly comprise coating, etching, template, sol-gen, and layer-by-layer assembly methods. The effects of patterned surface, wettability gradient surface, electrowetting surface, and wettability controllable surface on phase-change heat transfer enhancement were elaborated, particularly for the critical heat flux and heat transfer coefficients. This review of experimental and simulation results showed that surface wettability modification possesses a promising prospect in improving heat transfer performance. In this review, recommendations for the design of surface modification to promote the development of energy-efficient technologies in specific artificial environments were proposed. Further theoretical and experimental efforts need to create novel surfaces that can facilitate high-performance phase-change heat transfer across a range of applications.This work was supported by the National Natural Science Foundation of China (52376073), Key Research and Development Program of Shaanxi (2023-GHZD-54), and Shaanxi Qinchuangyuan "Scientist + Engineer" Team Construction Project (2022KXJ-049)

Experimental Investigation of Gravity Heat Pipe Exchanger Applied in Communication Base Station

AbstractThis paper proposes a gravity heat pipe exchanger used for cooling the communication base station to replace the air conditioning in winter and transition seasons. Tests were made on the gravity heat pipe exchanger of DHHP 3000 produced by Harbin Dawnhappy Heat Pipe Technology Incorporated. The experiment was performed in order to study the effects of the inlet air flow rate, temperature and the exchanger inclination angle on cooling capacity and efficiency of the heat pipe exchanger. As the indoor and outdoor air flow rate are equal, the cooling capacity of heat pipe exchanger increases with the air flow rate and it also increases with the increase of indoor air temperature and with the decrease of outdoor air temperature; The cooling efficiency decreases with the increase of air flow rate and it gradually reduces with the outdoor air temperature increases from 2°C to 18°C. Among the ratios of indoor to outdoor air flow rate of 0.4kg/s:0.5kg/s, 0.4kg/s:0.6kg/s and 0.5kg/s:0.6kg/s, the cooling efficiency of 0.4kg/s:0.6kg/s achieves the highest value. In addition, as the inclination angle varies from 5° to 50°, the maximum cooling efficiency can be obtained at angle of 20°