جستجوی مقالات مرتبط با کلیدواژه « Thermal comfort » در نشریات گروه « مکانیک »

In recent years, reducing energy consumption and greenhouse gas emissions in the building sector has attracted a lot of attention. As in other parts of the world, the construction sector in Iran also has a large share of energy consumption. As a result, low consumption and even zero energy buildings, as an alternative solution in solving this problem, have attracted the attention of scientists, researchers and policy makers. One of the main challenges in designing a zero energy building is to find the best combination of passive solutions to reduce consumption and optimize energy performance in the building in such a way that the energy performance of the building and the thermal comfort of the residents are not negatively affected. This article presents a method for multi-objective and multi-variable optimization based on building simulation, which is carried out in three main stages: building energy consumption simulation, two-objective optimization process and multi-criteria decision making for zero energy building design using renewable energy sources. Reproducible. The studied design parameters are: direction of the building, angle and depth and length of the protrusion of the shades, insulation thickness of external walls, temperature adjustment points for cooling and heating, ratio of window to wall area, heat transfer coefficient of windows and thickness of roof insulation. In addition, the considered renewable energy sources are: photovoltaic panels and wind turbines. In order to achieve a net zero energy building, considering maintaining the thermal comfort of the residents, a multi-objective genetic algorithm with non-dominated sorting has been used. Finally, in order to determine the most optimal answer in the Pareto diagram, the elimination and selection method compatible with reality has been used. The results show that climatic conditions and the appropriate selection of architectural parameters are very important and vital in reducing building energy consumption. Based on the results, the use of energy optimization solutions in Tehran leads to a 25.3% reduction in energy consumption. In addition, there is a significant potential for the use of photovoltaic systems in Tehran to provide energy for homes.

In this study, the performance of the air distribution system in the cabin of a single-aisle passenger plane with 42 passengers seated in two rows of three has been analyzed. Computational fluid dynamics method has been used to investigate the air distribution in the cabin. In this numerical analysis, the effect of changing the relative humidity inside the cabin, changing the speed of air entering the cabin and changing the way of air distribution inside the cabin has been investigated. In order to determine the thermal comfort in the cabin, two parameters including the average number of predicted votes and the percentage of predicted dissatisfaction have been investigated. The results show that with the increase of relative humidity from 0 to 10%, changes in static pressure do not cause major changes in passenger comfort. Also, at a speed of 1 m/s for air entering the cabin, due to better air circulation in the head and other organs, the passengers feel more thermal comfort and less static pressure changes on their head and body. Finally, by changing the air distribution system from the mixing system to the displacement system, it was observed that the mixing air distribution system is better in terms of thermal comfort for passengers. However, in terms of static pressure in the head and body area of passengers, the displacement air distribution system is better.

The present study aimed to investigate the effects of air inlet location and flow characteristics on the performance of a personalized ventilation system. For this purpose, a near-body personalized ventilation system is numerically simulated in an office room with the presence of a thermal manikin. Three air inlet arrangements (in front of the feet, in front of the abdomen, in front of the face) were modeled, two air temperatures (16 and 20℃) and two air velocities (1 and 2m/s) were assigned to each arrangement. Finally, airflow temperature distribution, velocity distribution, and the overall and local temperature and thermal sensation of different body segments are determined. In some cases, by changing the air inlet placement from the front of the feet to the abdomen and head, the whole-body thermal sensation is cooled by 0.54 and 0.6 units, respectively. In all cases, hands and head felt cooler than the wholebody thermal sensation, which shows that the bareness of a segment has a significant effect on its feeling in personalized ventilation systems. Unlike the foot, the head is an effective local segment for non-uniform cooling purposes in warm conditions, and due to its effect on the whole-body thermal sensation, cooling the head would be an effective way to reduce energy consumption.

Thermoregulatory models based on thermoreceptors have attracted the attention of researchers in recent years due to their conformity with the basis of human thermal perception. For this reason, various models have been presented such as STB, ITB, MSTB and JOSTB. In the present study and in continuation of previous studies, an individual multi-segment thermoregulatory bioheat (IMTB) model has been introduced which can evaluate the temperature of various segments of the body by considering the effects of individual parameters such as height, weight, age and gender. In this study, the body is subdivided into 17 segments, 3 layers and the blood circulatory system consists of arteries, veins and superficial veins. Also, the effects of individual parameters on physiological parameters, thermoregulatory mechanisms and heat transfer of the body have been investigated. Finally, the performance of the new model in predicting local and mean skin temperature was validated against different experimental data. The results indicate that by considering the individual parameters, the new model can precisely predict the local skin temperature with mean absolute error of 0.4℃.

In this study, the flow pattern, temperature distribution and thermal comfort index have been experimentally investigated in a room with personalized confluent jets ventilation (CJV) system for different diffusers’ heights of 30 and 160cm from the floor and for two inlet temperatures of 16 and 24°C and three different inlet angles of 0, 22.5 and 45 degrees. The results showed that the above cases can be significantly affected by changing in location of inlet diffuser. So that by placing the inlet diffuser at a height of 160 cm, the occupants’ upper body is strongly affected by the flow and the maximum air velocity in this region, depending on the change of inlet flow angle from zero to 45 degrees, can respectively reach about 1.5 to 1 m/s and this causes the draught dissatisfaction in the occupants’ upper body. However, by placing the diffuser under the desk and at a height of 30cm, the most dissatisfaction caused by draught occurs in the legs and feet. Finally, it can be concluded that the draught dissatisfaction is the most important factor that can limit the use of personalized confluent jets ventilation system.

In the present study, the effects of inlet cooling air temperature from the diffusers of under-floor air distribution system have been experimentally investigated on the occupants’ local thermal sensation. In the experiments, the inlet air temperature is controlled at 12°C, 16°C and 20°C, and the inlet velocity is kept constant. Also, the room thermal conditions have been controlled at the mean temperature of 24±0.5°C and mean relative humidity of 25±2%. During the experiment, 8 healthy male subjects with common office clothing and metabolic rate were exposed to an under-floor air distribution system for 30 min and their thermal sensation and satisfaction were assessed on the basis of thermal comfort standards. Based on the results, the head and chest thermal sensations are not significantly depended on inlet temperature. But, by decreasing the inlet temperature, the thermal sensation and satisfaction of hands and feet are decreased. Moreover, the results indicated that the overall body thermal sensation is significantly depended on the sensation of the body parts with extreme thermal conditions. Also, the results show that the feeling of air movement can be increased during the time; so, the subjects reported about 75% draught discomfort after 30 min exposure to under-floor air distribution system.

In swimming pools with spectators’ stand, due to differences in skin wetness, metabolic rates and clothing type of the swimmers and spectators, providing thermal comfort conditions for all residents is very difficult. Accordingly, a reasonable idea to provide the mentioned different comfort conditions is using the air curtain to aerodynamically separate the pool hall and the spectators’ stand. In these conditions,it is possible to use two different ventilation systems for these two parts. In the present study, an Olympic-size swimming pool with the spectators’ stand is modeled and distribution of velocity, temperature, relative humidity and chlorine concentration have been determined.Also, the results have been analyzed in both cases: using air curtain and without air curtain. The results show that the air curtain can significantly reduce the influence of chlorine pollutants on the spectators section, so the concentration of chlorine at spectators’ stand with the air curtain is about 0.00016 mg/m3 less than the case without air curtain.In this study,65 multi node local thermal comfort model has been used to determine the thermal comfort of individuals.In case with the air curtain, the standard deviation of thermal comfort index for first to third rows are 0.26, 0.25, and 0.28 respectively; and in the absence of air curtain, for first to third rows thermal comfort quantities the standard deviation of thermal comfort index for first to third rows are 0.33, 0.39 and 0.35, respectively.These results indicate that using the air curtain can leads the thermal sensation to be more favorable and more uniform.

Particle pollutants in indoor environment are a serious threat for human health. Therefore, it seems necessary to recognize and control the distribution of these particles. In the present study, the effect of air inlet angle of swirling diffusers in UFAD systems has been investigated on micron particles pattern distribution by considering the thermal comfort condition. For evaluating the flow and particle distribution, OpenFoam developed solver by the Eulerian-Lagrangian method and for two node model are used for predicting the flow and thermal conditions. Inlet angles are set in three cases: 30, 45 and 60. Based on the results, in all three cases, the TSENS index is in the comfort zone. But, by changing the inlet angle from 30 to 60, the vertical temperature difference can be reduced about 1 . The results showed that at inlet angle 30 and 60, the percentage of particles exited with 2.5 micrometers diameter were 32% and 55% of the total particles. In other words, increasing the inlet angle can leads to exit more amount of any size of particles from the room. In addition, by increasing particles size, larger particles removed faster from the breathing zone, and smaller particles will remain longer time in the air. In other words, smaller particles have a greater impact on the indoor air quality.