• Energy Research

In this study, passive cooling of a room using a solar chimney and water spraying system in the room inlet vents is simulated numerically in Yazd, Iran (a hot and arid city with very high solar radiation). The performance of this system has been investigated for the warmest day of the year (5 August) which depends on the variation of some parameters such as water flow rate, solar heat flux, and inlet air temperature. In order to get the best performance of the system for maximum air change and also absorb the highest solar heat flux by the absorber in the warmest time of the day, different directions (West, East, North and South) have been studied and the West direction has been selected as the best direction. The minimum amount of water used in spraying system to set the inside air averaged relative humidity <65 % is obtained using trial and error method. The simulation results show that this proposed system decreases the averaged air temperature in the middle of the room by 9–14 °C and increases the room relative humidity about 28–45 %.

Abstract This paper presents an experimental study of a new designed Trombe wall, which is a part of the southern wall of a test room, in terms of energy performance and heating comfort during winter operation for Yazd city (Iran) desert climate. The area of the Trombe wall is 50% of that of the southern wall of the test room. Hence, it occupies less space and reduces the implementation costs. Contrary to the traditional Trombe walls in which the absorber receives solar radiation from one direction, this innovative design enables the absorber to receive solar radiation from three directions (East, South and West), therefore, the absorbing surface of the wall is subject to the solar irradiation during the all day time (from sunrise to sunset). The experimental results revealed that the range of room temperature on the coldest winter days and weeks in Yazd is kept within 15–30 °C, and this implies that the present Trombe wall design is able to provide a comfortable indoor temperature with lower difference between the maximum and minimum temperatures due to the increased stored energy of the Trombe wall. Furthermore, the present innovative design of the Trombe wall channel causes the absorber temperature to reach around 47 °C on the coldest winter days, indicating the highest possible solar intensity received by the absorber. Analysis of the hourly stored energy of the Trombe wall reveals that the more solar intensity leads to the more energy absorption and the higher Trombe wall back surface temperature, which in turn causes the hourly stored energy to reach to a maximum of 5800 kJ/h in February.

In this paper a numerical comparison has been made between the heating performance of the new designed and normal Trombe wall under Yazd (Iran) desert climate. The new designed Trombe wall increases the indoor space and decreases the implementation cost of the Trombe wall. In addition, it can receive solar intensity from three directions while the normal Trombe wall can only receive the solar intensity from one direction. The numerical simulation shows that the new designed Trombe wall causes the all parts temperature to increase about 10 °C in comparison with the normal Trombe wall. The velocity through the vents and the channel in the new designed Trombe wall is about 0.03 and 0.01 m/s more than that of the normal Trombe wall respectively. Comparison of two systems shows that the maximum hourly stored energy of the new designed Trombe wall is about 1600 kJ/h more than that of the normal system. Also, the new designed Trombe wall improves the average daily heating efficiency about 27 %.

Abstract This paper presents an experimental study of a new designed Trombe wall in combination with solar chimney and water spraying system in a test room under Yazd (Iran) desert climate. The Trombe wall area is 50% of that of the southern wall of the building that occupies less space and reduces the implementation costs. The new design of the channel has caused the absorber to receive the solar radiation from three directions. Based on the results, the optimum mass flow rate and the nozzle diameter of the water spraying system has been obtained 10 l/h and 30 μm, respectively. The results indicate that the water spraying system decreases indoor temperature and increases indoor relative humidity by about 8 °C and 17%, respectively. The most effect of outdoor relative humidity variation is on indoor relative humidity, rather than indoor temperature. When outdoor temperature increases, both indoor relative humidity and the difference between indoor and outdoor relative humidity decreases. The results also showed that the stored energy of the Trombe wall plays important role in the air ventilation during non-sunny periods. Lastly, the water spraying system enhances thermal efficiency by approximately 30%.

Abstract This work presents an analysis on heat transfer process occurred in the Trombe wall system with a new channel design in Yazd (Iran) on the coldest and warmest days of winter. The primary objective was to investigate the impact of heat transfer types on the temperature variation of the Trombe wall back and absorber throughout the day. For this reason, the variations of Rayleigh number, convective heat transfer coefficient, and the rate of convection, conduction, and radiation heat transfer exchanged with the Trombe wall have been studied. The analysis of Rayleigh number variations for the channel inside revealed that there is a noticeable decrease in the early hours expressing a discernible decrease in the temperature difference between the absorber and the channel space. At night time, the absorber and channel temperatures drop approximately to the same value. Furthermore, the role of conduction transfer is more sensible than that of convection in the early and late hours. However, the convection dominates at the midday. It should be noted that due to new channel design, the radiation heat transfer rate is maximum in the early and late hours. The heat transfer is more significant on the coldest day because of higher temperature difference between the different parts of the Trombe wall system.