Performance Analysis And Optimization Of The Solar Trombe Wall System With Venetian Blind

With the improvement of life quality, the occupants; requirement for the indoor thermal comfort is getting higher and higher, which results in building energy consumption is growing for the heating, ventilation and air conditioning. Renewable energy technology is considered to be an important way to relieve building energy consumption, particularly building integrated solar technology. Trombe wall is a typically sustainable architectural technology of the solar utilization for space heating and ventilation. Some related research demonstrated that it can reduce a building's energy consumption for residential heating up to 30%. While the applicable range of a conventional Trombe wall cannot be promoted due to its overheating in summer,lower thermal resistance during winter night or prolonged cloudy periods and low aesthetic value. To that end, the idea of the Trombe wall combined with venetian blinds is introduced in the present paper, and two kinds of novel Trombe walls are proposed, namely, the Trombe wall with venetian blinds (VBTW) and the Trombe wall with PV blind (PVBTW). The blind angle can be controlled to achieve the higher thermal performance of the VBTW. Based on the problem of the existing PV-Trombe walls and the study on the VBTW, the PVBTW is then proposed and it can provide space heating, ventilation and at the same time the electrical output, which enables the more efficient solar energy utilization in different seasons.In terms of the VBTW system, the two sides of the venetian blinds are covered with the high absorptivity coating and the high reflectivity coating respectively for winter and summer operating modes. The experimental platform of the VBTW system is built based on a comparable hot box. Comparative experiments are carried out to investigate the performance of the room with the VBTW and that without the VBTW under different operating modes, including the air heating in winter and the ventilation in summer. The temperatures of the different components are recorded and used to validate the developed model. Dynamic numerical models on the VBTW system in winter and summer are developed respectively along with the experimental validation. Experimental and theoretical results indicate that in cold weather the optimum time to open air vents of the VBTW is approximately 1.5 h earlier than that of the conventional Trombe wall after sunrise. The air average temperature for room with the VBTW is about 5.5 ? higher compared to that with the conventional Trombe wall during the daytime. The heat loss of the VBTW is smaller during night periods.The room with VBTW can achieve basically comfortable in the daytime, while the room with a conventional Trombe wall and that without Trombe wall are slightly cool and cold. Additionally, the VBTW is found to be more applicable to the building where occupants work or study in the daytime, such as office room, school building.Moreover, according to the local thermal discomfort theory, the room temperature difference along the vertical direction for the room with the VBTW is higher than that with the conventional Trombe wall, which causes a percentage of dissatisfied of about 12% at the peak of solar radiation. To improve the undesired phenomenon, adjusting the blind angle and increasing a fan are recommended. Using the summer ventilation model, the parametric study is conducted considering the requirement of the outdoor air supply, including the blind angle, the air gap thickness, the wall material and thickness. The results show that the variations of the blind angle have a more significant effect on the cooling load compared to the variations of air gap thickness,the wall materials and thickness. In addition, it should be noted that in the case of 26? set point the cooling load becomes higher after using the VBTW with the blind angle of 15°.The PV blind in the PVBTW is designed and manufactured by laminating PV cells and venetian blinds together. The PVBTW module as well as two existing PV-Trombe wall modules in the open published literature are designed and built, one with PV cells attached to glass (PVGTW) and the other with that attached to mass wall (PVMTW). Then, comparative experimental studies on the PVBTW module, the PVGTW module and the PVMTW module are carried out with the variation of the inlet air velocity. Comparative experimental results on the PVBTW, PVGTW and PVMTW modules show that when the inlet air velocity is equal to 0.45 m/s, the daily electricity generation of the PVGTW module (0.32 kWh) is larger than that of the PVBTW module (0.23 kWh), while the average daily thermal efficiency of the PVBTW module (43.1%) is higher than that of the PVGTW module (23.8%) and the PVMTW module (33.4%). Combining heat gains and electricity generation, the PVBTW module is superior by 14.5% compared to the PVGTW and by 14.1%compared to the PVMTW with respect to the total efficiency. Based on the experimental results on the PVBTW module, the modified PVBTW is proposed, and then the numerical models on the three PV-Trombe wall together with three rooms(BIPVBTW, BIPVGTW and BIPVMTW) are developed, respectively. Under the weather conditions in Hefei (32°N,117°E), firstly, the optimum PV blind slat angles over three seasons (summer, winter and mid-term seasons) and time of day (9:00-17:00) are investigated. Next, comparative assessments of the three BIPV Trombe wall systems are conducted all year round in terms of thermal and electrical performance. According to the numerical results on the modified BPVBTW system,the BIPVGTW system and the BIPVMTW system, it is concluded that the annual heating gains of the modified BIPVBTW are the highest amongst the three BIPV Trombe wall systems, and the electrical performance of the modified BIPVBTW system is similar to that of the BIPVGTW system. After the annual cooling load and heating load reduction are converted into the corresponding electricity consumption reduction, the total electricity saving of the modified BIPVBTW system is over 45.7%higher compared to BIPVGTW system, and over 45.1% compared to the BIPVMTW system. Furthermore, annual CO2 emissions reduction of per unit BIPVBTW area is about 1.5 times that of the BIPVGTW/ BIPVMTW with the same size.