Increased carbon emission over the last decades is widely associated with numerous environmental issues and challenges, such as global warming and climate change. With the impact of carbon emissions becoming obvious and severe each day, stringent measures have been enacted to help reduce the overall carbon footprint. Among them is the Paris Agreement, an international treaty to strengthen the global response to climate change. Moreover, different countries have enacted different carbon neutrality laws and regulations, most of which revolve around the transition from fossil fuels to renewable energy.
Despite the remarkable efforts to reduce the overdependence on fossil fuels, it still accounts for a significant share of global energy consumption. In China, for example, coal accounts for 85% of the country’s primary energy consumption. To this end, significant research effort has been devoted to developing and promoting the use of clean energy technologies as an effective way of reducing pollution and carbon emissions. In particular, solar energy has drawn significant attention for potential use in the building heating field. Solar air collector (SAC) converts solar energy into heat by air fluid. It requires thermal energy storage devices to solve the supply-demand mismatch, thus prolonging utilization time.
Solar air thermal collection (SATC) energy systems mostly consist of vacuum tube (VT) and flat plate (FP) forms. While most studies have focused on FP because of its simple structure, there are few studies on VT forms due to its complex circular structure. However, VT-ATCSS have been shown to have higher efficiency than FP-ATCSS, especially in a low-temperature environment. Therefore, the application of VT air collectors in collecting solar energy is worth studying.
Herein, Dr. Tengyue Wang, Professor Yanhua Diao, Professor Yaohua Zhao and Professor Tingting Zhu from Beijing University of Technology developed a novel split-type vacuum tube SATC-stepped storage system (ST-VTSATC-SSS) to address pollution and carbon emission associated with coal-fired heating. Heat loss was reduced using VT air collector, while stepped thermal storage was conducted using paraffin and lauric acid, which served as phase change materials. A combination of louver fins and flat micro heat pipe arrays (FMHPA) were used to enhance the heat transfer performance of the phase change materials. Finally, ST-VTSATC-SSS performance was experimentally investigated. Their work is currently published in the journal, Renewable Energy.
The authors showed that during one of the coldest winter days with an ambient temperature of – 2.1°C and solar radiation intensity of 882 W/M2 , the ST-VTSATC-SSS achieved a remarkably high collector efficiency of 61.7% and collection-storage efficiency of 40.7%. The thermal collection-storage efficiency during the collection process could be improved by enhancing the air volume flow rate, with an optimal air volume flow rate reported to be 170 m3/h. On the other hand, enhancing the solar radiation intensity was observed to reduce the collection-storage efficiency because higher radiation increased the heat loss. Under ambient temperature of 20.1°C and solar radiation of 621 W/M2, a 55.3% average collection-storage efficiency was reported.
A heating application in the master bedroom (11.88 m2) of a Chinese rural building was conducted to validate the feasibility of the proposed ST-VTSATC-SSS. Results showed that it could save coal by 373.0 kg and reduce carbon emissions by 977.3 kg at a relatively cost-effective heating cost. It also reduced the emission of other greenhouse gases like sulfur oxide. Other advantages of this new method include improved collector efficiency, stable and effective heating performance, great installation flexibilities and low heating operation costs.
In summary, the design and experimental validation of a newly proposed ST-VTSATC-SSS was reported. Results revealed its capability to release heat rapidly. In a statement to Advances in Engineering, Professor Yanhua Diao, the corresponding author noted that the proposed ST-VTSATC-SSS is a promising low-cost and clean rural building heating method with a high capability of reducing the carbon footprint of the residential sector.
Wang, T., Diao, Y., Zhao, Y., & Zhu, T. (2022). Experimental investigation of a novel split type Vacuum Tube Solar Air Thermal Collection-stepped storage system (ST-VTSATC-SSS). Renewable Energy, 192, 67-86.