استفاده از شمع های انرژی برای ذخیره انرژی خورشیدی زیرزمینی
Abstract
1- Introduction
2- Methodology
3- Steady-state analysis
4- Transient-state analysis
5- Conclusions
References
Abstract
Conventional piles embedded with geothermal loops, referred to as energy piles, have been successfully used as heat exchangers for the ground source heat pump system. For heating-dominated regions, it is crucial for the ground source heat pump system to keep the ground thermal balance in the long run. Solar energy is the most feasible source to charge the ground manually. In this study, thermal performance of an energy pile-solar collector coupled system for underground solar energy storage was investigated using numerical modeling. The results suggested that a lower flow rate should be adopted for the energy pile-solar collector coupled system to save the operational cost of the circulation pump. For the case with a pile length of 30 m, the decrease in the rate of solar energy storage was about 2% when the mass flow rate was reduced from 0.3 to 0.05 kg/s. Throughout a year, the maximum daily average rate of solar energy storage reached 150 W/m. It was also found that to increase the length and the diameter of the pile improved the thermal performance of the system by keeping its temperature relatively lower. In addition, the effects of the pile-pile thermal interference on reducing the rate of solar energy storage after a one-year operation were quantified to be within 10 W/m for groups with the pile-pile spacing of 3 times the pile diameter.
Introduction
According to the International Energy Agency, buildings are responsible for almost 40% of total final energy consumption in the European Union, out of which 80% is due to the heat demand, accounting for 30% of the total CO2 emissions [1]. To reduce the carbon footprint and promote sustainable development, clean solar energy offers excellent potential for heat production to meet the demands of space heating in winter and domestic hot water production. Nevertheless, solar radiation varies daily and seasonally and is not constantly present. To cover the intermittency of the solar radiation, thermal energy storage is necessary so that heat can be extracted when the solar radiation is not available [2,3]. Based on the medium adopted, thermal energy storage can be classified as sensible, latent, and chemical heat storage. Of the common sensible mediums for thermal energy storage, the ground enjoys the advantage of enormous quantity and being widely accessible [4,5]. The conventional practice of underground thermal energy storage is burying heat exchange pipes into pre-drilled vertical holes, referred to as the borehole thermal energy storage [6]. Heat transfer occurs by circulating heat carrier fluid through the pipes. However, the cost of drilling deep holes can cause a breakdown of a project [4]. In addition, with the quick development of urbanization, the available free lands for drilling holes become increasingly more scarce and costly in cities. Both factors impede the application of the borehole thermal energy storage technology.