Abstract
This paper presents the results of the analysis of thermal issues and energy efficiency of three types of accumulators; namely stone-bed; water and phase change. Research experiments were carried out during April–October 2013 in a standard commercial semi-cylindrical high plastic tunnel with tomato cultivation of 150 m2. A stone-bed accumulator; with an area of almost 75 m2 was installed in the tunnel below ground level; while a water accumulator with a volume of 4 m3 was installed outside the tunnel. A phase change material (PCM) accumulator, with a volume of 1 m3 containing paraffin, was located inside the tunnel. The heat storage capacity of the tested accumulators and the energy efficiency of the process were determined based on the analyses of the 392 stone-bed charging and discharging cycles, the 62 water accumulator charging cycles and close to 40 PCM accumulator charging and discharging cycles. Dependencies in the form of easily measurable parameters; have been established to determine the amount of stored heat; as well as the conditions for which the effectiveness of these processes reaches the highest value. The presented analysis falls under the pro-ecological scope of replacing fossil fuels with renewable energy. As a result of the analysis; it was found that; in the case of a stone-bed; such an accumulator shows higher efficiency at lower parameters; that is, temperature difference and solar radiation intensity. In turn; a higher temperature difference and a higher value of solar radiation intensity are required for the water accumulator. The energy storage efficiency of the PCM accumulator is emphatically smaller and not comparable with either the stone-bed or the water accumulator.
Highlights
The overwhelming majority of the world’s energy comes from non-renewable sources, such as oil, coal, natural gas and uranium, which causes greenhouse gas emissions, global warming and related climate change
The analysis showed that throughout the entire season from 0.003 to 1.27 kWh of heat was supplied to the inside of the plastic tunnel from 1 square meter of accumulator surface during one cycle
The analysis showed that throughout the entire season from 0.003 to 1.27 kWh of heat was it can be stated that the dominating process during the2 accumulator charging was dehumidification, supplied to the inside of the plastic tunnel from 1 square meter of accumulator surface while during the discharge process it was humidified
Summary
The overwhelming majority of the world’s energy comes from non-renewable sources, such as oil, coal, natural gas and uranium, which causes greenhouse gas emissions, global warming and related climate change. Counteracting these adverse phenomena is a huge challenge for modern science and the economy, resulting in the need to conduct research into the possibility of using renewable energy sources as alternatives [1,2,3], with solar energy and methods of its acquisition, processing and storage being the most promising [4]. Heat storage is very important in the case of households and farm heating [10], with preparation of domestic hot water for households and farms and food processing being important factors
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