Development of Phase Change Material-Based Temperature Regulation Facility Inside Protected Agriculture Structure

Abstract

In arid agriculture, protected cultivation inside structures with polythene or shade net as covered material may be found beneficial to avoid aberrant weather conditions. However, significant amount of heat load is generated inside the structure due to high solar irradiation and trapping of outgoing longwave radiation due to protected covers, which lead to uncongenial conditions for sustainable plant growth. With a view to regulating temperature inside the protected cultivation structure, phase change material (PCM)-based temperature regulation facility was tried to develop through laboratory trials and experiments. Mixtures of paraffin liquid and paraffin wax in different ratios were prepared in the laboratory and heat change of the mixture material was recorded during heating and cooling process in a controlled water bath experimental setup. A mixture of paraffin liquid and wax in the ratio 10:1 was found suitable as a phase change material with melting temperature at about 35-38 degrees C. In the second stage, two heat exchanger structures consisting of GI sheet tank of 6.5 L capacity and aluminium fins attached at both sides of the tank for better heat transfer with air were designed and fabricated and these were tested inside small experimental structures with fibre glass sheet casing and covers. A decrease of inside temperature by 8-10 degrees C has been observed inside prototype structure with the incorporation of PCM material compared to one without it. Subsequently, the system was kept inside the PV clad enclosure (13.5 m(2)) and the performance of the enclosure was studied with chilli crop grown inside. The amount of heat stored by a single PCM storage system with 2.5 kg PCM materials was found about 1100-1200 kJ. An estimate indicates that it is sufficient to reduce the inside temperature by 1 degrees C for four hours if number of air change rate is 30 per hour. However, long-term trials are required to ascertain number of cycles of heating and cooling of the material.