Comparison between a solar system and a fuel boiler for greenhouse air-conditioning

Abstract

The object of this study was to compare economically a solar system for greenhouse conditioning in order to maintain the greenhouse air temperature at 12°C at night during the coldest months with a conventional heating system. The solar system consists of a polypropylene capillary heat exchanger; it also has two batteries of plaits respectively suspended in the air and buried into the ground of the greenhouse. During the day, the air-suspended exchangers recover solar energy in excess of the needs of the plants. This recovered energy is then stored into the greenhouse ground through the buried exchangers. At night the stored thermal energy is brought back by the suspended exchangers to heat the greenhouse air. The conventional heating system used in this comparative study is a 15 kW fuel boiler. The results show that the solar system was less powerful than the conventional system during some days of December and January. However, during the other months, it allowed better comfort in the greenhouse. It heats during the night and especially avoids overheating during the day that is very unfavourable to plant growth. Finally, the solar system gave an annual profit of fossil energy of 360 kWh.m −2 for the greenhouse. In Tunisia, there are 1400 hectares of greenhouses, and this system can provide energy savings of 5×10 9 kWh/y.