A solar cooling system for greenhouse food production in hot climates

摘要

This study is motivated by the difficulty of cultivating crops in very hot countries and by the tendency for some such countries to become dependent on imported food. Liquid desiccation with solar regeneration is considered as a means of lowering the temperature in evaporatively-cooled greenhouses. Previous studies demonstrated the technical feasibility of the desiccation-evaporation process, but mainly in the context of human dwellings. In the proposed cycle, the air is dried prior to entering the evaporative cooler. This lowers the wet-bulb temperature of the air. The cooling is assisted by using the regenerator to partially shade the greenhouse. The heat of desiccation is transferred and rejected at the outlet of the greenhouse. The cycle is analysed and results given for the climate of the The Gulf, based on weather data from Abu Dhabi. Taking examples of a temperate crop (lettuce), a tropical crop (tomato) and a tropical crop resistant to high temperatures (cucumber) we estimate the extension in growing seasons relative to (ⅰ) a greenhouse with simple fan ventilation (ⅱ) a greenhouse with conventional evaporative cooling. Compared to option (ⅱ), the proposed system lowers summers maximum temperatures by 5℃. This will extend the optimum season for lettuce cultivation from 3 to 6 months of the year and, for tomato and cucumber, from 7 months to the whole year.