The Watergy Greenhouse: A Closed System for Solar Thermal Energy Collection, Water Treatment and Advanced Horticulture 2005-01-2919

Project Watergy, funded by the European Community's Vth Framework in its Energy, Environment and Sustainable Development programme, consists in the development of a humid air solar collector system that follows the principle of a closed two phase thermosyphon. The first product of the project is a prototype for application in arid climate: a closed system for solar thermal energy capture, water recycling, water desalination and advanced horticultural use. It consists of a closed greenhouse connected with a vertical solar air collector which functions as a solar chimney. An air-water heat exchanger contained in a cooling duct inside the tower provides climate regulation of the greenhouse, powered by the buoyancy induced by the solar tower. The efficiency of the heat exchange processes is enhanced by the utilization of latent heat due to constant humidification/de-humidification of air in the process. The condensation associated with the cooling of the nearly saturated air also provides distillation of water. The thermal energy released in the process is stored outside the greenhouse for being used as heating or further water distillation during the night. Plants are an essential part of the whole process, being a means of grey water processing and a source of humidification of the air, and together with water and heat, biomass production is the main output of the system.

A detailed explanation of the system and its components is presented, describing the heat accumulators, the heat exchanger in the cooling duct, and the secondary collector which further heats and humidifies the air from the greenhouse on its way to the cooling tower. The horticultural concept of the greenhouse is also outlined. The functioning of the system is described, the main challenges encountered are explained, and the first results obtained after the first growing season under evaluation are presented.