Evaluation of a liquid radiation filter greenhouse in a desert environment

A 330 m² liquid radiation filter greenhouse (LRFG) has been designed, built, and tested under summer and winter desert conditions. The greenhouse was constructed of hollow polycarbonate cladding through which a liquid radiation filter (LRF) was circulated. The LRF absorbed most of the incident near infrared part of the solar radiation while transmitting most of the photosynthetically active radiation. In the cold season, the absorbed energy was transferred via a heat exchanger to a water tank. At night, the heat was returned to the greenhouse via the heat exchanger by circulating the LRF through the cladding. In summer, surplus absorbed energy was rejected to the environment by means of a cooling tower. The greenhouse remained almost closed at all times except for several hours at midday in summer. This enabled long periods of carbon dioxide (CO₂) fertilization. During these periods air entered the greenhouse at a rate of about one air change an hour via the CO₂ generator. When open, ventilation occurred passively through large gable windows. The gable windows and the CO₂ generator were fitted with insect screens, inhibiting the entrance of insects. Disease encouraging condensation on leaves was prevented by the thermal blanket effect of the relatively warm LRF circulating in the cladding at night. The structure and the functional elements of the greenhouse are described. Experimental results and the thermal performance of the LRFG during the winter and summer seasons are presented. CO₂ fertilization was possible during most of the daylight hours including during the summer when the greenhouse was closed about 7 to 10 out of 14 daylight hours. For the duration of the multi-year long experiment, no incidence of dew formation on plants was observed, and the use of fungicides and insecticides was 1/4 to 1/8 that of conventional greenhouses.