EVALUATION OF A LIQUID RADIATION FILTER GREENHOUSE IN A DESERT ENVIRONMENT

Abstract

A 330 m2 liquid radiation filter greenhouse (LRFG) has been designed, built, and tested under summer andwinter desert conditions. The greenhouse was constructed of hollow polycarbonate cladding through which a liquidradiation filter (LRF) was circulated. The LRF absorbed most of the incident near infrared part of the solar radiation whiletransmitting most of the photosynthetically active radiation. In the cold season, the absorbed energy was transferred via aheat exchanger to a water tank. At night, the heat was returned to the greenhouse via the heat exchanger by circulating theLRF through the cladding. In summer, surplus absorbed energy was rejected to the environment by means of a coolingtower. The greenhouse remained almost closed at all times except for several hours at midday in summer. This enabled longperiods of carbon dioxide (CO2) fertilization. During these periods air entered the greenhouse at a rate of about one airchange an hour via the CO2 generator. When open, ventilation occurred passively through large gable windows. The gablewindows and the CO2 generator were fitted with insect screens, inhibiting the entrance of insects. Disease encouragingcondensation on leaves was prevented by the thermal blanket effect of the relatively warm LRF circulating in the claddingat night. The structure and the functional elements of the greenhouse are described. Experimental results and the thermalperformance of the LRFG during the winter and summer seasons are presented. CO2 fertilization was possible during mostof 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 offungicides and insecticides was 1/4 to 1/8 that of conventional greenhouses.