Evaluation of a liquid radiation filter greenhouse in a desert environment

A 330 m(2) liquid radiation filter greenhouse (LRFG) has been designed, bui lt, and tested under summer and winter desert conditions. The greenhouse wa s constructed of hollow polycarbonate cladding through which a liquid radia tion filter (LRF) was circulated. The LRF absorbed most of the incident nea r infrared part of the solar radiation while transmitting most of the photo synthetically active radiation. In the cold season, the absorbed energy was transferred via a heat exchanger to a water tank. At night, the heat was r eturned to the greenhouse via the heat exchanger by circulating the LRF thr ough the cladding. In summer, surplus absorbed energy was rejected to the e nvironment by means of a cooling tower. The greenhouse remained almost clos ed at all times except for several hours at midday in summer. This enabled long periods of carbon dioxide (CO2) fertilization. During these periods ai r entered the greenhouse at a rate of about one air change an hour via the CO2 generator. When open, ventilation occurred passively through large gabl e windows. The gable windows and the CO2 generator were fitted with insect screens, inhibiting the entrance of insects. Disease encouraging condensati on on leaves was prevented by the thermal blanket effect of the relatively warm LRF circulating in the cladding at night. The structure and the functi onal elements of the greenhouse are described. Experimental results and the thermal performance of the LRFG during the winter and summer seasons are p resented. CO2 fertilization was possible during most of the daylight hours including during the summer when the greenhouse was closed about 7 to 10 ou t 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 fungi cides and insecticides was 1/4 to 1/8 that of conventional greenhouses.