The main goal of the present study was to evaluate the effects of two different glazing materials (fiberglass and polyethylene) on microclimatic conditions of gable-even-span single greenhouses at night during the winter season of 2007-2008. A complete solar heating system was utilized for heating the cucumber greenhouses located in the eastern area of the coastal delta, Egypt. Temperatures of inside and outside air, water in the storage tank, pipe surface of heat exchanger, floor surface (concrete), and air relative humidity were measured and recorded on a data-logger to analyze their correlation with the cucumber crop yield response. A mathematical model was developed to simulate microclimatic conditions for the cucumber greenhouse. The data showed that the daily average solar energy available was 13.345 kWh of which 7.138 kWh was stored in the storage tank of each solar energy system. There were daily variations during the experimental period that depended upon the water temperature in the storage tank at the beginning of each day, the ambient air 76 temperature, the rate of heat energy consumed at night to provide and maintain the air temperature within the greenhouses at the desired level, and the growth stage of the cucumber crop. The daily average heat energy consumed at night for heating the two greenhouses was 10.070 and 12.391 kWh and the polyethylene greenhouse consumed heat energy greater than the fiberglass greenhouse by 23.05 %. The heat energy consumed resulted in an increase of the inside air temperatures above the outside (12.6 degrees C) by 4.5 degrees C and 3.4 degrees C for fiberglass and polyethylene greenhouses, respectively. Under these conditions, the fiberglass and polyethylene covers provided, respectively, a heating effect of 4.5 degrees C and 3.4 degrees C. The nightly average air relative humidity inside and outside the two greenhouses was 56.5 %, 60.8 % and 54.4 %, respectively. The proportions of heat energy provided by utilizing the solar energy system for the two greenhouses, respectively, were 65.95 % and 55.68 %. Due to the optimal level of microclimatic conditions of the two greenhouses, they produced a fresh cucumber yield of 6.825 and 5.245 kg/m(2), respectively. Thus, the fiberglass greenhouse increased the fresh yield of cucumbers by 30.12 % as compared with the polyethylene greenhouse.
