A model greenhouse, covered with a transparent plastic material, 'Fabrene', was built without vegetation and tested in Calgary, Canada, with the primary objective o£ determining the effect of environmental temperatures on its performance characteristics. It is found that when the temperature of the intake hot air (Ji) and the Reynolds Number (RN) for air flow through the intake duct are kept constant, the performance of the greenhouse , characterized by surface membrane heat losses, overall

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... transfer coefficient, and efficiency, does not depend a great deal on changes in environmental temperature (Ja) under conditions o£ zero Solar Parameter (K). This finding is clearly confirmed by the fact that the Supply Air Temperature Drop (Ji-Je) between the inlet and outlet of the greenhouse varied only slightly in spite of the large variations in ambient temperatures under conditions of zero Solar Parameter and constant intake hot air temperature and Reynolds Number.