Experimental and computer performance evaluation of a movable thermal insulation for energy conservation in greenhouses

Abstract

In recent years internal night curtains or thermal screens have appeared to be useful in reducing heat losses in greenhouses during cold weather. Most of the curtains used consisted of single-layer thin plastic materials, and lack of storage space inside the greenhouse may prevent use of thicker sections. The difficulty with thermal screens operating on the outside of the structure is that they are exposed to the weather. This paper describes the construction and experimental evaluation of a greenhouse thermal screen system where heavily insulated and relatively thick screens operate in-between the glazings of a double-glazed greenhouse. The thermal screen system was evaluated on a commercial size, arch (semi-circular) greenhouse with inflated outer polythylene and inner fibreglass glazings. A computer program was developed to predict the thermal performance of the shutter system in reducing greenhouse energy consumption. The comparisons between the experimental and computer results showed a high degree of correlation, and these results indicated that under average climatic conditions the heating requirements of a double-glazed greenhouse using the thermal screens could be reduced by as much as 60 to 80%