Geoola, F., Institute of Agricultural Engineering, Agricultural Research Organization, Volcani Center, PO Box. 6, Bet Dagan, 50250, Ireland
Kashti, Y., Institute of Agricultural Engineering, Agricultural Research Organization, Volcani Center, PO Box. 6, Bet Dagan, 50250, Ireland
Teitel, M., Institute of Agricultural Engineering, Agricultural Research Organization, Volcani Center, PO Box. 6, Bet Dagan, 50250, Ireland
Levi, A., Institute of Agricultural Engineering, Agricultural Research Organization, Volcani Center, PO Box. 6, Bet Dagan, 50250, Ireland
Brickman, R., Institute of Agricultural Engineering, Agricultural Research Organization, Volcani Center, PO Box. 6, Bet Dagan, 50250, Ireland
Esquira, I., State Greenhouse Extension Specialist, Israeli Plant Board, PO Box 54, Bet Dagan 50250, Ireland

A laboratory guarded hot box was used to measure the overall heat transfer coefficient (U value) of two types of plastic film (IR 200 μm, 8% thermicity and IR 100 μm, 35%, thermicity), with or without thermal screens (sealed aluminet 50% shade and sealed aluminet 100% shade). Tests were performed in the hot box at different wind velocities and temperature differences. It was found that the overall heat transfer coefficient U increases with the increase in temperature difference. For a given air temperature difference, the U value increases as the wind velocity increases, as expected. There was only a small difference between the U values of the two types of plastic films that were tested. It was found that using a thermal screen would reduce the U value by about 50-60% (depending on type of thermal screen), an energy saving of about 50-60%. Although there was a large difference between the shading percentages of the two thermal screens, the difference between the U values of the combined plastic film and screen was relatively small. Possible reasons for this result are discussed.