Teitel, M., Institute of Agricultural Engineering, A.R.O., Volcani Center, P.O.Box 6, Bet Dagan 50250, Israel
Shklyar, A., Institute of Agricultural Engineering, A.R.O., Volcani Center, P.O.Box 6, Bet Dagan 50250, Israel
Segal, I., Institute of Agricultural Engineering, A.R.O., Volcani Center, P.O.Box 6, Bet Dagan 50250, Israel
Barak, M., Institute of Agricultural Engineering, A.R.O., Volcani Center, P.O.Box 6, Bet Dagan 50250, Israel

The main heating system in Israeli greenhouses is based on hot air, distributed in the greenhouse via perforated polyethylene sleeves. Recently there has been a growing trend among Israeli growers and designers to install hot-water tube systems in a larger percentage of new greenhouses. In both systems an ON-OFF controller is generally used to control the temperature. Experiments were conducted to compare the effects of the two heating methods on greenhouse microclimate and energy consumption. The experiments (done during night time only) showed that the thermal inertia of the heating tubes and water within them, keeps the air temperature in the crop environment high for a longer period of time than that observed with air heating. Consequently less heating cycles per night were observed with tube heating than with air heating. The humidity ratio at crop level changed during the heating cycles of either heating method; it was about 10% higher with air heating than with tube heating, at the peak of the heating cycle. Due to heat transfer by radiation between the heating tubes and the crop, the leaves in the lower part of the crop were generally warmer than the air. From energy calculations, it appears that there is no significant difference between the two methods in the energy consumption required to obtain the same temperature level inside a greenhouse, as long as the tubes and sleeves are positioned between the plant rows.1.