Thermal screens in greenhouses: Diurnal variations in heat consumption

This paper deals with unexpected variations in heat consumption in greenhouses equipped with thermal screens. The total heat saving effect of a thermal screen is a result of heat consumption both during the day and night. It has been observed that the heat consumption in daytime, after curtains are removed in the morning, is 17% higher than in an uninsulated greenhouse. This is due to the extra heat consumption needed for readjustment of the heating system and for heating the cool greenhouse structure. At night, when curtains are drawn, the opposite occurs due to the readjustment of the heating system to an insulated house. This leaves the heating system with an overcapacity of heat; this reduces heat consumption such that the heat saving effect of the curtains is overestimated by 11%. These amounts of heat must be included in the total diurnal heat consumption to reliably estimate the heat saving made by use of a thermal screen.