Comparison of Climate and Production in Closed, Semi-Closed and Open Greenhouses

A (semi-)closed greenhouse is a novel greenhouse with an active cooling system and temporary heat storage in an aquifer. Air is cooled, heated and dehumidified by air treatment units. Climate in (semi-)closed greenhouses differs from that of conventional open greenhouses. The aims of our research were first, to analyze the effect of active cooling on greenhouse climate, in terms of stability, gradient and average levels; second, to determine crop growth and production in closed and semi-closed greenhouses. An experiment with tomato crop was conducted from December 2007 until November 2008 in a closed greenhouse with 700 W m cooling capacity, two semi-closed greenhouses with 350 and 150 W m cooling capacity, respectively, and an open greenhouse. The higher the cooling capacity, the more independent the greenhouse climate was of the outside climate. As the cooling ducts were placed underneath the plants, cooling led to a remarkable vertical temperature gradient. Under sunny conditions temperature could be 5°C higher at the top than at the bottom of the canopy in the closed greenhouse. Cumulative production in the semi-closed greenhouses with 350 and 150 W m cooling capacity were 10% (61 kg m) and 6% (59 kg m) higher than that in the open greenhouse (55 kg m), respectively. Cumulative production in the closed greenhouse was 14% higher than in the open greenhouse in week 29 after planting but at the end of the experiment the cumulative increase was only 4% due to botrytis. Model calculations showed that the production increase in the closed and semi-closed greenhouses was explained by higher CO2 concentration. INTRODUCTION Energy consumption of Dutch greenhouse industry contributes to about 10% of the total national energy use and 79% of the total energy use of agriculture in the Netherlands (Lansink and Ondersteijn, 2006). For energy saving, closed and semi-closed greenhouses were innovated. A closed greenhouse has no window ventilation. Air is cooled and dehumidified by air treatment units (ATU), which mainly takes place in summer. Surplus heat as energy is stored in an underground aquifer and used in winter to warm the greenhouse (Opdam et al., 2005). A semi-closed greenhouse has a smaller cooling capacity than a closed greenhouse. Window ventilation is combined with active cooling when the temperature is too high to be managed by the active cooling system. The greenhouse macroand microclimates are distinctly different in (semi-)closed greenhouses compared to that of open greenhouses. A high CO2 concentration (about 1000 ppm) is one of the typical climate characteristics of the (semi-)closed greenhouse (De Gelder et al., 2005), which increases the production in the (semi-)closed greenhouse (Heuvelink et al., 2008). In particular, combination of high CO2 and high radiation that occurs during summer in a (semi-)closed greenhouse is impossible to be realized in an open greenhouse. However, there is little detailed information available on climate