1073 Monitoring of Climate Variables in Semi-Closed Greenhouses T.H. Gieling, J.B. Campen a , J.A. Dieleman, N. Garcia, H.J.J. Janssen, F.L.K. Kempkes, J.A.M. Kromwijka and M.G.M. Raaphorst Wageningen University and Research Greenhouse Horticulture Wageningen The Netherlands Keywords: carbon footprint, conditioned cultivation, durability, energy saving, sustainability Abstract Growers and Dutch government have concluded a covenant in which they express the ambition to reduce the carbon footprint of greenhouse production in order to improve the energy neutrality of newly built greenhouses. Conditioned cultivation in (semi-)closed greenhouses is seen as one of the instruments to reach this goal. It is appointed in the covenant to arrive in 2011 at 700 ha and in 2020 at 2,500 ha semi-closed greenhouses. This paper describes the instruments used to monitor the results of conditioned cultivation in eight semi-closed greenhouses in practice. It addresses the monitoring process, the installations involved and highlights some of the measured data. INTRODUCTION Semi-closed systems are a very promising concept for agronomy. In his overview of regenerative, semi-closed agricultural systems, Pearson (2007) mentions eight reasons to shift from conventional open or leaky systems to more closed, regenerative systems: “Current systems cause overconsumption of environmental resources, contribute to climate change, rely on increasingly expensive fossil fuel, and result in environmental (e.g., groundwater) contamination. Moreover, the agronomic-urban interface is growing, as are markets for ecologically friendly produce, the need for low-input farming systems in low-income regions, and disenchantment with the subsidization of conventional agriculture” (Pearson, 2007). The concept of conditioned cultivation in (semi-)closed greenhouses is widely accepted as a method to achieve a substantial contribution to the energy neutrality and durability in horticultural production (Ruijgrok et al., 2003). The semi-closed greenhouse concept claims to save energy by reduction of losses and by a - partly diurnal and partly seasonal - phase shift of heat (cold) usage and heat (cold) storage. Additional technical equipments (humidifiers, air conditioners, heat exchangers, fans, cold- and heat storage in sub-soil aquifers, double screens) are used to keep the air temperature and humidity within acceptable limits, even when the windows are closed (Bakker et al., 2006; Campen, 2006; de Zwart, 2008). Not only allow these techniques a shift of the climate to a different “spot in the Mollier diagram”, they also allow higher levels of CO 2 (≥1000 ppm) to be maintained (closed windows) at high global radiation (≥600 W/m 2 ). As a result of these adaptations production increases (~20% estimated by modelling). These ambitious goals require a paradigm shift. Cultivation in semi-closed greenhouses differs in essence from growing in conventional greenhouses. Cooling and heating by air conditioning ducts introduces temperature and humidity profiles that differ from the ones introduced by conventional heating and ventilation systems. Questions on how plants react to the new climate conditions provoked researchers to re-invent greenhouse growing in these new circumstances (Buwalda et al., 2006; Dieleman et al., 2006; Raaphorst et al., 2008; Qian et al., 2011). Novice users of semi-closed greenhouses are reluctant to follow strictly the cultivation rules that come with these new climate regimes. It forces growers to change a jouke.campen@wur.nl Proc. IS on High Technology for Greenhouse Systems - GreenSys2009 Ed.: M. Dorais Acta Hort. 893, ISHS 2011