Between 1998 and 2003, the company Ecofys from Utrecht developed and tested a new concept of an integrated climate and energy system that permits permanently closing the ventilation windows of a greenhouse. The technical concept consists of a combined heat and power unit, heat pump, underground (aquifer) seasonal energy storage as well as daytime storage, air treatment units, and air distribution ducts. Active air circulation is one of the key elements for controlling the climate (T, RH, CO2) at crop level. This paper discusses the technical aspects and the results of a trial using a fully closed 1400 m(2) demonstration greenhouse for tomato production. Results showed: 1) reduction in primary energy (fossil fuel) use of 20 and 35% respectively for an "island" closed greenhouse and a closed-conventional combination greenhouse, 2) increase in tomato yield of 20%, 3) an 80% reduction in chemical crop protection, and 4) a 50% reduction in use of irrigation water. The energy efficiency was improved by 50%. Finally, some preliminary environmental data will be shown for the first 14,000 m(2) of closed greenhouse installed at a commercial greenhouse operation. The concept of a fully closed greenhouse will be discussed in relation to sustainable greenhouse production.
