Closed greenhouse systems promise great savings in energy costs. In the GeslotenKas™ system, the greenhouse is considered as an energy source rather than a consumer. During the summer, the heat that builds up from the sun is drawn out of the greenhouse by the passage of cold water at about 6°C that is pumped up from an underground storage acquifer through an air conditioning unit. This subsequently warmed water is pumped down into another insulated underground storage aquifer where it is maintained at about 18°C as a source of warm water in the winter months. In the winter, the warm water is pumped back to the greenhouse where a portion is heated further to 55°C and is used to heat the greenhouse. The cooled water is then pumped back into the cold water aquifer for use in the summer. At the heart of the system is a heat pump linked to the air-conditioning system that blows cool air in summer and warm air in winter along plastic air ducts that hang under the gutters. Further distribution of the air is achieved through holes in the side walls of the ducts. This system permits energy savings of 30-40%, although a small boiler is recommended to cope with the heating requirement on very cold nights in the winter. Furthermore, a co-generator is necessary to supply CO2 and electricity. The warming and cooling systems need to be kept in balance and is necessary to monitor the acquifers to be certain that there is sufficient heat or cold with which to heat or cool the greenhouse according to the weather forecast. Sensors are installed during construction and connected to a central computer. If the relative humidity in the greenhouse become too high, moisture can be sucked out by the air-conditioning unit. Water savings of 40-50% have also been demonstrated using this closed system. "Fruit & Veg Tech" www.HortiWorld.nl For further information: Wilk van der Sande Fax 0031 174 248739, E-mail: wvds@wvds.nl, www.wvds.nl