H.F. de Zwart and B. Speetjens
The Next Generation Semi Closed Greenhouse is an improved version of earlier generations of (semi) closed greenhouses. The system provides renewable energy for the heating of greenhouses. The concept is based on an optimised utilisation of the air treatment units that have become widespread with the ‘New Cultivation’ in greenhouses. In this New Cultivation greenhouses, dehumidification is performed by a well-controlled inlet and even distribution of outside air. In the Next Generation Semi Closed greenhouse, the air treatment units are furbished with a cooling heat exchanger in the upstream air flow next to the heating block. The air circulation capacity is around 10 m³/ (m² h ). With the cold heat exchanger, the greenhouse can be internally dehumidified.
This enables to keep the windows shut during the cold period of the year, which prevents losses of sensible and latent heat. In summer, the same system can be used for gathering heat from the summertime heat surpluses to provide energy for wintertime use of a heat pump. These summertime heat surpluses are stored in an aquifer system, just like the common practice in previous generations of (semi) closed greenhouses. The system was tested on 3680 m² of a commercial greenhouse and compared in terms of energy consumption with a standard greenhouse operation. The experiments showed that at the system could provide a 25% contribution of sustainable energy in the heat demand.
At current energy prices the simple payback time of the investments for a Next Generation Semi Closed greenhouse will be around 7 ½ years. Besides this system, the study also analysed the perspectives of hygroscopic dehumidification. It showed to be a realistic dehumidification system for modern greenhouses. The energy saving potential of hygroscopic dehumidification is likely to be even higher than that of a system based on condensation on a cold surface. The economic outlook depends largely on the price of the regenerator, the machine that extracts the water out of the desiccant solution.
Sponsors are the PT, Ministry of Economic Affairs and 'Kas als Energiebron'.