The new concept Next Generation Semi-closed greenhouse is truly a successor to earlier generations. That is the conclusion of research done by WUR Greenhouse Horticulture. The study shows that the system generates 25 to 30% energy savings at lower cost than previous generations.
The Next Generation system is based on dehumidification and heat concentration. Growers can apply the technique without major changes in their production strategy. The earn-back period with a gas price of 30 cents is about 7 years.
In recent years the development of the (semi) closed greenhouse has showed that it is possible to heat greenhouses using excess heat from the summer as renewable energy, saving around 30%. However, the technique is not utilized to its full extend, due to the high cost of a semi-closed greenhouse.
Less cooling capacity
In the design of the Next Generation Semi-closed greenhouse less cooling capacity is assumed, making it possible to use the installation as dehumidifier. The system focuses on keeping the greenhouse closed in the winter, instead of closing the greenhouse in the summer. The cooling capacity is around 50 W / m².
The concept has been tested by a grower. Calculations showed that the heat demand of 40m³ of natural gas per m² per year could be reduced to 30 m³ / (m² year). The small cooling capacity led to a large number of equivalent full load operating hours. All components in the system are used intensively, which lowers the cost of capital.
Dehumidification and heat collection can also be carried out by contacting greenhouse air with a hygroscopic salt solution. The energy saving potential is probably somewhat higher, but improving the economic parameters all depends on the price of the regenerator.