PERFORMANCE OF COMBINED HEATING AND DEHUMIDIFICATION SYSTEM FOR GREENHOUSES

The proposed Combined Heating and Dehumidification (CHD) system is intended to provide the desired climatic conditions in closed greenhouses, as expressed in temperature and humidity. The proposed CHD system is based on a refrigeration cycle for drying the air, and a heat exchanger for heating. This framework offers an innovative approach to the solution of the problem of excess humidity. As a result, expensive energy will be saved, on the one hand, and the conditions in the greenhouse will be optimized, on the other hand. In order to provide the required conditions and for the purpose of efficiency and saving of energy consumption in greenhouses, it is suggested to apply the following two approaches: Reduction of heat consumption - through improvement of the greenhouse insulation. Improvement of the greenhouse insulation may be achieved through the use of a double, inflated covering, and a thermal screen. These means were developed and examined in the 1970s, because of the energy crisis. Refrigeration cycle using - to dry the greenhouse air artificially while maintaining the desired humidity. Thus, it is suggested to activate a refrigeration cycle in the greenhouse, so that the air which is initially cooled and releases water, is subsequently heated. This means that there is a process of conversion of energy from latent heat into sensible heat with no losses to the surroundings. This procedure will allow condensation of all of the water vapor emitted from the foliage and the ground. Prototype of the proposed CHD was designed, constructed and implemented in the greenhouse. The CHD prototype was installed in the experimental greenhouse (1100 m2) which comprising common heating system, thermal screen and force ventilation system. This greenhouse was examined under several operation modes. The proposed and comparable greenhouse operation modes were intended to maintain temperature of 18°C and relative humidity of 80%. The experimental results indicate that under the proposed greenhouse operation mode, the CHD prototype capability of removing close to 700 kg of water per night (40 kg/h); energy saving of about 80% in comparison to without thermal screen and with ventilation greenhouse operation mode and 60% in comparison to with thermal screen and with ventilation greenhouse operation mode.