The humidification-dehumidification (HD) greenhouse is a relatively new
technology. In addition to the humidification process and cultivation normally
present in greenhouses in arid countries, the HD greenhouse also integrates a
dehumidification process. In these greenhouses, saline or brackish water is
evaporated in the ordinary evaporative cooling pads (i.e. 1st humidifier) before
passing through the main crop growing section. The air is further loaded with
more moisture by passing it through a 2nd humidifier. This humidification
process is then followed by a dehumidification process to condense as much
water vapour as possible. The main purpose of the HD greenhouses is to find a
cheap means of desalinating saline water for the sake of using the condensate
for irrigation.
Most of previous attempts to improve the performance of the HD
greenhouses have used a trial-and-error approach. An alternative approach is
to use simulation models. Due to the absence of such models, this research
study aims at developing a simulation model capable of simulating the
significant processes of the HD greenhouses. The developed model is an
integration of three sub-models each of which simulates one element of the HD
greenhouse. The simulated elements are humidifiers, cultivation area (i.e.
microclimate) and dehumidifiers. The integrated model can be used for design
and optimisation purposes.
Because it was difficult to find an HD greenhouse where the accuracy of the
integrated model can be tested, the three sub-models were tested separately.
When the simulation results were confronted against the experimental results, a
good accuracy was obtained for the three sub-models. It was found that the HD
greenhouse model was able to predict the humidification rate with a good
accuracy within the range of conditions used for calibration. The model was,
then, used to simulate a hypothetical Quonset-type cucumber-cultivated
greenhouse using weather data obtained from the site of the HD greenhouse in
Oman. The simulation results were similar to the expected results.The applications and limitations of the HD greenhouse model are discussed
in this study. Future investigations to further study and, if necessary, improve
the accuracy of the HD greenhouse are highly recommended
