PREDICTING NIGHT-TIME CONDENSATION IN A MULTI-SPAN GREENHOUSE USING COMPUTATIONAL FLUID DYNAMIC SIMULATIONS

Condensation occurring on the inside greenhouse cover is a major issue because the consequent dripping causes plant diseases. One of the available and most widespread tools to tackle it, is natural ventilation; another effective technique is dehumidification. Both approaches have important drawbacks, ventilation entails a loss of H2O and a loss of energy (by lowering the inside temperature), while dehumidification implies an energy cost. This work aims to deepen the knowledge of the condensation phenomenon in order to be able to handle it in a better and efficient way. Condensation was studied through a set of CFD simulations, of a 3 multi-span greenhouse with natural roof ventilation under night-time Mediterranean climate conditions. The model paid particular importance to the exchange of energy by radiation between the greenhouse and the sky. A user defined function was developed and linked to the CFD model to study condensation on the greenhouse cover. Different radiative sky temperatures as well as different soil heat fluxes were investigated. Preliminary results show that the condensation process takes approximately two hours to reach a steady state condition, when condensation rate equals the transpiration rate. Moreover the condensation rate trends (against time) obtained for different boundary conditions (equivalent sky temperature and soil heat flux) show very similar development pattern, that could mean that the condensation phenomena during night could be foreseen through some proposed equations that link condensation rate with relevant external conditions.