COMPUTATIONAL FLUID DYNAMIC MODELLING OF NIGHT-TIME ENERGY FLUXES IN UNHEATED GREENHOUSES

The objective of this work was to develop a CFD model designed to study the night-time climate of an unheated greenhouse. A three-span sloped-roof greenhouse was considered for the simulations. For the first set of simulations, a single layer of polyethylene (PE with a thickness of 0.2 mm) was used as a cladding material. A second set of simulations were run for a greenhouse with the same dimensions but with an internal horizontal curtain of 0.2 mm thick PE. The CFD model used the Boussinesq approach and included a radiation sub-model, so that sky thermal radiation could be simulated. On clear nights, greenhouse air temperature was 2.5 K cooler than outside air. It was also observed that the roof temperature was up to 4.4 K cooler than outside air. On overcast nights, greenhouse air was 3.6 K warmer than outside air. The effect of the internal PE curtain was significant: in all cases, greenhouse air temperature was higher than that of outside air. According to simulations, using the curtain can induce increases in air temperature of around 2.8 K on clear nights. While roof temperature was not significantly affected by the curtain, curtain temperature was clearly higher than roof temperature. The increase in temperature of the curtain may have the practical effect of reducing dew formation and dripping over the crops. Further simulations are presently being conducted to assess the potential for reducing thermal losses in greenhouses using other materials and methods.