Sonic anemometry to evaluate airflow characteristics and temperature distribution in empty Mediterranean greenhouses equipped with pad–fan and fog systems

Sonic anemometry has been used to analyse two greenhouse evaporative cooling systems: a pad–fan system and a low pressure water/air fog system. These systems were used in empty greenhouses to simulate the microclimatic conditions produced inside Mediterranean greenhouses when crops are seeded in nurseries or transplanted in commercial greenhouses. Evaporative cooling systems could be necessary in the future for all Mediterranean greenhouses to reduce excess heat and to maintain certain levels of relative humidity on hot days from spring to autumn. The pad–fan system proved capable of maintaining more favourable conditions than the fog system. The best results were obtained by combining the evaporative pads with shading screens (differences of 1.4–1.8 °C between inside and outside temperature). The main drawbacks of the pad–fan system were the horizontal and vertical temperature gradients, with a maximum temperature difference between pads and fans of up to 11.4 °C, and a maximum difference of 6.7 °C between heights of 2 m and 1 m. However, inside temperature and relative humidity were more stable over time in the greenhouse using the pad–fan system. The fog system required higher energy consumption (7.2–8.9 kWh) than the pad–fan system (5.1 kWh) for continuous operations over 1 h. Nevertheless, the average water consumption of the pads (122.3 l h−1) is greater than that of the fog system (9.4 l h−1).