An experimental study of the cooling performance and airflow patterns in a model Natural Ventilation Augmented Cooling (NVAC) greenhouse

A Natural Ventilation Augmented Cooling (NVAC) greenhouse is a natural ventilation greenhouse that is improved by coupling natural ventilation with a non-conventional misting system. In the design, an added inside roof, called the NVAC roof, prevents unevaporated water droplets from reaching the crop foliage and guides the cooled air into the main area of the greenhouse. Previous work on the cooling performance of the NVAC greenhouse design investigated temperature and relative humidity within the greenhouse under field conditions. To investigate the cooling capabilities and the nature of the airflow in the NVAC greenhouse, a network of thermocouples and a three-dimensional sonic anemometer were used for the measurement of temperature, relative humidity and air velocities inside a 1:4 model single-span NVAC greenhouse. The cooling performance of the NVAC greenhouse design without plants varied from a temperature reduction of 1.9-12.6 °C and relative humidity increase of 1.4-31.2% RH depending on the ambient conditions. The NVAC greenhouse reduced vapour pressure deficit by 0.3-4.9 kPa. Although temperature distributions were more uniform under natural ventilation, the amount of cooling was significantly greater with the use of the NVAC design, compared to none. It was shown that the NVAC greenhouse can provide air movement in the greenhouse at velocities up to 0.38 m s−1 without the use of fans. The average turbulence intensity of the air inside the greenhouse was increased to 0.32 with the use of the NVAC design, compared to 0.19 under natural ventilation.