Field trials of the Natural Ventilation Augmented Cooling (NVAC) greenhouse. (October 2018) - McCartney, Lucas
Abstract : Many greenhouse designs rely solely on natural ventilation, which makes them suitable for use in mild climates or for the production of heat-tolerant crops. The Natural Ventilation Augmented Cooling (NVAC) greenhouse is naturally ventilated and improved by augmenting the thermal buoyancy with a strategically placed misting system. The greenhouse structure comprises tall sidewalls, oversized side vents, a roof vent, and an additional inside roof. The misting system is located above the gutter level of the greenhouse and sprays a mist of water between the top roof and the added inside roof. The added roof guides the cooled air towards the main space of the greenhouse and prevents water droplets from reaching the crop. Testing was performed in Trents, Barbados, where an empty NVAC greenhouse (without plants) provided cooling ranging from 1.3 to 3.6 °C relative to outside temperatures, while increasing relative humidity by 5.7–17.7%. This is in contrast to inside temperatures being warmer than outside temperatures in most natural ventilation greenhouses. The NVAC greenhouse is an affordable design, using far less electricity than a pad and fan system in a comparably sized greenhouse. The NVAC misting system can be used intermittently or continuously to reduce greenhouse temperatures year-round or to extend growing seasons. Site-specific conditions such as natural variations in weather must be considered as they play a role in the performance of the NVAC greenhouse. Accordingly, an automation system can help improve usage. Highlights: The NVAC design improves the usage of natural ventilation greenhouses. Field testing was accomplished in Barbados. Cooling varied from 1.3 to 3.6 °C. Relative humidity increased by 5.7–17.7%. The system uses a fraction of the electricity used by comparable technologies.