Using computational fluid dynamics (CFD) to improve high tunnel ventilation

High tunnels are cost effective, plastic film-covered growing structures that use very little to no modern environmental control technology. Natural ventilation is used to control temperature and, to a certain extent, humidity in these structures. Typically, ventilation openings are created along the sides and sometimes the roofs by manually rolling up a section of the plastic film cover. Operators have to account for daily and seasonal changes to control the indoor environment. In this paper, we focus on summer ventilation. During the summer, it is important to maximize the air exchange rate within high tunnels in order to maintain inside temperatures as close to the outside temperature as possible. Computational fluid dynamics (CFD) simulations were used to evaluate summer ventilation in empty high tunnels and populated with Rubus idaeus (red raspberry). The CFD models were developed and validated using environmental data (wind speed and direction, air temperature and relative humidity, soil temperature and heat flux, leaf temperature, and net incident radiation) collected from high tunnels located at the Pennsylvania State University High Tunnel Research and Education Facility (Rock Springs, PA, USA). Two ventilation designs (a conventional system with only roll-up side vents and another such system supplemented with a roof vent) were evaluated and results are reported in this paper.