Ventilation and Cooling Modeling and Lyout of Fans, Pads and Vents of an Octagonal Greenhouse

IntroductionGreenhouse technology is a flexible solution for sustainable year-round cultivation of many horticulture products, particularly in regions with adverse climate conditions or limited water and resources. Greenhouses are the structures that provide the desired conditions for plant growth throughout the all seasons. Plant growing and crop production in the greenhouses require proper ventilation conditions to provide optimal temperature, relative humidity and CO2 and to minimize the toxic gases. Ventilation method of greenhouse is depending on the design of greenhouse ventilation and cooling is usually done by evaporative pad and fan systems or fan and vent systems. Recently different designs, different structures and different layouts of fans, pads and vents are used in greenhouses. Layout of fans, pads and vents affects the performance of ventilation systems. The aim of this study was to layout the fans, pads and vents to provide best air flow in an octagonal greenhouse. Materials and MethodsIn this study, three layouts of evaporative pad and fan systems and vents were modeled by computational fluid dynamics (CFD) method. For computational fluid dynamic of inside greenhouse airflow, the air flow was considered to be compressible. In order to estimate density, velocity and temperature, the Navier- Stokes equation included momentum, state, energy, continuity was used. For modeling the fluid flow, all necessary and dependent parameters of climate were considered based on the concentration and air pressure at the level of the open sea. Fluid flow equations were solved by finite volume technique. Three mentioned layouts of this study were 1- fans on the roof of the pyramids and vents on the wall of the pyramids, 2- pads and fans on the greenhouse side walls and 3- pads on the greenhouse side walls and fans on the roof of the pyramids (parallel pads). The performances of each arrangement can be improved by the speed of the fans, the size of the vents. The main equation in fluid flow simulation using CFD can be done by the following set of equations in which the continuity equation in the form of indicial notation can be presented as: Moreover, the momentum equation can be written by the following form: The equation 4 shows the state equation in a fluid flow interaction. All technical calculations and CFD simulations were done by Solidworks 2018 software.Results and DiscussionThe results showed that octagonal greenhouse by a specific form of the vents on the walls and fans on the roof could provide a circular air flow around the plants in the greenhouse. However, due to different powers of the fans, different velocity and different shape of air circulation could be achieved. When pads and fans are located on the greenhouse side walls, uniform air flow from the pads move uniformly throughout the greenhouse and then exit from opposite fans which causes desired air flow in the greenhouse. When the fans are located on the roof of the pyramids and pads are located on the side walls parallel, pad surface increases in the greenhouse and thus relative humidity increases and temperature decreases.ConclusionsBecause of the specific shape of the vents in octagonal greenhouse, different air velocity and different shape of air circulation will be achieved when different power of the fan is used. This causes that the octagonal greenhouse can be used in different climate conditions. When the fans are located on the roof of the pyramids and pads are located on the side walls, temperature decreases and relative humidity increases and this layout is desirable for hot and dry climate. An octagonal greenhouse can be used in different climate by using a suitable layout of fan, pad and vents