Greenhouse natural ventilation by buoyancy forces.

Convective transfers mainly determine the energy and mass balances which regulate the micro-climate inside a greenhouse. Air flow and temperature patterns induced by natural ventilation through greenhouse roof openings are only considered here. Flow visualizations were performed on a half scale test cell simulating the absorption of solar radiation at the floor surface of a single-span greenhouse. Temperature and air flow patterns were observed in a steady regime i) with a single sided roof vent and ii) with two symmetrical one. An air inflow always take place at the lower part of the openings and feed a single convective loop which follows the walls of the greenhouse before escaping through the upper part of the vents. These natural convective patterns were numerically simulated by means of a Computational Fluid Dynamic code (CFD 2000TM). It was found that the convective cell, velocity values and the temperature profiles were generally in good agreement with the experimental results.