Simulation and control of ventilation rates in greenhouses

A simple model is presented, which enables the calculation of ventilation in a commercial rose-growing greenhouse (greenhouse). The model represents the greenhouse as three vertically stacked horizontal segments and addresses the energy and vapor transfer among these segments and between them the plant canopy and the external environment. The model equations show how ventilation can be calculated from the heat and vapor balances and how they can describe the internal microclimate. Air exchange rates obtained by the model are similar to published results obtained by tracer experiments and CFD. The model can be updated and calibrated for various conditions and structures, in accordance with online measurements of transpiration, leaf temperature, air temperatures and humidity at several heights above ground level. By making some assumptions, representative plant temperatures (RPTs) can be calculated instead of being measured. The validity of the model assumptions is established by comparing numerical results with experimental data. Good agreement is obtained between the numerical output of the model and the experimental measurements, for most times of the day. The simplified model is used to demonstrate the calculation of representative plant temperatures when forced ventilation is applied to cool the plants. Further study is still necessary to make the model applicable to complete days and throughout the season. Once the model is fully established and proven it will be used for sophisticated greenhouse climate control.