Real-time control of the greenhouse environment by computer modelling : A thesis submitted in partial fulfilment of the requirements for the requirements for the degree of Master of Engineering in Lincoln University

Abstract

The energy balance for a greenhouse canopy is complicated, since the transfer of energy cannot be assumed to be taking place between the canopy and a homogeneous air layer. Also the presence of a heating system is an additional energy source within the canopy itself. Therefore, to simplify the procedure, a step by step approach will be adopted. First of all, the transport phenomena around a single leaf will be considered. From this a more practical energy balance of the canopy will be derived. This simplified energy balance for the canopy can be used to solve the leaf temperature by knowing the air temperature, wet bulb temperature, solar radiation and net radiation inside the greenhouse.

A computer program is developed to monitor air temperature, wet bulb temperature, solar radiation and net radiation inside the greenhouse and simulate the leaf temperature. This program also controls the greenhouse environment. For this the leaf temperature was set to be controlled between 14⁰c and 25⁰c.

The test results from the leaf temperature model produced an accuracy of + 1.64⁰C to -1.38⁰C of the actual leaf temperature. Since the control was to keep the leaf temperature between 14⁰C and 25⁰C, the accuracy obtained is acceptable. Therefore, it can be concluded that this project was successful.