Optimal control of greenhouse climate

The reason why essentially constant day and night set point temperatures are used to control greenhouse heating is simple – this was the only way in which the first thermostats could be used, and this practice continued. However, in nature plants do not experience constant temperatures, so there is no fundamental reason why the greenhouse temperature should be held constant. Thus a variable heating temperatures could be considered, especially if doing so gave some specific benefit. A novel form of heating control has been tested on a commercial nursery. The heating temperature was varied from hour to hour throughout the day in a way designed to reduce heat consumption. The primary goal of the experiments, however, was not to minimise heating but rather to determine the grower’s reaction to this form of varying temperature control.

Key results:

1. A computer program has been implemented on a commercial nursery to minimise heat consumption.
2. The computer program runs on a PC which communicates with a commercial greenhouse computer system.
3. The PC receives Met Office’s weather forecasts remotely via a modem.
4. The computer program varies the temperature set point on an hourly basis.
5. The calculated temperature set point was shown to vary inversely with the wind speed.
6. After the initial hesitation, the grower gain confidence in this novel form of control.

1. To demonstrate the feasibility of implementing a novel form of control of greenhouse heating, and
2. To examine the practical implications to the grower of variable greenhouse temperatures.