The setpoints, and periods for temperature and ventilation are set relative to sunrise and sunset. This normally evolves from daytime temperature to night and vice versa, in order to avoid condensation inside the greenhouse.

Normally, 2-3 hours before sunrise, the temperature is increased 1-2 ° C per hour, so that perspiration causing heat stroke early in the morning in the culture, is received in a higher temperature air.

At sunset we proceed similarly, but in this case with a negative rate change. The air temperature is also modified as light availability so the higher light levels, the higher working temperatures will be in order to obtain better performance in crops.

1.1.- Control of heating

To control air temperatures by heating in hot water intallations, a process that integrate the air temperature with water temperature in the heating circuit is used. To do the maximum and minimum temperatures in the heating circuit are defined, and the controller acts on the 3-way mixing valve.

Another control system consist in taking into account the outside air temperature, wind speed and solar radiation. Knowing the thermal global constant of the greenhouse (the temperature swing between the interior and exterior) and wind speed, temperature heating circuit can be defined as well as the defendant thermal load of the facility.

In hot air generators systems, control is simple, these are switched on and off according to a hysteresis band of about 2-3 ° C, for connection and disconnection. If the installation includes several teams distributed along the surface of the greenhouse, you can set a sequential start following a spatial distribution from high to low numbers.

1.2.- Temperature control by ventilation

The control is performed with the ventilation installation, mainly windows zenith. The rate of ventilation of a greenhouse depends on:

• The degree of opening of the ventilation system
• The speed of the wind
• And the temperature difference between the inside and the outside.

This may be a data rate to be computed controller and a energy balance and mass to proceed to an adjustment in the position of the windows. Measuring the wind direction is used for the opening in order, the ventilation oriented downwind is operated first, followed if necessary, by upwind oriented, for which a delay is established to the opening of the latter.