EN - iSii compact: How to set up the Ventilation control

EN - iSii compact: How to set up the Ventilation control

  

Question

How to set up the Ventilation control?

 Answer 

The setpoints for ventilation can be found as follows:

 

 

The ventilation vents will be controlled in the following cases:
  1. Too high greenhouse temperature
  2. Too high relative humidity
  3. Favorable outside conditions (Meteo)
  4. Wind
The opening of the vents will be limited during:
  1. Frost 
  2. Storm
  3. Rain

Ventilation – Temperature 

In this case the setpoint for greenhouse temperature is 20 °C.

 

The leeside is released if the measured greenhouse temperature is 1 °C higher than the setpoint.



The wind side is released if the measured greenhouse temperature is 2 °C higher than the setpoint.

The calculated vent position depends on “P-actuation: influence medium – large ventilation”.
The standard setpoint is 1. 
A value smaller than 1 means a larger calculated P-band, so less ventilation.
A value larger than 1 means a smaller calculated P-band, so more ventilation.

 
 

Ventilation – RH 



The RH setpoint in this case is 80%.

The leeside and the wind side are released if the measured RH is 0% higher than the setpoint. Usually only the leeside is used to control RH.


 
The minimum vent position is used when the measured RH is higher than 85%.
At a measured RH of 90% the vent position is 5%.

The calculated vent position for RH:


Measured RH %
Calculated vent position for RH in %
84
0
85
0
86
1
87
2
88
3
89
4
90
5
91
5
 

Ventilation – Meteo 

 

The ventilation meteo is a precontrol for the outside conditions.
If the outside conditions are favorable, vents are opened before it becomes too warm in the greenhouse – a precontrol..

Favorable outside conditions are:
  1. It is not too cold
  2. There is not much wind
  3. It is sunny
The calculated vent position depends on “P-actuation: influence medium – large ventilation”.
The standard setpoint is 1. 
A value smaller than 1 means a larger calculated P-band, so less ventilation.
A value larger than 1 means a smaller calculated P-band, so more ventilation.

Ventilation – Wind

 


With stronger winds, there is more air exchange. This is usually not desired. Therefore the vent position can be decreased when the wind is stronger.
The setpoints for this decrease must be set separately for leeside and wind side.

The maximum vent position during stronger winds:

Wind speed m/s
Maximum vent position lee side %
0
100
2
100
4
84
6
68
8
52
10
36
12
20
14
20
 

Ventilation – Frost limitation



A frost limitation is intended to keep the vents closed during freezing, to prevent vents from opening while they are jammed.
The setpoints for this limitation must be set separately for leeside and wind side.
In this case the vents will remain closed if the outside temperature is below 1 °C.

Ventilation – Storm limitation

 

A storm limitation is intended to prevent the greenhouse from vacuuming in case of storm. Usually a vent limitation storm is only set on the leeside.

In this case the limitation storm is set when the wind velocity is above 13 m/s. The limitation can vary from 1 to 3% depending on the measured greenhouse temperature.

Ventilation – Rain limitation



A vent limitation rain is intended to prevent the crop from getting wet during rain. The setpoints for this limitation must be set separately for leeside and wind side..

Ventilation – Open vents after limitations

 

After a limitation period for frost, storm or rain, it is desirable that the vents are opened, if necessary in steps.
In the above example, the vents are opened in 5 steps, with an interval time of 1 minute.