The Priva Compass has the ability to control both irrigation and misting valves.  Irrigation valves are used to bring water and nutrients to the roots of the plants and misting valves (also known as fogging valves) are primarily used for humidity and temperature control.  This article explains how misting valves are utilized in the Priva Compass.

Misting control

Misting valve setup

Each Priva Compass zone can have up to forty irrigation/mist valves.  Each of these forty valves can be set up to be either irrigation or mist valves.  To select between a mist or a irrigation valve, the grower needs to go to the valve settings page and select a strategy for the valve. If the misting strategy is selected for a particular valve, the valve can be used as method of increasing humidity or decreasing temperature. Once the misting strategy is selected, the misting strategy card appears in the climate control dashboard.

Misting valve control

The simplest misting valve consists of a single valve in a greenhouse zone. If the humidity level goes too low or the temperature goes to high, the misting valve turns on.  The misting nozzles introduced a water vapour into the greenhouse to raise the humidity and lower the temperature. 

Pulsed misting cycles

One of the challenges with misting is that when the misting valves turn on, it can add a lot of water vapor into the greenhouse. Since it takes time for the temperature and humidity sensor to detect the change, the situation can occur that when a change in humidity is measured at the sensor, too much water vapor has been added to the greenhouse and the humidity levels climb too high.   To resolve this issue,  the Compass also has the option of pulsed misting.

When controlling misting valves using pulsed misting, the valves are set to go on for a fixed duration. After the valves have been on for the specified length of time, they will turn off for an interval.  The grower can adjust the interval between mist cycles based on the amount of light that is measured. If it is cloudy, there can be a longer interval between mist cycle.  As the measured light intensity increases, the duration of the misting cycle does not change but the time interval between misting cycles decreases. 

Misting pump

In addition to the misting valves, there is often a misting pump in the system.  The misting pump pressurizes the water for the system and turns on whenever one of the misting valves turns on.  In order to control a misting pump, a basic water system license is needed.  The misting valve also needs to be linked to the misting pump.

Multiple misting valves in one zone

If the misting pump capacity is not high enough to provide pressurized water for the entire greenhouse zone at once, multiple misting valves can be set up in a single zone.   All the misting valves need to be tied to the misting pump which is controlled as a water system.  Within the water system, the grower can set how many mist valves are allowed to operate at the same time. This will be based on the capacity of the pump. The water system will ensure that the misting valves turn on in sequence.  

One of the challenges of using multiple misting valves is that each of the valves is monitoring the temperature and humidity levels independently.  A situation could occur where the first mist valve turns on because the humidity is too low but the humidity rises before the last valve runs. Since the humidity is high enough, the last valve does not run.  To ensure that this does not happen, it is recommended to set up one misting valve for control and set up the other misting valves as slave valves. Slave valves will only start a misting cycle if the master valve starts a cycle.

Misting valves in multiple zones

It is possible to have one misting pump for multiple zones.  When multiple zones are calling for misting, the water system will sequence the valves so that each zone gets equal opportunity for misting.