EN - Airmix ventilate to cool
Air cooling
Growers are increasingly bound by rules to prevent light emission from lighting. This means that the blackout screen must be closed when the light is on. The greenhouse temperature and humidity will then increase. Airmix can be used to limit the greenhouse temperature under a closed screen, by means of ventilation.
During ventilation, warm - and relatively humid - greenhouse air is exchanged with cold outside air, which is also drier.
Growers demands
Growers may have the following wishes regarding the greenhouse temperature under the screen for uniform crop growth as above (image):
- greenhouse temperature must be limited by blowing in cold (outside) air
- must be uniform and stable due to high precision and intelligent control
- may only be a fraction higher than the set heating temperature
Virtually no 'dead zone' is tolerated between heating with the heating pipes and ventilation with Airmix.
For example, the ventilation temperature is 18.2 degrees Celsius with a heating temperature of 18.0 degrees Celsius.
Intelligent solution
The solution is a control whereby the Active Air: ventilation temperature - temperature at which cold air is blown in - is barely higher than the (calculated) heating temperature. While cold air is blown in, the measured greenhouse temperature does not rise any further. See also the graph below; the measured greenhouse temperature is stable. The values (reading line, last column) show that the measured greenhouse temperature is almost equal to the Active Air: ventilation temperature and hardly higher than the calculated greenhouse temperature.
Optimalisation
The iSii Active Air module makes recirculation and ventilation possible. During ventilation, the Airmix outside air damper is opened further as the greenhouse temperature rises. The starting moment is the Active Air: ventilation temperature that is exceeded. The control does not prevent the greenhouse temperature from rising any further. The outside air damper is controlled proportionally. This means that the outside air damper is opened further as the greenhouse temperature rises. The damper position does not change if the greenhouse temperature remains too high unchanged.
Proportional and Integral
With an additional Custom Control, the outside air damper is opened further if the temperature exceedance persists. The damper will not only open further due to a (too) high greenhouse temperature, but also if it remains too warm under the screen. In addition, the Custom Control can also regulate the greenhouse temperature and not, as with Active Air, only the outlet temperature. This makes it possible to achieve the goal demanded by the grower, namely limiting the greenhouse temperature under the screen. A stable greenhouse temperature that is barely higher than the heating temperature, under a closed screen.
Custom control, 2 posibilities
If the above is desired, additional custom operation is recommended. One custom control per Active Air unit.
Active Air controls the discharge temperature as standard with the position of the outside air damper. The outlet temperature appears to be 1 to 2 degrees lower than the set heating temperature, for sufficient ventilation. This is easy to realize with influence on the set value VIP in the custom control, see examples below.
Example 1: Control of outlet temperature
The set 'Active Air: ventilation temperature' applies as a (copy) target value for the custom control.
This value is reduced by a maximum of 3 as the greenhouse temperature rises in relation to the 'Active Air: ventilation temperature'. See image.
Explanation
If the greenhouse temperature is higher than the 'Active Air: ventilation temperature', the discharge temperature is controlled by opening the outside air damper (further).
With a difference of 0.8 degrees Celsius, the computer strives for an outlet temperature that is 3 degrees Celsius lower than the set 'Active Air: ventilation temperature'.
Example 2 Control of greenhouse temperature (recommended)
The set 'Active Air: ventilation temperature' applies as a (copy) target value for the custom control.
This setting is added to a value of 0.2. See image. This results in a temperature of 18.2 degrees Celsius at which the outside air valve is opened.
Explanation
If the greenhouse temperature is higher than the 'Active Air: ventilation temperature', the outside air flap is opened (further) to maintain the ventilation temperature.
If the greenhouse temperature is higher than the 'Active Air: ventilation temperature', the outside air flap is opened (further) to maintain the ventilation temperature.
For sufficient ventilation it is important that there is sufficient cold air above the screen.
So the windows must be open when the screen is closed.
The positive effect of ventilation with Active Air can therefore be disturbed by rain, storm and frost.
Contact your technical partner for detailed information, a proposal and installation.
From iSii version 11 the improvement is possible with a custom control.
Version 11 requires an additional (dummy) data output connector, version 12 does not.
Switch off Active Air when irrigation is active, see below
Supplement, do not release fans when irrigation is active
To switch off the Airmix fans during irrigation, all valves in the Airmix group must be connected to the Combination valve 'Airmix from department ...'.
The control of this combination valve has two functions:
- The first function is to interrupt the Airmix fan control
- The second function of the combination valve is to create a Din on the Datapoint, with which the Airmix fans are also switched off by software.
For the Din we would apply a Custom Alarm. The advantage is that this also draws the customer's attention to the fact that the Airmix of department ... has been switched off due to irrigation.
The detection of the Custom Alarm can be used to make the release '0' during irrigation, so that the Airmix is also switched off by software. For each Active Air group, both 1 combination valve and 1 Custom Alarm are required.
Always consult your technical partner with the above option:
combination valve and matrix irrigation valves do not mix.
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