With rising outside temperatures the need for fresh air also rises in order to achieve sufficient levels of evaporation and cooling. In general the air inlet is usually controlled based directly on CO2 or controlled based on RH and limited by CO2. In both situations reliable CO2 measurement is vital. The first global control can be done by checking the outdoor CO2 measurement value. This should normally be somewhere between 350 and 400 ppm. Higher values can briefly be measured (for example during mist). If in doubt, carry out a complete check.
First of all, replace the paper filters often used in some CO2 sensors. Use a zero setting cartridge to check the zero setting on the CO2 sensors, then check the hoses and magnetic valves in the growing rooms and outside for leakage. The zero setting cartridge must be connected to the hose in a vertical position. When air from the growing room or outside is measured, the value on the CO2 sensor should read 0 ppm. If not, there is a leak somewhere allowing mixed air to reach the CO2 sensor. If the CO2 measurement remains doubtful, recalibrate the sensor using calibration gas.
Jan Gielen, Specialist climate & energy C point