THE CONTROL OF CARBON DIOXIDE CONCENTRATION IN GREENHOUSES
The first system, suitable for research purposes, comprises an infra-red gas analyser to which is connected an electronic controller which varies the mean rate of flow of carbon dioxide injected into the greenhouse. The rate of gas injection is proportional to the deviation of gas concentration below the desired level. Close control of gas concentration is achieved and the apparatus may also be used for other gases, such as nitrous oxide, which can be detected by infra red gas analysis.
The second system, suitable for commercial purposes, uses deionised water as an analytical fluid. The change in electrical conductivity of deionised water on coming into contact with air containing carbon dioxide is used to operate a solenoid valve via a transitorised control circuit. Though less sensitive than infra red gas analysis, the conductivity method is much simpler and cheaper.