Abstract A practical method for measuring leakage and low level ventilation in greenhouses is presented that is based on the use of carbon dioxide (CO2) as tracer gas. When natural gas is used for heating, as is done in the Netherlands, carbon dioxide can be obtained from the exhaust gases of the heating system. A dynamic form of the tracer gas method is employed, known as the decay rate method. Six small greenhouse compartments were injected with CO2 up to a level of 2000 v.p.m. (volume per million volume) and then the injection was stopped. The ventilation rate was calculated from the decay rate of the concentration. A relation was established that describes the ventilation rate as a function of wind speed and ventilator aperture. CO2 can also be used as a tracer gas in greenhouses containing crops, provided the CO2 exchange by the plants is included in the calculation. A test was made to compare a simple CO2 measuring device, which is commonly used by growers, with the infra-red gas analyser that was used in the experiments. It was found that the simple device allowed the proposed method to be used in practice.
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