Pure (bottled or piped) carbon dioxide is commonly supplied to increase productivity of greenhouse crops. As ventilation is necessary for controlling temperature, particularly under sunshine (when a high CO_2 concentration would be most desired) there is a need for optimal management of supply, in order to ensure the maximum net return from cost of carbon dioxide supplied and increase in harvest. The optimal concentration depends on many factors: the expected increase of yield thanks to carbon dioxide supply under given climate conditions; the actual ventilation rate; the value of yield and the cost of carbon dioxide. We combined a calculation of the "value" of carbon dioxide supply with an algorithm to calculate the ventilation rate, into a calculation on-line of the optimal supply rate. The algorithm was implemented and tested into a commercial climate control computer.
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