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Optimal control of carbon dioxide enrichment in tomato greenhouses

Bailey, B.J.
Acta horticulturae 2002 no.578 pp. 63-69
carbon dioxide, carbon dioxide enrichment, carbon markets, combustion, greenhouse production, greenhouses, heat, heat treatment, heaters, models, natural gas, photosynthesis, prices, tomatoes
Strategies for enriching tomato production greenhouses with pure CO2 and CO2 obtained from the combustion of natural gas in greenhouse heaters or CHP units were compared on the basis of the financial margin between crop value and the combined costs of CO2 and natural gas. Models were used to estimate crop net photosynthesis, heating and ventilation requirements, CO2 consumption and crop value. For enrichment using pure CO2 the comparison showed how the most economic CO2 control set point changed with the price of CO2. The best performance was obtained with optimal control in which the CO2 concentration was adjusted continuously to maximise the financial margin. With exhaust gas CO2, the storage of excess heat produced by the heater or CHP unit when operated during the day to provide CO2 increased the financial margin. Without heat storage it was preferable to dissipate the excess heat directly to the external environment than to use the greenhouse heating system as this increased the ventilation requirement. For the same gas price, the financial margin with a CHP unit only exceeds that of a boiler when a heat store is used and excess heat is dissipated via the greenhouse heating system.