Optimal control strategies for carbon dioxide enrichment in greenhouse tomato crops-Part 1: Using pure carbon dioxide

Abstract Two optimal control strategies for carbon dioxide (CO 2 ) enrichment in greenhouse tomato crops have been developed. One uses pure CO 2 from a storage tank and the other uses CO 2 contained in the exhaust gases of boilers burning natural gas. The optimal strategies maximize the financial margin between crop value and the combined costs of the CO 2 used for enrichment and the natural gas used for heating. In this paper, the strategy for optimal control using pure CO 2 is presented and compared with strategies used by growers. The optimal strategy for enrichment with exhaust gas derived CO 2 is presented in an accompanying paper. Simulations show that at a cost of £0·09 kg −1 for pure CO 2 and £0·10 m −3 for natural gas, the optimal enrichment strategy would increase the annual margin of crop value over CO 2 and heating costs by £4·6 m −2 (27%) compared to a basic control strategy of enrichment to a concentration of 1000 v.p.m. (parts per million by volume) when ventilators are 2 concentration was expressed as an algebraic function of solar radiation, wind speed and ventilator opening angle, and so enabled a quasi-optimal value to be obtained using variables measured by greenhouse environmental controllers. The quasi-optimal equation, with coefficients averaged from simulations over 4 years, gave an increased margin over the basic control strategy of £4·4 m −2 (26%).