A greenhouse climate simulation model, employing linked first-order integral and differential equations, was adapted to predict the microclimate within carbon-dioxide-enriched open-top chambers (OTCs) suitable for climate change research. The simulation model was validated using experimental measurements from a prototype OTC test rig constructed at Silsoe Research Institute; this model was then used to investigate the effect of employing a controlled combination of air recirculation and ventilation on carbon dioxide consumption for a chamber containing wheat plants.Control criteria for a controlled-ventilation OTC were investigated using the simulation and verified experimentally; results showed that a 2°C temperature excess limit within the chamber could be achieved in practice for a chamber exhibiting minimal wind incursion through the open-top, provided that a mechanical ventilation rate of 6 air changes minute - 1 was provided during periods of peak solar flux. Furthermore, the simulation suggested that, by applying controlled ventilation and recirculation to OTCs, it is feasible to reduce the daily consumption of enrichment gas to achieve 560 μ mol mol - 1 concentration within a 3 m-diameter and 3 m-high chamber located at an exposed site to 15 kg in comparison to the estimated 100 kg required when continuous ventilation is employed.