A computer model of a plant growth chamber, capable of both steady-state and transient simulations, has been developed to assess the performance and design of bioprocessors. Two approaches that employ a spreadsheet program and a simulation package to estimate system mass and energy balances are used. Parameters that describe hardware and plant characteristics are input to the model. The model provides predictions of the environmental conditions in the growth chamber, the production of biomass, the exchange of carbon dioxide and oxygen, and the transpiration of water. The model has been customized to characterize the Salad Machine at NASA Ames Research Center. Predictions resulting from the simulation of the customized model are compared with hardware test data for model validation.