NASA is funding a research project at the University of Missouri - Columbia as part of a more general effort to learn about the human physiological response to the types of exercise that astronauts perform on EVA missions. The authors created a dynamic state-space mathematical model representing the thermal behavior of the NASA environmental chamber located at the Ames Research Center. This model predicts chamber performance from which the authors identify modifications to the system which will improve its accuracy and usefulness. Simulation results closely match expected values for chamber performance. Recommendations are presented to improve chamber performance and instrumentation measurement accuracy.