The mild UK climate makes many low-energy cooling systems both technologically and economically feasible. In this study, EnergyPlus, the newest US energy simulation program, is used to evaluate the potential energy savings of several different systems for a recently built building outside of London. UK. Results from validation studies are briefly presented with the conclusion that EnergyPlus provides sufficient accuracy for most energy simulation applications. Systems evaluated include chilled ceilings, displacement ventilation, natural ventilation, night cooling. and a traditional VAV system. Unusual features of the building model are presented. Results show that systems that maximize free cooling from outside air have the best energy performance, and that natural ventilation alone cannot provide year-round comfort in the building studied. but would be effective as part of a hybrid system.