Discusses in some detail the concept of using and emulator/tester to evaluate the performance of a building energy management system (BEMS). Emphasises the testing of BEMS application algorithms with a description of the expected behaviour of scheduled start/stop, duty-cycling, demand-limiting, optimal start/stop, economiser and ventilation/recirculation algorithms plus the data needed to evaluate them. Proposes for use with with the emulator/tester preliminary rating criteria, weather conditions, building/HVAC type and building use conditions. Briefly describes expected test results to show how they might be compared with baseline data to provide a rating methodology.KEYWORDS: Energy management, computer programs, controls, testing, performance, algorithms.