In this paper we report the findings of a survey conducted to evaluate the energy-conservation performance of an office building some time after construction, and present the results of a simulation that was performed to identify possible improvements to the building’s cogeneration system. The indoor thermal environment was monitored over winter and summer, recording temperature and humidity variations and the vertical distribution of indoor air temperature. The simulation involved examining the effects of modified air-conditioning system operation, based on indoor humidity, ventilation temperature and survey data. The current energy-conservation performance of the cogeneration system is identified on the basis of the survey data, and suggested improvements for future operation based on the simulation results are proposed.