The purpose of this research project was to evaluate the accuracy of building energy simulation software by comparing actual building energy use to the results obtained from commercially available building energy simulation software. The building used in this project was the Iowa Energy Center's Energy Resource Station located on the DMACC campus in Ankeny, Iowa. Three different types of heating, ventilating and air-conditioning (HVAC) systems were used in the study. These systems were variable-air-volume with terminal reheat (VAVRH), constant-air-volume with terminal reheat (CAVRH), and four-pipe fan coil unit (4PFCU).;Three building energy simulation programs were used. The programs were DOE2, HAP and TRACE. These programs represent a wide range in the level of detail available for energy simulation software. Site weather data were used to build weather files for each program. Input data files representing the Energy Resource Station and its mechanical systems and equipment were used for each computer model.;Results from this research project show that the energy simulation programs predict cooling and heating energies better in cases with non-dynamic building operation than in cases with dynamic operation. The results also show that the programs do a better job of predicting heating energy than in predicting cooling energy. This was true for both dynamic and non-dynamic building operation.;Of three HVAC system types used in the study, the CAVRH system best matched the experimental results for all three programs. All three programs showed significant differences in cooling and heating energy predictions when they used the 4PFCU system. In the VAVRH system the programs predicted the heating energy reasonably well, but did not predict the cooling energy well. In general comparisons, the DOE2 program predicted the cooling energy best among the programs, and all three programs predicted the heating energy similarly.;Only the DOE2 program was used for the daylighting validation study. Prediction of lighting energy in the test rooms was very well matched to the measured lighting energy. The prediction of illuminance in the rooms showed differences depending on the orientation of the rooms.