Calculation Standards in OpenBuildings Energy Simulator can be changed between CIBSE and ASHRAE as required. Likewise, units can be changed between Metric and Imperial.
To change these settings in an existing project only, please right-click on Project in the project tree, and select Properties.
To change the Default settings for the software, please select Defaults under the Data Managers tab, and select Application. Any new projects created thereafter will adopt these settings.