Design simulation calculations can be time consuming to run. Many factors are considered during the calculation process. Not least of these would be air flow networks, window opening criteria and occupancy schedules Method et al. All of this can be considered over large number of days, and potentially for a large number of rooms. In the case of PartL (level 5) this may need to be considered three times to calculate the Notional, Reference and actual building.
There are a number of things that can be done to speed up the calculation process.
The first four options, below, are general good practice and will help with any program that requires a lot of resources to function correctly. The final items are Design Simulation specific.