Sefaira uses EnergyPlus as our backend energy simulation engine for both sizing and energy calculations 

EnergyPlus performs a building simulation by reading two input files, an EnergyPlus input file that describes the building geometry, internal loads, ventilation requirements and building systems and  statistical weather file for the given location.

Sefaira creates EnergyPlus input file based on your geometry and other input choices and we make sure that each object in the input file follows the EnergyPlus syntax reqirements.

Correct input syntax unfortunately doesn't guarantee the successful EnergyPlus simulation. Occasionally during the simulation EnergyPlus can get to the point of instability that can not be resolved in which case it ends the simulation with an early termination.

Even though that all the inputs available in Sefaira are in the industry accepted ranges, sometimes the choice of extreme and uncommon input values together with some building and zoning geometry details that we are not able to control can lead to an early termination.

Finding the cause for the failed EnergyPlus simulation requires a deeper analysis because it can vary from case to case.

The best way to avoid unexpected termination of the EnergyPlus simulation is to try to stick to the following rules and apply better practice inputs 

1) Avoid high percentage of window to wall ratios in zones that have relatively small footprint comparing to the zone enclosing wall surfaces.

Use "Override Glazing Ratio" to select smaller ratios that would work or combine small zones with other  zones.

Ignore zones (especially perimeter ones) that have very small areas and high internal and solar loads. Good rule of thumb is that zones should be at least 50 ft2 (5m2) or bigger 

2) Avoid extremely high occupancy in the zone especially in the zone that has solar and high plug loads or lighting power density. Also, even though that the maximum occupancy of 1.1 ft2/person (0.1 m2/person) is available, it is not recommended.

An occupancy of 30 ft2/person (2.8 m2/person) is a much safer target even for a highly populated zones

3) Avoid non-convex zones (see below).

Use "Perimeter/Core" option in the "Zoning" tab to avoid non-convex zones

4) Avoid huge difference between the cooling set point and the cooling setback especially if the operating hour is finishing early in the day (see below) to avoid overheating of the zone

Keep the difference between the cooling setpoint and setback not to be more than 20F (11C) 

5) Avoid maximum or high values for plug loads and lighting power density because they can contribute to the overheating of the space.  Choose values that are recommended via plugin defaults