The Unitary single zone option allows you to model simple single constant volume direct-expansion (DX) based HVAC configurations with several different heating options. Direct expansion includes single packaged rooftop systems commonly seen in commercial buildings and split systems commonly seen in residential buildings. In this system, local cooling coils are used to condition air which is supplied to the zone through a local air delivery system. Air delivery can be set up to ensure minimum fresh air supply and there are options for economisers to provide free cooling and heat recovery.
Note: With Unitary single zone systems each zone has its own 'AHU' and so, unlike the Unitary multizone, CAV and VAV Compact HVAC types, Unitary single zone systems take all their data from the zone level.
You can model unitary single zone systems with or without outside air. If you include Air distribution with your Unitary single zone system then heating and cooling will only operate when the Air distribution operation schedule is on.
If you do not want to include outside air in your system, you should uncheck the Mechanical ventilation 'On' check box. In this case heating/cooling availability is determined entirely from the heating/cooling operation schedules under the Heating and Cooling headers.
EnergyPlus needs both the heating coil and cooling DX coil to be defined so even if heating or cooling is not selected in the input, DesignBuilder will include both coils in the IDF data supplied to EnergyPlus and schedule the appropriate coil to be off.