Why are fuel consumptions reported by DesignBuilder different from those reported by EnergyPlus?

At the end of an EnergyPlus simulation, DesignBuilder reads the EnergyPlus output file eplusout.eso. Much of the data is stored and displayed without further processing but in some cases, the outputs are processed to ensure that they are consistent with the DesignBuilder model data. DesignBuilder output data will differ from the data that can be found in the Simulation Summary tab in these cases:

Simple HVAC 

Simple HVAC Heating and Cooling Fuel

DesignBuilder applies a fuel type and a CoP to the idealised heating and cooling systems used in Simple HVAC, whereas EnergyPlus displays the unprocessed loads under 'District heating'. This is because the idealised systems in EnergyPlus are considered to be met directly without the use of HVAC equipment through a district heating/cooling type system.

Simple HVAC DHW Fuel

Like the heating and cooling in Simple HVAC, the Simple HVAC DHW system is modelled as a simple water heater which does not need a heat source so it is considered to be provided by district heating and loads are displayed directly in EnergyPlus output. In DesignBuilder the DHW loads reported by EnergyPlus are multiplied by the DHW CoP value at the building level (when the DHW type is the Same as HVAC) or the DHW CoP at the zone level for all other DHW type settings.

Compact HVAC 

(legacy option available only in DesignBuilder version 4 and previous versions)

Compact HVAC DHW Fuel

Same as Simple HVAC DHW Fuel. 

the Simple and Compact HVAC DHW system is modelled as a simple water heater which does not need a heat source so it is considered to be provided by district heating and loads are displayed directly in EnergyPlus output. In DesignBuilder the DHW loads reported by EnergyPlus are multiplied by the DHW CoP value at the building level (when the DHW type is the Same as HVAC) or the DHW CoP at the zone level for all other DHW type settings.

Compact HVAC VAV/CAV Gas AHU/Preheat coil Fuel

Preheat and AHU heating coils of fuel type 'Gas' will report different fuel consumption values in DesignBuilder compared with EnergyPlus. This is because DesignBuilder calculates the fuel consumption of gas heating coils in a simple way by multiplying the heating load by a simple gas heating coil CoP entered on the HVAC tab. EnergyPlus performs a more complex calculation using the same CoP value but also incorporating performance curves during the simulation.

Compact HVAC Unitary Cooling Fuel

Unitary cooling coils will report different fuel consumption values in DesignBuilder compared with EnergyPlus. This is because DesignBuilder calculates unitary cooling fuel consumption a simple way by multiplying the cooling load by a simple CoP entered on the HVAC tab. EnergyPlus performs a more complex calculation using the same CoP value but also incorporating performance curves during the simulation.

Compact HVAC Unitary Heating and Cooling Fuel

If a distribution loss has been applied then this is added outside of EnergyPlus and won't be included in EnergyPlus results which do not account for distribution losses.