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:
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 use of HVAC equipment through a district heating/cooling type system.
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 building level (when the DHW type is the Same as HVAC) or the DHW CoP at zone level for all other DHW type settings.
See also: Calculation of DesignBuilder Output from EnergyPlus Report Variables
The are some cases where optimisation, parametric analysis and UA/SA calculations produce different results from the standard EnergyPlus simulations.
Important Advice for using the Life Cycle Cost (LCC) KPI in parametric simulations (optimisations, parametric analysis and UA/SA):
The LCC total present value KPI requires the Detailed HVAC model option to be used as it uses settings on the Economics model data tab which is only available for Detailed HVAC. The LCC total present value values calculated in optimisation and other parametric simulations will only correspond with the value calculated directly by EnergyPlus if the basis for calculation is the same. In practice this means that the following 2 further requirements must be met:
Any additional Adjustment costs on the Component cost dialog should be removed. To do this set all costs to zero and the Regional adjustment factor to 1.
The 1-BeginningOfYear Discounting convention on the Life cycle cost dialog must be used. This should be the case by default for models created in v7 onwards.
DesignBuilder calculates building the LCC KPI during parametric simulations by adding:
the sum of the base construction cost line items (as calculated on the Cost and Carbon tab) to
the LCC value calculated by E+ without the line item construction costs.
The addition is done by DesignBuilder at the time of generating the result for the LCC KPI, after the E+ optimisation simulation has been completed.
This simplification in the calculation of the LCC KPI is necessary because it is not currently possible for DesignBuilder to feed in parametrically varied cost results to the E+ inputs for the corresponding parametric variant. The rationale behind the approximation used by DesignBuilder in the calculation of the optimisation LCC KPI is that the base cost calculated on the cost and carbon tab is close to the more correct Present Value base construction cost used by E+ and so it can be added to the LCC present value calculated in E+ with no construction costs included. I.e. the “Present Value Factor” for Construction Costs (reported in the “Present Value for Recurring, Nonrecurring and Energy Costs” Summary report table) is close to 1.
Unless conditions 2 and 3 above are met, this simplified approach generates different results from the case where the base construction costs are fed into E+ for a full LCC calculation taking into account the Present Value of the construction costs and a range of other adjustments and factors included in the full E+ financial calculation method, which is based on NIST.