Optimisation Objectives

Accessed from Parametric, Optimisation and UA/SA Analysis Settings dialog

 

Tip: The Optimisation Objectives dialog should be used with caution because there is no Cancel button, so once the dialog is opened, any changes made cannot be undone and upon closing of the dialog, the objective will be saved, replacing the previous one, with the settings currently being shown on the screen. In the case where you have mistakenly added an objective (or made incorrect changes while editing an existing one) you can close the dialog and then delete the incorrect objective on the Objectives tab on the main Edit Parametric, Optimisation and UA/SA Analysis Settings dialog. Alternatively if you haven't made any other changes since opening the main dialog , simply press Cancel on that dialog to lose all changes.

Name

Your name for the objective for your reference, e.g. "Minimise ASHRAE 55 discomfort hours"

Objective KPI

Select the Objective Key Performance Indicator (KPI) from the list. You can find more detailed descriptions of many of these outputs on the Simulation Detailed Results page.

 

ClosedView the full list of KPIs

 

Comfort

All comfort outputs are for the whole building using an area-weighted average of discomfort calculated for each zone. Note that the comfort-related outputs are termed "discomfort" because by convention DesignBuilder aims to minimise objectives and in the context of standardising optimisation outputs it is better to minimise discomfort than to maximise comfort.

 

Cost

Important note: The Operational cost (Opex) and LCC total present value KPIs both require settings on the Economics model data tab be made, which in turn requires the Detailed HVAC model option to be used.

Tip: You can carry out powerful analyses to simultaneously optimise whole life cycle cost and whole life cycle environmental impact performance using DesignBuilder's optimisation tools. Choose the LCC and LCA KPIs for this sort of analysis.

Daylight

No daylight-specific KPIs are available in current versions of DesignBuilder.

Energy and Loads

Environmental impact

Heat gains

Unmet loads

The unmet load hours KPIs described below are the same values as those reported in the EnergyPlus Summary report. The Unmet load hours are described in more detail in the ASHRAE 90.1 Appendix G PRM Reference topic and also in the DesignBuilder LEED and ASHRAE 90.1 Appendix G User Guide.

 

Custom script

You can add your own custom script KPIs which allow you to read and, if necessary post-process, simulation results from any EnergyPlus output file or other source and write it to a specific database table using the API. You can use either CS-Scripts or Python scripts to do this. Note that the name you give to your Custom script KPI is important as it will be used to reference it in the script that you write.

 

The Custom script mechanism works as follows. For each simulation:

 

  1. In the AfterEnergySimulation hook that is called immediately after the simulation has been completed and results have been loaded to DesignBuilder, the script must create a new site level table called "ParamResultsTmp". It is necessary to first remove any existing table of the same name.
  2. The "ParamResultsTmp" table has 2 fields.
  3. Records should be added to the table, one for each custom script KPI used in the simulation.
  4. The first field in each record (index 0) should match the name of the KPI, the second field (index 1) should be the value to be read for this KPI for the current simulation.
  5. DesignBuilder reads the table after the script has finished executing and results are loaded to the optimisation, UA/SA or parametric analysis system.

 

The easiest way to understand how the system works is to view an example script:

 

Example Custom Script KPI

 

In the example script linked to above there are 2 Custom script KPIs: "District Heating Energy (kWh)" and "District Cooling Energy (kWh)". Data for these is read from the "End Uses" table in the eplustbl.csv output file using the built in EpNet library.

Note: While all simulations will call the AfterEnergySimulation hook, only parametric simulations processes actually read the ParamResultsTmp table created in the script.

User defined

No user-defined options are currently available.

Minimise or Maximise

Select whether you wish to maximise or minimise the selected objective. By convention objectives are usually set up in such a way that the objective is minimised. For example for a comfort-related objective it is usual to minimise discomfort rather than maximise comfort. Minimising both objectives means that the Pareto Front will form the lower left portion of the scatter plot showing all results which is the conventional way to display optimisation results.