Advanced tab on Model Options dialog.


You can simplify and speed up simulations (sometimes quite significantly) by lumping zones, walls and windows and/or eliminating unnecessary zones and elements from the model.  The following options are available:

Merge zones of same activity

This option reduces the number of zones by merging zones having the same activity.

Merge zones connected by holes

This option merges zones which are connected by holes drawn at surface level (not the holes used to represent the airflow path in virtual partitions). You can merge one or more zones within the same block or across multiple blocks.


A tutorial illustrates the Merge zone connected by holes model option.

Merge zone by selection

Check this option if zones are to be merged by selection using the Merge zones dialog.

Lump similar windows on surface

Causes all windows on a zone surface having the same area, construction, frame/dividers, shading etc to be lumped into a single opening. Lumping only occurs in zones which have no lighting control. The EnergyPlus Window Multiplier mechanism is used. For models having surfaces with many similar windows this option can provide a worthwhile reduction in simulation times.


Note: With Calculated natural ventilation you should not use this option if you have repeated windows having same size, glazing type and shading on a surface but different % Glazing opens and/or Operation schedule because any differences in the natural ventilation settings are not accounted for when checking for similar windows on a surface.

You should also switch this option off if you are running simulations to generate boundary conditions for CFD or for graphical data plotting.


DesignBuilder does not allow a multiplier for windows to be used for zones with daylight lighting control or if the 3-Full interior and exterior Solar distribution option is set. This is because for daylight control or Full interior and exterior Solar distribution, EnergyPlus must know where each of the individual windows is located to properly calculate the solar and visible light transmitted.


This is currently the only 'Simplification' option switched on by default for new models.

Lump similar cracks

This option causes all cracks in a zone which are facing the same direction and have similar height to be lumped into a single crack. This option applies only when the natural ventilation model option is Calculated.

Lump walls and windows (developer option)

Reduces the number of walls and windows. This is currently a research only tool because it has undocumented restrictions. It is not available for general users

Generate fully enclosed zones

Check the Generate fully enclosed zones checkbox to model Link surfaces.  This has 2 main effects on the model:


  1. Extra Link surfaces are generated to connect adjacent blocks together for both visual continuity and to allow fully closed zones to be generated.  
  2. The volume enclosed by the link surfaces and the inter-block partition is included in the zone volume. This volume is essentially the thickness of the block wall x inter-block partition area).

Show block connection surfaces in Navigator

When the Generate fully enclosed zones model option is selected you can choose to show the Link body edge surfaces in the Navigator (or not) through this option. These surfaces are not shown by default.

Model 'Unconditioned' zones as simple R-value to outside

Including complex roof structures in the model can sometimes cause simulations to run slowly for little benefit in accuracy. This option allows you to exclude such spaces from the calculations adding in their place a single R-value resistance to outside. The resistance can be used as a way to include the 'buffering' of the occupied space by the semi-exterior zones without sacrificing simulation speeds.


Note: Any openings (window, doors, vents, sub-surfaces and holes) in semi-exposed surfaces do not include the additional R-Value when this option is selected.


By default this option is off and roofspace zones (and all other semi-exterior unconditioned zones) are modelled as separate zones in calculations.

R-Value to outside

The R-value added to the outside of semi-exposed elements when Model 'Unconditioned' zones as simple R-value to outside option (above) is set.


You can enter an R-Value of 0 if you don't want to include a resistance between semi-exposed elements and outside. In this case it your responsibility to include the effect of the adjacent Unconditioned zone in the semi-exposed constructions themselves.


Tip: You can calculate approximations for R-Value to outside by adjusting the R-Value until the results match those of the equivalent simulation with Model 'Unconditioned' zones as simple R-value to outsideswitched off.