Shoebox Model

The Shoebox model is based on the EnergyPlus “ZoneHVAC:IdealLoadsAirSystem” component. It models a core zone and a perimeter zone. Mechanical Ventilation and Natural Ventilation are modelled using the “DesignSpecification:OutdoorAir” and the “ZoneVentilation:WindandStackOpenArea” components.

Advanced settings under the Building tab

These settings adjust the parameters for the shoebox model used for the energy simulations.

Variable Default Value Explanation
Core depth (m) 3 The depth of the shoebox core zone.
Room width (m) 3 The width of the shoebox.
Perimeter offset (m) 3 The depth of the shoebox perimeter zone.
envr 0.1 The external sensor spacing for the annual solar radiation incidence analysis that determines shoebox location.
fdist 0.01 The internal sensor spacing for the annual solar radiation incidence analysis that determines shoebox location.

Larger values of envr and fdist reduce accuracy but speed up simulations, especially with large numbers of buildings. Radiation sensor generation and anlaysis tends to be the biggest bottleneck in running large models. However, modifying fdist and envr is not reccomended.

End uses

End uses are reported using EnergyPlus Meters for each shoebox and multiplied by a weighting factor. A mapping of the EnergyPlus meters to (=>) the UMI Results name are shown in the following table.

EnergyPlus Variable UMI Output
Zone Lights Electric Energy SDL/Lighting
Zone Electric Equipment Electric Energy SDL/Equipment
Zone Ideal Loads Supply Air Total Heating Energy SDL/Heating
Zone Ideal Loads Supply Air Total Cooling Energy SDL/Cooling
Water Use Equipment Heating Energy SDL/Domestic Hot Water
Zone Windows Total Transmitted Solar Radiation Energy SDL/Window Radiation

Accessing the Shoebox IDFs

If you want to access the idfs created for each shoebox, go to c/umi/temp/energy after simulation. Under two filename subdirectories, open the eplus folder. From there you will find “group#” folders, with as many groups as there are templates. Each group has a number of sample folders under it. The samples are based on the number of shoeboxes required by the radiation mapping. You can navigate to an individual sample and open up the .idf file from there and simulate in the standard EP-launch. If you want to process the resulting data, you can use the command “UmiExportShoeboxWeights” in the Rhino command line. This command creates a .json file that maps each shoebox file back to the original model. The weights can be used to extrapolate the individual idf results out to the full model results if repeated across all samples and groups.