Standard Method
This is the default method. You can find detailed information on how to use the 1-Standard ground modelling method in the Ground Modelling - Standard Method section.
Location tab on model data at Site level
Checking this checkbox is equivalent to selecting the 3-Ground domain option in the description below under Ground modelling method. Unchecking this checkbox is equivalent to selecting the 1-Standard option below.
DesignBuilder provides 4 different ways to model the heat transfer between the ground, the external environment and the building. Select the method to be used from the options below.
Note: For heating and cooling design calculations, the 1-Standard method is always used regardless of the Ground modelling method selected.
Standard Method
This is the default method. You can find detailed information on how to use the 1-Standard ground modelling method in the Ground Modelling - Standard Method section.
Kiva Basic Method
Kiva enables detailed modelling of the ground while requiring a minimal amount of data to be entered. The Kiva Basic option provides an easy introduction to Kiva ground simulations and is ideal for modelling smaller buildings where a single Kiva foundation object can realistically be used to represent the ground, foundations, insulation and its adjacencies to the building. Note that the Ground monthly temperatures, Ground deep temperatures, Shallow deep temperatures described below are not used in Kiva simulations.
When the 2-Kiva Basic Ground modelling method option is selected, 2 more items are revealed below: Kiva foundation settings and Kiva foundation. These are the only additional settings that needs to be entered to define the ground modelling, adjacencies etc.
DesignBuilder automatically calculates the fraction of floor perimeters that are exposed to outside based on the model surface adjacencies.
Note: This option is exactly equivalent to the 4-Kiva Full option when the Kiva adjacency checkbox is checked at building level and the Kiva foundation selected at building level with no further overriding settings made at block, zone and surface levels.
Select a Kiva foundation settings component that defines the soil thermal and surface properties, the extent of the domain and some calculation options.
Select a single Kiva foundation object to define the extent and properties of any insulation and details of the walls and footings.
Note: These settings are automatically applied to all ground adjacent surfaces in the model when using the 2-Kiva Basic ground modelling method.
Ground Domain Method
The EnergyPlus Ground domain system provides a relatively quick and easy way to access the advanced ground modelling capabilities of the Slab and Basement preprocessor tools which in older versions of EnergyPlus had to be run as external utilities with a manual process required to feed the outputs from the preprocessors as inputs to EnergyPlus. See the EnergyPlus Auxiliary Programs help for more information on these legacy utilities.
The way that the temperature boundary conditions for the simulations are handled is defined on the Ground Undisturbed Temperatures tab of the Ground domain dialog. Calculations are based on the hourly weather data and soil properties. Note that the Ground monthly temperatures, Ground deep temperatures, Shallow deep temperatures described below are not used in Ground domain simulations.
Select the 3-Ground domain option to activate the ground domain model. This reveals an option to select the number of ground domain objects to use in the study. The number entered here will enable the display of that number of ground domain objects as shown below.
You will normally need to create new Ground domain objects to define the exact situation for your model.
Note: Ground domains are not used in any heating and cooling design calculations. In this case surfaces adjacent to ground and assigned with ground domain objects use the Ground monthly temperatures as the other side.
Note: You must connect the ground domains defined and selected here to ground adjacent surfaces to complete the domain definition. Wall surfaces that are underground can be selected as basements and any floor that has any ground contact can be defined as having either slab or basement contact.
Tip: Domain-surface connection settings can be made at any of building, block, zone and surface levels. Setting data at building, block or zone level provides a quick way to associate multiple ground adjacent surfaces to a ground domain.
Kiva Full Method
Kiva enables detailed modelling of the ground while requiring a minimal amount of data to be entered. The Kiva Full option provides access to the full EnergyPlus Kiva ground capability which allows accurate simulations of the ground, foundations, insulation and its adjacencies to the building. It is an improvement on the ground domain method in terms of accuracy, flexibility and execution speed. Note that the Ground monthly temperatures, Ground deep temperatures, Shallow deep temperatures described below are not used in Kiva simulations.
DesignBuilder automatically calculates the fraction of floor perimeters that are exposed to outside based on the model surface adjacencies.
When the 4-Kiva Full Ground modelling method option is selected, the Kiva foundation settings must also be selected here at site level. Also each ground-adjacent surface has an option to allow it to be selected as having an adjacency with a Kiva foundation. You should normally check the option and select the appropriate Kiva foundation.
Select the Kiva foundation settings component that defines the soil thermal and surface properties, the extent of the domain and some calculation options.
Select the texture to be used to represent the ground in the rendered view on the Visualisation screen.
This is a decimal number between 0.0 and 1.0 and is used to characterize the average reflectivity of the ground throughout the year. Ground reflectance data is used to calculate the ground reflected solar radiation. This fractional amount is used in the following equation:
GroundReflectedSolar = (BeamSolar x COS(SunZenithAngle) + DiffuseSolar) x GroundReflectance
Reproduced from the IBPSA BEM Book.
Important Note: Reflection from the ground is calculated even if the Reflections option is not used, but if reflections are not calculated the ground plane is considered unobstructed, i.e., the shadowing of the ground by the building itself or by component blocks is ignored. Shadowing of the ground-reflected radiation by component blocks is only taken into account if the Reflections option is used.Conclusion: Switch Reflections on for accurate shading calculations.
The ground surface reflectance is also used to quantify the reflection of visible light in the Daylighting calculations.
Some typical ground reflectance values are shown for various surface types below.
| Surface Type | Surface Reflectance |
| Water (large angle of incidences) | 0.07 |
| Coniferous forest (winter) | 0.07 |
| Bituminous and gravel roof | 0.13 |
| Dry bare ground | 0.20 |
| Weathered concrete | 0.22 |
| Green grass | 0.26 |
| Dry grassland | 0.2 to 0.3 |
| Desert sand | 0.4 |
| Light building surfaces | 0.6 |
Ground Reflectance of Foreground Surfaces from ASHRAE 2009 HOF, Source: Adapted from Thevenard and Haddad (2006).
The default ground reflectance is 0.2.
A number between 0.0 and 10.0 which is used to modify the basic ground surface reflectance when snow is on the ground. Note that the value of GroundReflectanceUsed (below) must be <=1.
GroundReflectanceUsed = GroundReflectance x ModifierSnow
During simulations, the ground is considered to be snow-covered when the SnowDepth data in the hourly weather file is > 0.
From the IBPSA BEM Book:
| Site exposure | Reflectance of snow-covered ground |
| Typical city centre | 0.2 |
| Typical urban site | 0.4 |
| Typical rural site | 0.5 |
| Isolated rural site | 0.7 |
The default modifier is 2 for both solar and daylight radiation, giving an overall default reflectance for snow covered ground of 0.2 x 2 = 0.4, suitable for a typical urban site.
A number between 0.0 and 10.0 which is used to modify the basic ground surface reflectance when snow is on the ground. Note that the value of DaylightingGroundReflectanceUsed (below) must be <=1.
DaylightingGroundReflectanceUsed = GroundReflectance x ModifierSnow
During simulations, the ground is considered to be snow-covered when the SnowDepth data in the hourly weather file is > 0.
There are 12 fields allowing you to represent the mean ground temperature for each month of the year. These temperatures are used as the outside surface temperature for surfaces adjacent to ground.
Note that the depth at which these temperatures apply depends on the thickness of the ground construction (see above) added to the main floor/wall construction.
Caution: It is generally not appropriate to use the "undisturbed" ground temperatures calculated by the weather converter and provided in the header of EnergyPlus hourly weather files as these values are too extreme for the soil under typical conditioned buildings. A reasonable default value of 2°C less than the average monthly indoor building temperature is appropriate for large buildings. For smaller buildings, the ground temperatures will be somewhere between that value and undisturbed ground temperatures.
More information about determining appropriate ground temperatures is given in Ground Modelling and in the EnergyPlus Auxiliary Programs document.
There are 12 fields allowing you to represent the undisturbed deep ground temperature for each month of the year. These temperatures are used when the 1-DeepReference ground temperature option is used in a 15-Follow ground temperature Setpoint manager.
Tip: Undisturbed deep ground temperatures can usually be obtained from the weather file header.
There are 12 fields allowing you to represent the undisturbed shallow ground temperature for each month of the year. These temperatures are used when the 1-ShallowReference ground temperature option is used in a 15-Follow ground temperature Setpoint manager.
Tip: Undisturbed shallow ground temperatures can usually be obtained from the weather file header.
Building energy code and standards like ASHRAE 90.1, 90.2 and California Title 24 require the underground wall constructions and slabs-on-grade or underground floors not to exceed certain maximum values of C-factor and F-factor, which do not specify detailed layer-by-layer materials for the constructions. If using the normal approach (layer by layer) of ground constructions, users would need to create a pseudo wall or floor construction to match the thermal performance such as thermal mass effect and U-factor, and rely on the EnergyPlus Basement and Slabs tools to generate the monthly ground temperatures.
A simplified approach is introduced to create equivalent constructions and model the ground heat transfer through underground walls and ground floors for the building energy code compliance calculations. The approach is to create constructions based on the user defined C or F factor with two layers: one concrete layer (0.15 m thick) with thermal mass, and one fictitious insulation layer with no thermal mass.
There are 2 ways to define the ground temperatures for F-factor and C-factor calculations which are defined through making one of the settings for the FCFactorMethod ground temperature source: