Location tab on model data at Site level
This data are defines the elevation of the site relative to sea level (in m or ft) and is passed directly to EnergyPlus for use in pressure-related calculations. It is also used to calculate air density within DesignBuilder when calculating volumetric flow rates from cooling loads.
The site orientation is the angle of the site plan view relative to North. For example enter 45 to rotate the building(s) clockwise by 45°.relative to North (screenshot example below). This is the quickest and most reliable way to rotate all the buildings on the site relative to North and allows you to keep your x and y axes aligned with the building.
North is indicated by the direction of the North arrow in the sketch plan view (above).
Warning: Rotating the building(s) is also possible but once this has been done it is more difficult to make further geometric edits because, for rotations other than 90, 180 or 270°, the x and y axes will be out of alignment with the building. Also major rotations can increase the risk of geometric issues in the model.
Tip: You can navigate to building level and use the Measure tool to measure the angle between 2 lines on a floor plan to calculate the Site orientation.
Implementation Details
In DesignBuilder v6 and later, the Site orientation defined here is accounted for in the EnergyPlus IDF input data by rotating the geometry of all site and building objects. In previous versions the EnergyPlus Building, North Axis object was used instead.
Because DesignBuilder now handles all rotation itself, it is possible for it to accurately apply additional building rotations in addition to site rotation entered here. Building rotations are applied to all building objects (not site objects) about the geometric centre of the building in the x-y plane.
Building rotation applies to a) LEED baseline auto-rotation and b) parametric analysis, optimisation, uncertainty and sensitivity analysis when the Building rotation variable is selected.
The site’s terrain affects how the wind hits the building – as does the building height. In addition, the external conduction method usually has its own parameters for the calculation. The options available are:
1-Sheltered - maps to the EnergyPlus "City " setting for towns, city outskirts and the centre of large cities.
2-Normal - maps to the EnergyPlus "Suburbs" setting for "rough, wooded country, suburbs".
3-Exposed - maps to the EnergyPlus "Country" setting for "flat, open country"
When the Calculated Natural ventilation option is set, the exposure to wind model data affects the pressure coefficients used . It also affects the calculation of U-values (though these are not used in EnergyPlus simulations).
When the Scheduled Natural ventilation option is set, the exposure to wind model data affects infiltration when using one of the options normalised to exposed façade area, i.e. 2-m3/h-m2 at 50 Pa and 3-m3/h-m2 at 4 Pa. It acts through the wind exposure class as explained in the Technical notes under Infiltration rate.
Important note: When the wind exposure setting is changed, the U-value for each construction in the Constructions database is recalculated because the wind exposure affects the external heat transfer coefficient. This is necessary to ensure that the info panel data remains up to date and for local calculations such as SBEM which rely on U-values being up to date.