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What input is needed?

External boundary conditions

Location

The location describes where in the world the building to be simulated is located. This is important in order to calculate the position of the sun at any time in the simulation.

Location data is:

• Position on earth wiht northern/southern latitude and westernstern longitude
• Time zone
• Altitude above sea level

Solar paths for different northern latitudes and seasons

Climate

Typically, a climate object is assigned to the location. It mainly contains a file in a space separated ASCII format (*.prn) describing the timeline of weather conditions during the simulation period.

For sizing of cooling or heating loads, national standards often provide syntetic weather for statistically determined extremely hot and cold so called design days. This design day data is always given in the location object. For downloaded locations, it is taken from an ASHRAE database and contains separate design days for each month. For all other locations, the user can manually define two design days for winter and summer conditions. Design periods can also be described with timeline data using a climate file for any period of time. This is then done in the according simulation type setup.

The reason why there are two separate objects for location and climate is, that in most cases the climate information is coming from measurements that are taken at a different geographical position than the one of the simulated building.

It is important to know that only the position in the Location object is relevant for the calculation of the sun position and that the solar radiation data can get unrealistic, if the latitude differs too much between the Location and the Climate object, while a different longitude only leads to a time shift that can be corrected together with the time zone that is also given in the Location object.

It is also obious that a lot of weather data (in particular air temperature and humidity, cloudiness, wind and Albedo) can be wrong if the altitude above sea level differs too much between the Location and the Climate object.

Wheather data that must or can be considered in an IDA ICE simulation:

Wind profile

The wind profile is important for studies where pressure coefficients are given to get a wind dependent infiltration, but has also an influence on external surface heat transfer coefficients.

It is important to know, that in an IDA ICE models, you wil not get a wind speed that differs between different heights in the building. The wind profile only causes the wind speed for the entire building to be corrected if the height of the wind measurement (defined in the ‘Climate’ object) deviates from the ceiling height of the highest building volume.

Wind profile data is:

• Factor for wind speed, when building height is at wind measurement height
• Exponent, charactrizing the rate at which wind speed increases with height

By default, the suburban wind profile is selected, which means that a building of half the height of the wind measuement is exposed to only 56 % of the measured wind speed and a building of the same height as the wind measurements is exposed to 67 % of the measured wind speed etc.

Site shading and orientation

To get correct insolation on surfaces that are exposed to the sun (like windows or solar panels) it is important to have correct geometrical information of all potential shading objects, as well as their transparencies. Such shading objects can be placed in different locations in the software, depending on what their position relates to: Site shading objects will not move, when the building is relocated on the property, while shading objects placed on a face of a building body will move together with the building and window related objects will move together with the window (see also shading objects).

Of course, the site orientation is important for calculating the position of the sun and thus the solar radiation on the sunlit surfaces. It can be adjusted by adapting the north direction on the site map.

Ground properties

In order to consider a reasonable dynamic behaviour for constructions against ground, a model according ISO 13370 is used. This model takes the depth and size of the walls and slabs from the building geometry and the pyhical properties of the ground from a specific input whose default values can be customised by the user.

The main ground properties are its thermal conduction, its density and its specific heat.

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