Starting from specified initial conditions, WUFI computes the temporal evolution of the temperature and moisture distributions in the building component. This evolution is determined not only by the underlying transport equations which govern the processes in the component, but also by the heat and moisture exchange with its surroundings. Thus there are heat and moisture flows through the surfaces, the direction and magnitude of which depend on the conditions in the component as well as on the conditions in the surroundings. The latter are described by the boundary conditions.
Since WUFI has been developed specifically for application in building physics, the surrounding medium is the ambient air (outdoor air, indoor air). Since it is furthermore designed to calculate the behaviour of building components exposed to the weather, it seems natural to describe the condition of the surrounding air in terms of meteorological parameters like temperature, relative humidity, solar radiation etc. In this way, WUFI keeps in close touch with building practice and can use existing measured data.
The choice of expressing the boundary conditions in terms of meteorological parameters does not prevent you from applying WUFI to laboratory investigations like imbibition or drying experiments, since the laboratory conditions can be expressed in meteorological terms as well.
WUFI needs the following climate data for each time step:
- the rain load vertically incident on the exterior surface in [Ltr/m²h]. For the determination of this rain load, the inclination and orientation of the surface must be taken into account.
- the solar radiation vertically incident on the exterior surface in [W/m²]. For the determination of the amount of radiation, the inclination and orientation of the surface must be taken into account.
- the temperature of the exterior air in [°C]
- the relative humidity of the exterior air (0..1)
- the temperature of the interior air in [°C]
- the relative humidity of the interior air (0..1)
- the barometric pressure in [hPa]. Since the barometric pressure has only a minor effect on the calculation, specification of a mean value over the calculation period can be sufficient.
- the long-wave atmospheric counterradiation [W/m²], if radiation cooling is to be accounted for during the night.
The weather file may contain measured weather data (such as IBP weather data), or synthetic but realistic weather data (such as the Test Reference Years), or completely artificial data (which describe, for example, a laboratory experiment).
Since WUFI's main application is the investigation of the hygrothermal behavior of building components exposed to natural weather, it is set up to read files that contain measured weather data. However, measured data can not always be used directly:
As mentioned above, WUFI needs the rain load and the radiation load incident on the wall or roof surface under investigation. Since rain and radiation are directed quantities, these loads depend on the orientation and the inclination of the individual building component. Unfortunately, in conventional weather measurements they are usually only recorded for horizontal surfaces.
It is possible, however, to compute them from conventional weather data. The rain load can be determined from the normal rain and the wind velocity and direction. The amount of radiation can be determined from the global (or direct) and diffuse radiation incident on a horizontal surface. WUFI performs these conversions automatically and the user only needs to supply the conventionally measured weather data. In the current WUFI version, this requires a file in *.WET or *.TRY or *.DAT or *.IWC or *.WAC or *.WBC format. Depending on the format, files provided by the user (as opposed to the files supplied with WUFI or files preregistered in the database) may also require a supporting *.AGD file which supplies geographical data on the climate location.
On the other hand, WUFI can also read files which directly contain the required rain and radiation loads as determined for the specific surface in question, so that no further conversion is necessary. This may be convenient if
- you want to convert the weather data with more sophisticated algorithms than WUFI does, or if
- you want to employ data that have been directly measured at the surface in question and thus need not be converted, or if
- you want to use data synthesized by your own climate simulator, or if
- you want to use data which describe the conditions of a laboratory experiment,
These files must be in *.KLI format.
The following sections explain these file formats in detail:
The *.WET Format for Climate Data
The *.TRY Format for Climate Data
The *.DAT Format for Climate Data
The *.IWC Format for Climate Data
The *.WAC Format for Climate Data
The *.WBC Format for Climate Data
The *.KLI Format for Climate Data
The *.AGD File
The method used by WUFI to convert radiation data is described in the Frequently Asked Questions section.
Sources for Climate Data
Several climate files are supplied with WUFI. The following are some sources offering weather data for additional locations. WUFI can read the respective file formats; the user must judge to which degree these data are useful and appropriate for his specific application.
Additional information of different sources for climate date are discribed here.