2D:CollectingTheNecessaryData

Collecting the Necessary Data

Of course, WUFI needs some data to perform the calculations. However, the equations built into WUFI have been formulated in terms of quantities that are well known or readily available, or can easily be measured or estimated.

This is what WUFI needs:

Material data

These quantities define the hygrothermal behaviour of the materials:

Basic Data:

• bulk density [kg/m³]
• porosity [m³/m³]
• specific heat capacity of dry material [J/kgK]
• thermal conductivity of dry material [W/mK]
• water vapor diffusion resistance factor of dry material [-]

Hygric Extensions:

• moisture storage function [kg/m³],
  as a table or approximated by sorption moisture at 80% RH (w80) and free saturation (wf),
• liquid transport coefficient for suction [m²/s],
  as a table or generated from the water absorption coefficient (A-value),
• liquid transport coefficient for redistribution [m²/s],
  as a table or generated from the water absorption coefficient (A-value),
• moisture-dependent thermal conductivity [W/mK],
  as a table or generated from the moisture-induced thermal conductivity supplement,
• moisture-dependent vapor diffusion resistance factor [-],
  as a table.

These material data are further discussed in the topic Material Data.

The definition of the water vapor diffusion resistance factor (a.k.a. µ-value)and related quantities is discussed in the topic Water Vapor Diffusion.

For mathematical reasons, the basic data are required as a minimum for each calculation; otherwise, the transport equations are not fully defined.
The hygric extensions are refinements of the simulation model that are not mathematically required, but they may well be necessary to fully and appropriately describe the hygrothermal situation.

Climate data

These quantities define the boundary conditions at the surfaces of the building component:

• rain load on the surface [Ltr/m²h],
  as dependent on the inclination and orientation of the building component,
• short-wave (solar) radiation flux density [W/m²],
  as dependent on the inclination and orientation of the building component,
• air temperature [°C],
• relative humidity (0..1),
• mean barometric pressure [hPa],
  over the calculation period,
• atmospheric counterradiation [W/m²],
  if radiation cooling is to be accounted for during the night.

For each time step, WUFI reads these data from a climate file. Since the rain load and the radiation flux are directional quantities, they must be evaluated in dependence of the orientation and inclination of the building element. This evaluation can be done with a preprocessor or by WUFI itself during the calculation.

In the former case, the preprocessed data are written to a file of *.KLI type, in the latter case WUFI expects climate data in *.WET or *.TRY or *.DAT or *.IWC or *.WBC or *.WAC format.

You can create files with your own data in any of these formats in order to use them with WUFI.

Climate data and the climate file formats are further discussed in the topic Climate Data.

Surface transfer coefficients

These quantities specify the coupling between the climate data and the conditions in the building component:

• heat transfer coefficient [W/m²K]
• vapor diffusion thickness, a.k.a. sd-value [m]
  allows to account for the diffusion-retarding effect of paint coats, wallpapers, vapor retarders etc., if present, without the need to explicitly include these layers in the component assembly,
• short-wave (solar) radiation absorptivity [-],
• long-wave (thermal) radiation emissivity [-]
  (can or must often be neglected, since data on sky and ground counterradiation are rarely available),
• rain water absorption factor [-]
  describes the reduction of rain water volume available for suction on non-horizontal surfaces, since some water splashes off on impact.

The water vapor transfer coefficients are automatically calculated from the heat transfer coefficients and need not be specified separately.

The coefficients listed here are further discussed in the topic Surface Transfer.

The definition of the vapor diffusion thickness and related quantities is discussed in the topic Water Vapor Diffusion.

Initial conditions

The temperature and mosture fields of the building component must be initialized with starting values for the temperature and the relative humidity. Currently, WUFI-2D only allows constant values for both across each element of the component.

The initial conditions are further discussed in the help topic for the dialog Initial Conditions.