For customers of AnTherm/SolRad there is now the possibility to evaluate the influence of solar radiation and the long-wavelength radiation to and from the external surfaces of a building construction with regard to thermal transmission and temperature distribution.
Since the influences of the radiations are dependent on their orientations, there can be several „exterior spaces“. An exterior space could, for instance, be subdivided into the spaces „south wall vertical“, „west wall vertical“ and „oblique roof“. In the course of the evaluation, three diurnal variations of the radiation air temperature and the related thermal transmission resistances are assigned to these three spaces.
The radiation air temperature is a fictional temperature which is influenced both by the solar radiation and the long-wavelength radiation exchange. If an AnTherm user specifies the radiation air temperature instead of the exterior air temperature, this means that not only the diurnal solar radiation is considered but also the long-wavelength radiation exchange between the exterior surfaces of the exterior building components on the one hand and the sky and the terrestrial environment on the other. The use of the radiation air temperature implies that the absorption and reflection processes occur at the exterior building component surfaces. The used method is capable of exactly reproducing these processes.
Until now, the user specified outside air temperatures in AnTherm as exterior boundary conditions. In the stationary case, this is a single value. In the instationary, periodic case this is the 24 values of a diurnal cycle.
SolRad Version 4.1 or higher and AnTherm Version 9.136.2 or higher are now connected via an interface. The diurnal variations of the radiations computed by SolRad (global radiations in Wm-2) at the project site can be exported from SolRad for a chosen date and orientation by clicking the „Export“ button.
These exported result files can then be imported in AnTherm in order to compute radiation air temperatures and thermal transmission resistances.
Short Instructions Guide:
1. Program SolRad
1.1 In SolRad, open the project from which you would like to export the data and click the button „Export“.
1.2 Choose date and orientation. The orientation corresponds to an exterior surface of an exerior component appearing in an AnTherm model.
1.3 Enter the filename as which the data to be exported should be saved. Mind that you might have to export radiations on differently orientated exterior building components.
1.4 Confirm the export by clicking „OK“.
The data are now exported and are then available for being imported to AnTherm.
Repeat the steps 1.2 to 1.4 until the radiations on all exterior building component orientations that appear in the AnTherm model have been exported.
2. Program package AnTherm
The computation of the radiation air temperatures from the outside air temperatures and the solar radiations imported from SolRad can be done for the stationary and for the instationary, periodic case. To ensure compatibility with SolRad, it is only possible to calculate with period length being one day in the instationary case.
The computation of the radiation air temperaturs not only leads to a temperature value (in stationary case) or a diurnal cycle of the temperatures (in the periodic case) but also a thermal transmission resistance which has to be assigned to the considered exterior space.
Since the thermal transmission resistances have been entered in AnTherm when the geometric modelling happens but the assignment of the boundary conditions only happens in the course of the evaluation (the actual computation), it is necessary to compute the radiation air temperatures before the geometric modeling, either by using the tool „Radiation Temperatures Calculator“ or the „Periodic/Harmonic Data Editor“ in the menu „Tools“. The thermal transmission resistances assigned to the radiation air temperatures have to be linked by the user to the exterior spaces in the course of the geometry input.
2.1 Stationary Computation
2.1.1 Choose the „Radiation Air Temperatures Calculator“ in the menu „Tools“.
2.1.2 Into the field „Outside Air Temperature“, enter the diurnal average of the exterior air temperature for the day for which SolRad computed the radiations. Usually this value matches the long-year monthly average at the project site.
2.1.3 Into the field „Enviroment Air Temperature“, enter the diurnal average of the surface temperature of the terrestrial environment. In almost all cases this value matchs the diurnal average of the outside air temperature. The exceptions are cases with heavy snow or bodies of water.
2.1.4 Into the field „Global Radiation“, enter the diurnal average of the area-related global radiation to the exterior surface of the considered exterior building component in Wm-2. This value can be either manually derived from the program SolRad or automatically imported from the result file by clicking the button „Import“.
2.1.4 In the field „Absorption of Sun Radiation“ the color of the exterior surface of the considered exterior building component is classified. The absorption number specifies the percentage of the solar radiation hitting the surface that is absorbed; the remainder is reflected. In case of „average“ color 60% of the solar radiation is absorbed by the surface and 40% is reflected (classification according to EN ISO 13791).
2.1.5 The „Environment Radiation Percentage“ determines the percentage by which the terrestrial environment is „seen“ by the exterior surface of the exterior building component. Assuming that the terrestrial environment is defined by a horizontal layer, the remaining percentage defines the long-wavelength radiation exchange between the surface and the sky. The percentage thus is 0 for a flat root, 0.5 for a vertical wall and 1.0 for a horizontal jetty. This factor can be either entered manually or imported from SolRad by clicking the „Import“ button.
2.1.6 By clicking the button „Calculate“, the diurnal average of the radiation air temperature and the related thermal transmission resistance are computed. The resistance has to be assigned to the exterior surface of the exterior building component to which the orientation and the solar radiatioon apply. The value of the radiation air temperature later has to be assigned to the same surface or the same exterior space. The method sketched in 2.1.4 to 2.1.6 has to be repeated for all differently orientated surfaces or for surfaces with the same orientation but different colors.