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.
2.2 Periodic Computation
2.2.1 Choose the „Periodic/Harmonic Data Editor“ in the menu „Tools“.
2.2.2 After clicking „File“ you can either enter the outside air temperature again („New Periodic Data“) or read the already entered and stored diurnal cycle („Open …“). If you enter the data anew, you have to choose „Regular Points“. The period length has to be a day (86400 sec) and the number of intervals („#intervals“) 24. With these settings the input of the hourly values of the outside air temperature is settled.
2.2.3 The import of global radiations calculated by SolRad in advance is done by selecting „File“ and then „Import“ and „SolRad“ once again.
2.2.4 The assignment of the color occurs in the next window. Regarding the significance of the input the things said for 2.1.4 apply here in an analogous fashion. By clicking „Import“, the diurnal cycle of the radiation air temperatures is calculated.
2.2.5 The thermal transmission resistance assigned to the diurnal variation of the radiation air temperature has to be written down and, in the course of entering the geometry, assigned to the exerior space.
2.2.6 By choosing „File – Save as“ the computed diurnal cycle of the radiation air temperature is saved along with the diurnal cycle of the outside air temperature. Thus it can be used for evaluation after the modelling of the geometry and the computation.
2.2.7 In the course of the evaluation the column „Periodic Data“ ist to be chosen in the window „Boundary Coniditions“. Via „File – Open“ the diurnal cycles of outside air temperature and radiation air temperature are imported upon choosing the filename determined in 2.2.6.
2.2.8 As a boundary condition for the chosen exterior space, the entered diurnal variation of the air temperature („Apply“) or the computed diurnal variation of the radiation air temperature („Apply StraLu“) can be chosen. If the latter has been chosen, AnTherm will check whether the thermal transmission resistance entered for the exterior space match the computed value. If that is not the case, a warning message is displayed.