Heat demand calculation using TEASER does not match radiator based heating

[FWuellhorst]

Describe the bug
The ideal heater in AixLib assumes only convective heat transfer. This leads to low surface and operative temperatures, and, overall, reduces the heat demand. To better compare results with radiators / floor heating systems to ideal heaters, the ideal heater should have a fraRad parameter. This feature should go into AixLib after we performed parameter studies to check all influences fraRad has and how it compares to real heat transfer systems.