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Local heating of thermal weak points

: Krus, Martin; Wurm, Sabrina

Hajek, P. (Ed.) ; TU Prague, Grada for Faculty of Civil Engineering:
CESB 2013, Central Europe towards sustainable building : Sustainable building and refurbishment for next generations; 26th - 28th June 2013, Prague, Czech Republic
Prague: Technical University of Prague, 2013
ISBN: 978-80-247-5015-6
Central Europe Towards Sustainable Building Conference (CESB) <2013, Prague>
Conference Paper
Fraunhofer IBP ()

Within the framework of this paper it is investigated, whether it is more reasonable to use local heating to avoid mould growth on thermal bridges than a higher ventilation rate of the rooms. Three different thermal bridges, external wall edge, balcony slab and floor slab support, are investigated at the locations Hof (cold location), Würzburg (moderate location) and Freiburg (warm location). A common apartment in the center of a multi-story apartment house is taken as a basis. With a "basic" air change rate of 0.3 h-1, when mould growth occurs on all three thermal bridges, it is investigated from which ventilation rate mould growth can be avoided on the selected thermal bridges, and how much heat loss for ventilation is generated (results for a "basic" air change rate of 0.5 h-1 are presented in the extended version of this paper). Then, with the same "basic" air change rate the use of a heating cable is simulated as an alternative to the additional ventilation rate, whereby the heating capacity of the heating cable as well as the operation period can be varied. The energy demand and the primary energy demand are compared.
The results show that the energy demand for the use of the heating cable is lower at all investigated thermal bridges and locations than for the additional window ventilation. However, if the primary energy demand is compared by considering the primary energy factor of the various energy carriers, the use of the heating cable is not always the better choice. This is especially true, if energy carriers with a smaller primary energy factor are used for heating (district heating or regenerative energies). From the building physical and energetic point of view it is reasonable to solve the problem of thermal bridges by adequate thermal insulation. The additional heating 'of then nal weak points as a temporal solution is an adequate measure from the energetic as well as financial point of view, which can be better suited than additional window ventilation. However, the additional risk of fire must also be taken into consideration.