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### Heat losses from large buildings through the ground

The heating demand of a building is strongly influenced by transmission heat losses through the ground, if the total thermal conductance of the building constructions in contact with the ground is in the same order as the thermal conductance of the building envelope in contact with the air. This will be the case in particular for such buildings, where the building constructions in contact with the ground take up a considerable part of the total area of the building envelope. On the one hand this situation is given for small buildings provided with a basement. On the other hand transmission heat losses through the ground are important for buildings with big floor areas in direct contact to the ground, e.g. for big halls.

Transmission heat losses from a basement of a residential building were investigated in [1] and [2]. This paper deals with heat losses through various slab on ground constructions normally used for big industrial halls.

Calculations of the heat flow through building constructions in contact with the ground are special cases on principle in that they cannot be done using the ordinary constant, one-dimensional (1D) thermal model. On the one side the heat flow through the ground can be described only using two or three spatial coordinates. From this heat losses through the ground are to be calculated using two- and three-dimensional (2D and 3D) thermal models. On the other side in most cases of interest the very big heat storage capacity of the ground involved in such heat flow calculations cannot be ignored, so that a non-steady calculation method is required.

For most slab shaped building constructions in contact with the air the thermal quality of the construction with regard to heat losses can be characterized by an U-value in good approximation. Contrary to this the declaration of a U-value alone makes no sense for slab on ground constructions. The well known fact that the heat loss through a slab-shaped building construction can be calculated in good approximation by multiplying the U-value of the slab with it's area and with the difference of the air temperatures between internal and external environment is no longer true for slab on ground constructions. The heat flow through slabs on ground is not only influences by the U-value and the area of the slab but also by the geometry of the building construction in contact with the ground and by the thermal characteristics of the surrounding soil. For that reason quantitative statements concerning the heat through the ground are only true for the specific building under consideration.

In this paper a case study concerning different insulation levels of a slab on ground construction is performed for an industrial hall with largely fixed geometry. From this study qualitative conclusions concerning the effectiveness of slab insulation is drawn.

... The limitation of the heating demand of industrial halls often requires a reduction of the transmission heat losses through the ground. Generally calculations of heat losses through the ground require a three-dimensional, non-steady treatment. ...

The above essay have been incorporated with friendly permission from Klaus Kreč, Büro für Bauphysik, A-3562 Schönberg am Kamp, Veltlinerstr. 9, Österreich/Austria .

[1] K. Kreč, "Wärmeverluste über erdbodenberührte Bauteile Fallstudie beheizter Kellerraum", WKSB 33,32-35 (1993)
[2] K. Kreč, "Lufttemperatur im unbeheizten Kellergeschoß; eine Fallstudie", WKSB 34,42-47 (1994)