When the temperature of the inner surface of the enclosing structures falls below the dew point, moisture from the indoor air may condense on it. Thermal characteristics of building materials, outdoor and indoor air temperatures and dew points are random variables or processes. This necessitates a probabilistic assessment of the possibility of thermal failures by the criterion of condensate formation in areas of increased heat transfer of enclosing structures. This work is performed in order to analyze the probabilistic thermal reliability of the characteristic units of brick walls of residential buildings erected in the second half of the 20th century, in the design condition and after thermal modernization by installing additional facade insulation. To analyze the level of thermal reliability, six characteristic units of brick walls were selected. The nodes were analyzed in the initial state, taking into account the uniform facade insulation, as well as with additional local insulation of areas of increased heat transfer. The calculations were performed according to the previously developed author's method, which is based on estimating the probability of falling of the random temperature of the inner surface of the wall below the random temperature of the dew point. The initial data take into account the statistical characteristics of the following random variables: conditional heat transfer resistance of the wall in the zone of heat conduction, dew point temperature, indoor air temperature, outside air temperature for each month of the heating period. The result of the calculation is the probable annual duration of the state of thermal failure according to the criterion of condensate formation on the inner surface of the walls in the critical areas of the nodes. It is established that the units of brick walls with a thickness of 51 cm in the design condition have an insufficient level of thermal reliability. Uniform facade insulation allows to reduce the duration of thermal failures of three nodes from the six considered to values not exceeding 10 minutes during the year. In some areas of the other three nodes (adjacency of the side and top faces of the window, adjacency of reinforced concrete balcony slab) the duration of thermal failures remains unacceptably long even when performing additional local insulation of these areas.

walls of residential buildings, heat-conducting inclusions, condensate, thermal failure duration

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