An Impact of Air Permeability on Heat Transfer through Partitions Insulated with Loose Fiber Materials

Abstract

The paper presents the problem of windwashing in partitions including air permeable thermal insulations. There are technical solutions, which deliberately accept the filtration of air in the insulating layer, guided by the necessity of possible drying of building materials. Some scientific papers even suggest that the air infiltration decrease the heat losses through ventilation. In result there occur heat losses in building heat balance which are underestimated and therefore difficult to take into account during calculations. Heat changes on the inner surface of the building partition occur with a delay to the initiation of the wind. However, even the short-term local wind speed loads on thermal insulations result in temperature decreasing and therefore possible condensation on the inner surface of the building partition. The article presents laboratory measurements of air permeability of loose mineral wool and laboratory investigation of the impact of air filtration on heat transfer in lightweight partitions filled with loose thermal insulation.

Heat Losses Caused by the Temporary Influence of Wind in Timber Frame Walls Insulated with Fibrous Materials

“…The properties of these materials were investigated in the laboratory and are presented in the works [3,37]. Figure 1 shows the thermal conductivity of the materials as a function of density.…”

“…The simulation was performed using the Control Volume Method implemented in the Delphin 5.8 software (Institute of Building Climatology, Dresden, Germany). The thermal insulation properties were adopted on the basis of the laboratory measurements presented in [3,37]. The simulation model of the frame wall filled with loose thermal insulation is presented in Figure 3.…”

“…However, fiber materials, such as mineral wool, wood wool and hemp fiber, are most often used for insulation purposes, either as loose-fill thermal insulation materials or in the form of mats/slabs. The thermal insulation fiber materials are characterized by varying air permeability, depending on their density [3]. Air infiltration, resulting from the impact of wind blowing through the walls, depends on the surrounding conditions, mainly on the temperature differences and on the atmospheric pressure at both sides of the wall [4,5].…”

“…The influence of wind pressure and the time of its impact on the thermal performance of a wall insulated with 150 and 250 mm thick fiber material was considered. The simulations were based on the results of the material properties (thermal conductivity and air permeability as a function of material density) examined in the laboratory that were published in [3,37]. The novelty of the article is a description of the characteristics of fibrous insulation materials of plant origin subjected to various models of air load (air filtration and wind washing) and the consolidation of the results with the characteristics of the traditional insulation material, i.e., mineral wool.…”