Refinement of thermal engineering calculations results taking into account actual materials characteristics

. The article presents the laboratory studies results of building materials thermophysical characteristics used in the construction of experimental wooden buildings. In the framework of laboratory experiments, the thermal conductivity and humidity of structural and thermal insulation materials samples were evaluated. The analysis and comparison of the results obtained with the characteristics of the materials declared by the manufacturers and in the reference data is carried out. The results of thermal engineering calculation refinement of the of the enclosing structures of experimental wooden buildings, taking into account the results of laboratory studies of the thermophysical characteristics of building materials used in construction, are presented. The thermal engineering calculation of the enclosing structures of the frame part of experimental buildings has been refined taking into account the actual thermal conductivity of building materials. The influence of the actual thermophysical characteristics of building materials on the results of thermal engineering calculation in comparison with the design values was evaluated. Further directions of research are presented in terms of the influence of cold bridges and inhomogeneities of structures on the thermal characteristics of the thermal contour of the building.


Introduction
Within the framework of the study, the design and construction of two identical experimental buildings (model objects) in the territories of the Murmansk region and the Republic of Karelia were implemented. The model objects are intended for scientific research in the field of "green" technologies and energy-efficient construction [1,2,3]. In the design and construction of buildings in Murmansk and Petrozavodsk, the same spaceplanning and design solutions were used [4,5,6]. The choice of building materials and technologies was based on the use of materials and technologies that most fully represent the concept of "green construction". Wood was used as the main structural material of buildings. The main thermal insulation materials are materials that are positioned by manufacturers as environmentally friendly [7]. This article discusses the results of laboratory studies of thermal conductivity and humidity of the main structural materialwood, and plate thermal insulation materials. The results of laboratory studies are used to refine the thermal engineering calculation of the enclosing structures of experimental buildings.
One of the objectives of the research program [8,9,10] is to determine the actual thermophysical characteristics (thermal conductivity and humidity) [11,12] used in the construction of building materials. This study is necessary to evaluate the actual characteristics of materials [13] in comparison with the characteristics declared by manufacturers or given in the reference literature. As a result of laboratory studies, the thermal conductivity and humidity of the main structural material -wood and plate thermal insulation materials were determined. The actual values obtained as a result of laboratory studies were used to refine the thermal engineering calculation of the enclosing structures of the frame part of the building.

Materials and methods
The wood for the manufacture of log cabin and frame elements for both buildings was harvested in the Prionezhsky Central Forestry of the Republic of Karelia in the period from December 15 to December 31, 2019. The harvested wood was debarked and laid out for atmospheric drying. The period of atmospheric drying was 4 months -from January to May 2020. After atmospheric drying, the wood acquired a humidity of 20-30% (air-dry wood). The frame elements and rounded logs were manufactured in May 2020. The finished house kit was stored in atmospheric conditions on the basis of the manufacturer until the start of construction. The humidity of the finished elements during storage was 25%.
The following plate materials were used as thermal insulation materials during construction: ISOROC Super Warm mineral wool plates, AKOTHERM FLAX linen mats and Flaxan Briz plate material.
ISOROC Super Warm mineral wool slabs are positioned by the manufacturer as the warmest mineral wool insulation in slabs for individual housing construction. The strength of the plates (20 kPa) allows the material to retain its shape during operation and does not shrink over time. The density of the material is 26 kg/m 3 . It is supplied both in plates with dimensions of 1x0.61 m and in rolls.
ACOTHERM FLAX thermal insulation boards are made of natural flax fiber (85%) and polyester fiber binder (15%). The density of the material is 30 kg/m 3 . It is supplied in plates with dimensions of 1x0.6 m.
Flaxan Briz is made from seashore (42.5%) with the addition of cannabis (42.5%). Polyester fiber (15%) is used as a binding component. The density of the material is 32-35 kg/m 3 . It is supplied in plates with dimensions of 1.05x0.6 m.
To determine the thermophysical characteristics of the materials used, the methodology reflected in the interstate standard GOST 7076-99 "Building materials and products. Method of determination of steady-state thermal conductivity and thermal resistance".
The thermal engineering calculation was performed for the most severe conditions for the two experimental buildings under consideration -for the territory of Murmansk. The calculation was carried out on the basis of the following initial data on the basis of the code of rules SP 131.

Results and discussion
Sampling of materials was carried out during the construction of experimental buildings: in Petrozavodsk -in July -September 2020, in Murmansk -in October -December 2020 ( Fig. 1). After sampling, samples of materials were stored in atmospheric conditions. The production of test samples was carried out in July 2020 ( Fig. 2 and 3). After manufacturing, the samples were placed in an airtight container and stored under identical conditions. To determine the moisture content of the samples, the SHIMADZU MOC-120H humidity analyzer was used. The analyzer determines the moisture and dry residue content by heating the sample with an infrared lamp and measuring the mass change as a result of evaporation. The thermal conductivity meter ITP-MG4 "100" was used to determine the thermal conductivity. The device allows you to determine the thermal conductivity and thermal resistance of materials at an average sample temperature from +15 °C to +42.5 °C under stationary thermal conditions. From each of the selected materials, five samples were made with dimensions in terms of 100x100 mm. The thickness of the samples varied from 15 to 24.4 mm.
Initially, its humidity was determined for each of the samples. During the humidity test, the initial mass of the sample, humidity and mass of the sample after measurement were recorded (Fig. 4). Then, the sample was placed in the chamber of the thermal conductivity meter and the thermal conductivity and thermal resistance were measured (Fig. 5). After determining the thermal conductivity, the sample was again placed in the humidity analyzer to measure the mass of the sample.      Table 1 presents the measurement results in the form of arithmetic mean values for each material studied. As can be seen from the data in the table, the value of the thermal conductivity of wood is lower than calculated, and the thermal conductivity of plate fibrous thermal insulation materials is higher. According to the results of measuring the moisture content of wood samples, it can be estimated as dry, since its humidity does not exceed 8-10%. The moisture content of samples of dense fibrous materials with natural flax and hemp fibers is higher than that of a basalt fiber-based material. ISOROC Super Warm mineral wool slabs showed the best result in thermal conductivity among the studied plate thermal insulation materials. The refinement of the thermal engineering calculation was carried out for the frame part of the experimental buildings. The layout of the design sections is shown in Figure 6. Design section No. 5 is not considered in this study. Figure 7 shows the composition of the layers of the structure in the considered design sections. The layers of enclosing structures in the sections under consideration are taken as follows (inside -out): -Design section No. 1 (Fig. 7, a)    At the design stage, the thermal engineering calculation was carried out on the basis of reference data on the thermal characteristics of building materials. During the construction of experimental buildings, samples of materials were taken. After sampling, samples of materials were stored in atmospheric conditions. After manufacturing, the test samples were placed in an airtight container and stored under the same conditions. The actual thermophysical characteristics of the used building materials were determined in laboratory conditions. Data on reference and actual (obtained by laboratory tests) are given in Table 1. At the next stage of the research, a clarifying thermal engineering calculation of the enclosing structures was performed, taking into account the actual thermophysical characteristics of the building materials used. Thermal engineering calculations were carried out according to the cross section of the main thermal insulation material and taking into account the need to achieve the energy efficiency class of the building A+ (exceeding the normative values of heat transfer resistance) [10]. The results of thermal engineering calculations for the sections under consideration are shown in Table 2.

Conclusions
Based on the results of laboratory studies and analysis of the results obtained, the following conclusions can be formulated: 1. The actual thermal conductivity of wood is lower than the calculated values. 2. For the studied plate fibrous thermal insulation materials, the actual thermal conductivity is higher than the stated (calculated).
3. Plate thermal insulation materials with the inclusion of natural flax and hemp fibers have higher humidity than basalt fiber-based materials. This can be explained by the fact that natural flax and hemp fibers absorb moisture to a greater extent.
4. The installation manufacturability of slab materials with the inclusion of natural fibers (flax, hemp and seaweed) is lower than that of a basalt fiber-based material. During the manufacture of samples, it was revealed that materials with natural fibers are poorly cut when using a standard tool.
5. In the clarifying thermal engineering calculation, the values of the thermal conductivity of materials that do not take into account the operating conditions are used. Experimental buildings are operated in wet conditions, therefore, with the actual operation of enclosing structures, the thermal conductivity of the structure will be higher, and the real resistance to heat transfer will be lower. Additional studies are planned to determine the thermophysical characteristics of the enclosing structures of experimental buildings in real operating conditions [8,9,13].
6. The actual thermal conductivity of thermal insulation materials Flaxan Briz and ACOTHERM FLAX significantly exceeds the reference values, therefore, the thermal insulation resistance in the design sections No. 4 and No. 6 is significantly lower than the design values. Taking into account the actual operating conditions with high humidity, the actual characteristics of these thermal insulation materials will significantly affect the energy efficiency of the structure.
7. The issue of taking into account the inhomogeneities of the structure (frame elements, crates and air layers) and their influence on the thermal and physical characteristics of the enclosing structure as a whole deserves special attention and research.
During the construction of experimental buildings, backfill types of thermal insulation materials were also used -wood chips and eco-wool. The results of laboratory studies of these thermal insulation materials and updated data on thermal engineering calculations will be reflected in a separate study.