Technical and Economic Aspects of the Choice of Enclosing Wall Structures with a Similar Heat Flow for Low-rise Housing Construction

Shakirova Veronika Aleksandrovna PhD in Architecture Engineering Architect, "Prodom" LLC 660041, Russia, Krasnoyarskii krai, g. Krasnoyarsk, ul. Prospekt Svobodnyi, 82, korpus 24(A), aud. 501 veronika-arch@mail.ru Other publications by this author

Tolochko Ol'ga Romanovna Assistant, Department of "Building Design and Real Estate Expertise", Siberian Federal University 660041, Russia, Krasnoyarsk Krai, Krasnoyarsk, Prospekt Svobodny str., 82, building No. 24, office 3-06 otolochko@sfu-kras.ru

The commissioning of low-rise housing in general in the Russian Federation has consistently positive dynamics in the context of the last five years, which is confirmed by the statistical data in graph 1. At the level of the studied subject – the Krasnoyarsk Territory, the dynamics of low-rise housing commissioning indicators behave more chaotically, which can be explained by local problems in the market of construction products in the region and greater exposure to economic instability in the post-crisis period after 2014 and during the global coronavirus pandemic after 2020. Nevertheless, the data in graph 1 indicate the cyclical nature of the sphere of low-rise housing construction with a decline and subsequent growth of indicators ^{[1, 2]}.

Graph 1. The share of low-rise housing commissioning in the total volume of housing commissioning in the Russian Federation

The most popular wall designs for low–rise construction are multilayer structures. This structure is a load-bearing wall, which is insulated from the outside with a layer of thermal insulation material, which is protected from external climatic influences by a layer of facade decoration. Additional finishing goals are to improve the operating conditions of the structure, increase durability and artistic and aesthetic expressiveness of the capital construction object. The modern market of building materials is extremely diverse, it offers a wide range of materials for facade decoration, such as plaster, facing brick, plank, ventilated facade systems, etc. As part of the study, the most relevant types of multilayer structures and exterior wall facade finishing options were considered.

The purpose of the study is to determine the most optimal design of the exterior wall in low-rise housing construction based on a comparison of thermal and economic indicators.

Research objectives:

-to identify the most common types of multilayer wall structures used in low-rise housing construction, and to determine the thickness of the layers of the structure with approximately similar heat flow;

-perform thermal engineering calculation of multilayer structures;

-calculate the estimated cost of construction, the most common types of multilayer wall structures, using the basic index method.

During the study of the identified design solutions of multilayer wall enclosing structures, a thermal engineering calculation of the following five most common design options was performed:

1. brick exterior wall (1 - brick, 2 - thermal insulation, 3 - plaster, 4 - facing brick (Fig. 1a));

2. the outer wall of aerated concrete (1 - aerated concrete, 2 - thermal insulation, 3 - plaster, 4 - facing brick (Fig. 1b));

3. reinforced concrete exterior wall (1 - reinforced concrete, 2 - thermal insulation, 3 - plaster, 4 - facing brick (Fig. 1b));

4. the outer wall of the heat block (1, 1.1 - heat block, 2 - insulation, 3 - plaster (fig. 1g));

5. the outer wall is made of timber (1 - timber, 2 - thermal insulation, 3 - wooden board (Fig. 1d)).

Figure 1. Structural solutions of multilayer wall enclosing structures

(a - brick, b - aerated concrete, c - reinforced concrete, d - heat block, d - timber)

The structural solutions of multilayer wall enclosing structures shown in Fig. 1 have different designs and facade finishes, but at the same time have a similar heat flow, which acts as a unifying feature, since each structure must be able to provide the required indoor air temperature in harsh climatic conditions of a sharply continental climate. The main advantage of these structures is their reliability and durability. The placement of the insulation between the bearing and facing layer reduces the likelihood of accelerated destruction of the insulation, and the presence of an air layer in the structure significantly improves the humidity condition of fences ^{[3, 4]}.

The methodological basis of the research is a set of methods of scientific cognition: methods of systematic, logical, statistical analysis, statistical research, methods of comparison, systematization, grouping, generalization, as well as graphical methods of data visualization. The methods of determining the heat flow, reduced heat transfer resistance in multilayer wall structures using COMSOL Multiphysics PCs and the method of determining the estimated cost by the basic index method using GOSSTROYSMET Online PCs are applied.

To carry out thermal engineering calculations, it is necessary to determine a number of initial data:

-climatic indicators (Table 1);

-thermal engineering indicators of the materials used for enclosing structures (Tables 2-6);

-boundary conditions:

-the heat transfer coefficient of the outer surface, ? _ext, W/(^m2* ^o S) of the wall fence – 12 ^[5];

-the heat transfer coefficient of the inner surface, ? _int, W/ (^m2 * ^o S) of the wall fence is 8,7 ^[5].

Table 1. Climate indicators

The thermal engineering calculation took into account the values of thermal conductivity, depending on the operating conditions, A – 80% from SP 50.13330.2012 ^[5].

The normalized temperature difference ?tn between the temperature of the internal air and the temperature of the inner surface of the external enclosing structures ^[5] for the residential part is 4.0 ° C.

The degree-day of the heating period (GSOP) for external enclosing structures is determined by the formulas (5.2) ^[5] (^about S*day):

GSOP = (t _in-t _from)*z _from.

The values of the basic required and normalized heat transfer resistances of external enclosing structures are determined according to Table 3 ^[5]:

- exterior walls (^m2*^o S/W):

R ^tr _st.lived. = a*GSOP+b;

R ^norm _st.lived. = R ^tr _st.lived. *0.63.

For a flat element, the specific heat loss is determined by the formulas (E.6) and (E.3) ^[5] (^m2*^o S/W):

R ⁰ _usl=1/? _int+? _n/? _n+1/? _ext.

Reduced heat transfer resistance according to Table 3 ^[5] (^m2*^o S/W):

R ⁰ _pr=R ⁰ _usl *r.

where r is the coefficient of thermal uniformity (r=0.80)

Therefore:

GSOP = 6454 ^o S*day;

Rtr st.core =3.66 ^m2*^o S/W;

Standard st.veins =2.31 ^m2*^o S/W

For type 1 construction (brick):

R ⁰ _usl=4.51 ^m2*^o S/W;

R ⁰ _pr= 3.61 m2*^o S/W.

The resulting value of _rp=3.61 m2 * ^o S/W is lower than the base value of the required heat transfer resistance R ^tr _st.veins. = 3.66 m2 * ^o S/ W, but above the normalized R ^norm_.veins.= 2.31 m2* ^o S/W.

The considered design meets the requirements of ^[5].

The reduced resistance to heat transfer is: ^R _st.core =3.61 m2 * ^o S/W.

Table 2. Thermal engineering indicators of wall construction materials type 1

Figure 2. Minimum temperature on the surface of a type 1 wall (brick)

For type 2 structures (aerated concrete):

R ⁰ _usl=6.11 m2* ^o S/W;

R ⁰ _pr= 4.89 m2*^o S/W.

The obtained value of the ^R _{of the core}=4.89 m2 *^o S/W is higher as the base value of the required heat transfer resistance R ^tr _{st. veins} = 3.66 m2 * ^o S/W, and the normalized R of the ^normalized _{core. = 2.31} m2 * o S / W.

The considered design meets the requirements of ^[5].

The reduced resistance to heat transfer is: ^R _st.core= 4.89 m2 * ^o S/W.

Table 3. Thermal engineering indicators of wall construction materials type 2

Figure 3. Minimum temperature on the surface of a type 2 wall (aerated concrete)

For type 3 structures (reinforced concrete):

R ⁰ _usl =4.28 m2* ^o S/W;

R ⁰ _pr= 3.42 m2*^o S/W.

The obtained value of the ^R _{of the core} = 3.42 m2 * ^o S/W is lower than the base value of the required heat transfer resistance R ^tr _st.veins. = 3.66 m2 * ^o S/ W, but above the normalized R ^norm_.veins.= 2.31 m2* ^o S/W.

The considered design meets the requirements of ^[5].

The reduced resistance to heat transfer is: ^R _st.core =3.42 m2 * ^o S/W.

Table 4. Thermal engineering indicators of wall construction materials type 3

Figure 4. Minimum temperature on the surface of a type 3 wall (reinforced concrete)

For construction of 4 types (expanded clay concrete):

R ⁰ _usl=4.39 m2* ^o S/W;

R ⁰ _pr= 3.51 m2*^o S/W.

The obtained value of the ^R _{of the core} =3.51 m2 * ^o S/W is lower than the base value of the required heat transfer resistance R ^tr _st.veins. = 3.66 m2 * ^o S/ W, but above the normalized R ^norm_.veins.= 2.31 m2* ^o S/W.

The considered design meets the requirements of ^[5].

The reduced resistance to heat transfer is: ^R _st.core =3.51 m2 * ^o S/W.

Table 5. Thermal engineering indicators of wall construction materials type 4

Figure 5. Minimum temperature on the surface of the type 4 wall (heat block)

For construction of 4 types (expanded clay concrete):

R ⁰ _usl =4.25 m2 * ^o S/W;

R ⁰ _pr= 3.40 m2*^o S/W.

The obtained value of the ^R _{of the core} = 3.40 m2 * ^o S/W is lower than the base value of the required heat transfer resistance R ^tr _st.veins. = 3.66 m2 * ^o S/ W, but above the normalized R ^norm_.veins.= 2.31 m2* ^o S/W.

The considered design meets the requirements ^[5].

The reduced resistance to heat transfer is: ^R _st.core =3.40 m2 * ^o S/W.

Table 6. Thermal engineering indicators of wall construction materials type 5

Figure 6. Minimum temperature on the surface of a type 5 wall (timber)

After thermal engineering calculations, to compare economic indicators, a local estimated calculation was performed using the basic index method of all types of structures at the price level for Q4 2022, the calculation result is shown in Table 7.

The calculation methodology is based on the following regulatory sources: Order of the Ministry of Construction of the Russian Federation dated 12/21/2020 No.812/PR ^[9], Order of the Ministry of Construction of the Russian Federation dated 12/11/2020 No. 744/PR ^[10], Order of the Ministry of Construction of the Russian Federation dated 08/04/2020 No. 421/pr ^[11], Letter of the Ministry of Construction of the Russian Federation dated 11/27/2022 No. 63135-IF/09 ^[12].

Table 7. Calculated indicators

          Graph 2 shows a summary diagram reflecting the relationship between the thermal engineering and economic indicators of the studied wordy structures of the exterior walls of low-rise housing construction.

Graph 2. Summary of the calculation results.

               Based on the conducted research, the following conclusions were formed:

1. The studied structural solutions of multilayer structures of exterior walls of low-rise housing construction meet the requirements of SP 50.13330.2012 ^[5].

2. As the most effective wall structure in terms of the value of heat flow in the construction of low-rise residential buildings, a structure using aerated concrete can be considered, while the least effective thermal engineering indicators for reinforced concrete and timber wall structures.

3. Of the studied structural solutions for exterior walls, the most optimal design solution from the point of view of comparing thermal engineering and economic indicators is a construction made of a heat block.

4. As a promising direction for the development of further research, a more detailed comparison of the design solutions of multilayer exterior walls of low–rise housing construction according to the main group of wall materials - concrete mixtures, in view of the obtained qualitative indicators of the heat block is considered.