STUDY OF THE CURRENT STATE OF THE İSSUE OF İNCREASİNG ENERGY EFFİCİENCY İN PROTECTİVE STRUCTURES Текст научной статьи по специальности «Техника и технологии»

UOT 693

STUDY OF THE CURRENT STATE OF THE iSSUE OF iNCREASiNG ENERGY EFFiCiENCY iN PROTECTIVE STRUCTURES

ALiYEV MUSTAFA ALi

Azerbaijan University of Architecture and Construction PhD, Ass.prof.

ORUJOV JALiL BAHLUL

Azerbaijan University of Architecture and Construction

Master

Abstract: Regulatory documents impose high requirements on the degree of thermal protection of a building and require the use of only reported values of thermal and technical parameters (heat transfer coefficient, vapor permeability, moisture retention, etc.) in calculations. However, the norms practically do not take into account the fluctuations (dance) of temperature and humidity in thick layers of protective walls as a result of the influence of climatic conditions during the operation of the building, the influence of other subjective factors (malfunctions of ventilation systems, accidents in heat and water supply networks, non-stationarity of heat and mass exchange processes in protective structures, etc.). Deviation of the moisture regime parameters from the parameters adopted in the design can primarily affect the actual value of the heat transfer coefficients of material layers and the resistance of the protective structure to heat transfer.

Key words: thermal conductivity, heat transfer, energy efficiency, protective structure, heat protection, heat loss, thermal resistance, vapor permeability

Energy efficiency of a building characterizes all the thermal and technical characteristics of the object under consideration and its engineering systems. These systems provide a given initial level of thermal energy consumption to ensure optimal microclimate parameters in the rooms, which depends on many factors, including the degree of thermal insulation of the protective structures. Practical studies show that heat loss due to air infiltration through protective structures accounts for 30-40% of the total heat loss balance of high-rise buildings. Thus, the main source of heat loss in high-rise buildings is its window structures. For example, the specific heat flux through a double-glazed window is approximately 5 times greater than the heat passing through the walls. Considering that the glazing area in houses is 15-20% of the wall area, it can be assumed that the heat loss through the walls reaches its maximum. Therefore, the issue of increasing the thermal insulation of protective structures is the main concept of an energy-efficient building.

Thermal protection of buildings is a general set of thermal and physical properties of its protective structures. Providing walls with vapor insulation prevents the accumulation of moisture on the surface of the walls and the formation of condensate in the structural sections during the operation of the building. In addition, protective structures must have the necessary strength, rigidity, durability, durability, provide reliable protection from external climatic influences, and also meet general architectural, operational and sanitary-hygienic requirements.

The main norms and rules for thermal protection of buildings are specified in the regulatory documents: IN and Q 23-02-2003 (thermal protection of buildings) [2]. These norms and rules establish three main normative indicators for thermal protection of buildings:

- The calculated value of the resistance to heat transfer of individual layers of the protective structures of the building (also for the external wall);

- Sanitary-hygienic indicator, this indicator determines the normative temperature difference between the temperature of the internal air and the temperature of the surfaces of the protective structures (also for the external wall);

- Specific heat energy consumption for heating the building, this indicator determines the temperature difference between the protective structures of the building;

For external walls, the required thermal resistance (Rt.o. m2-°C/Wt) to ensure the first indicator is a necessary condition that its total thermal resistance (Rum. ) is not greater than: Rt. > Rt.o. [2].

The required thermal resistance (Rt.o. m2-°C/Wt) is determined depending on the daily temperature indicator set for the heating period for the construction area according to IN and Q, which in turn is calculated from the calculated temperature of the indoor air in the rooms ( td , °C), the calculated temperature of the outdoor air (the coldest five-day temperature, tb , °C ) and the length of the heating period (K, day). The required thermal resistance Rt.o. , m2-deg/Wt, for the facade of the building is calculated according to the norms of IN 23-101-2004 [4].

In order for the external walls to provide the second indicator of thermal protection of buildings (sanitary and hygienic indicator), the normative temperature difference between the calculated temperature of the internal air (td , °C) and the temperature of the internal surface of the structure should not be greater than the value qtn specified in the norms and rules of IN and Q 2302-2003 [2].

In order to ensure the fulfillment of the third condition for thermal protection of buildings that meet energy saving requirements, the specific heat energy consumption for heating 1m2 of the building or 1m3 of its volume qe.w. should be less than or equal to the normalized value of the specific consumption (qn), i.e.

4e.w. (1)

The value of qn is determined for buildings of different types, depending on their purpose, according to the norms and rules of IN and Q 23-02-2003, and its value is calculated according to the methodology [4].

The requirements for thermal protection for residential buildings are considered to be met if the requirements of the first and second or second and third indicators are met at the same time, and in this case the minimum value of the first indicator (Rmin.) calculated according to the methodology [2] is allowed. Ensuring the third indicator due to the insignificant increase in the total thermal resistance of the protective structures can be achieved by choosing rational volume-planning solutions in accordance with the microclimate-maintaining systems, which is possible only when designing new buildings. Therefore, for buildings in operation, the external walls of which are designed according to previously valid norms, as a rule, compliance with the regulatory requirements of the first and second indicators is a necessary condition.

In addition to the three main standard indicators mentioned above, the norms and rules of IN and Q 23-02-2003 [2] also indicate another requirement, the conditions for ensuring the absence of condensate on the inner surface and joints of protective structures, according to which:

At the calculated temperature of the outside air during the cold season, the temperature of the inner surface of the outer protective structure should not be lower than the dew point of the inside air (tsh, °C);

The vapor permeability resistance of the protective structure Rb, m2-h-Pa/mg, (in the range from the inner surface of the structure to the possible condensate level) should not be less than the required thermal resistance to vapor permeability Rb1 (provided that moisture does not accumulate in the protective structure during the annual operation period) and Rb2 (provided that moisture accumulation in the protective structure is limited during the period of average monthly negative temperatures of the outside air). The calculation rules for thermal resistance to vapor transmission [5], the graphical-analytical method for calculating the moisture state during water vapor diffusion in stationary conditions [8, 9], the calculation of protective structures at the permissible limit value of moisture [7], the methodology for calculating the moisture regime of the structure [6] are shown.

In construction areas with a design temperature of outside air -35° ^ -40°, the parameters considered above are normalized according to the norms and rules of energy demand and heat

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protection IN 23-331-2001 (energy efficiency in residential and public buildings) [7], and take the following values:

- dew point temperature td = 11.6 °C [2];

- required thermal resistance Rta = 4.14 m2-°C/Vt , [2];

- total thermal resistance Rt. = 1.70 m2-°C/Vt , [4];

- calculated indoor air temperature ti = 21 °C [3];

- calculated outside air temperature (cold five-day period) tx = -39 °C [3];

- length of heating period K = 240 gun, [3];

- standard temperature drop Ats = 4°, [2];

- degree-day during the heating period D = 7850 degree-day, [3];

- It is proposed to accept the reported values of heat - technical indicators in accordance with operating conditions A (dry and normal mode of rooms).

The selection of optimal thermal protection of protective structures is associated with the need to conduct a thermal-technical report, which is a prerequisite for knowing the thermal conductivity coefficients of building materials in accordance with the operating conditions of the structure. The norms and rules of IN 23-101-2004 provide the values of thermal conductivity coefficients for a weight value of the dry and wet state of building materials in accordance with operating conditions A (dry and normal mode of rooms) and B (damp and wet mode of rooms), as well as a methodology for determining the effectiveness of the thermal insulation properties of building materials [2]. However, in the conditions of real operation of protective structures, the humidity regime may differ significantly from the calculated value depending on the climatic conditions of the construction region. For example, in cold regions characterized by severe climatic conditions, protective structures are exposed to the effects of sharp changes in daily temperature and humidity parameters throughout the year (mainly in the interseasonal periods). In the interseasonal periods, the difference between day and night temperatures is more than 20°C, and the maximum precipitation (up to 5055% of annual precipitation) falls on the second half of the summer months, during the rainy season. The current standards practically do not take into account the impact of the factor of sharp changes in temperature and humidity on the structural layers as a result of the characteristics of climatic conditions during operation, as well as the impact of other subjective factors that occur during the operation of the building (malfunctions of ventilation systems, accidents in heat and water supply networks, etc.). As a result of increasing humidity in building materials, their thermal conductivity increases. This is due to the mixing of air into the wet liquid, which has a thermal conductivity of a wet liquid that is greater than the thermal conductivity of air, Xn.m.=0.53 W/m-°C. At negative temperatures, when water turns into ice inside the material (Xice = 0.53 W/m-°C), the thermal conductivity of the material increases even more. For example, the thermal conductivity of penoizol with a density of 25 kg/m3 in a dry state is 0.029, and in a state of maximum sorption moisture it is 0.045, that is, 35% more, and at negative temperatures it is 0.050. Changes in the moisture content of building materials result in a change in their volume, which leads to loosening of the material structure and a decrease in the longevity of the structure as a whole. In addition, high humidity in structures affects the humidity regime of the air environment in rooms (humidity increases), which is considered undesirable from a hygienic point of view.

Thus, the process of moisture formation and accumulation in structures can be considered the most damaging factor, which leads to the collapse of the structure, a decrease in thermal protection, the formation of a fungal network on the surface of the structure, etc. Deviation of humidity parameters from the values adopted during the design primarily affects the change in the actual value of the thermal conductivity of the materials of the protective layers, as well as the resistance of the protective structure to heat transfer.

From the above, it can be concluded that the design of protective structures according to current standards does not provide an unconditional guarantee of their operational reliability. Failure to model non-stationary heat-humidity processes occurring in structures at the design stage, taking

into account the climatic conditions of the construction region during operation, leads to an increase in heat losses and premature failure of structures.

Thermal insulation indicators of external walls have been practically applied in construction projects since the 2000s, while until this period, thermal insulation indicators were adopted in accordance with the norms IN and Q II-B.3, II-A/7 -1962 "Construction Thermal Engineering". Until 1972, design norms were adopted in accordance with IN and Q II-.3-79 ("Construction Thermal Engineering").

For example, according to these norms, the total resistance to heat gain is 1.0 m2-°C/W, and the normative temperature drop, depending on the purpose of the building, is Atn (6^7) °C. The climatic conditions of the construction region are taken into account to a limited extent, and the thermal energy, which depends on the degree-day indicator of the heating period, is not taken into account at all.

In this regard, all buildings designed according to old standards and currently in operation are built with single-layer walls and do not meet the requirements of the modern required level of thermal protection in terms of energy efficiency (the first and third indicators of the currently valid standards), as well as sanitary and hygienic (the second indicator of the currently valid standards) and require additional thermal protection.

The report on the humidity regime of external protective structures in non-stationary conditions allows for a more accurate determination of the moisture content of the material in the structure (including in the thermal insulation layer) and the use of materials depending on the humidity.

The thermal resistance of multilayer protective structures can be determined by taking into account the moisture content of building materials. The thermal insulation properties of the layers of protective structures are determined as the ratio of the layer thickness (5) to its thermal conductivity (A), which is called the thermal resistance of that layer. The thermal resistance of multilayer protective structures is calculated by the following formula [9] :

Where S2 Sn are the thicknesses of the structural layers, m; X1, X2, Xn are the thermal conductivity coefficients, vt/m- °C; Ri, R2, Rn (m2 • °C/vt) are the thermal resistances of the As a result of convection inside the room and the influence of wind from the external environment, the constantly moving air flow sharply reduces its speed in front of the structure surface. Air moving at a low speed has a higher thermal insulation capacity than air moving at a high speed, therefore, the small moving air zone directly in front of the structure surface plays the role of an additional thermal protection layer [10], which is characterized by the concept of heat exchange resistance, and its value is determined as 1/«d, and for the external surface as 1/«x . Taking into account the heat transfer coefficients of the internal and external surfaces of the structure, its total thermal resistance is determined by the following formula.

(2-3) characterize the thermal conductivity properties of building materials forming layers A. Heat transfer in thick layers of building materials forming a layer exposed to moisture occurs in several ways. Heat from the solid body of the layer and the wet liquid layer passes directly through heat transfer, and from layers filled with moist air, heat passes through convection and radiation in addition to heat transfer. In the process of moisture exchange, heat is transferred in the form of liquid and vapor-like moisture. Therefore, the thermal conductivity coefficients of individual materials depend on the chemical-mineralogical composition of the composition forming the material, density, temperature, and moisture content of the material. However, if the mineralogical composition and density of the materials are relatively constant over time, then the moisture content

(2)

(3)

and temperature of the materials always change during operation. Various researchers give empirical formulas expressing the dependence of the thermal conductivity coefficients of individual materials on moisture content. The following dependence is proposed to determine the thermal conductivity of a wet material: [10]:

An = A • (1 + W • 2/100) (4)

Where X is the thermal conductivity of dry material, W/m- s; W is the moisture content of the material, %; Z is the coefficient of increase in thermal conductivity for 1% moisture.

For modern new generation thermal insulation materials (penoizol, new types of expanded polystyrene, etc.), it is necessary to clarify the dependence (4) and the value of Z. The value of Z for each material is determined individually by experiment, and the construction norms and rules do not provide a standard method for determining the dependence of the heat transfer coefficient of building materials on their degree of moisture. Due to the limited availability of this data in the literature on new generation thermal insulation materials and their absence in regulatory documents, the dependence (4) for penoizol and expanded polystyrene materials was clarified in laboratory conditions using a special method.

Results

1. Heat loss due to air infiltration from protective structures accounts for 30-40% of the total heat loss balance of buildings, in connection with which increasing the thermal insulation performance of protective structures is a very important and urgent issue. The modern concept of energy saving in the construction industry dictates the development of energy-efficient protective structures using high-quality thermal insulation materials.

2. Regulatory documents impose high requirements on the degree of thermal insulation of a building and require the use of only reported values of thermal and technical parameters (heat transfer coefficient, vapor permeability, moisture retention, etc.) in calculations. However, the norms practically do not take into account the fluctuations (dance) of temperature and humidity in thick layers of protective walls as a result of the influence of climatic conditions during the operation of the building, as well as the influence of other subjective factors (malfunctions of ventilation systems, accidents in heat and water supply networks, non-stationarity of heat and mass exchange processes in protective structures, etc.). Deviation of the humidity parameters from the parameters adopted in the design can affect, first of all, the actual value of the heat transfer coefficients of the material layers and the resistance of the protective structure to heat transfer. Accordingly, the design of protective structures according to the current standards does not unconditionally guarantee their operational reliability. Failure to model non-stationary heat-moisture processes occurring in structures at the design stage, taking into account the climatic conditions of the construction region during operation, leads to an increase in heat losses and premature failure of structures.

3. Various methods have been developed and are being applied to increase the energy efficiency of protective structures based on the use of multilayer structures made of materials with low thermal conductivity, but to assess their effectiveness, a methodology for calculating the thermal and technical parameters of materials is required, which affect the dynamics of the heat and moisture exchange process between the material layers of the building structure and the environment under non-stationary operating conditions.

4. Methods for calculating the thermal-humidity state of protective structures in non-stationary mode have been proposed by a number of scientists, but the large volume and complexity of calculations using the analytical method have not found wide application in design practice, and these calculations can only be realized with the use of computer software.

5. Modern computer programs allow modeling non-stationary heat exchange processes that depend on real, constantly changing internal and external climatic conditions.

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