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Abstract

Содержание

Introduction

In the public sector spending is a major expenditure for heating buildings. Important issue is their insulation. One solution to this problem is to install on the building of ventilated facades. Curtain walls are used in our country, about one and a half decades. This technology is applicable to both new buildings and old buildings. In the first case, this technology allows to save on the thickness of the outer wall during the construction and operating costs. In the second case - to extend the life of the building, to update its appearance, reduce operating costs. Due to the simplicity and efficiency of ventilated facades is beneficial economic solution.

1. Theme urgency

The problem of energy conservation is a priority for the development of science, technology and engineering. A special place in the solution of this problem is given the outer walls of public buildings. Thermal performance of which do not provide the required level of thermal protection.

Provide modern requirements given heat transfer resistance of external walls of buildings, using single and homogeneous structure, subject to the appropriate thickness is not possible. Therefore, it becomes obvious need for the development of new technical solutions of inhomogeneous exterior walls of the elements of the piece.

2. Goal and tasks of the research

The aim is to develop the theoretical foundations and prediction of heat-shielding properties of inhomogeneous exterior walls.

To achieve this goal it is necessary to solve the following problems:

  1. Develop a methodology to create the optimal building envelope that meets the strength, heat engineering, technological, environmental, economic, architectural and aesthetic requirements
  2. Develop a long-term technical solutions of inhomogeneous exterior walls of buildings.
  3. Develop a physical and mathematical model of unsteady heat loperenosa in inhomogeneous external walls of buildings.

3. Fundamentals

Over the past years, a lot of computational work in the field of numerical simulation of gas dynamics and heat and mass transfer in ventilated facades. However, despite increasing in recent years, the amount of computational work devoted ventilated facades, the task of developing proven engineering calculation methods of facade systems today remains relevant. Therefore, great importance attaches to the experimental study of ventilated facades.

Temperature calculation requires knowledge of air velocity and heat transfer coefficients in the air gap. Non-linear relationships between them, does not allow to obtain simple formulas for their determination. Therefore, the calculation of temperature, air velocity and other parameters of the heat and mass transfer in the air gap n rovoditsya numerically.

The calculation of heat and mass transfer in a ventilated air gap is a complex task. Between the surfaces of cladding and insulation is radiant heat transfer from the radiant heat transfer coefficient, which depends on temperature. Convective heat transfer occurs between the air gap and in structural elements. Convective heat transfer coefficients depend on the air velocity, air temperature and structural elements. Air velocity in the gap, in turn, depends on the medium temperature. A temperature calculation requires knowledge of the rate of air flow and heat transfer coefficients in the air gap. Non-linear relationships between them, including empirical equation does not permit a calculation formulas for their determination. Therefore, the calculation of air temperature and other parameters in the air gap should be an iterative numerical method. As a result of this calculation determines the temperature, the rate of air flow and other parameters of heat and mass transfer in the gap.

It is interesting to analyze the impact of various factors on the maximum rate of air flow in the gap. If the velocity is known, the air temperature can be calculated. The calculations were performed for the following parameters and values of the temperature front: - the thermal resistance of the wall (from the inside air to the surface of the insulating layer in the gap, excluding the heat transfer resistance in the gap) - 3.4 m2·°C/Wt - thermal resistance of the wall (from outside air to the surface of the liner in the gap, too, without taking into account the heat transfer resistance in the gap) - 0.06 m2·°C/Wt; - the thickness of the air gap - 0,06 m - height of the facade with a gap - 10 m - indoor air temperature - 20 ° C - the outside temperature - 20 ° C.

Подход к унификации синтеза автоматов Мура

drawing 1 – The dependence of the maximum speed of the air in the gap on the outside temperature at different values of the thermal resistances of the walls with insulation

Подход к унификации синтеза автоматов Мура

drawing 2 – The velocity of air from the air gap ambient air at various gap widths d

Подход к унификации синтеза автоматов Мура

drawing 3 – The dependence of the thermal resistance of the air gap, R, on the outdoor temperature at different values of the thermal resistance of the wall, R

Подход к унификации синтеза автоматов Мура

drawing 4 – The effective thermal resistance of the air gap, R, the width of the gap, d, for different values of the height of the facade, L

In all cases, the air speed increases with a decrease in ambient temperature. Image front height twice leads to a slight increase in air velocity. Reduced thermal resistance walls leads to increased air velocity is increased due to heat flow, and thus the temperature difference in the gap. The width of the gap significantly affects the speed of the air decreases the values of d air velocity is reduced, due to the increased resistance.

To calculate the heat loss through the fence more important is the relative influence of the effective thermal resistance of the air gap, because it determines how much heat loss is reduced. Although the greatest absolute value of the effective resistivity is achieved when the maximum thermal sorotivlenii wall greatest impact effective thermal resistance of the air gap for thermal has the minimum value of thermal sorotivlenii wall. Thus, when R = sorotivlenii wall 1 m2·°C/Wt and tn = 0 ° C due to heat losses the air gap is reduced by 14%.

Conclusion

The proper functioning of exterior wall construction with a ventilated air gap in the operation, particular attention should be paid to determining the thickness of the ventilated air space and air tightness main exterior wall construction (masonry and insulation). These important parameters necessary to determine, given the provision of very rapid pressure equalization outside air (the outside of the facade) and pressure in a ventilated air space under variable wind exposure. Rapid equalization of pressure and ambient air pressure in a ventilated air gap is necessary in order to avoid hitting a ozhdevyh drops in a ventilated air gap and excessive wind loads at variable wind exposure. In measurements on existing ventilated facades air velocity in a ventilated air gap is v = 0,3 - 0,4 m / s.[2, 3].

Master's thesis devoted to the actual problem: increase the thermal resistance of external walls of buildings

This master's work is not completed yet. Final completion: December 2013. The full text of the work and materials on the topic can be obtained from the author or his head after this date.

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