How to work closed air layers. Aerial layers

The article discusses the design of the heat-insulating system with a closed air layer between the thermal insulation and the wall of the building. It is proposed to use vapor-permeable inserts in thermal insulation in order to prevent moisture condensation in air layer. The method of calculating the area of \u200b\u200binserts, depending on the conditions of use of thermal insulation is given.

This Paper Describes The Thermal Insulating System Having Dead Air Space Between The Thermal Insulation and The Outer Wall of the Building. Water Vapour-Permeable Inserts Are Proposed for Use in the The Thermal Insulation in Order to Prevent Moisture Condensation in The Air Space. The Method for Calculating The Area of \u200b\u200bthe Inserts Has Been Offered Depending On The Conditions of the Thermal Insulation Usage.

Introduction

The air layer is an element of many enclosing buildings designs. The work explores the properties of enclosing structures with closed and ventilated by air layers. At the same time, the features of its use in many cases require solutions to the problems of construction heat engineering in specific terms of use.

Known and widely used in construction construction of the heat-insulating system with ventilated air layer. The main advantage of this system in front of light plaster systems is the possibility of performing work on the warming of buildings all year round. The fastener system of the insulation is at first attached to the enclosing structure. The insulation is attached to this system. The outer protection of the insulation is installed on it at some distance, so the air layer is formed between the insulation and the outer fence. The design of the insulation system allows the air layer ventilation in order to remove excess moisture, which ensures a decrease in the amount of moisture in the insulation. The disadvantages of this system include the complexity and necessity, along with the use of insulating materials, apply siding systems that provide the necessary clearance for moving air.

A well-known ventilation system is known in which the air layer is adjacent directly to the wall of the building. The thermal insulation is made in the form of three-layer panels: the inner layer is the heat insulating material, the outer layers - aluminum and aluminum foil. This design protects the insulation from penetration of both atmospheric moisture and moisture from the premises. Therefore, its properties do not deteriorate in any operating conditions, which allows you to save up to 20% insulation compared to conventional systems. The disadvantage of these systems is the need to ventilate the interlayer to remove moisture migrating from the premises of the building. This leads to a decrease in the thermal insulation properties of the system. In addition, the thermal losses of the lower floors of the buildings increase, as the cold air entering the interlayer through the holes at the bottom of the system, it takes some time to heat up to the steady temperature.

Warming system with closed air layer

A system of thermal insulation is possible, similar to a closed air layer. Attention should be paid to the fact that the movement of air in the layer is necessary only to remove moisture. If you solve the problem of removing moisture in a different way, without conducting, we obtain the system of thermal insulation with a closed air layer without the above disadvantages.

To solve the task, the thermal insulation system must be viewed in Fig. 1. The heat insulation of the building should be performed with vapor-permeable inserts from the heat-insulating material, for example, mineral wool. The heat insulation system must be arranged in such a way that the removal of the pair from the layer is ensured, and the humidity was below it below the dew point in the layer.

1 - wall of the building; 2 - fasteners; 3 - thermal insulation panels; 4 - PARRODOWAL INSTRUCTIONS

Fig. one. Heat insulation with vapor-permeable inserts

For a saturated pair pressure in the layer, you can record the expression:

Neglecting the thermal resistance of the air in the layer, the average temperature inside the layer is determined by the formula

(2)

where T IN., T Out. - air temperature inside the building and outdoor air, respectively, o C;

R. 1 , R. 2 - resistance to heat transfer walls and thermal insulation, respectively, m 2 × ° C / W.

For a couple migrating from the room through the wall of the building, you can record the equation:

(3)

where P in, P. - partial pressure of steam indoors and layers, PA;

S. 1 - the area of \u200b\u200bthe outer wall of the building, m 2;

k. PP1 - Wall Parry Permeal Coefficient, equal:

here R. PP1 \u003d M 1 / l. 1 ;

m 1 is the coefficient of vapor permeability of the material of the wall, mg / (m × h × pa);

l. 1 - wall thickness, m.

For a steam migrating from the air layer through vapor-permeable inserts in the thermal insulation of the building, you can record the equation:

(5)

where P Out. - partial pressure of steam in the outer air, Pa;

S. 2 - the area of \u200b\u200bvapor-permeable thermal insulation inserts in the thermal insulation of the building, m 2;

k. PP2 - Parry permeability coefficient inserts, equal:

here R. PP2 \u003d M 2 / l. 2 ;

m 2 is the vapor permeability coefficient of the material of the vapor-permeable insert, mg / (m × h × pa);

l. 2 - insert thickness, m.

Equating the right parts of equations (3) and (5) and solving the obtained equation for the pair balance in the layer relatively P., I get the value of the vapor pressure in the layer in the form:

(7)

where E \u003d S. 2 /S. 1 .

After writing out the condition of the absence of moisture condensation in the air layer in the form of inequality:

and deciding it, we obtain the required importance of the ratio of the total area of \u200b\u200bvapor-permeable inserts to the area of \u200b\u200bthe wall:

Table 1 shows the data obtained for some options for enclosing structures. In the calculations it was assumed that the thermal conductivity coefficient of vapor-permeable insert is equal to the thermal conductivity coefficient of the main heat insulation in the system.

Table 1. Meaning ε for various wall options

The examples shown in Table 1 show that the construction of heat insulation with a closed air layer between thermal insulation and a wall of the building is possible. For some wall structures, as in the first example from Table 1, you can do without vaporummant inserts. In other cases, the area of \u200b\u200bvapor-permeable inserts may be insignificant compared to the insulated wall area.

Heat insulation system with controlled heat engineering characteristics

The design of heat-insulating systems has undergone substantial development over the past fifty years, and today the designers have a large selection of materials and structures: from the use of straw to vacuum insulation. It is also possible to use active thermal insulation systems, whose features allow them to include in the system of power supply of buildings. In this case, the properties of the heat-insulating system can also vary depending on the environmental conditions, providing a constant level of heat loss from the building, regardless of the outdoor temperature.

If you specify a fixed heat loss level Q. Through the fencing structures of the building, the required meaning of the resistance of the heat transfer will be determined by the formula

(10)

Such properties may have a thermal insulation system with a transparent outer layer or with a ventilated air layer. In the first case, solar energy is used, and in the second, the energy of the soil heat can be used together with a soil heat exchanger.

In a system with transparent thermal insulation, with a low position of the Sun, its rays are almost without losses passing to the wall, it is heated by reducing the heat loss from the room. In the summer, with a high position of the Sun above the horizon, the sun's rays are almost completely reflected from the building wall, thereby preventing the overheating of the building. In order to reduce the inverse heat flux, the heat insulating layer is made in the form of a cellular structure, which plays the role of traps for sunlight. The disadvantage of such a system is the impossibility of the redistribution of energy by the facades of the building and the lack of the accumulating effect. In addition, the effectiveness of this system directly depends on the level of solar activity.

According to the authors, the ideal thermal insulation system must, to some extent, resemble a living organism and widely change its properties depending on the environmental conditions. With a decrease in the outdoor temperature, the heat-insulating system should reduce heat loss from the building, with an increase in the outdoor temperature - its thermal resistance can decrease. In the summer, the flow of solar energy into the building should also depend on external conditions.

The thermal insulation system offered to the thermal insulation system is largely formulated by the properties. In fig. 2a shows the wall circuit with the proposed insulating system, in fig. 2B is a temperature schedule in the heat insulating layer without and with the presence of an air layer.

The heat insulating layer is made with a ventilated air layer. When air moves in it with a temperature higher than in the appropriate point of the graph, the temperature of the temperature gradient in the layer of thermal insulation from the wall to the layer decreases compared to thermal insulation without a layer, which reduces heat loss from the building through the wall. At the same time, it should be borne in mind that the decrease in heat loss from the building will be compensated by a warmth of the air flow in the layer. That is, the air temperature at the outlet from the layer will be less than at the entrance.

Fig. 2. The diagram of the heat insulation system (A) and the temperature schedule (b)

The physical model of the problem of calculating the heat loss through the wall with the air layer is presented in Fig. 3. The heat balance equation for this model has the following form:

Fig. 3. Calculation diagram heat loss through a protective design

When calculating heat fluxes, conductive, convective and radiation mechanisms of heat transfer are taken into account:

where Q. 1 - thermal flow from the room to the inner surface of the enclosing structure, W / m 2;

Q. 2 - thermal flow through the main wall, W / m 2;

Q. 3 - thermal flow through the air layer, W / m 2;

Q. 4 - thermal flow through a layer of thermal insulation for the layer, W / m 2;

Q. 5 - heat flow from the outer surface of the enclosing structure into the atmosphere, W / m 2;

T. 1 , T. 2 - temperature on the wall surface, o C;

T. 3 , T. 4 - temperature on the surface of the layer, o C;

T. K., T A. - the temperature in the room and outdoor air is appropriate, about C;

s - Permanent Stephen Boltzmann;

l 1, L 2 is the coefficient of thermal conductivity of the main wall and thermal insulation, respectively, W / (M × ° C);

e 1, E 2, E 12 is the degree of black of the inner surface of the wall, the outer surface of the heat insulation layer and the degree of black of the surfaces of the air layer, respectively;

a B, A H, A 0 is the heat transfer coefficient on the inner surface of the wall, on the outer surface of the heat insulation and on the surfaces that limit the air interval, respectively, W / (m 2 × ° C).

Formula (14) is recorded for the case when air in the layer is fixed. In the case when air with a temperature is moving in the layer at u T. U, instead Q. 3 Considers two streams: from blowing air to the wall:

and from blowing air to the screen:

Then the system of equations falls into two systems:

The heat transfer ratio is expressed in the number of Nusselt:

where L. - Characteristic size.

Formulas for calculating the number of Nusselt were taken depending on the situation. When calculating the heat transfer coefficient on the inner and outer surfaces of the enclosing structures, formulas were used:

where Ra \u003d PR × GR is a rift criterion;

GR \u003d. g.× b × d T.× L. 3 / N 2 - the number of grashaf.

When determining the number of grains food, the difference between the temperature of the wall and the ambient temperature was chosen as a characteristic temperature difference. The characteristic dimensions were taken: the height of the wall and the thickness of the layer.

When calculating the heat transfer coefficient a 0 inside the closed air layer, the formula was used to calculate the number of nusselt:

(22)

If the air inside the interlayer was moving, a more simple formula was used to calculate the number of nusselt:

(23)

where RE \u003d. v.× d / n - the number of Reynolds;

d - the thickness of the air layer.

The values \u200b\u200bof the number of PRANDTLL PR, the kinematic viscosity N and the thermal conductivity coefficient L B depending on the temperature were calculated by linear interpolation of table values \u200b\u200bfrom. Systems of equations (11) or (19) were solved numerically by iterative refinement relative to temperatures T. 1 , T. 2 , T. 3 , T. four . For numerical modeling, a thermal insulation system based on thermal insulation, similar to polystyrene foam, with a thermal conductivity coefficient of 0.04 W / (m 2 × ° C) was chosen. The air temperature at the input of the layer was assumed to be 8 o C, the total thickness of the thermal insulating layer is 20 cm, the thickness of the layer d. - 1 cm.

In fig. 4 shows the graphs of the dependence of the specific heat loss through the insulating layer of the conventional heat insulator in the presence of a closed heat insulating layer and with a ventilated air layer. A closed air layer almost does not improve the properties of thermal insulation. For the considered case, the presence of a heat-insulating layer with a moving air flow More than twice the heat loss through the wall at an outdoor temperature minus 20 ° C. The equivalent resistance value of the heat transfer of such thermal insulation for this temperature is 10.5 m 2 × ° C / W, which corresponds to the layer expanded polystyrene foam more than 40.0 cm thick.

D. d.\u003d 4 cm with fixed air; Row 3 - air velocity 0.5 m / s

Fig. four. Charts of the specific heat loss

The effectiveness of the thermal insulation system increases as the outdoor temperature decreases. At the outdoor temperature of 4 o with the efficiency of both systems is the same. Further increase in temperature makes it inappropriate to use the system, as it leads to an increase in the level of heat loss from the building.

In fig. 5 shows the dependence of the temperature of the outer surface of the wall on the outdoor temperature. According to fig. 5, the presence of an air layer increases the temperature of the outer surface of the wall at a negative temperature of the outer air compared to conventional thermal insulation. This is explained by the fact that moving air gives its warmth both inner and the outer layers of thermal insulation. With high outer air temperature, such a thermal insulation system plays the role of the cooling layer (see Fig. 5).

Row 1 - ordinary thermal insulation, D. \u003d 20 cm; A number 2 - in thermal insulation there is an air slot 1 cm wide, d.\u003d 4 cm, air speed 0.5 m / s

Fig. five. Highlightness of the outdoor surface of the wallfrom the outdoor temperature

In fig. 6 shows the dependence of the temperature at the output of the layer from the outdoor temperature. The air in the layer, cooled, gives its energy to the enclosing surfaces.

Fig. 6. Temperature dependence on the output of the layerfrom the outdoor temperature

In fig. 7 shows the dependence of the heat loss from the thickness of the outer layer of thermal insulation at the minimum outer temperature. According to fig. 7, at least heat loss is observed when d. \u003d 4 cm.

Fig. 7. Dependence of heat loss from the thickness of the outer layer of thermal insulation with minimal outdoor temperature

In fig. 8 shows the dependence of the heat loss for the outdoor temperature minus 20 ° C from air velocity in the layer with different thickness. The approach of air velocity is higher than 0.5 m / s insignificantly affects the properties of thermal insulation.

Row 1 - d. \u003d 16 cm; Series 2 - d. \u003d 18 cm; row 3 - d. \u003d 20 cm

Fig. eight. Dependence of heat loss from air velocitywith different thickness of the air layer

It should be paid to the circumstance that the ventilated air layer makes it possible to effectively control the heat loss level through the surface of the wall by changing the air velocity from 0 to 0.5 m / s, which is impossible to be carried out for conventional thermal insulation. In fig. 9 shows the dependence of the air velocity from the outdoor temperature for a fixed level of heat loss through the wall. Such an approach to thermal protection of buildings allows to reduce the energy intensity of the ventilation system as the outdoor temperature increases.

Fig. nine. The dependence of the speed of air from the outdoor temperature for fixed level heat loss

When creating a thermal insulation system under consideration in the article, the main source is the issue of energy source to increase the temperature of the pumpable air. As such a source, it is assumed to take the heat of the soil under the building by using the soil heat exchanger. For more efficient use of soil energy, it is assumed that the ventilation system in the air layer should be closed, without atmospheric air supply. Since the air temperature entered into the system in winter, below the soil temperature, the problems of moisture condensation do not exist here.

The most efficient use of such a system is seen in combination of two sources of energy: solar and soil heat. If you appeal to the previously mentioned systems with a transparent heat insulation layer, it becomes obvious to the desire of the authors of these systems to implement in one way or another the idea of \u200b\u200ba thermal diode, that is, to solve the problem of directional transmission of solar energy to the building wall, taking measures that prevent the heat flux movement in the opposite direction.

As an outer absorbing layer, a metal plate was painted in a dark color. And the second absorbing layer can be an air layer in the thermal insulation of the building. Air moving in a layer, climbing through the soil heat exchanger, heats the soil in sunny weather, accumulating solar energy and redistributing it through the facades of the building. The heat from the outer layer internal can be transmitted using heat diodes made on heat tubes with phase transitions.

Thus, the proposed thermal insulation system with controlled thermal characteristics is based on structures with a thermal insulation layer having three features:

- ventilated air layer, parallel building construction;

- source of energy for air inside the layer;

- a system for controlling the parameters of the air flow in the layer, depending on the outer weather conditions and air temperature in the room.

One of the possible design options is the use of a transparent thermal insulation system. In this case, the thermal insulation system must be supplemented by another air layer adjacent to the wall of the building and having a message with all the walls of the building, as shown in Fig. 10.

The heat insulation system shown in Fig. 10, has two air layers. One of them is between thermal insulation and transparent fence and serves to prevent the building overheating. For this purpose there are air valves connecting the layer with the outer air at the top and bottom of the heat insulating panel. In the summer and at the moments of high solar activity, when the hazard overheating occurs, the damper building opens, providing ventilation by outer air.

Fig. 10. Transparent thermal insulation system with ventilated air layer

The second air layer adjoins the building wall and serves to transport solar energy in the building shell. This design will allow the use of solar energy to the entire surface of the building during the light day, providing, besides, the effective accumulation of solar energy, since the battery performs the entire volume of the walls of the building.

It is also possible to use traditional heat insulation in the system. In this case, the source of thermal energy can be a soil heat exchanger, as shown in Fig. eleven.

Fig. eleven. Thermal insulation system with a soil heat exchanger

As another option, you can offer for this purpose the ventilation emissions of the building. In this case, to eliminate moisture condensation in the layer, removed air is necessary to skip through the heat exchanger, and in the layer, start the outer air heated in the heat exchanger. From the layer, the air can enter the ventilation room. Air heats up, passing through the soil heat exchanger, and gives its own energy of the enclosing structure.

The required element of the thermal insulation system should be an automatic control system for its properties. In fig. 12 shows a block diagram of the control system. Management occurs based on the analysis of information from temperature and humidity sensors by changing the mode of operation or disconnect the fan and opening and closing the air dampers.

Fig. 12. Block diagram of the control system

The block diagram of the operation of the ventilation system with controlled properties is shown in Fig. 13.

At the initial stage of operation of the control system (see Fig. 12) on the measured values \u200b\u200bof the outdoor temperature and indoors in the control unit, the temperature is calculated in the air layer for the conditions of still air. This value is compared with the air temperature in the southern facade layer when the heat-insulating system is constructed, as in Fig. 10, or in a soil heat exchanger - when designing the heat insulating system, as in Fig. 11. If the calculated temperature value is greater than or equal to the measured, the fan remains off, and the air dampers in the layer are closed.

Fig. 13. Block diagram of the fan system algorithm with managed properties

If the value of the calculated temperature is less measured, includes a circulation fan and open the flaps. In this case, the heated air energy is given to the wall structures of the building, reducing the need for thermal energy for heating. At the same time, the value of air humidity in the layer is measured. If the humidity approaches the condensation point, the flap opens, connecting the air layer with the outer air, which ensures the prevention of moisture condensation on the surface of the layer walls.

Thus, the proposed thermal insulation system allows you to actually control the heat engineering properties.

Test of the layout of the heat insulation system with controlled heat insulation by using ventilation emissions of the building

The experiment scheme is presented in Fig. 14. The layout of the thermal insulation system is mounted on a brick wall of the premises of the upper part of the elevator shaft. The layout consists of thermal insulation representing the steamproof thermal insulation plates (one surface - aluminum with a thickness of 1.5 mm; the second is an aluminum foil), filled with polyurethane foam with a thickness of 3.0 cm with a thermal conductivity coefficient of 0.03 W / (m 2 × ° C). The heat transfer resistance plate is 1.0 m 2 × o C / W, brick wall - 0.6 m 2 × ° C / W. Between the thermal insulation plates and the surface of the building of the building - the air layer with a thickness of 5 cm. In order to determine the temperature modes and the movement of the heat flux through the fencing design, the temperature and heat flux sensors were installed in it.

Fig. fourteen. Scheme of experimental system with controlled heat insulation

The photograph of the mounted thermal insulation system with power supply from the system for utilizing the heat of ventilation emissions is presented in Fig. fifteen.

Additional energy inside the interlayer is supplied with air, taken at the output of the heat recovery system of ventilation emissions of the building. Ventilation emissions were closed from the exit of the ventilation miner of the GP Corps "Institute Niptis them. Ataeva S. S., "was fed to the first intake of the recovery (see Fig. 15a). On the second intake of the recuperator, the air was supplied from the ventilation layer, and from the second release of the recuperator - again into the ventilation layer. Air of ventilation emissions cannot be supplied directly into the air layer due to the risk of moisture condensation inside it. Therefore, the ventilation emissions of the building first passed through the heat exchanger-heat exchanger, the air from the interlayer was added to the second entrance. In the recuperator, it was heated and the fan was supplied to the air layer of the ventilation system through the flange, mounted at the bottom of the heat insulating panel. Through the second flange, the air was removed from the panel and closed the cycle of its movement at the second inlet of the heat exchanger. During the work, the registration of information coming from the temperature sensors and the heat flux set by the figures is carried out. fourteen.

To manage the operation modes of fans and removes and registering the parameters of the experiment, a special data control and processing unit was used.

In fig. 16 shows the charts of temperature change: outdoor air, indoor and air air in various parts of the layer. From 7.00 to 13.00, the system goes to the stationary mode of operation. The difference between the temperature at the air inlet into the layer (sensor 6) and the temperature at the outlet of it (sensor 5) was about 3 o C, which indicates the consumption of energy from the passing air.

Fig. sixteen. Temperature change graphs: a - outdoor air and indoor air;b - air in different parts of the layer

In fig. 17 shows graphs of the dependence on the temperature of the surfaces of the wall and thermal insulation, as well as the temperature and heat flux through the fencing surface of the building. In fig. 17b clearly fixes the decrease in the heat flux from the room after supplying heated air into the ventilating layer.

Fig. 17. Time dependency graphics: a - the temperature of the surfaces of the wall and thermal insulation;b - Temperature and heat flux through a building enclosing surface

Experimental results obtained by the authors confirm the possibility of managing the properties of thermal insulation with a ventilated layer.

Conclusion

1 An important element of energy efficient buildings is its shell. The main directions of development of the reduction of heat loss of buildings through the enclosing structures are associated with active thermal insulation, when the enclosing structure plays an important role in the formation of the parameters of the indoor interior. The most visual example is the enclosing design with the presence of an air layer.

2 authors proposed the construction of heat insulation with a closed air layer between the thermal insulation and the wall of the building. In order to prevent the condensation of moisture in the air layer without a decrease in thermal insulation properties, it is considered to be used in thermal insulation of vapor-permeable inserts. A method was developed for calculating the inserts area depending on the conditions of use of thermal insulation. For some wall structures, as in the first example from Table 1, you can do without vaporummant inserts. In other cases, the area of \u200b\u200bvapor-permeable inserts may be insignificant relative to the area of \u200b\u200bthe insulated wall.

3 developed a technique for calculating the heat engineering characteristics and the design of the heat-insulating system, which has controlled heat engineering properties. The design is made in the form of a system with a ventilated air layer between two layers of thermal insulation. When moving in the air layer with a temperature is higher than in the appropriate wall with a conventional thermal insulation system, the temperature gradient in the layer of heat insulation from the wall to the layer decreases compared to thermal insulation without layers, which reduces heat loss from the building through the wall. As an energy to increase the temperature of the pumped air, it is possible to use soil heat under the building using soil heat exchanger, or solar energy. Developed methods for calculating the characteristics of such a system. An experimental confirmation of the reality of the use of a thermal insulation system with controlled heat-engineering characteristics for buildings was obtained.

BIBLIOGRAPHY

1. Bogoslovsky, V.N. Construction thermal physics / V.N. Bogoslovsky. - SPb.: Avok-North-West, 2006. - 400 s.

2. Building thermal insulation systems: TCP.

4. Design and device of the insulation system with a ventilated air layer based on panels of three-layer facade: P 1.04.032.07. - Minsk, 2007. - 117 p.

5. Danilevsky, L. N. On the issue of reducing the level of heat loss of the building. The experience of Belarusian-German cooperation in construction / L. N. Danilevsky. - Minsk: Strindo, 2000. - P. 76, 77.

6. ALFRED KERSCHBERGER "SOLARES BAUEN MIT TRANSPARENTER WARMEDAMMUNG". Systeme, Wirtschaftlichkeit, Perspektiven, Bauverlag GmbH, Weisbaden Und Berlin.

7. Die ESA-SOLARDASSADE - DAMMEN MIT LICHT / ESA-ENERGIESYSTEME, 3. PASSIVHAUSTAGUNG 19 BIS 21 FEBRUAR 1999. BREGENZ. -R. 177-182.

8. Peter O. Braun, Innovative GeBaudehullen, WaRmetechnik, 9, 1997. - R. 510-514.

9. Passive house as an adaptive system of life support: theses of reports of international reports. scientific school. conf. "From the thermal sanitation of buildings - to the passive house. Problems and solutions "/ L. N. Danilevsky. - Minsk, 1996. - P. 32-34.

10. Heat insulation with controlled properties for buildings with low heat loss: Sat. Tr. / GP "Institute Niptis them. Ataeva S. S. "; L. N. Danilevsky. - Minsk, 1998. - P. 13-27.

11. Danilevsky, L. Thermal insulation system with controlled properties for a passive house / L. Danilevsky // Architecture and construction. - 1998. - № 3. - P. 30, 31.

12. Martynenko, O. G. Free convective heat transfer. Directory / O. Martynenko, Yu. A. Sokovishin. - Minsk: Science and Technology, 1982. - 400 p.

13. Mikheev, M. A. Fundamentals of heat transfer / M. A. Mikheev, I. M. Mikheev. - M.: Energia, 1977. - 321 p.

14. Outdoor ventilated building fence: Pat. 010822 Evraz. Patent Office, IPC (2006.01) E04V 2/28, E04V 1/70 / L. N. Danilevsky; Applicant GP "Institute Niptis them. Ataeva S. S. ". - № 20060978; Intrusted 05.10.2006; publ. 12/30/2008 // Bull. Eurasian Patent Office. - 2008. - № 6.

15. Outdoor ventilated building fence: Pat. 11343 Rep. Belarus, IPC (2006) E04B1 / 70, E04B2 / 28 / L. N. Danilevsky; Applicant GP "Institute Niptis them. Ataeva S. S. ". - № 20060978; Stage. 05.10.2006; publ. 12/30/2008 // Afijynyy Bul. / Nats. Tsangr Iztelektal. Ulsnastsi. - 2008.

Initial data for layers of enclosing structures;
- wood floor (tipped board); δ 1 \u003d 0.04 m; λ 1 \u003d 0.18 W / m ° C;
- parosolation; Unnecessarily.
- air layer: RPr \u003d 0.16 m2 ° C / W; δ 2 \u003d 0.04 m λ 2 \u003d 0.18 W / m ° C; ( Thermal resistance of a closed air layer >>>.)
- insulation (Stirore); δ ut \u003d? m; λ ut \u003d 0.05 W / m ° C;
- chernovaya Pol (board); δ 3 \u003d 0.025 m; λ 3 \u003d 0.18 W / m ° C;

As we have already noted to simplify the heat engineering calculation, an increase in the coefficient is introduced ( k.), which brings the value of the calculated heat resistance to the recommended heat resistance of the enclosing structures; For the insiding and basement overlap, this coefficient is 2.0. The required heat resistance is calculated based on the fact that the outdoor temperature (in the subfield) is equal; - 10 ° С. (However, everyone can put the temperature that it considers the necessary case).

We consider:

Where RT - required heat resistance,
tB - Calculated indoor air temperature, ° C. It is accepted on SNOP and equals 18 ° C, but because we all love heat, then we offer the temperature of the inner air to raise up to 21 ° C.
tN - Calculated outdoor air temperature, ° C, equal to the average temperature of the coldest five days in a given area of \u200b\u200bconstruction. We offer temperature in the subfield tN To take "-10 ° С", of course for the Moscow region a large stock, but here in our opinion it is better to retire than not to take. Well, if you follow the rules, the outdoor temperature of the TN is accepted according to SNOP "Construction climatology". Also, the necessary regulatory value can be found in local construction organizations or district architecture departments.
ΔT N · α in - The work in the denoter of the fraction is: 34.8 W / m2 - for the outer walls, 26.1 W / m2 - for coatings and attic floors, 17.4 W / m2 ( in our case) - for adhesive overlaps.

Now calculate the thickness of the insulation from extruded polystyrene foam (styrofoam).

Where Δ Ut - thickness of the insulation layerm;
Δ 1 ...... Δ 3 - thickness of individual layers of enclosing structuresm;
λ 1 ...... λ 3 - thermal conductivity coefficients of individual layers, W / m ° С (see Builder's Directory);
RPR - thermal resistance of the air layer, m2 ° C / W. If the airflow is not provided in the enclosing structure, then this value is excluded from the formula;
α B, α n - coefficients of heat transfer of the inner and outer surface of the overlapequal to 8.7 and 23 W / m2 ° C, respectively;
λ UT - the thermal conductivity coefficient of the insulation layer (In our case, the staport is extruded polystyrene foam), W / M ° C.

Output; In order to satisfy the requirements for the temperature regime of the house, the thickness of the insulation layer of polystyrene foam plates located in the base floor overlap along wooden beams (the thickness of the beam 200 mm) should be at least 11 cm. Since we initially set overestimated parameters, then options may be the following; This is either a pie of two layers of 50 mm styrofoor plates (minimum), or a pie of four layers of 30 mm styroforal plates (maximum).

Construction of houses in the Moscow region:
- Building a house of foam block in the Moscow region. Thickness of the walls of the house of foam blocks >>>
- Calculation of brick wall thickness during the construction of a house in the Moscow region. >>>
- Construction of a wooden brusade house in the Moscow region. The thickness of the wall of the brusade house. >>>

Note. When there is one or both surfaces of the air layer, the aluminum foil thermal resistance should be increased by 2 times.

Appendix 5 *

Schemes of heat-conducting inclusions in enclosing structures

Appendix 6 *

(Reference)

The reduced resistance to the heat transfer windows, balcony doors and lamps

* in steel bindings

Notes:

1. To the soft selective coatings of glass include coatings with thermal emission less than 0.15, to solid - more than 0.15.

2. The values \u200b\u200bof the resisters of heat transfer of light openings are given for cases when the ratio of glazing area to the filling area of \u200b\u200bthe light opening is 0.75.

The values \u200b\u200bof the resistances of the heat transfer shown in the table are allowed to be used as calculated in the absence of such values \u200b\u200bin standards or technical specifications on designs or not confirmed by test results.

3. The temperature of the inner surface of the structural elements of the windows of buildings (except production) should be no lower than 3 ° C at the calculated temperature of the outer air.

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1.3 Building as a single energy system.
2. The heat transfer through the external fences.
2.1 Basics of heat transfer in the building.
2.1.1 thermal conductivity.
2.1.2 Convection.
2.1.3 Radiation.
2.1.4 Thermal resistance of the air layer.
2.1.5 The heat transfer coefficients on the inner and outer surfaces.
2.1.6 Heat transmission through a multi-layer wall.
2.1.7 The reduced heat transfer resistance.
2.1.8 Temperature distribution by cross section of the fence.
2.2 humidity regimen of enclosing structures.
2.2.1 Reasons for the appearance of moisture in fences.
2.2.2 Negative consequences of moisturizing outdoor fences.
2.2.3 Communication of moisture with construction materials.
2.2.4 Wet air.
2.2.5 Material moisture.
2.2.6 Sorption and desorption.
2.2.7 Parry permeability of fences.
2.3 Air permeability of external fences.
2.3.1 Basic provisions.
2.3.2 Pressure difference on the outer and inner surface of the fences.
2.3.3 Air permeability of building materials.

2.1.4 Thermal resistance of the air layer.

To make uniformity resistance heat transfer closed aircraftslocated between the layers of the enclosing construction, called thermal resistance R.P, m². ºС / W.
The heat transfer circuit through the air layer is presented in Fig. 5.

Fig.5. Heat exchange in air layer.

Clauses available to air flows are produced by worsening the thermal insulation characteristics of the walls. The gaps are closed (as well as closed pores of the foam material) are heat insulating elements. Old-rectified voids are widely used in construction to reduce heat loss through enclosing structures (slots in bricks and blocks, channels in concrete panels, gaps in double-glazed windows, etc.). Empties in the form of unexploded aircraft are used in the walls of baths, including frameworks. These voids are often the main elements of heat shields. In particular, it is the presence of voids with a hot side of the wall that allows the use of low-melting foams (polystyrene foam and polyethylene foam) in the deep zones of the walls of high-temperature baths.

At the same time, emptiness in the walls are the most insidious elements. It is necessary to break the wind insulation in the smallest degree, and the entire system of voids can become a single blowing outlet, turning off the heat insulation system all external thermal insulation layers. Therefore, empties are trying to make small in size and is guaranteed to take apart from each other.

To use the concept of thermal conductivity of air (and even more so used the ultra-low value of the thermal conductivity of the fixed air 0.024 W / m) to evaluate heat transfer processes through real air it is impossible, since the air in large voids is an extremely mobile substance. Therefore, in practice, empirical (experimental, experimental) ratios are used for heat engineering calculations of heat transfer processes. Most often (in the simplest cases) in heat transfer theory it is believed that the thermal flow from the air to the surface of the body in the air is equal Q \u003d αΔT.where α - empirical coefficient of heat transfer "fixed" air, ΔТ. - The difference in the surface temperatures of the body and air. In normal conditions of residential premises, the heat transfer coefficient is equivalent to approximately α \u003d 10 W / m² Grad. It is this figure that we will adhere to the estimated calculations of the heating of the walls and the human body in the bath. With the help of air flows at a speed V (m / s), the heat flux increases by the magnitude of the convective component Q \u003d βvΔtwhere β approximately equal 6 W sec / m³ hail. All values \u200b\u200bdepend on the spatial orientation and surface roughness. Thus, according to the current standards of SNIP 23-02-2003, the coefficient of heat transfer from air to the inner surfaces of the enclosing structures is taken equal to 8.7 W / m² of degrees for walls and smooth ceilings with weakly protruding ribs (with the height of the height of the "H" to the distance "A »Between the faces of the neighboring Ryubers H / A< 0,3); 7,6 Вт/м² град для потолков с сильно выступающими рёбрами (при отношении h/a > 0.3); 8.0 W / m² Grad for windows and 9.9 W / m² Grad for anti-aircraft lamps. Finnish specialists take the coefficient of heat transfer in the "fixed" air of a dry sauna equal to 8 W / m² of degrees (which within measurement errors coincides with the value we receive) and 23 W / m² of degrees in the presence of air flows at an average of 2 m / s.

So small meaning of heat transfer coefficient in conventionally "fixed" air α \u003d 10 W / m² The hail corresponds to the concept of air as the heat insulator and explains the need to use high temperatures in the saunas for the rapid warming of the human body. With regard to walls, this means that with characteristic heat loss through the walls of the bath (50- 200) W / m², the difference in air temperatures in the bath and temperatures of the internal surfaces of the walls of the bath can reach (5-20) ° C. This is a very big value, often in no way and is not taken into account. The presence of a strong air convection in the bath allows to reduce the temperature difference in half. Note that such high temperature differences characteristic of baths are not allowed in residential premises. So, normalized in SNiP 23-02-2003, the temperature difference between air and the walls should not exceed 4 ° C in residential areas, 4.5 ° C in public and 12 ° C in production. Higher temperature differences in residential premises inevitably lead to the sensations of cold from the walls and dew lunas on the walls.

Using the introduced concept of heat transfer coefficient from the surface into air, the emptiness inside the wall can be considered as a sequential arrangement of heat transfer surfaces (see Fig. 35). Increased air zones, where the above temperature differences Δt are observed, called border layers. If there are two empty gaps in the wall (or double-glazing) (for example, three glasses), then there are 6 border layers in fact. If through such a wall (or glass) passes a heat flux 100 W / m², then on each border layer temperature changes to ΔT \u003d 10 ° С, and on all six layers, the temperature difference is 60 ° C. Considering that heat flows through each separately the border layer and across the entire wall are generally equal to each other and are still 100 W / m², the resulting heat transfer coefficient for the wall without voids ("double-glazed glass with one glass) will be 5 W / m² hail, for a wall with one empty layer (double-glazed windows) 2.5 W / m² degrees, and with two empty layers (double-glazed windows with three stalks) 1.67 W / m² degrees. That is, the more emptiness (or the more glass), those warm the wall. In this case, the thermal conductivity of the material of the walls (stalk) in this calculation was supposed to be infinitely large. In other words, even from a very "cold" material (for example, steel), it is possible in principle to make a very warm wall, providing only the presence in the wall of the set of aircrafts. Actually, on this principle, all glass windows work.

To simplify estimated calculations, it is more convenient to use the heat transfer coefficient α, and its inverse value is heat transfer resistance (thermal resistance of the boundary layer) R \u003d 1 / α. The thermal resistance of two border layers corresponding to one layer of the material of the wall (one glass) or one air gap (layer) is equal R \u003d 0.2 m² hail / w, and three layers of the material of the wall (as in Figure 35) - the sum of the resistance of the six border layers, that is, 0.6 m² of degree / W. From determining the concept of heat transfer resistance Q \u003d Δt / r It follows that, with the same heat flux of 100 W / m² and the thermal resistance of 0.6 m² of hail / W, the temperature difference on the wall with two air layers will be the same 60 ° C. If the number of air sucks to increase to nine, then the temperature drop on the wall with the same heat flux 100 W / m² will be 200 ° C, that is, the estimated temperature of the inner surface of the wall in the bath with a heat flux 100 W / m² will increase from 60 ° C to 200 ° С (if on the street 0 ° C).

The heat transfer coefficient is the resultant indicator, comprehensively summarizing the consequences of all physical processes occurring in the air in the surface of the heat transfer or heat-visible body. With small drops of temperatures (and small heat fluxes), the convective streams of air are small, heat transfer mainly occurs conscutely due to thermal conductivity of fixed air. The thickness of the boundary layer would have made a small amount, just a \u003d λr \u003d 0.0024 m, where λ \u003d 0.024 W / m hail - thermal conductivity coefficient of fixed air, R \u003d 0.1 m²grad / W -Termic resistance of the boundary layer. Within the boundary layer, the air has different temperatures, as a result, due to the gravitational forces, the air at the hot vertical surface begins to pop up (and in the cold - dive), gaining speed, and turbulizes (cuddled). Due to the vortices, air heat transfer increases. If the contribution of this convective component is formally introduced into the thermal conductivity coefficient value λ, then the increase in this thermal conductivity coefficient will respond to a formal increase in the thickness of the boundary layer a \u003d λr. (As we will see below, approximately 5-10 times from 0.24 cm to 1-3 cm). It is clear that this is a formally increased thickness of the boundary layer correspond to the size of air flow and the vortices. Without deepening in the subtleties of the boundary layer structure, we note that the understanding of the fact that the heat transforming can "fly up" up with a convective flow, and without reaching the next plate of the multilayer wall or the next glass glass plate is noted. This corresponds to the case of caloric heating of air, which will be discussed below when analyzing shielded metal furnaces. Here, we consider the case when air flows in the layer have a limited height, for example, 5-20 times larger than the thickness of the layer δ. At the same time, circulation flows arise in air layers, which actually participate in the transfer of heat in conjunction with conductive heat flows.

With small thicknesses of the aircraft, the counter flow of air in opposite walls of the gap begin to influence each other (mixed). In other words, the thickness of the air layer becomes less than two unperturbed border layers, as a result of which the heat transfer coefficient increases, and the heat transfer resistance decreases accordingly. In addition, at elevated temperatures of the walls of the aircraft, the role of heat transfer processes is beginning to play. The refined data in accordance with the official recommendations of SNIP P-3-79 * are given in Table 7, from where it can be seen that the thickness of the unperturbed border layers is 1-3 cm, but a significant change in heat transfer occurs only with the thicknesses of aircraft less than 1 cm. This means In particular, that airbags between the glazed windows should not be less than 1 cm thick.

Table 7. Thermal resistance of a closed air layer, m² hail / W

Their tables 7 also follows that the more warm air layers have lower thermal resistance (it is better to pass through themselves heat). This is due to the effect on the heat transfer mechanism, which we will consider in the next section. We note at the same time that the viscosity of the air grows with the temperature, so the warm air turbulizes worse.

Fig. 36.. The symbols are the same as in Figure 35. Due to the low thermal conductivity of the material of the walls, temperatures occur ΔTc \u003d QRC.where RC is thermal wall resistance Rc \u003d ΔC / λC (Δc - wall thickness, λc - thermal conductivity coefficient of the wall material). With an increase in the temperature drops, ΔTc decreases, but the temperature differences on the border layers ΔT are stored unchanged. This is illustrated by the distribution of the tweuter relating to the case of a higher thermal conductivity of the wall material. Heat flow across the wall Q \u003d Δt / r \u003d ΔTc / rc \u003d (tweuter - tvneshn) / (3RC + 6R). The thermal resistance of the boundary layers R and their thickness and do not depend on the thermal conductivity of the material of the walls λc and their thermal resistance RC.

Fig. 37.: a - three layers of metal (or glass), located apart from each other with gaps of 1.5 cm, equivalent to wood (wooden board) with a thickness of 3.6 cm; b - five layers of metal with 1,5 cm gaps, equivalent to wood with a thickness of 7.2 cm; V - three layers of plywood 4 mm thick with gaps of 1.5 cm, equivalent to wood with a thickness of 4.8 cm; r - three layers of polyethylene foam 4 mm thick with gaps of 1.5 cm, equivalent to wood with a thickness of 7.8 cm; D - three layers of metal with 1,5 cm gaps filled with an effective insulation (expanded polystyrene foam, polyethylene foam or mining), equivalent to wood with a thickness of 10.5 cm. The adopted gaps are conditional, equivalent wood thicknesses in the examples of A-G are poorly changed when changing The values \u200b\u200bof the gaps within (1-30) see

If the wall structural material has low thermal conductivity, then when calculating it is necessary to take into account its contribution to the heat resistance of the wall (Fig. 36). Although the contribution of voids is usually significant, the filling of all empties with an effective insulation allows (due to the complete stop of the air movement) significantly (3-10 times) increase the thermal resistance of the wall (Fig. 37).

By itself, the possibility of obtaining quite suitable for baths (at least summer) warm walls of several layers of the "cold" metal, of course, is interesting and used, for example, the Finns for fire protection of walls in the saunas near the furnace. In practice, however, such a solution is very difficult due to the need for mechanical fixation of parallel metal layers by numerous jumpers, which play the role of unwanted "bridges" of cold. One way or another, even one layer of metal or tissue "warms" if the wind is not blocked. On this phenomenon, tents, yurts, plague, which, as you know, are still used (and used in centuries) as a bath in nomadic conditions. So, one layer of tissue (anyway, as if unsuccessful) only twice the "cold" brick wall with a thickness of 6 cm, and heated hundreds of times faster. However, the tent fabric remains much colder air in the tent, which does not allow to realize how much long steam modes. In addition, any (even small) gusts of the fabric immediately lead to powerful convective heat lines.

The greatest value in the bath (as well as in residential buildings) have air interlayers in the windows. At the same time, the resistance of the heat transfer windows is measured and is calculated on the entire area of \u200b\u200bthe window turnout, that is, not only on the glass part, but also on the binding (wooden, steel, aluminum, plastic), which, as a rule, has the best heat insulating characteristics than glass. For orientation, we give the normative values \u200b\u200bof the thermal resistance of the windows of different types to SNIP P-3-79 * and cellular materials, taking into account the thermal resistance of the outer boundary layers inside and outdoors (see Table 8).

Table 8. The reduced resistance of heat transfer windows and window materials