Estimated outdoor air temperature of cities. Construction heat engineering
Lab #1
Exercise: choose the thickness of the insulating layer for the attic floor from piece materials, in a residential building in Starodub. Panel construction: internal bearing layer - reinforced concrete, 120 mm, insulating layer - claydite gravel with a density g 0=600 kg/m 3, screed - from cement-lime mortar, 40 mm. The maximum thickness of a heater - 300 mm.
We determine the required reduced resistance to heat transfer OK from the conditions of energy saving:
According to SNiP 2.01.01-82 "Construction climatology and geophysics", we determine for the city of Starodub:
In accordance with the chapter of SNiP "Residential buildings", we accept the design temperature of the internal air as 18 ° С, because
According to the table 1, applying interpolation, we determine the value:
for attic floors, residential buildings at GSOP=4000 °C×day, m2×°C/W, and at GSOP=6000°C×day, m2×°C/W. The geometric interpretation of linear interpolation is shown in the figure. The value corresponding to GSOP=4121°C×day, we calculate:
We determine the required resistance to heat transfer from sanitary and hygienic and comfortable conditions:
According to the table 2 coefficient n, taking into account the position of the OK in relation to the outside air, is equal to 1.
According to the table 3 normative temperature difference between the temperature of the internal air and the inner surface of the OK coatings and attic floors Dtн=3 °С.
According to the table 4 heat transfer coefficient inner surface OK av=8.7 W/m2×°С.
According to the application map, 1 humidity zone is normal. The humidity regime of the premises is normal (in accordance with the chapter of SNiP "Residential buildings" and Table 6). According to the table 7 operating conditions OK - B.
According to Appendix 2, we accept the calculated coefficients of thermal conductivity of the materials used in the construction:
reinforced concrete 2500 kg/m3 - l1=2.04 W/m×°С;
expanded clay gravel (GOST 9759-83) 600 kg/m3 - l2=0.20 W/m×°C;
cement-lime mortar - l3=0.81 W/m×°С.
In the main condition of the heat engineering calculation, we equate the right and left parts, substitute the expression for Ro and open it for the case of a three-layer OK:
We express the thickness of the insulating layer from the last equation and calculate it:
Conclusion: the thickness of the insulation layer of 0.6967 m is unrealistic for this design, since the total thickness of the attic floor will be 0.12 + 0.6967 + 0.04 = 0.857 m, and the weight of the panel size 3 ´ 3 m will be at least (0.12 ´ 2500+0,697´ 600+0,04´ 1600)´ 3´ 3=7040 kg (2500 and 1600 kg/m 3- density, respectively, of reinforced concrete and cement-lime mortar in a dry state). Thus, the use of expanded clay gravel with a density of 600 kg / m 3impossible under the given operating conditions.
Let us determine the required coefficient of thermal conductivity of the insulating layer at a maximum thickness of 300 mm. The thickness of the insulating layer in this case can be d 2=0.46-0.12-0.04=0.3 m.
To do this, we express from general condition thermotechnical calculation is not the thickness, but the thermal conductivity of the insulating layer:
According to Appendix 2, we determine that expanded clay gravel used in the production of two-layer panels has a close coefficient of thermal conductivity Expanded vermiculite (GOST 12865-67) 100 kg/m3 (l=0.08 W/m×°C).
Conclusion: we accept the following design of the attic floor for operation in a residential building in Starodub: the bearing layer is reinforced concrete, 120 mm, the insulating layer is expanded clay gravel with a density of 100 kg / m3, 300 mm, the screed is cement-lime mortar, 40 mm.
Reduced resistance to heat transfer wall panel of this design is
which is greater than the required resistance to heat transfer.
Lab #2
Determining the possibility of condensation on the inner surface of the OK
Exercise: for the enclosing structure designed in example 1, check the possibility of condensation on its inner surface for two cases:
- The design does not contain heat-conducting inclusions.
- The design has a reinforced concrete heat-conducting inclusion of type IV with dimensions a=85 mm, c=250 mm.
Initial data for calculation:
outdoor air temperature t n= -31 ° FROM;
temperature according to August psychrometer:
dry bulb temperature (indoor air temperature) tw =21 ° FROM;
wet bulb t ow=19 ° FROM.
We determine the temperature of the inner surface of the OK for the design without heat-conducting inclusions. The total reduced resistance to heat transfer OK has already been determined in example 1: R about =4.02 m 2×° C/W. The values of the coefficients n and a in also coincide with those adopted in Example 1. By formula (11), we have
We determine the temperature of the inner surface of the OK in the region of the heat-conducting inclusion according to the formula (12).
The resistance of the OC to heat transfer outside the heat-conducting inclusion coincides with the total reduced resistance of the OC to heat transfer Ro:
The resistance of the OC to heat transfer in the region of the heat-conducting inclusion is determined by the formula (4) as for a thermally homogeneous multi-layer (three-layer) fence, taking into account (5), (6):
M2×°C/W.
To determine the coefficient h, we calculate and. According to the table 9, interpolating, we determine h=0.39.
According to formula (12), we determine the temperature of the inner surface of the OK in the area of the heat-conducting inclusion
Determine the dew point temperature
According to the psychrometer data (tdry=td=21°С, tdry=19°С, Dt=tdry-tvl=2°С), we determine relative humidity air using the table. eleven:
j=81%.
According to the temperature of the internal air t in =21 ° C, using the table. 12, we determine the maximum elasticity of water vapor:
E=18.65 mm. rt. Art.
According to formula (14), we determine the actual elasticity of water vapor:
mm. rt. Art.
Using table. 12 “in reverse order”, we determine: at what temperature the given value of the actual elasticity will become maximum. As follows from the table, the value is 15.09 mm. rt. Art. corresponds to a temperature of 17.6 °C. It is the dew point temperature.
tp=17.6 °С. insulation ceiling condensate wall
a) Since the temperature of the dew point is lower than the temperature of the inner surface of the OK outside the heat-conducting inclusion (tp = 17.6< tв=19,51 °С), в этих местах образования конденсата при данных температурно-влажностных условиях не ожидается.
b) At the same time, in the region of the heat-conducting inclusion, the temperature of the inner surface of the OC is lower than the dew point temperature (tw=19.87 > tp=17.6 °C). Thus, in the region of the heat-conducting inclusion on the inner surface of the OC, the formation of condensate is impossible.
Lab #3
Exercise : choose a heater for the outer wall of a residential building in Tula. The wall is made in the form of lightweight (well) masonry 2 bricks thick with an insulating layer.
The outer and inner layers of masonry are ½ brick thick. The dressing between the outer and inner layers is carried out through 6 bricks (between the faces of the walls of the wells). Ordinary clay brick on cement-sand mortar. Approximately take slag-pumice concrete with a density of 1200 kg / m as a heater 3. Ignore finishing layers.
We determine the required reduced resistance of the OC to heat transfer, as shown in the example of calculating a homogeneous OC.
We determine the required reduced resistance to heat transfer OK from the conditions of energy saving:
According to SNiP 2.01.01-82 "Construction climatology and geophysics", we determine for the city of Tula:
In accordance with the chapter of SNiP "Residential buildings", the design temperature of the internal air is assumed to be 18 °C.
We calculate the degree-day of the heating period:
According to the table 1, using interpolation, we determine the value: for the walls of residential buildings at GSOP=4000 °C×day, m2×°C/W, and at GSOP=6000°C×day, m2×°C/W. The geometric interpretation of linear interpolation is shown in the figure. The value corresponding to GSOP=4513°C×day, we calculate:
In the further calculation, we enter the value obtained from the energy saving condition as the maximum.
Operating conditions OK (as in the same example) B.
According to Appendix 2, we accept the calculated coefficients of thermal conductivity of the materials used in the construction:
Ordinary clay brick on cement-sand mortar - lbrick = 0.81 W / m × ° С; slag-pumice concrete with a density of 1200 kg/m3 - lheat = 0.47 W/m×°C;
For calculation, we accept a part of the structure that contains the wall of the "well" and half of the "well" on each side. The structure is uniform in height, so the calculation is carried out for a section with a height of 1 m.
By planes parallel to the direction of the heat flow, we cut the structure into 3 thermally homogeneous sections, of which 1 thand 3 thare multilayered (and identical in this case), and 2 th- single layer.
We determine the thermal resistance of the sections: for a single-layer section 2 according to the formula (6):
for identical three-layer sections 1 and 3 according to the formula (5)
We determine the thermal resistance OK Ra according to the formula (8). Since the calculation is carried out for a structure section with a height of 1 m, the areas of the sections are numerically equal to their length.
= m2 ×° C/W.
By planes perpendicular to the direction of the heat flow, we cut the structure into 3 single-layer sections (we will conditionally designate them as 4 th, 5thand 6 th), of which 4 thand 6 thare thermally homogeneous (and identical in this case), and 5 th- heterogeneous.
We calculate the thermal resistance of each section:
for thermally homogeneous sections according to the formula (6):
for a non-homogeneous section, the procedure applied in paragraph 4 should be used:
Considering only this section, by planes parallel to the direction of the heat flow, we cut it into three homogeneous single-layer sections (5-1, 5-2 and 5-3, sections 5-1 and 5-3 are the same).
We determine the thermal resistance of each section according to the formula (6):
We determine the thermal resistance of the 5th section according to the formula (8):
We determine the thermal resistance of OK Rb as the sum of the resistances of individual sections:
Let us evaluate the applicability of this technique in our case.
which is less than the allowed 25%. In addition, the wall structure is flat. Thus, the calculation method is applicable in this case.
Calculate the reduced thermal resistance OK by the formula (9):
We calculate the total resistance of the OC to heat transfer according to the formula (7):
Conclusion: the use of expanded clay gravel with a density of 800 kg / m3 in this design as a heater does not provide heat transfer resistance sufficient for a residential building in Moscow:
It is required to use more thermally efficient materials, or to increase the thickness of the masonry, or to increase the distance between the walls of the "wells".
Literature
- SNiP II-3-79**. Construction heat engineering / Gosstroy of the USSR. - CITP Gosstroy USSR, 1986. - 32 p.
- SNiP 2.01.01-82. Building climatology and geophysics / Gosstroy of the USSR. - M.: Stroyizdat, 1983. - 136 p.
BUILDING REGULATIONS
Construction heat engineering engineering heat technology Introduction date - 03/01/2003
FOREWORD
1. DEVELOPED: NIISF Gosstroy of the USSR with the participation of NIIES and TsNIIpromzdaniy Gosstroy of the USSR, TsNIIEP housing of Gosgrazhdanstroy, TsNIIEPselstroy of the USSR, MISI them. V. V. Kuibyshev of the Ministry of Higher Education of the USSR, All-Russian Central Scientific Research Institute of Education, All-Union Central Council of Trade Unions, Research Institute of General and Communal Hygiene. A. N. Sysin of the Academy of Medical Sciences of the USSR, Research Institute of Mosstroy and MNIITEP of the Moscow City Executive Committee.
2. PREPARED: Design Academy "KAZGOR" in connection with the revision of state standards in the field of architecture, urban planning and construction and translation into the state language.
3. PRESENTED BY: Department of technical regulation and new technologies in construction of the Committee for Construction Affairs of the Ministry of Industry and Trade of the Republic of Kazakhstan (MIIT RK).
5. These SNiP RK represent the authentic text of SNiP II-3-79* "Construction Heat Engineering" in Russian, extended validity on the territory of the Republic of Kazakhstan from 01/01/1992 by letter of the State Arkhstroy of the Republic of Kazakhstan dated 01/06/1992 No. AK-6-20- 19 and recommended for use with * letter of the Ministry of Construction of the Republic of Kazakhstan dated 03.03.97 No. AK-12-1-9-318 and translation into the state language.
6. IN PLACE: SNiP II-3-79*.
1. General Provisions
2. Resistance to heat transfer of enclosing structures
3. Heat resistance of enclosing structures
4. Heat absorption of the floor surface
5. Resistance to air permeation of building envelopes
6. Resistance to vapor permeability of enclosing structures
Attachment 1*. Humidity zones of the territory of Kazakhstan and the CIS
Annex 2. Operating conditions of enclosing structures, depending
from the humidity regime of rooms and humidity zones
Application 3*. Thermal performance of building materials and structures
Annex 4. Technical resistance of closed air gaps
Application 5*. Schemes of heat-conducting inclusions in enclosing structures
Application 6*. Reference. Reduced resistance to heat transfer of windows,
balcony doors and skylights
Appendix 7. Coefficients of absorption of solar radiation by outdoor material
Enclosing surfaces
Annex 8. Heat transmission coefficients of sun protection devices
Application 9*. Air permeability of materials and structures
Application10*. Ruled out
Annex 11*. Resistance to vapor permeability of sheet materials
and thin layers of vapor barrier
Application 12*. Ruled out
Application 13*. Reference. Thermal homogeneity coefficient r
panel walls
1. General Provisions
1.1. These norms of building heat engineering must be observed when designing enclosing structures (external and internal walls, partitions, coatings, attic and interfloor ceilings, floors, filling openings: windows, lanterns, doors, gates) of new and reconstructed buildings and structures for various purposes (residential, public 1 , production and auxiliary industrial enterprises, agricultural and warehouse 2) with normalized temperature or temperature and relative humidity of indoor air.
1.2. In order to reduce heat losses in winter and heat gains in summer, the design of buildings and structures should include:
a) space-planning solutions, taking into account the provision of the smallest area of enclosing structures;
b) sun protection of light openings in accordance with the standard value of the heat transmission coefficient of sun protection devices;
c) the area of light openings in accordance with the normalized value of the coefficient of natural illumination;
d) rational use of effective heat-insulating materials;
e) sealing of porches and folds in the fillings of openings and interfaces of elements (seams) in external walls and coatings.
1.3. The humidity regime of the premises of buildings and structures in the winter, depending on the relative humidity and temperature of the indoor air, should be set according to Table. one.
Table 1
1 The nomenclature of public buildings in this chapter of SNiP was adopted in accordance with appendix. 1* to SNiP RK 3.02-02-2001.
2 Further in the text, for brevity, buildings and structures: warehouse, agricultural and industrial industrial enterprises, when the norms apply to all these buildings and structures, are combined by the term "production".
Humidity zones of the territory of Kazakhstan and the CIS should be taken according to adj. one*.
The operating conditions of enclosing structures, depending on the humidity regime of the premises and the humidity zones of the construction area, should be established according to adj. 2.
1.4. Waterproofing of walls from moistening with ground moisture should be provided (taking into account the material and construction of the walls):
horizontal - in the walls (external, internal and partitions) above the blind area of a building or structure, as well as below the floor level of the basement or basement floor;
vertical - the underground part of the walls, taking into account hydrogeological conditions and the purpose of the premises.
1.5*. When designing buildings and structures, it is necessary to provide for the protection of the inner and outer surfaces of the walls from the effects of moisture (industrial and domestic) and atmospheric precipitation (by lining or plastering, painting with waterproof compositions, etc.), taking into account the material of the walls, their operating conditions and the requirements of regulatory documents on design of certain types of buildings, structures and building structures.
In multilayer external walls of industrial buildings with a damp or wet regime of premises, it is allowed to provide for the installation of ventilated air layers, and in case of direct periodic moistening of the walls of the premises, a ventilated layer with protection of the inner surface from moisture.
1.6. In the outer walls of buildings and structures with a dry or normal regime of premises, it is allowed to provide non-ventilated (closed) air gaps and channels with a height not exceeding the floor height and not more than 6 m.
1.7. Floors on the ground in rooms with normalized indoor air temperature, located above the blind area of the building or below it by no more than 0.5 m, must be insulated in the area where the floor adjoins the outer walls 0.8 m wide by laying a layer of inorganic moisture-resistant insulation on the ground thickness, determined from the condition of ensuring the thermal resistance of this layer of insulation is not less than the thermal resistance of the outer wall.
AT Construction heat engineering data from related scientific fields are used (theories of heat and mass transfer, physical chemistry, thermodynamics of irreversible processes, etc.), methods modeling and similarity theory (in particular, for engineering calculations of the transfer of heat and matter), which ensure the achievement of a practical effect under various external conditions and various ratios of surfaces and volumes in buildings. Great importance in Construction heat engineering have full-scale and laboratory studies of temperature and humidity fields in enclosing structures buildings, as well as the determination of thermophysical characteristics building materials and designs.
Methods and conclusions Construction heat engineering are used in the design of enclosing structures that are designed to create the necessary temperature and humidity and sanitary conditions (taking into account the operation of heating, ventilation and air conditioning systems) in residential, public and industrial buildings. Meaning Construction heat engineering especially increased due to industrialization of construction, a significant increase in the use (in various climatic conditions) of lightweight structures and new building materials.
The task of providing the necessary thermal properties of external enclosing structures is solved by giving them the required heat resistance and resistance to heat transfer. Permissible permeability of structures is limited by the given resistance to air penetration. The normal moisture state of structures is achieved by reducing the initial moisture content of the material and the device moisture insulation, and in layered structures, in addition, by the appropriate arrangement of structural layers made of materials with different properties.
The resistance to heat transfer must be high enough to ensure hygienically acceptable temperature conditions on the surface of the structure facing the room during the coldest period of the year. The heat resistance of structures is assessed by their ability to maintain a relatively constant temperature in the premises with periodic fluctuations in the temperature of the air adjacent to the structures and the flow of heat passing through them. The degree of thermal stability of the structure as a whole is largely determined by physical properties the material from which the outer layer of the structure is made, perceiving sharp temperature fluctuations. When calculating the thermal stability, methods are used Construction heat engineering, based on the solution of differential equations for periodically changing heat transfer conditions. Violation of the one-dimensionality of heat transfer inside the enclosing structures in places of heat-conducting inclusions, in panel joints and wall corners causes an undesirable decrease in temperature on the surfaces of structures facing the room, which requires a corresponding increase in their heat-shielding properties. The calculation methods in these cases are associated with the numerical solution of the differential equation of the two-dimensional temperature field ( Laplace equations ).
The distribution of temperatures in the enclosing structures of buildings also changes when cold air penetrates into the structures. Air filtration occurs mainly through windows, structural joints and other leaks, but to some extent through the thickness of the fences themselves. Appropriate methods for calculating changes in the temperature field under steady air filtration have been developed. The resistance to air penetration of all elements of the fences must be greater than the standard values established Building codes and regulations.
When studying the moisture state of enclosing structures in Construction heat engineering the processes of moisture transfer occurring under the influence of the transfer potential difference are considered. The transfer of moisture within the hygroscopic moisture content of materials occurs mainly due to diffusion in the vapor phase and in the adsorbed state; in this case, the partial pressure of water vapor in the air filling the pores of the material is taken as the transfer potential. In the USSR, a graphic-analytical method for calculating the probability and amount of moisture condensing inside structures during the diffusion of water vapor under steady-state conditions has become widespread. A more accurate solution for non-stationary conditions can be obtained by solving differential equations for moisture transfer, in particular, using various devices computer technology, including those using methods of physical analogy (hydraulic integrators).
Lit.: Lykov A.V., Theoretical basis building thermal physics, Minsk, 1961; Bogoslovsky V.N., Building thermal physics, M., 1970; Fokin K. F., Construction heat engineering of enclosing parts of buildings, 4th ed., M., 1973; Ilyinsky V. M., Construction thermal physics, M., 1974.
V. M. Ilyinsky.
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