External entrance doors: wooden, plastic and metal. Heat Transfer Resistance of Exterior Doors and Gates Aluminum Entrance Exterior Doors

The required total heat transfer resistance for external doors (except balcony doors) must be at least 0.6
for the walls of buildings and structures, determined at the estimated winter temperature of the outside air, equal to the average temperature of the coldest five-day period with a probability of 0.92.

We accept the actual total heat transfer resistance of external doors
=
, then the actual heat transfer resistance of external doors is
, (m 2 ·С)/W,

, (18)

where t in, t n, n, Δt n, α in – the same as in equation (1).

The heat transfer coefficient of external doors k dv, W/(m 2 ·С), is calculated using the equation:

Example 6. Thermal engineering calculation of external fences

Initial data.

Residential building, t = 20С .

Values of thermal characteristics and coefficients tхп(0.92) = -29С (Appendix A);

α in = 8.7 W/(m 2 ·С) (Table 8); Δt n = 4С (Table 6).

Calculation procedure.

We determine the actual heat transfer resistance of the outer door
according to equation (18):

(m 2 ·С)/W.

The heat transfer coefficient of the external door k dv is determined by the formula:

W/(m 2 ·С).

2 Calculation of the heat resistance of external fences during the warm period

External fencing is checked for heat resistance in areas with an average monthly air temperature in July of 21°C and above. It has been established that fluctuations in the external air temperature A t n, С, occur cyclically, obey the sinusoidal law (Figure 6) and cause, in turn, fluctuations in the actual temperature on the inner surface of the fence
, which also flow harmoniously according to the law of a sinusoid (Figure 7).

Thermal resistance is the property of a fence to maintain a relative constant temperature on the inner surface τ in, С, with fluctuations in external thermal influences
, С, and provide comfortable conditions in room. As you move away from the outer surface, the amplitude of temperature fluctuations in the thickness of the fence, A τ , С, decreases, mainly in the thickness of the layer closest to the outside air. This layer with a thickness of δ pk, m, is called a layer of sharp temperature fluctuations A τ, С.

Figure 6 – Fluctuations in heat flows and temperatures on the surface of the fence

Figure 7 – Attenuation of temperature fluctuations in the fence

Thermal resistance testing is carried out for horizontal (covering) and vertical (wall) fences. First, the permissible (required) amplitude of temperature fluctuations of the internal surface is established
external fencing taking into account sanitary and hygienic requirements in the expression:

, (19)

where t nl is the average monthly outdoor temperature for July (summer month), С, .

These fluctuations occur due to fluctuations in the design temperatures of the outside air
,С, determined by the formula:

where A t n is the maximum amplitude of daily fluctuations in the outside air for July, С, ;

ρ – solar radiation absorption coefficient by the outer surface material (Table 14);

I max, I av - respectively the maximum and average values of total solar radiation (direct and diffuse), W/m 3, accepted:

a) for external walls - as for vertical surfaces of western orientation;

b) for coatings - as for horizontal surface ;

α n - heat transfer coefficient of the outer surface of the fence under summer conditions, W/(m 2 ·С), equal to

where υ is the maximum of the average wind speeds for July, but not less than 1 m/s.

Table 14 – Solar radiation absorption coefficient ρ

Material of the outer surface of the fence	Absorption coefficient ρ

Protective layer roll roofing light gravel
Red clay brick
Silicate brick
Facing natural stone(white)
Lime plaster, dark gray
Light blue cement plaster
Cement plaster dark green
Cream cement plaster

Magnitude of actual vibrations on the inner plane
,С, will depend on the properties of the material, characterized by the values of D, S, R, Y, α n and contributing to the attenuation of the amplitude of temperature fluctuations in the thickness of the fence A t. Attenuation coefficient determined by the formula:

where D is the thermal inertia of the enclosing structure, determined by the formula ΣD i = ΣR i ·S i ;

e = 2.718 – base of natural logarithm;

S 1 , S 2 , …, S n – calculated coefficients of heat absorption of the material of individual layers of the fence (Appendix A, table A.3) or table 4;

α n – heat transfer coefficient of the outer surface of the fence, W/(m 2 ·С), is determined by formula (21);

Y 1, Y 2,…, Y n is the coefficient of heat absorption of the material on the outer surface of the individual layers of the fence, determined by formulas (23 ÷ 26).

where δi is the thickness of individual layers of the enclosing structure, m;

λ i – thermal conductivity coefficient of individual layers of the enclosing structure, W/(m·С) (Appendix A, Table A.2).

The heat absorption coefficient of the outer surface Y, W/(m 2 ·С), of an individual layer depends on the value of its thermal inertia and is determined in the calculation, starting from the first layer from the inner surface of the room to the outer one.

If the first layer has D i ≥1, then the heat absorption coefficient of the outer surface of the layer Y 1 should be taken

Y 1 = S 1 . (23)

If the first layer has D i< 1, то коэффициент теплоусвоения наружной поверхности слоя следует определить расчетом для всех слоев ограждающей конструкции, начиная с первого слоя:

for the first layer
; (24)

for the second layer
; (25)

for nth layer
, (26)

where R 1 , R 2 ,…, R n – thermal resistance of the 1st, 2nd and nth layers of the fence, (m 2 ·С)/W, determined by the formula
;

α in – heat transfer coefficient of the inner surface of the fence, W/(m 2 ·С) (Table 8);

Based on known values And
determine the actual amplitude of temperature fluctuations of the internal surface of the enclosing structure
,C,

. (27)

The enclosing structure will meet the heat resistance requirements if the condition is met

(28)

In this case, the enclosing structure provides comfortable room conditions, protecting against the effects of external heat fluctuations. If
, then the enclosing structure is not heat-resistant, then it is necessary to use a material with a high heat absorption coefficient S, W/(m 2 ·С) for the outer layers (closer to the outside air).

Example 7. Calculation of the heat resistance of an external fence

Initial data.

Enclosing structure consisting of three layers: plaster made of cement-sand mortar with a volumetric mass γ 1 = 1800 kg/m 3, thickness δ 1 = 0.04 m, λ 1 = 0.76 W/(m·С); insulation layer made of ordinary clay brick γ 2 = 1800 kg/m 3, thickness δ 2 = 0.510 m, λ 2 = 0.76 W/(mС); facing sand-lime brickγ 3 = 1800 kg/m 3, thickness δ 3 = 0.125 m, λ 3 = 0.76 W/(m·С).

Construction area - Penza.

Estimated internal air temperature tв = 18 С .

The humidity level of the room is normal.

Operating condition – A.

Calculated values of thermal characteristics and coefficients in the formulas:

t nl = 19.8С;

R 1 = 0.04/0.76 = 0.05 (m 2 °C)/W;

R 2 = 0.51/0.7 = 0.73 (m 2 °C)/W;

R 3 = 0.125/0.76 = 0.16 (m 2 °C)/W;

S 1 = 9.60 W/(m 2 °C); S 2 = 9.20 W/(m 2 °C);

S 3 = 9.77 W/(m 2 °C); (Appendix A, Table A.2);

V = 3.9 m/s;

A t n = 18.4 С;

I max = 607 W/m 2 , , I av = 174 W/m 2 ;

ρ= 0.6 (Table 14);

D = R i · S i = 0.05·9.6+0.73·9.20+0.16·9.77 = 8.75;

α in = 8.7 W/(m 2 °C) (Table 8),

Calculation procedure.

1. Determine the permissible amplitude of temperature fluctuations of the internal surface
external fencing according to equation (19):

2. Calculate the estimated amplitude of fluctuations in outside air temperature
according to formula (20):

where α n is determined by equation (21):

W/(m 2 ·С).

3. Depending on the thermal inertia of the enclosing structure D i = R i ·S i = 0.05 · 9.6 = 0.48<1, находим коэффициент теплоусвоения наружной поверхности для каждого слоя по формулам (24 – 26):

W/(m 2 °C).

4. We determine the attenuation coefficient of the calculated amplitude of fluctuations of the external air V in the thickness of the fence using formula (22):

5. We calculate the actual amplitude of temperature fluctuations of the internal surface of the enclosing structure
, С.

If the condition, formula (28), is met, the structure meets the requirements of heat resistance.

The difference between the external entrance door to a house (cottage, office, store, industrial building) and the internal entrance door to an apartment (office) is in the operating conditions.

External entrance doors to a building are a barrier between the street and the interior of the house. Such doors are exposed to sunlight, rain, snow and other precipitation, changes in temperature and humidity.

External doors installed at the entrance to the building (at the exit to the street). These can be either access doors at the entrance to an apartment building, or doors to a private single-apartment house or cottage; external doors can also be part of the entrance group to an office building, a store, or an industrial or administrative building. Despite the fact that all these external doors have different requirements, all external entrance doors, along with strength, must have increased weather resistance (resist dampness, solar radiation, temperature changes).

Wooden external entrance doors

Wood is a traditional material used to make doors. Solid wood external entrance doors are used for installation in cottages and private houses. Wooden external doors according to GOST 24698 installed in multi-apartment residential buildings and public buildings. External wooden doors are made single- and double-leaf, with glazed and blind panels or frames. All wooden external entrance doors have increased moisture resistance.

Possessing low thermal conductivity (thermal conductivity coefficient of wood λ = 0.15—0.25 W/m×K depending on the species and humidity), wooden doors provide high reduced heat transfer resistance. A wooden front door does not freeze in winter, is not covered with frost on the inside, and the locks do not freeze (unlike some metal doors). Since metal is a good conductor, it quickly conducts cold from the street into the house, which leads to the formation of frost on the inside of the door and frame and freezing of the locks.

External wooden entrance doors type DN according to GOST 24698 are installed in standard doorways in the external walls of buildings.

Dimensions of standard doorways:

opening width - 910, 1010, 1310, 1510, 1550 1910 or 1950 mm
opening height - 2070 or 2370 mm

Plastic external entrance doors

Plastic (metal-plastic) external entrance doors are made, as a rule, glazed from polyvinyl chloride profiles (PVC profile) for door blocks according to GOST 30673-99. Single- or double-chamber glazing is used. glued double-glazed windows according to GOST 24866 with a heat transfer resistance of at least 0.32 m²×°C/W.

Plastic (metal-plastic) external entrance doors combine an affordable price and high performance characteristics. Having low thermal conductivity (0.2-0.3 W/m×K depending on the brand), polyvinyl chloride (PVC) makes it possible to produce warm plastic doors (according to GOST 30674-99) with a heat transfer resistance of at least 0.35 m²×°C/W (for a single-chamber double-glazed window) and at least 0.49 m²×°C/W (for a double-chamber double-glazed window), while the reduced heat transfer resistance of the opaque part of the filling of door blocks made of plastic sandwiches not lower than 0.8 m²×°C/W.

In a room that is not equipped with a cold vestibule, to eliminate condensation, frost and ice, a door with high heat-insulating properties should be installed. Wooden and plastic doors have the highest thermal insulation rates, so metal-plastic doors are an ideal option for an external entrance door to a single-family residential building or office.

Metal external entrance doors

In the production of metal doors, either extruded profiles from aluminum alloys (aluminum doors) or hot-rolled and cold-rolled sheets and long products in combination with bent steel profiles (steel doors) are used.

A metal exterior door, by definition, will be cold, since steel, and especially aluminum alloys, conduct heat remarkably well (low-carbon steel has a thermal conductivity coefficient λ about 45 W/m×K, aluminum alloys - about 200 W/m×K, that is, steel is approximately 60 times worse in thermal insulation than wood or plastic, and aluminum alloys are about 3 orders of magnitude worse.).

And on a cold surface, by definition, moisture will condense if the air in contact with it has excess humidity for a given temperature (if the temperature of the inner surface of the entrance door drops below the dew point of the indoor air). The use of decorative panels on a metal door without a thermal break will prevent freezing (frost formation), but not the formation of condensation.

The solution to the problem of freezing of metal exterior doors is the use of “warm” profiles with thermal inserts in the production of exterior entrance doors (the use of thermal breaks made from materials with low thermal conductivity) or a device, that is, the installation of another door (vestibule) that cuts off the warm and humid air of the main interior room from the outer entrance door. For external metal doors (facing the street), the equipment of a thermal vestibule is a prerequisite ( clause 1.28 SNiP 2.08.01"Residential buildings").

Aluminum external entrance doors

Aluminum external entrance doors GOST 23747 are made, as a rule, glazed using pressed profiles according to GOST 22233 from aluminum alloys of the aluminum-magnesium-silicon system (Al-Mg-Si) grades 6060 (6063). For glazing, single- or double-chamber glued double-glazed windows are used in accordance with GOST 24866-99 with a heat transfer resistance of at least 0.32 m²×°C/W.

Aluminum alloys do not contain heavy metal impurities, do not emit harmful substances when exposed to ultraviolet rays, and remain operational in any climatic conditions with temperature changes from − 80°C to + 100°C. The durability of aluminum structures is over 80 years (minimum service life).

Aluminum alloys grades 6060 (6063) are characterized by fairly high strength:

calculated resistance to tension, compression and bending R= 100 MPa (1000 kgf/cm²)
temporary resistance σ in= 157 MPa (16 kgf/mm²)
yield strength σ t= 118 MPa (12 kgf/mm²)

Aluminum alloys are better than any other material used in the manufacture of doors in retaining their structural properties under temperature changes. After appropriate surface treatment of aluminum products, they become resistant to corrosion caused by rain, snow, heat and smog of large cities.

Despite the fact that aluminum alloys used in the manufacture of extruded frame profiles and external door leaves have a very high thermal conductivity coefficient λ about 200 W/m×K, which is 3 orders of magnitude higher than that of wood and plastic, due to constructive measures using thermal breaks from materials with low thermal conductivity, it is possible to significantly increase the heat transfer resistance in “warm” aluminum profiles with thermal inserts to 0, 55 m²×°C/W.

Hinged aluminum exterior doors are most often installed in shopping and business centers, shops, banks and other buildings with high traffic, where the main requirement is high reliability of the door structure. In the manufacture of external entrance doors, as a rule, “warm” profiles with thermal inserts are used. But quite often in practice, in order to save money, “cold” aluminum profiles are used in vestibule systems in the presence of a thermal curtain.

Steel entrance external doors

Steel external entrance doors in accordance with GOST 31173 have the greatest strength. They are usually made blind.

Perm production company "GRAN-Stroy" carries out custom manufacturing and installation of external steel metal entrance doors in accordance with GOST 31173. The cost of ordered external steel doors depends on their configuration and finishing class. The minimum price for a steel exterior door is 8,500 rubles.

The external entrance door leaf is made of hot-rolled steel sheet in accordance with GOST 19903 with a thickness of 2 to 3 mm on a frame made of rectangular steel pipe with a cross-section from 40×20 mm to 50×25 mm. The inside is finished with tinted smooth or milled plywood with a thickness of 4 to 12 mm. Door leaf thickness up to 65 mm. Between the steel sheet and the plywood sheet there is insulation, which also performs the function of sound insulation. The doors are equipped with one or two mortise three- or five-point locks with lever and/or cylinder mechanisms of the 3rd or 4th class according to GOST 5089. Two sealing circuits are installed in the vestibule.

The basic regulatory requirements for entrance doors are set out in the following sets of building codes and regulations (SP and SNiP):

SP 1.13130.2009 “Fire protection systems. Evacuation routes and exits”;
SP 50.13330.2012 “Thermal protection of buildings” (updated edition of SNiP 02/23/2003);
SP 54.13330.2011 “Multi-apartment residential buildings” (updated version

Amendments to the Federal Law “On Technical Regulation”, which allowed the sale on the territory of the Russian Federation of products certified for compliance with the norms and requirements of foreign regulations, significantly facilitated the activities of importing companies and retail chains, but not the choice of metal doors by Russians. Even the European EN, international ISO and the German DIN standards most often used in Russia are quite difficult to get acquainted with for free, and the regulations of the USA (ANSI), Japan (JISC) or Israel (SII) and China (GB/T), from where A large share of imported metal doors are supplied to our country - this is simply unrealistic for the vast majority of our compatriots.

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As a result, the risks of buying metal doors that do not meet the operational characteristics of the very concept of a security steel door are very high. Moreover, the advertising labels (“elite”, “prestigious”, “safe”, “armored” metal doors) that are universally “hung” on steel door blocks by selling companies in the vast majority of cases do not correspond to the meaning put into these symbols. Thus, “elite” metal doors with a visually good cladding with wooden overlays can have a honeycomb filling of the leaf with cardboard, which makes them an effective heat exchanger in winter, and the hall or corridor behind the entrance doors can, in terms of temperature, be an internal chamber of the refrigerator. “Armored” metal doors are a sheathing metal sheet 0.6-0.8 mm thick, which can be opened with an ordinary can opener, and “safe” metal door panels with a good set of incredibly expensive locks can be removed from the door frame or together with the frame from the opening using a pry bar and a nail puller or kick it out.

A higher probability of getting an entrance door with good performance properties is to buy metal doors certified to comply with the norms and requirements of Russian standards, but you need to know at least the basic standardized parameters that determine the level of quality and serviceability of a metal door. The basic standard that determines the design and basic operational properties of a metal door in Russia is GOST 31173-2003 “Steel door blocks”, and the level of protection of locking mechanisms is GOST 5089-2003 “Locks and latches for doors. Technical conditions".

Fireproof metal doors in terms of fire resistance, smoke and gas tightness, but not protective properties are regulated by GOST R 53307-2009 “Building structures. Fire doors and gates. Test method for fire resistance", and bulletproof and explosion-proof metal doors - a number of provisions of GOST R 51113-97 "Banking protective equipment. Requirements for burglary resistance and test methods."

The frames of metal door leaves are made from long rolled products in accordance with GOST 1050-88 “Calibrated long rolled products, with special surface finishing from high-quality carbon structural steel”; sheet metal is used for cladding in accordance with GOST 16523-97 “Rolled thin sheets of high-quality and ordinary quality carbon steel of general quality purpose" or GOST 16523-97 "Rolled thick sheets of carbon steel of ordinary quality" (for reinforced or protective metal doors), less often according to GOST 5632-72 "High-alloy steels and corrosion-resistant, heat-resistant and heat-resistant alloys."

Important: “Armored”, “safe” metal doors, like “iron” doors, do not exist by definition. Metal doors for residential premises are not manufactured in burglary resistance classes higher than V (GOST R 51113-97) for technical reasons - increased strength properties entail an increase in the mass of the finished door block to values incompatible with installation in conventional wall openings and operation of doors at manual opening of the canvas. Massive doors with high burglary resistance classes are used in bank vaults and have electromechanical control drives.

GOST 31173-2003 standards, simplified for understanding.

GOST 31173-2003 classifies and normalizes metal doors according to:

resistance to burglary, determined by the class of strength characteristics and the class of protective properties of locking mechanisms - standard metal doors with strength class M3 and III - IV class security properties of locks according to GOST 5089-2003, reinforced metal doors with strength class M2 and III - IV class security properties of locks, security metal doors with strength class M1 and class IV security properties of locks;

Important: Strengthening the protective properties of metal doors (burglary resistance) depends on the strength properties of the door block (with increasing strength characteristics from class M3 to M1, the burglary resistance of a metal door increases). Even standard doors cannot have locks with security properties lower than class III, and the level of security properties increases from class I to class IV. The class of security properties of a lock is determined not by its design or brand, but by the number of secrets that should be for locks with: cylinder mechanism of class III - 10 thousand, class IV - 25 thousand; disk cylinder mechanism of class III - 200 thousand, class IV - 300 thousand; lever mechanism of class III - 50 thousand, class IV - 100 thousand.

mechanical characteristics (strength classes), determined by the magnitude of static loads applied in the plane, in the free angle zone, in the area of the door hinges, as well as dynamic loads applied in the direction of opening the door and shock loads in both directions of opening the door.

Important: Strength class M1 has the best mechanical characteristics, strength class M3 has the worst, but any metal door sold today must have mechanical characteristics not lower than strength class M3;

according to thermal protection properties determined by the reduced heat transfer resistance - class 1 with a reduced heat transfer resistance of at least 1.0 m2 °C/W, class 2 with a reduced heat transfer resistance from 0.70 to 0.99 m2 °C/W, class 3 with a reduced heat transfer resistance of 0.40 -0.69 m2 °C/W.
Important: The best heat-insulating properties have metal doors of class 1, the worst - class 3, but any metal doors cannot have a reduced heat transfer resistance below the threshold value of class 3 - 0.4 m2.°C/W, which corresponds to that used in European regulations acts, the heat transfer coefficient Uwert is no more than 1/0.4 = 2.5 W/(m2K). It must be remembered that for Moscow, from October 1, 2010, according to the standards of the City Program “Energy-saving housing construction in the city of Moscow for 2010-2014. and for the future until 2020" the reduced heat transfer resistance of enclosing structures (windows, balcony and external entrance doors) must be no less than 0.8 m2.°C/W, and according to EnEV2009 standards for external doors the upper threshold value of the heat transfer coefficient is not more than 1.3 W /(m2K). Therefore, in the capital, metal doors entering from the street must be certified for heat-insulating properties of classes 1 or 2;

air and water permeability, determined by indicators of volumetric air tightness and water tightness limit - classes 1-3.

Important: The air and water permeability of a metal door deteriorates from class 1 to class 3, but the air tightness of any metal door for residential premises must be at least class 3 and not more than 27 m3/(h m2);

in terms of sound insulation, determined by the airborne noise insulation index Rw - class 1 with an airborne noise reduction of 32 dB, class 2 with an airborne noise reduction of 26-31 dB, class 3 with an airborne noise reduction of 20-25 dB.

Important: Metal doors of class 1 have the best soundproofing properties, class 3 has the worst, but the airborne noise insulation index is determined in the frequency band from 100 to 3000 Hz, corresponding to spoken language, telephone or alarm clock calls, TV with built-in speakers, radio, and does not characterize the ability a metal door to block the noise of cars, airplanes, etc., as well as structural noise transmitted through the rigidly connected structure of the house/building;

reliability of operation, determined by the number of cycles of opening/closing of the door leaf. This value for internal metal doors must be at least 200 thousand, and for external entrance metal doors at least 500 thousand.

Important: A metal door must be certified for compliance with the norms/requirements of Russian regulations, but with differentiation based on basic operational properties and resistance to burglary. If the manufacturer/selling company claims compliance of a metal door with foreign regulations, then comparative information with similar (or similar) indicators of Russian standards must be provided.

Metal doors deserve greater confidence, for which not only a certificate is provided, but also test reports confirming compliance of operational parameters and resistance to burglary with Russian standards. Ideally, a metal door should have a passport in accordance with the requirements of GOST 31173-2003, which, in addition to manufacturing details and design features, indicates:

mechanical class;
reliability (opening cycles);
breathability at? P0 = 100 Pa (value in m3/(h.m2) or class);
airborne noise insulation index Rw in dB;
reduced heat transfer resistance in m2.°C/W.

Using table A11, we determine the thermal resistance of external and internal doors: R nd = 0.21 (m 2 0 C)/W, therefore we accept double external doors; R ind1 = 0.34 (m 2 0 C)/W, R ind2 = 0.27 (m 2 0 C)/W.

Then, using formula (6), we determine the heat transfer coefficient of external and internal doors:

W/m 2 o C

2 Calculation of heat losses

Heat losses are conventionally divided into basic and additional.

Heat losses through internal enclosing structures between rooms are calculated if the temperature difference on both sides is >3 0 C.

The main heat losses of premises, W, are determined by the formula:

where F is the estimated area of the fence, m2.

Heat losses, according to formula (9), are rounded to 10 W. The temperature t in corner rooms is taken to be 2 0 C higher than the standard one. We calculate heat losses for external walls (NS) and internal walls (WS), partitions (PR), ceilings above the basement (PL), triple windows (TO), double external doors (DD), internal doors (DV), attic floors (PT) ).

When calculating heat losses through the floors above the basement, the temperature of the coldest five-day period with a probability of 0.92 is taken as the outside air temperature tn.

Additional heat losses include heat losses that depend on the orientation of the premises in relation to the cardinal directions, from wind blowing, from the design of external doors, etc.

The addition for the orientation of enclosing structures to the cardinal points is taken in the amount of 10% of the main heat losses if the fence is facing east (E), north (N), northeast (NE) and northwest (NW) and 5% - if west (W) and southeast (SE). Addition for heating the cold air rushing in through the external doors at a building height N, m, we take 0.27 N from the main heat losses outer wall.

Heat consumption for heating the supply ventilation air, W, is determined by the formula:

where L p – supply air flow, m 3 / h, for living rooms we accept 3m 3 / h per 1 m 2 of living space and kitchen area;

 n – density of outside air equal to 1.43 kg/m3;

c – specific heat, equal to 1 kJ/(kg 0 C).

Household heat emissions complement the heat output of heating devices and are calculated using the formula:

, (11)

where F p is the floor area of the heated room, m 2.

The total (total) heat loss of a building Q floor is defined as the sum of heat losses from all rooms, including staircases.

Then we calculate the specific thermal characteristic of the building, W/(m 3 0 C), using the formula:

, (13)

where  is a coefficient taking into account the influence of local climatic conditions (for Belarus
);

V building – volume of the building, taken according to external measurements, m 3.

Room 101 – kitchen; t in =17+2 0 C.

We calculate heat loss through the outer wall with a northwest orientation (C):

external wall area F= 12.3 m2;

temperature difference t= 41 0 C;

coefficient taking into account the position of the outer surface of the enclosing structure in relation to the outside air, n=1;

heat transfer coefficient taking into account window openings k = 1.5 W/(m 2 0 C).

The main heat losses of the premises, W, are determined by formula (9):

Additional heat loss for orientation is 10% of Q main and is equal to:

Heat consumption for heating the supply ventilation air, W, is determined by formula (10):

Household heat emissions were determined using formula (11):

Heat consumption for heating the supply ventilation air Q veins and household heat emissions Q household remain the same.

For triple glazing: F = 1.99 m 2, t = 44 0 C, n = 1, heat transfer coefficient K = 1.82 W/m 2 0 C, it follows that the main heat loss of the window Q main = 175 W, and additional Q ext = 15.9 W. Heat loss of the outer wall (B) Q main = 474.4 W, and additional Q add = 47.7 W. Floor heat loss is: Q pl. =149 W.

We sum up the obtained values of Q i and find the total heat loss for this room: Q = 1710 W. Similarly, we find heat loss for other rooms. The calculation results are entered into Table 2.1.

Table 2.1 - Heat loss calculation sheet

Room number and its purpose

Fence surface

Temperature difference tв – tн

Correction factor n

Heat transfer coefficient k W/m C

Main heat losses Qbas, W

Additional heat loss, W

Heat. to the filter Qven, W

Life heat output Qlife, W

General heat loss Qpot=Qmain+Qext+Qven-Qlife

Designation

Orientation

Size a, m

Size b,m

Area, m2

For orientation

Continuation of Table 2.1

ΣQ FLOOR= 11960

After the calculation, it is necessary to calculate the specific thermal characteristics of the building:

where α-coefficient, taking into account the influence of local climatic conditions (for Belarus - α≈1.06);

V building – volume of the building, taken according to external measurements, m 3

We compare the resulting specific thermal characteristic using the formula:

where H is the height of the building being calculated.

If the calculated value of the thermal characteristic deviates from the standard value by more than 20%, it is necessary to find out the reasons for this deviation.

Because <then we accept that our calculations are correct.

In one of the previous articles, we discussed composite doors and briefly touched upon blocks with thermal breaks. Now we are dedicating a separate publication to them, since these are quite interesting products, one might say - already a separate niche in door construction. Unfortunately, not everything is clear in this segment; there are achievements and there is farce. Now our task is to understand the features of the new technology, to understand where the technological “goodies” end and where the marketing games begin.

To understand how thermally separated doors work, and which of them can be considered as such, you will have to delve into the details and even remember a little school physics.

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This is a natural process of striving for balance. It consists in the exchange/transfer of energy between bodies with different temperatures.
Interestingly, hotter bodies give off energy to colder ones.
Naturally, with such recoil, the warmer parts cool down.
Substances and materials transfer heat with unequal intensity.
The definition of thermal conductivity (denoted c) calculates how much heat will pass through a sample of a given size, at a given temperature, per second. That is, in applied issues, the area and thickness of the part, as well as the characteristics of the substance from which it is made, will be important. Some indicators for clarity:
- aluminum - 202 (W/(m*K))
- steel - 47
- water - 0.6
- mineral wool - 0.35
- air - 0.26

Thermal conductivity in construction and for metal doors in particular

All building envelopes transmit heat. Therefore, in our latitudes, there is always heat loss in the home, and heating is always used to replenish it. Windows and doors installed in openings are disproportionately thinner than walls, which is why there is usually an order of magnitude more heat loss here than through walls. Plus increased thermal conductivity of metals.

What problems look like.

Naturally, the doors that are installed at the entrance to the building suffer the most. But not for everyone, but only if the temperature inside and outside is very different. For example, the common entrance door is always completely cold in winter; there are no particular problems with steel doors for an apartment, because it is warmer in the entrance than outside. But the door blocks of cottages operate at the temperature limit - they need special protection.

Obviously, in order to eliminate or reduce heat transfer, it is necessary to artificially equalize the internal and “outboard” temperatures. In essence, a large air gap is created. Traditionally, there are three paths taken here:

Allow the door to freeze by installing a second door block from the inside. The heating air does not make its way to the front door, and there is no sudden temperature change - no condensation.
They always make the door heated, that is, they build a vestibule outside without heating. It equalizes the temperature on the outer surface of the door, and the heating warms up its inner layers.
Sometimes it helps to organize a thermal air curtain, electric heating of the canvas or a heated floor near the front door.

Of course, the steel door itself must be insulated as much as possible. This applies to both the cavities of the box and the canvas, as well as the slopes. In addition to cavities, claddings work to resist heat transfer (the thicker and “fluffier” the better).

Thermal Break Technology

The eternal dream of the developer is to defeat heat transfer forever and irrevocably. The disadvantages are that the warmest materials are usually the most fragile and weakest, due to the fact that heat transfer resistance is highly dependent on density. To strengthen porous materials (which contain gases), they need to be combined with stronger layers - this is how sandwiches appear.

However, the door block is a self-supporting spatial structure that cannot exist without a frame. And here other unpleasant moments appear, which are called “cold bridges.” This means that no matter how well the steel entrance door is insulated, there are elements that go right through the door. These are: the walls of the box, the perimeter of the canvas, stiffening ribs, locks and hardware - and all this is made of metal.

At one point, manufacturers of aluminum structures found a solution to some pressing issues. They decided to divide one of the most thermally conductive materials (aluminum alloys) with a less thermally conductive material. The multi-chamber profile was “cut” approximately in half and a polymer insert was made there (“thermal bridge”). To ensure that the load-bearing capacity was not particularly affected, a new and rather expensive material was used - polyamide (often in combination with fiberglass).

The main idea of such design solutions is to increase the insulation properties and avoid the creation of additional door blocks and vestibules.

Recently, high-quality entrance doors with thermal break, assembled from imported profiles, have appeared on the market. They are made using similar technology as “warm” aluminum systems. Only the supporting profile is created from rolled steel. Of course, there is no extrusion here - everything is produced on bending equipment. The profile configuration is very complex; special grooves are made to install the thermal bridge. Everything is arranged in such a way that the polyamide part with an H-shaped cross-section fits along the line of the web and connects both halves of the profile. The assembly of products is carried out by pressure (rolling), the connection of metal and polyamide can be glued.

Such profiles are used to assemble the load-bearing frame of the canvas, the posts and lintels of the frame, as well as the threshold. Naturally, there are some differences in the cross-section configuration: the stiffening rib can be a simple square, but to ensure a quarter or overflow of the canvas onto the vestibule it is a little more complicated. The sheathing of the load-bearing frame is carried out according to the traditional scheme, only with sheets of metal on both sides. The peephole is often abandoned.

By the way, there is an interesting system where the canvas on polymer harpoons (with elastic seals) is literally completely assembled from a profile with a thermal break. Its walls are replaced by sheathing sheets.

Naturally, “fun” doors have also appeared on the market, which mercilessly exploit the concept of thermal break. At best, some tuning of an ordinary steel door is done.

First of all, manufacturers remove stiffeners. Immediately, problems arise with the spatial rigidity of the canvas, resistance to deflection, “clumpy” opening of the skin, etc. As a way out, underdeveloped stiffeners are sometimes attached to metal sheathing sheets. Some of them are fixed on the outer sheet, the other part - on the inner one. In order to somehow stabilize the structure, the cavity is filled with foam, which simultaneously performs a form-building function and glues both sheets together. There are models where a metal mesh/grid is inserted into the foam so that an attacker cannot cut a through hole in the canvas.
The extreme end faces of the door leaf and frame may even have small dividing inserts, albeit with unknown characteristics. In general, the whole structure is not much different from ordinary Chinese doors. We just have a thin shell, only filled with foam.

Another trick is to take an ordinary door with ribs (given the cunning approach to the matter - usually low-grade) and insert cotton wool into the door leaf and, in addition, a layer of, for example, polystyrene foam. After this, the product is given the title of “thermal break sandwich” and is quickly sold as an innovative model. According to this principle, all steel door blocks can be written into this category, because insulation and decorative finishing significantly reduce heat loss.