Calculation of floor heat loss on the ground in ugv. Estimated heat loss of a room according to SNP Calculation of heat loss through an uninsulated floor on the ground

Usually, the heat loss of the floor in comparison with similar indicators of other building envelopes (external walls, window and door openings) is a priori assumed to be insignificant and taken into account in the calculations of heating systems in a simplified form. Such calculations are based on a simplified system of accounting and correction coefficients of heat transfer resistance of various building materials.

If we take into account that the theoretical substantiation and methodology for calculating the heat loss of a ground floor was developed a long time ago (i.e., with a large design margin), we can safely speak about the practical applicability of these empirical approaches in modern conditions. Coefficients of thermal conductivity and heat transfer of various building materials, insulation and floor coverings are well known, and no other physical characteristics are required to calculate the heat loss through the floor. According to their heat engineering characteristics floors are usually divided into insulated and non-insulated, structurally - floors on the ground and logs.

The calculation of heat loss through an uninsulated floor on the ground is based on general formula assessment of heat loss through the building envelope:

where Q- main and additional heat loss, W;

A- total area of the enclosing structure, m2;

tv , tн- temperature inside the room and outside air, оС;

β - the share of additional heat losses in the total;

n- correction factor, the value of which is determined by the location of the enclosing structure;

Ro- resistance to heat transfer, m2 ° С / W.

Note that in the case of a homogeneous single-layer floor overlap, the heat transfer resistance Rо is inversely proportional to the heat transfer coefficient of the non-insulated floor material on the ground.

When calculating heat loss through a non-insulated floor, a simplified approach is used, in which the value (1+ β) n = 1. It is customary to produce heat loss through the floor by zoning the heat transfer area. This is due to the natural heterogeneity of the temperature fields of the soil under the floor.

The heat loss of the non-insulated floor is determined separately for each two-meter zone, the numbering of which starts from the outer wall of the building. In total, it is customary to take into account four such strips with a width of 2 m, considering the temperature of the soil in each zone to be constant. The fourth zone includes the entire surface of the non-insulated floor within the boundaries of the first three strips. Heat transfer resistance is taken: for the 1st zone R1 = 2.1; for the 2nd R2 = 4.3; respectively for the third and fourth R3 = 8.6, R4 = 14.2 m2 * оС / W.

Fig. 1. Zoning of the floor surface on the ground and adjacent recessed walls when calculating heat loss

In the case of recessed rooms with an unpaved base of the floor: the area of the first zone adjacent to the wall surface is taken into account in the calculations twice. This is quite understandable, since the heat losses of the floor are summed up with the heat losses in the adjacent vertical enclosing structures of the building.

The calculation of heat loss through the floor is carried out for each zone separately, and the results obtained are summed up and used for the heat engineering substantiation of the building project. The calculation for the temperature zones of the outer walls of recessed rooms is made according to formulas similar to those given above.

In the calculations of heat loss through an insulated floor (and it is considered as such if its structure contains layers of material with a thermal conductivity of less than 1.2 W / (m ° C)), the value of the heat transfer resistance of an uninsulated floor on the ground increases in each case by the heat transfer resistance of the insulating layer:

Ru.s = δs / λs,

where δу.с- thickness of the insulating layer, m; λw.s- thermal conductivity of the insulating layer material, W / (m ° C).

Gyms, saunas, billiard rooms are often located in basements, not to mention the fact that sanitary standards in many countries allow even bedrooms to be placed in basements. In this regard, the question arises about heat loss through basements.

Basement floors are in conditions where average temperature fluctuations are very small and range from 11 to 9 ° C. Thus, the heat loss through the floor, although not very large, is constant throughout the year. According to computer analysis, heat loss through an uninsulated concrete floor is 1.2 W / m 2.

Heat losses occur along stress lines in the soil to a depth of 10 to 20 m from the ground surface or from the base of the building. A polystyrene insulation device with a thickness of about 25 mm can reduce heat loss by about 5%, which is no more than 1% of the total heat loss in a building.

The device of the same roof insulation can reduce heat loss in winter time by 20% or improve the overall thermal efficiency of the building by 11%. Thus, in order to save energy, roof insulation is significantly more efficient than basement floor insulation.

This position is confirmed by the analysis of the microclimate inside the building in the summer. In the case when Bottom part the foundation walls of the building are not insulated, the incoming air heats the room, however, the thermal inertia of the soil begins to affect the heat loss, creating a stable temperature regime; at the same time, heat loss increases, and the temperature inside basements decreases.

Thus, free heat exchange through the structures contributes to the maintenance of summer indoor temperatures at a comfortable level. Thermal insulation under the floor significantly disrupts the conditions for heat transfer between the concrete floor and the ground.

The device of floor (internal) thermal insulation from an energy point of view leads to unproductive costs, but at the same time it is necessary to take into account the condensation of moisture on cold surfaces and, in addition, the need to create comfortable conditions for humans.

To mitigate the feeling of cold, thermal insulation can be applied by placing it under the floor, which will bring the floor temperature closer to the room temperature and isolate the floor from the underlying layer of earth, which has a relatively low temperature... Although such insulation can increase the temperature of the floor, it does not normally exceed 23 ° C, which is 14 ° C lower than the temperature of the human body.

Therefore, to reduce the sensation of cold from the floor in order to provide the most comfortable conditions, it is best to use carpeting or arrange a wooden floor over a concrete base.

The last aspect to be considered in this energy analysis concerns the heat loss at the junction of the floor with the wall not protected by the backfill. Such a node is found in buildings on a slope.

As the analysis of heat losses shows, significant heat losses are possible in this zone in winter. Therefore, to reduce the influence of weather conditions, it is recommended to insulate the foundation along the outer surface.

Heat loss through the floor located on the ground is calculated by zones according to. For this, the floor surface is divided into 2 m wide strips parallel to the outer walls. The lane closest to outside wall, denote the first zone, the next two stripes - the second and third zones, and the rest of the floor surface - the fourth zone.

When calculating the heat loss of basements, the division into strips-zones in this case is made from the ground level along the surface of the underground part of the walls and further along the floor. In this case, the conditional resistances to heat transfer for zones are taken and calculated in the same way as for an insulated floor in the presence of insulating layers, which in this case are the layers of the wall structure.

The heat transfer coefficient K, W / (m 2 ∙ ° С) for each zone of the insulated floor on the ground is determined by the formula:

where is the heat transfer resistance of the insulated floor on the ground, m 2 ∙ ° С / W, calculated by the formula:

= + Σ, (2.2)

where is the resistance to heat transfer of the non-insulated floor of the i-th zone;

δ j is the thickness of the j-th layer of the insulating structure;

λ j - coefficient of thermal conductivity of the material of which the layer is composed.

For all zones of the non-insulated floor, there is data on the resistance to heat transfer, which are taken by:

2.15 m 2 ∙ ° С / W - for the first zone;

4.3 m 2 ∙ ° С / W - for the second zone;

8.6 m 2 ∙ ° С / W - for the third zone;

14.2 m 2 ∙ ° С / W - for the fourth zone.

In this project, the floors on the ground have 4 layers. The floor structure is shown in Figure 1.2, the wall structure is shown in Figure 1.1.

An example of a heat engineering calculation of floors located on the ground for room 002 ventilation chamber:

1. The division into zones in the ventilation chamber is conventionally shown in Figure 2.3.

Figure 2.3. Division into zones of the ventilation chamber

The figure shows that the second zone includes part of the wall and part of the floor. Therefore, the coefficient of resistance to heat transfer of this zone is calculated twice.

2. Determine the resistance to heat transfer of the insulated floor on the ground, m 2 ∙ ° С / W:

2,15 + = 4.04 m 2 ∙ ° С / W,

4,3 + = 7.1 m 2 ∙ ° С / W,

4,3 + = 7.49 m 2 ∙ ° С / W,

8,6 + = 11.79 m 2 ∙ ° С / W,

14,2 + = 17.39 m 2 ∙ ° С / W.

The methodology for calculating the heat loss of premises and the procedure for its implementation (see SP 50.13330.2012 Thermal protection buildings, paragraph 5).

The house loses heat through the enclosing structures (walls, ceilings, windows, roof, foundation), ventilation and sewerage. The main heat losses go through the enclosing structures - 60–90% of all heat losses.

In any case, accounting for heat loss must be made for all enclosing structures that are present in a heated room.

In this case, it is not necessary to take into account the heat losses that are carried out through the internal structures, if the difference in their temperature with the temperature in neighboring rooms does not exceed 3 degrees Celsius.

Heat loss through enclosing structures

Heat loss premises mainly depend on:
1 Temperature differences in the house and outside (the greater the difference, the higher the losses),
2 Heat-shielding properties of walls, windows, doors, coatings, floors (the so-called enclosing structures of the room).

Fencing structures are generally not homogeneous in structure. And usually they consist of several layers. Example: shell wall = plaster + shell shell + exterior decoration... This structure can also include closed air spaces (example: cavities inside bricks or blocks). The above materials have different thermal characteristics. The main such characteristic for a structure layer is its heat transfer resistance R.

Where q is the amount of heat that is lost square meter enclosing surface (usually measured in W / m2)

ΔT is the difference between the temperature inside the calculated room and outside temperature air (temperature of the coldest five-day period ° C for the climatic region in which the calculated building is located).

Basically, the internal temperature in rooms is taken. Residential premises 22 ° C. Non-residential 18 оС. Water treatment zones 33 ° C.

When it comes to a multi-layer structure, the resistances of the layers of the structure add up.

δ — layer thickness, m;

λ - design factor thermal conductivity of the material of the structure layer, taking into account the operating conditions of the enclosing structures, W / (m2 оС).

Well, we've sorted out the basic data required for the calculation.

So, to calculate heat losses through the enclosing structures, we need:

1. Heat transfer resistance of structures (if the structure is multilayer then Σ R layers)

2. The difference between the temperature in the calculation room and outside (temperature of the coldest five-day period ° C.). ΔT

3. Fencing area F (Separate walls, windows, doors, ceiling, floor)

4. The orientation of the building in relation to the cardinal points is also useful.

The formula for calculating heat loss by a fence looks like this:

Qlim = (ΔT / Rlim) * Flim * n * (1 + ∑b)

Qlim - heat loss through enclosing structures, W

Rlim - resistance to heat transfer, sq.m. ° C / W; (If there are several layers then ∑ Rlim layers)

Fogr - area of the enclosing structure, m;

n is the coefficient of contact of the enclosing structure with the outside air.

Walling	Coefficient n
1. Outer walls and coverings (including ventilated with outside air), attic ceilings (with a roof made of piece materials) and over driveways; ceilings over cold (without enclosing walls) undergrounds in the Northern construction and climatic zone
2. Ceilings over cold basements communicating with the outside air; attic floors (with a roof from roll materials); ceilings over cold (with enclosing walls) underground and cold floors in the Northern construction and climatic zone	0,9
3. Overlapping over unheated basements with skylights in the walls	0,75
4. Ceilings over unheated basements without skylights in the walls, located above ground level	0,6
5. Overlapping over unheated technical undergrounds located below ground level	0,4

Heat losses of each enclosing structure are counted separately. The amount of heat loss through the enclosing structures of the entire room will be the sum of heat losses through each enclosing structure of the room

Calculation of heat loss through floors

Uninsulated floor on the ground

Usually, the heat loss of the floor in comparison with similar indicators of other building envelopes (external walls, window and door openings) is a priori assumed to be insignificant and taken into account in the calculations of heating systems in a simplified form. Such calculations are based on a simplified system of accounting and correction coefficients for heat transfer resistance of various building materials.

If we take into account that the theoretical substantiation and methodology for calculating the heat loss of a ground floor was developed a long time ago (i.e., with a large design margin), we can safely speak of the practical applicability of these empirical approaches in modern conditions. The thermal conductivity and heat transfer coefficients of various building materials, heaters and floor coverings are well known, and other physical characteristics are not required to calculate heat loss through the floor. According to their thermotechnical characteristics, the floors are usually divided into insulated and non-insulated, structurally - floors on the ground and logs.

Calculation of heat loss through an uninsulated floor on the ground is based on the general formula for assessing heat loss through the building envelope:

where Q- main and additional heat loss, W;

A- total area of the enclosing structure, m2;

tv , tн- temperature inside the room and outside air, оС;

β - the share of additional heat losses in the total;

n- correction factor, the value of which is determined by the location of the enclosing structure;

Ro- resistance to heat transfer, m2 ° С / W.

Fig. 1. Zoning of the floor surface on the ground and adjacent recessed walls when calculating heat loss

Ru.s = δs / λs,

where δу.с- thickness of the insulating layer, m; λw.s- thermal conductivity of the insulating layer material, W / (m ° C).

The essence of thermal calculations of premises, to one degree or another, located in the ground, is reduced to determining the influence of atmospheric "cold" on their thermal regime, or rather, to what extent a certain soil insulates a given room from atmospheric temperature effects. Because the thermal insulation properties of the soil depend on too many factors, then the so-called 4-zone technique was adopted. It is based on the simple assumption that the thicker the soil layer, the higher its thermal insulation properties (to a greater extent, the influence of the atmosphere is reduced). The shortest distance (vertically or horizontally) to the atmosphere is divided into 4 zones, 3 of which have a width (if it is a floor along the ground) or a depth (if these are walls along the ground) of 2 meters, and the fourth has these characteristics equal to infinity. Each of the 4 zones is assigned its own permanent heat-insulating properties according to the principle - the farther the zone (the larger it is serial number), the less the influence of the atmosphere. Omitting the formalized approach, we can make a simple conclusion that the farther a point in the room is from the atmosphere (with a multiplicity of 2 m), the more favorable conditions(from the point of view of the influence of the atmosphere) it will be located.

Thus, the counting of conditional zones begins along the wall from the ground level, provided there are walls along the ground. If there are no walls along the ground, then the first zone will be the floor strip closest to the outer wall. Further, zones 2 and 3 are numbered 2 meters wide. The remaining zone is zone 4.

It is important to consider that a zone can start on the wall and end on the floor. In this case, you should be especially careful when making calculations.

If the floor is not insulated, then the values of the heat transfer resistances of the non-insulated floor by zones are:

zone 1 - R n.p. = 2.1 m2 * C / W

zone 2 - R n.p. = 4.3 m2 * C / W

zone 3 - R n.p. = 8.6 m2 * C / W

zone 4 - R n.p. = 14.2 m2 * C / W

To calculate the resistance to heat transfer for insulated floors, you can use the following formula:

- resistance to heat transfer of each zone of the non-insulated floor, m2 * C / W;

- insulation thickness, m;

- coefficient of thermal conductivity of the insulation, W / (m * C);