3. CALCULATION OF HEATING DEVICES AND EQUIPMENT 3.1. The choice of type and calculation of heating devices

The choice of the type of heating devices is made simultaneously with the choice of the heating system in accordance with the requirements of the standards [2, adj. 11] and references [4, ch. eight]. The higher the requirements for the microclimate of the premises, the higher the requirements for the choice of heaters. Schemes, characteristics and applications of various devices are given in [4-6].

Residential buildings may use radiators, panels and convectors, as well as heating elements embedded in walls, floors and floors. Heating devices give off heat energy to the room by convection and heat radiation (radiation). In premises with increased requirements for the microclimate, devices should be provided in which heat emission prevails by radiation — there is one or several flat surfaces facing the room. These properties have built-in wall heating panels, steel, modern aluminum radiators. In rooms with reduced requirements for the comfort of the air environment (corridors, staircases, etc.), appliances that give off heat mainly by convection can be used — ribbed convectors, finned tubes, cast iron radiators.

Pig-iron radiators (Fig. 3.1) are assembled from separate sections using ductile iron nipples, which have an external right-hand side on one side and a left-hand thread on the other side. When rotating the nipple, it is screwed simultaneously into two connected sections, bringing them together. For sealing joints, gaskets made of pro-corrugated cardboard are used.

Steel radiators (Fig. 3.2) consist of two stamped steel sheets interconnected by resistance welding and forming a series of parallel channels or one serpentine channel for the passage of coolant. Such heating devices, compared to cast iron ones, have about half the weight, they are cheaper, they require less installation costs. However, due to the corrosive ability of steel, special treatment of water used as a coolant is required, which significantly limits the scope of application of steel radiators.

In recent years, the use of cast aluminum radiators (Fig. 3.3), having smaller dimensions (depth 70–80 mm versus 140 mm in cast iron radiators) and a more attractive design, has expanded. These radiators have a relatively large flat surface facing the room, which increases the heat transfer by radiation. In addition, narrow vertical channels are arranged in the sections, in which the natural draft of the heated air occurs, the air velocity and heat transfer by convection increase.

The calculation of heating devices consists in determining the surface area Fр and the number of elements of heating devices. In real projects all heating devices of the system are calculated, in the course project, devices should be calculated on the riser included in the calculated large ring.

In the calculation process, the calculated density of the heat flow of the heating device qpr , W / m2, is determined first

, (3.1)

where qnom is the nominal density of the heat flux under standard operating conditions, W / m2, is adopted popril. 9; Dtср - the difference between the average temperature of the coolant in the device and the air temperature in the room, ° C; n, p, spr - coefficients depending on the type of device, given in ADJ. 9; Gpr - the flow of water passing through the device, kg / h .

The parameters in the expression (3.1) are determined by the formulas:

· For two-pipe system

Gpr = 3.6 ; (3.2)

· For one pipe system

Gpr = a Gст, (3.3)

where Qpr - thermal load of the device, W; c, tg, tо - see the explication to formulas (2.8), (2.12); a is the coefficient of water flowing into the device, depending on the ratio of the diameters in the device node and determined by adj. eight;
Gst - water flow according to the riser according to the hydraulic calculation, kg / h;

Δtcp = 0.5 (tin + tout) - tin, (3.4)

where tвx, tвых, tвн - respectively the temperature of the coolant at the inlet and outlet of the heater, the air temperature in the room, ° C:

· For two-pipe systems, tвx = tg, tvyh = tо;

· For monotube tbx, is defined as ti for the water supply section of the device from the expression (2.8), and tout is defined as

tvyh = tvkh - 3,6 . (3.5)

The calculated area Fр, m2, heating device is defined as

Fp = . (3.6)

When using cast iron radiators determine the estimated number of sections

Np = , (3.7)

where b4 - coefficient taking into account the method of installation of the radiator in the room; b3 - coefficient taking into account the number of sections in one radiator; f is the heating surface area of ​​one section, m2.

The coefficients b are given in ADJ. 6, and the area f - in app. 9.

When calculating steel radiators or convectors, according to the calculated area Fp, the number of heaters placed in the room is found,

. (3.8)

When using imported aluminum radiators due to the lack of empirically determined coefficients for the calculation according to the method adopted in Russia, it is permissible to use the manufacturer’s method. Thus, the manufacturer of radiators Calidor SUPER gives the calculated heat output of one section with overall dimensions of 577 × 97 × 80 mm under standard operating conditions (coolant flow through the device is 0.1 l / s, the difference between the average coolant temperature in the device and the air temperature is 70 ° С, supply heat carrier in the device from top to bottom) qc = 199 W, the correction factor for the difference in temperature difference kt is assigned according to the table. 3.1. Mismatch of other working conditions with standard conditions is not taken into account.

Table 3.1

Correction table kt

The estimated number of sections is determined by the formula

N = . (3.9)

The calculation begins with the determination of Gpr by the formula (3.3).

Gpr = 0.43 · 191 = 82.13 kg / h.

The Gst value for riser 1 was previously determined as a result of the hydraulic calculation of the heating system, Gst = 191 kg / h. Wicking coefficient is determined by ADJ. 8, α = 0.43.

The water temperature at the inlet to the first heating device corresponds to tg, t1in = 105 ° C. The water temperature at the inlet to the sixth heater is determined in Example 2:
t6in = 75.7 ° C, Qst = 7300 W.

By the formula (3.5) is determined by the temperature of water from the devices:

= 105 - = 86.74 ° C;

= 75.7 - = 61.1 ° C.

By the formula (3.4) is calculated the average temperature of the devices and the temperature difference between the device and the indoor air:

t1cр = 0.5 · (105 + 86.74) - 20 = 75.9 ° С;

t6ср = 0.5 · (75.7 + 61.1) - 20 = 48.4 ° С.

The calculated density of the heat flux is calculated by the formula (3.1). The required values ​​for the corresponding type of heater are written out from ADJ. 9. In the example, these are sectional radiators MS-140-108:

W / m2;

W / m2.

The calculated areas of heating devices are determined by the formula (3.6). The coefficients of the operating conditions of the device are taken from ADJ. 6:

m2;

m2

The number of sections in the devices is determined by the formula (3.7) (coefficient accepted as 6; coefficient - up to 9; coefficient previously taken to be equal to one):

.

.

All data are summarized in table. 3.2.

Table 3.2

Calculation of heating devices