Calculation of the area of ​​air ducts and shaped designs: how to design the structure and calculate the figures

The main parameter that characterizes the effectiveness of ventilation systemIs the air flow. It is defined as the sum of values ​​in some areas with a stable flow duct limited by taps or valves. On each such square section calculation is performed ducts and fittings. When determining the shape of air ducts and their quadrature main parameter is the air flow rate. Her point in the standards and building regulations (the joint venture). For main pipelines it should not exceed 8 m / s for connections - not more than 5 m / s. A place in the room limited by the arrival rate to 3 m / s.

Why do I need the calculation of the area of ​​air ducts and fittings?

Determination of squaring the duct is needed to create a well-functioning ventilation system and the optimization of its characteristics:

• transported air volume;
• velocity air masses;
• noise;
• energy consumption.

In addition, the calculation should provide a list of additional performance. For example, the proper temperature in the premises. I.e ventilation system should remove excess heat and moisture and minimize heat loss. The maximum / minimum temperature and the rate of air arriving in the space provided to the respective standards.

Regulated and qualitative parameters of inlet air, namely: its chemical composition, the amount of suspended particles, the presence and concentration of hazardous elements, etc.

What data are needed to calculate the performance characteristics of the air ducts?

First of all, taken into account the basic parameters of the construction, such as the appointment of the building itself, the volume of space, the number of permanent stay of personnel and visitors, especially the production process (for commercial buildings) and etc.

Design ventilation systems carried out in accordance with the following regulations:

• SP 60.13330.2016 (current edition of SNIP 41-01-2003);
• SP 7.13130.2013;
• GOST 12.1.005-88 and others.

How to calculate the area of ​​various sections of the duct types?

Calculating squaring ducts of different cross-sections has its own characteristics, as the air flow from them will vary significantly even with the same parameters, the speed of movement of air masses and area. In addition, when calculating the ventilation networks a large extent and / or branching Guide humidity and the air temperature (if it exceeds + 20 ° C). Also, the aerodynamic drag of air ducts and fittings, depending on the shape and manufacturing material (different friction coefficients). Inclusion of these parameters is expressed by using a different correction factors calculated in the formulas.

Important information! quadrature channel parameters and the speed of movement of the air flows inversely proportional. That is, when a large cross section of the duct to provide the necessary volume of transported air at sufficient velocity.

Calculating squaring is performed by two parameters taken from the standards (in fact, these parameters describe the ventilation rate):

1. air flow rate - R (m³ / h);
2. air flow rate - V (m / s).

Formula duct area operates the air flow parameters taken from the standards:

S = R / k × V, where

K - the coefficient equal to 3600.

There are alternative formula that operate on other factors, for example:

S = R × 2,778 / V.

When using a large ducts is substantially reduced air flow noise and power consumption for their movement. However, consumption of materials such structures is much higher, which increases their cost.

Significant impact on the efficiency of air flow movement has sectional shape. In rectangular ducts airflow resistance gets larger. However, a rectangular form is more convenient for installation, particularly when space and can be placed very close to the main building structure. Round air ducts are aerodynamically better, but not always fit into the interior. A product with high aesthetic indices have a much greater value. Considering The given facts, as an alternative to recommended pay attention to the oval air ducts, combining ergonomics and efficiency.

How to calculate the area of ​​a circular duct?

To calculate the diameter of the round ventkanala used normative-sectional area:

The actual area is obtained from the formula:

How to calculate the area of ​​rectangular duct?

For rectangular boxes are used the same formula as for round. The length of the sides is calculated as follows:

Dp - diagonal of a rectangle inscribed in a circle (equivalent circle diameter actually);

a, b - side.

The actual area of ​​recognizable formula:

Also to calculate the basic parameters designers use table.

Calculation oval duct area

Oval duct diameters are calculated from its area. We use the following formula:

Diameter:

R - ovaloid perimeter of the circle,

The area of ​​the oval duct calculated by the formula:

a, b - large and small diameter oval, respectively.

Calculating square shaped pieces duct

When creating distributed systems ventilation using different shaped products:

• bends - tees with the same or different cross-section;
• duck - removal s-shaped;
• umbrella;
• adapters:

• between different sections of one form (usually different diameters);
• between different types of sections (for example, from rectangular to circular).

Each of the presented fittings calculated for individual formulas, so that their overall calculation is quite complex. Even experienced designers need engineering assistance in the calculation of the area of ​​the duct. To do this they use special programs.

What programs exist to determine the parameters of duct fittings?

It has developed many programs for the calculation of the area of ​​the duct fittings:

• Vent-Calc v2.0 - a universal means of design and calculation of key parameters ventilation systems. According to the developers, the key parameters for the calculation is the air flow rate and the length of the duct. Having received these data from the operator, the program automatically generates a prototype ventilation network indicating the aerodynamic resistance of each branch is bounded by shaped articles. The sum of these indicators is the basis for the selection of the power venting installation. More recently, this software package has become free;
• MagiCAD - software for the design of all types of utilities. Project files can be imported into the ADT and AutoCAD;
• GIDRV 3.093 - a calculator for calculating the area of ​​the duct and fittings for natural type ventilation taking into account the aspiration of the building;
• Fans 400 - specialized software for calculating the smoke ventilation;
• Ducter 2.5 - a program for calculating the area of ​​the duct fittings.

There are a few more simple programs and macros written based on Microsoft Excel. In general, they perform the calculation of aerodynamics ducts of various cross-sections.

Also on some sites you can find online calculators duct surface area, which offer companies engaged in the provision of services.

Calculator for the required cross-section of the duct

Calculation of the air velocity in the duct

The calculation is based on data on the exchange of air taken from the regulatory documentation. This parameter is expressed as a multiple of - number of times the complete substitution of air in the room for one hour. In this case, the formula for determining the required volume will be:

V = K × W, where

V - volume of incoming air (m³ / h);

K - multiplicity (per hour);

W- the volume of the room.

Thus, obtaining the desired air volume to the room, we determine the rate at which it must act, according to the formula:

S - the speed of movement of the air mass (m / s);

V - volume of used air (m³ / h);

P- pipe section area (cm²).

for household ventilation systems velocity of air flow should not exceed 4.3 m / s. Otherwise it is necessary to increase the area of ​​the duct to prevent the occurrence of noise.

Calculation of duct system resistance

When calculating the total resistance of the ventilation system must be considered as a pressure loss performance on the straights, and in places of greatest resistance.

It is necessary to take into account both the shape and material of manufacture of air ducts. products are the most common of:

• galvanized sheet thickness 0.4-0.6 mm;
• stainless steel - it is quite rare, mainly in the chemical, pharmaceutical and food industries;
• metal and plastic - consist of a layer of foamed polyethylene or polyurethane, sandwiched between two layers of corrugated aluminum. It is lightweight and high sound and thermal insulation properties (thermal conductivity coefficient does not exceed 0.019 W / (m ° K)).
• flexible ducts - have a circular cross section, composed of several layers of aluminum laminated polyester film, on a frame of steel wire. Have limitations on the length of use, as they have a high aerodynamic resistance.

pressure loss on the straight sections

To determine the aerodynamic drag on straight air ducts of different cross sections are used the following formulas:

ΔP = R x L x n, where

ΔP - total pressure loss in the duct;

R - partial loss of friction;

L - the length of the straight portion;

n - refinement coefficient which depends on the roughness of the material.

λ - an indicator for the drag friction;

d - the cross section diameter;

Pf - design pressure in the system.

K - an indicator characterizing the roughness of the material from which is made a duct;

Re- Reynolds number;

v - an air speed in a straight section;

u - kinematic viscosity of the air environment.

Loss of pressure on the local resistance

In the duct system has the greatest resistance to air flow space: turns, bends, tees, space-sectional changes to the adapters. Calculation of aerodynamic losses made separately, as each type of shaped article has individual resistance coefficients.

The formula of the pressure loss in each section taking into account the local resistance coefficient:

where S - velocity, ρ - air density.

Important! Air density is dependent on its temperature. For example, at 20 ° C the density of air will be 1.2 kg / m³. This option is also taken from the tables in the relevant normative sources.

The total pressure loss formula in shaped products:

Σξ - the sum of the parameters of local resistance.

Calculation of materials for ducts and fittings

With an area of ​​straight sections, the number and type of fittings can easily determine the amount of material that will be used in their manufacture. For example, for the manufacture of circular section duct sections 100 mm in diameter and 1 m in length will be necessary to 0.314 m² tin.

This is easily calculated from the formula:

π × D (100 mm = 0.1 m) × L (1 m) = 3,14 × 0,1 × 1 = 0.314 m².

Similarly, the calculated amount of material for straight sections of the rectangular ducts.

To calculate the fittings there is no specific formula. More precisely, they are: for each of the molded products form a separate specific formula. But to carry out their manual calculation is inappropriate. As a rule, the required amount of material calculated empirically after the production of patterns cutting.

Calculating the net heating power

air temperature entering the premises is strictly regulated. For example, for residential constructions minimum value is + 18 ° C. To calculate the power used heating equipment you must know the minimum standards of the temperature value of the climatic zone where the building is located. The difference between these temperatures is the main factor determining the power of the heating device. At the same time, it is not necessary to use the most powerful heater capable of providing heating facilities with minimal external temperature. If ventilation has a capacity control system, at the time of the maximum load on the heater just reduced the intensity of the air supply.

Calculation of the power of the heater is carried out according to the formula:

R - calculated power heating device (heat exchanger or heater) (kW);

Δt - air temperature difference at the inlet to the ventilation system and fed into the room, (° C);

Q - the performance of the ventilation system (m³ / h);

τv- volumetric heat capacity of air depends on the set of values ​​of humidity, temperature and pressure, but is taken as coefficient 0.336 W × (h / m / ° C).

findings

Calculation of square meters of the duct with the use of modern software is not such a difficult process. However, in the regeneration of complex distributed systems experience great importance is the use of different materials and fittings. Also to consider the possibility of heat loss, condensation, isolation from noise and vibration. A number of other factors resulting from the operation.