According to the principle and effect of the curtain, there can be gate and mixing types. In the first case, the curtain maximally or completely prevents (blocks) air access to the enclosed space; the air velocity from the installation to create such curtains should be high (up to 25 m/s). Such curtains are arranged at low outdoor temperature and frequent opening of doors. In mixing type installations, the rushing cold air is mixed with the heated air of the heat curtain. As a result, warm air enters the room through the door and the curtain, which does not create a feeling of cold blowing.

1. What is the reason for the location of outdoor air intake devices in ventilation systems?

2. Name the main types of fans by type and design.

3. What is the reason for the mandatory installation of the filter in front of the heat exchange equipment (heaters and coolers)?

4. Give an example in which cases it is advantageous to use electric air heaters.

5. What are the advantages of using water heaters?

6. Why the range of air velocity in heat exchange equipment is strictly limited?

7. What is the fundamental difference between water (water-glycol) and freon air coolers?

8. What measures are envisaged to reduce noise in ventilation systems?

9. Which device is used to prevent air flow when the fan is turned off?

10. In which places of the building are provided air heat curtains with heated air?

According to the type of section, the ducts are divided into round, square or rectangular. Circular air ducts are much stronger than rectangular ones, and their manufacture is less laborious.

However, circular air ducts often do not fit into the interior of public and civil buildings. In addition, in a confined space (under false ceilings, etc.), as a rule, only rectangular air ducts can be used.

According to the manufacturing method, the air ducts can be folded or welded. (Fig. 16.).

The first ones are connected with seam seams. The thickness of the metal for such ducts should not exceed 2.0 mm (if aluminum is used) and 1.0 mm (if corrosion-resistant steel is used).

The welded air ducts are connected by an overlap weld. The thickness of the metal with this type of connection is allowed in the range of 1.2 -3.0 mm.

Fig.16. Types of seam and welded joints of metal ducts:

1 – on a simple recumbent seam; 2 – on a double–cut seam; 3 – on an angular seam; 4 – on a transverse seam; 5 – on a seam with a latch; 6 – with a connecting bar; 7 – on zigs; 8 – butt; 9 – butt–to–butt with flanging; 10 – lap; 11 – corner

This type of duct is classified as dense.

All the various ventilation systems are assembled from only four standard parts.

The first is pipes with a length of 2000 mm or 2500 mm, depending on the metal used.

The second is from water, usually consisting of two or three segments and two glasses with an average radius of curvature equal to the diameter (Fig.17). They are used for general exchange ventilation systems.

Fig. 17. Outlet for air ducts

The third is rectangular bends, which are characterized by only two neck radii: 150 mm (for bends with a side less than 1000 mm) and 300 mm (with a larger size).

The fourth is the tees (branch nodes) of circular cross section. They exist in 3 versions:

– normalized, they are characterized by low coefficients of local resistance, but are laborious to manufacture;

– direct embedding;

– rectangular tees, they are usually equipped with one-sided unified transitions, which allows you to establish a constant ratio of the duct route from the wall along which it is laid.