Heater (water heater or electric heating elements).

Soft insert made of rubberized fabric with flanges on both sides. The flanges are made of a galvanized tire connected by corners.

Quick-release air filter.

Insulated air valve with electric drive.

To create a balance of the incoming and outgoing air from the room, exhaust ventilation is used, which can be represented by:

• autonomous axial fans installed directly in the wall;

• roof fans installed on the roof;

• centrifugal fans mounted on brackets in the wall or on metal roof structures;

• duct fans in a shell-shaped housing or in a box-shaped housing installed in a network of air ducts (have a nozzle at the inlet and a diffuser at the outlet, and in the case of installing a two-way suction fan – two at the inlet and one at the outlet).

• exhaust ventilation units equipped with fans, flexible inserts, control valves and assembled in a single housing (Fig. 6).

Fig.6 Exhaust system

Supply and exhaust ventilation systems can significantly reduce heating costs by using heat recovery. The heat removed from the room air can be used to heat the supply air in special heat exchangers called recuperators.

Such a system, using a cross-flow recuperator and made in the form of a monoblock, is characterized by a high efficiency of heat recovery, reaching 70%, and provides at least a twofold reduction in operating costs for air heating due to heat recovery (Fig.7).

Fig.7. Supply and exhaust system with recovery

Heat recovery units are designed for the organization of supply and exhaust ventilation in comfortable air conditioning systems, i.e. they change the temperature and humidity of incoming fresh air taking into account the climatic conditions inside the serviced room.

The cross-flow plate regenerative heat exchanger is made of a heat-conducting material having the property of selective permeability with respect to water molecules (practically the membrane is impermeable with respect to molecules of other gases and substances). Due to this, the difference in the partial pressures of water vapor in the outdoor and exhaust air leads to the transfer of moisture from one stream to another. In the cold season, water molecules from the wetter exhaust air penetrate through the membrane into the outside air stream, humidifying it. In the warm season, water molecules from the wetter outdoor air penetrate into the exhaust air stream, preventing excessive humidification of the room.

To heat the air in the supply ventilation units, heaters (air heaters) are used.

Fig.8. Water heater

High-temperature water or steam is used as a heat carrier for heaters. When the heating liquid is water, the heaters are marked as HW, when steam is marked as HS.

Heaters designed to work with a steam coolant are manufactured single – pass, with a water coolant-both single-pass and multi-pass. In single-pass heaters, the coolant passes through the entire bundle of tubes simultaneously from one collector to another, and in multi-pass collectors are separated by internal partitions that repeatedly change the direction of movement of the coolant, which increases the speed of water movement through the tubes and, as a consequence, increases the heat transfer of the heater. The connection of fittings in single-pass heaters is diagonal, and in multi-pass ones it is one-sided (Fig. 9).

Fig. 9. The flow diagram of the coolant in the heaters:

a – single–pass; b – multi-pass

Fins in the form of plates (plate heaters) or wound steel tape (spiral-wound heaters) are placed on the tubes to increase the contact area with the air passing through the heater. The outer fins are galvanized to reduce corrosion and better contact of the fins with the tubes. Fittings for the coolant are welded into the collectors, and to protect the fins from damage from the side, side shields are welded between the collectors. Flanges are used to connect the heater to adjacent elements of the ventilation system.