Supply ventilation system

Supply ventilation systems are designed to supply air into the room. Fresh air is supplied, as a rule, after preliminary preparation, which may include: heating, cleaning, cooling and hydration.

Classification of types of supply ventilation

Supply ventilation systems are classified according to a number of criteria:

ductless, in which fresh air enters the room directly through the supply openings in the walls or windows of the building;

channel, in which fresh air is supplied to the premises through a duct system.

• According to the design of the ventilation network:

prefabricated, consisting of individual elements interconnected by air ducts;

monoblock, which use a supply ventilation unit, structurally combining several elements of the system in a separate housing (filter, air heater, fan, air heater (grilles, diffusers, etc.), cooler, valves, control system equipment, etc.).

• According to the ventilation method:

local, which supply a stream of fresh air to certain places in the room;

complex, carrying out a complete and uniform air exchange in the room.

emergency (smoke) systems, preventing the spread of smoke and contributing to the safe removal of people from the building in case of fire.

The performance of air handling units can vary from several tens (mini-supplies) to several tens of thousands (central air handling units) of cubic meters of air per hour.

The heating element (heater) in winter provides heating of fresh air to the temperature of supply to the room (from 18-20° to 27-29°C).

How the ventilation system works

A typical supply mechanical ventilation system consists of the following components:

• Air intake grille. Through it, outside air enters the ventilation system. These grilles, like other elements of the ventilation system, are round or rectangular. Air intake grilles not only perform decorative functions, but also protect the ventilation system from rain drops and foreign objects.

• Air valve. Serves to prevent outside air from entering the room when the ventilation system is off. The air valve is especially necessary in winter, because without it, cold air and snow will enter the room uncontrollably. As a rule, air dampers with an electric drive are installed in supply ventilation systems, which makes it possible to fully automate the control of the system: when the fan is turned on, the valve opens, and when it is turned off, it closes.

• Filter . This element is necessary to protect both the ventilation system itself and the ventilated premises from dust, fluff, and insects. Usually, one coarse filter is installed in the system, which traps particles larger than 10 microns. If increased requirements are imposed on air purity, then fine filters (for particles up to 1 micron) and extra fine filters (detain particles up to 0.1 microns) can be additionally installed. The filter material in the coarse filter is a fabric made of synthetic fibers, such as acrylic. The filter must be periodically cleaned of dirt and dust, usually at least once a month.

• Heater or air heater. It is intended for heating of air which moves from the street in winter time. The heater can be water (hot water temperature must be at least 70 ° C) or electric. For small air handling units, it is more profitable to use electric heaters, since the installation of such a system is less expensive. For large rooms (more than 100 m2), it is advisable to use water heaters, otherwise the cost of electricity will be very high. To significantly reduce the cost of heating cold air, a recuperator is used - a device in which cold supply air is heated due to heat exchange with the warm air being removed. The air streams do not mix.

• Silencer. Since the fan is a source of noise, a silencer must be installed nearby to prevent noise from spreading through the ducts. The main source of noise during fan operation is turbulent air turbulence on its blades, that is, aerodynamic noise.

• Fan. Serves to supply fresh air to the room and create the necessary pressure of the air flow in the network.

• Air ducts. After leaving the silencer, the processed air flow is ready for distribution to the rooms.

For these purposes, an air duct network is used, consisting of air ducts and fittings (tees, bends, adapters). The main characteristics of air ducts are the cross-sectional area, shape (round or rectangular) and rigidity (there are rigid, semi-flexible and flexible air ducts).

The flow rate in the duct must not exceed a certain value, otherwise the duct will become a source of noise. Therefore, the size of the air ducts is selected based on the calculated value of air exchange and the maximum allowable air velocity. Rigid air ducts are made of galvanized sheet and can be round or rectangular. Semi-flexible and flexible air ducts are round and made of multilayer aluminum foil. The round shape of such air ducts is given by a frame made of steel wire twisted into a spiral. This design is convenient because the air ducts can be folded like an accordion during transportation and installation. The disadvantage of flexible ducts is the high aerodynamic resistance caused by the uneven inner surface, so they are used only in small areas.

• Air distributors. Through the air distributors, the air from the duct enters the room.

By design, air distributors and air removal devices are very diverse:

• Air distribution grilles;
• Plafonds (diffusers);
• Perforated panels
• Slotted air distribution devices;
• Nozzle air distributors, etc.

According to the geometric shape of the jet supplied by air distribution devices, can be:

• Compact jets are formed when air is released from cylindrical pipes, round and rectangular holes.
• Flat jets are formed by the outflow of air from the slotted channels of air curtains, active distribution air ducts, and rectangular elongated holes.
• Fan jets are formed by distributing air through nozzles with a flat disk installed across the stream.
• Incomplete fan jets are formed when air is released through gratings with blades diverging at a certain angle. Such a jet gradually transforms into a compact jet. Conical jets (a kind of fan jets) are created when air is released through nozzles with a cone or plafonds in the form of diffusers in them with a flat reflective disk.

As a rule, grilles (round or rectangular, wall or ceiling) or diffusers (plafonds) are used as air diffusers. In addition to decorative functions, air diffusers serve to evenly disperse the air flow throughout the room, as well as to individually adjust the air flow directed from the air distribution network to each room.

• Adjustment and automation systems. The last element of the ventilation system is the electrical panel, in which the ventilation control system is usually mounted.

In the simplest case, the control system consists only of a switch with an indicator that allows you to turn the fan on and off. However, most often they use a control system with automation elements, which turns on the heater when the supply air temperature drops, monitors the cleanliness of the filter, controls the air valve, etc. Thermostats, hygrostats, pressure sensors, etc. are used as elements of the control system.

Supply system control

For ventilation of apartments and small offices, small ventilation systems are actively used today: a network of air ducts with a supply unit. Managing modern equipment is convenient and simple. With the help of a remote control panel, it is possible to carry out a five-stage adjustment of the air supply, in winter, smoothly adjust the temperature from 5 to 28 ° C. In addition, some appliances have a timer that turns on the unit on a specific day of the week or time of day.

It is also possible to connect an external exhaust fan. Automation will ensure synchronous switching on and off of the supply and exhaust fans. In case of an accident, the control is equipped with a protection system. The unit is reliably protected from overheating. Thermal protection is built into the winding of the fan motor. When triggered, it stops the fan, signaling with an emergency lamp. The heating elements of the air heater are equipped with thermostats that protect against overheating and fire.