Table of Contents
Ventilation is understood as the air exchange of rooms regulated naturally or artificially creating the comfortable air environment conforming sanitary and hygienic to requirements.
Bad ventilation leads to reduction of content in blood of oxygen and violation of work of respiratory and blood systems of the person. “Oxygen hunger” not only leads to deterioration in health, but also to depressions, irritation, apathy, insomnia and another, not palatable, to effects. It is natural that about any comfortable stay in the house with badly organized ventilation, there cannot be speech.
For this reason ventilation systems are installed in any rooms of the big area. Periodically the problem can be removed airing, but it is almost impossible in the winter, plus to that is together with air dust, insects, smells and other, not too pleasant, additions get to the room.
For the solution of such problems there are also vent systems. Let’s consider their basic concepts and terms and we will get acquainted with the used equipment making similar systems.
Types of ventilation systems
Ventilation is separated on several key parameters:
- “pumping” — productivity by air;
- static pressure — air pressure in kPa;
- noise level in dB;
- heater power (in the plenum ventilation for measurement of heating of the entering air), kW.
Selection of specific parameters happens depending on assignment, the sizes and location of the ventilated room, the number of the people who are in it.
Classification of ventilation systems happens on the main signs:
- exhaust or the incoming to destination;
- artificial or natural on way of movement of air;
- all-exchange or local on service zones.
- Natural ventilation
During creation of this type of ventilation any electric equipment (electric motors, fans) is not used. Occurs as a result of natural factors: differences between temperatures outside and indoors, because of change of pressure under the influence of wind or height. Systems are simple in mounting and are inexpensive. But the overall performance is in big dependence on external factors (the directions and wind speeds, air temperatures, etc.). Therefore it will not be possible to solve many problems of ventilation by means of natural systems.
- Artificial ventilation
One more name – mechanical ventilation, is applied when natural ventilation is not enough. When mounting devices and the equipment are used (filters, air heaters, fans and other) which move, clean, cool or heat air. Systems practically do not depend on external conditions and give or delete from the room air independently. Most often the mixed ventilation providing use of both types meets.
- The plenum ventilation
The incoming systems drive fresh air into rooms. If it is necessary, it can be purified from dust and be warmed.
- Exhaust ventilation
Unlike the incoming, does not give, and deletes the heated and contaminated air from internal rooms. Both views at the same time are usually used. In that case productivity of both systems is balanced. Otherwise in the building not comfortable pressure – excessive or insufficient will be created.
- Local ventilation
Intends for giving (incoming) fresh or removals (exhaust) of the contaminated air. It is applied in cases when places, replacement of air in which are localized, it does not allow distribution of the air contaminated or heated in some rooms on all building. For example, the system can be calculated on giving to jobs of fresh air for temperature reduction. In such cases it is effective, especially taking into account rather small cost.
- All-exchange ventilation
Differs from local and ventilates all room entirely. Also is both exhaust, and the incoming. The plenum all-exchange ventilation, as a rule, is established with filtering and heating of volume of the arriving air. Because of it such systems have to be mechanical. The exhaust all-exchange ventilation as for it it is required processings of the deleted air, can be quite simpler than the incoming therefore it is often carried out in the form of established in opening on wall or in fan window. If the deleted volume of small, then rather inexpensive natural exhaust ventilation. At the large processed volumes mechanical ventilation is applied.
Structure of vent system
The structure of design depends on system type, the most difficult and often used look is the plenum mechanical (artificial) ventilation. Let’s consider the components making it in air moving direction, beginning from entrance.
- Airintaking grid
The grid passes the outside air coming to system. As well as any other element can be rectangular or round shape. Performs decorative functions, but besides airintaking grids serve also for protection of internal space against the contamination caused by hit of foreign objects or atmospheric precipitation: snow, rain, hail.
- Air valve
Intends for closing of system in the switched-off state, does not start up air in the room. It is most necessary in winter time as without it cold air will get to the room. In most cases it is usually supplied with the electric drive which allows to automate its work completely. At switching off of heater and the fan the valve is closed, and at inclusion opens again.
Protects both the ventilated rooms, and system from hit of insects, down and dust. The preliminary filter intended for delay of particles not less than 10 millimeters is most often used. There are also complementary filters for cleaning thin or especially thin. The first for 1 micron, the second – for 0.1 microns.
The filtering material in similar preliminary filters – synthetic fabric, for example, acrylic. Periodically, at least once a month, the filter has to undergo cleaning from the dirt which has got on it. On it the pollution control sensor measuring difference between air pressure at entrance and exit from the filter can be installed – it increases at its pollution.
Air heaters — heaters, warm up the air given to cold season from the street. Can be electric or water (connected to long-distance heating). Application of electric heaters as its mounting is much cheaper is more favorable to the incoming installations having small power. More than 100 squares are desirable to use heaters to the areas water, otherwise expenditure for electricity will be too big.
There is one more, low-cost way of heating of the arriving air – mounting of the recuperator. This device heats the incoming cold air the deleted warm, without mixing them among themselves.
Is basis of all systems of artificial ventilation. About two parameters are selected: on the total pressure and productivity (amount of the pumped-over air). Can structurally be axial, and centrifugal or radial. At axial fans high performance, but low total pressure. If ways of the air overtaken by the similar fan the obstacle in the form of grid, turns or air duct just very long meets, flow rate decreases significantly. Therefore systems which air duct has branched design use radial fans – they create flows with high pressure. One more important characteristics – dimensions and noise level. They depend on the brand of the equipment.
- Air duct
For distribution on rooms air goes on the airwater network consisting of directly air duct and shaped products: adapters, turns, T-couplers). Main characteristics of air duct:
1) rigidity (can be flexible, semi-flexible and rigid);
2) area of internal section;
3) form (rectangle or circle).
Flow rate, passing through air duct, cannot exceed certain values, otherwise it becomes noise source. The volume of the pumped-over air depends on the area of internal section of air duct, that is its size is selected depending on the maximum allowable speed of the movement of air flow and calculated value of air exchange.
At production of rigid air ducts galvanized tin is used, they can be both rectangular, and round. At flexible and semi-flexible the round shape, and for production undertakes multilayer aluminum foil. The round shape is stiffened by framework from steel wire suite in spiral. The design is convenient for transportation as it develops “accordion”. But they have shortcoming — high aerodynamic resistance, is formed because of roughnesses of inside face. Therefore flexible and semi-flexible systems on small extent sites, most often complete with rigid are applied.
- Air distributors
Via the distributor air gets directly to the ventilated rooms. Usually in such quality plafonds (diffusers) or grids act (ceiling, wall, rectangular, round). Except decorative function the distributor evenly disseminates air stream and allows to regulate its direction individually.
- Systems of automatic equipment and adjustment
The guidance system which is built in in electric board is the last element of vent system. In the simplest options it includes only the switch with the indicator. But the automatic system of management which is responsible for inclusion of heater at fall of temperature is more often used, manages air valve, watches condition of the filter and other functions. For system sensors as which act are used: pressure sensors, hygrostats, thermostats and other equipment.
Calculation and characteristics of vent systems
Calculation of the following parameters is necessary for selection of ventilation equipment:
- heater power;
- flow rate of air and working pressure of air duct;
- productivity by air;
- system noise limit.
Productivity by air
When calculating required level of pumping studying of floor plan with explication (the indication of the area and purpose of each of rooms) is necessary. At first for each room the necessary ventilation rate serving as indicator of that how many times within hour indoor air will be replaced completely is defined. So, for example, indoors with ceilings 3 meters and of 50 square meters, double air exchange will correspond to 300 kb. m/h.
This indicator depends on the power of the heat-generating equipment, purpose of the room performed in it works, the number of the people residing here and is defined by CONSTRUCTION NORMS AND REGULATIONS. The majority of premises demands single air exchange, and office 2 — 3 multiple. Having summed up all calculated values received for each of rooms required productivity by air turns out. For apartments typical values of productivity will be 100-800 cubic meters an hour, for offices — 1000-10000 cubic meters an hour, for cottages of 1000-2000 cubic meters an hour.
Flow rate of air, noise limit, working pressure
The following calculations concern design of airdistributing network: air ducts, shaped products, air distributors. First of all, the scheme of air ducts is formed. According to the made scheme the above-mentioned interconnected parameters are calculated. Necessary working pressure is calculated proceeding from type of air duct and its diameter, the number of transitions between different diameters and turns and is defined by fan power.
Than it is more on the route of different diameters and turns, the it is longer, the internal pressure created by the fan has to be higher. Diameter of air duct affects also flow rate, usually it is limited to 13 — 15 m/s. If this indicator is exceeded, noise level increases and pressure losses increase. But use “silent”, with large diameter, air duct perhaps not always as large designs cannot be hidden in interceiling space. It leads to compromises of design and search of optimum combination of all three factors.
This equipment warms up the outside air given by the plenum ventilation to cold weather. Heater power depending on the required temperature, system productivity, and the minimum outside temperature is calculated. The parameters depending on temperature correspond to weather conditions of this area.
Air handling is included into concept of ventilation, but at the same time most often is arranged irrespective of other vent systems and is made by means of separate devices: conditioners or Split systems.
The biggest distribution at Split systems, consisting of the internal and external block. External contains the compressor, the condenser and the fan. It is installed out of the room: on external wall, on the attic, balcony or roof, any place providing ventilation with common air. Internal blocks are installed in rooms, work almost silently, distribute air and maintain its temperature in the set framework.
Systems enter multi-Split a little (2-5 pieces) the internal blocks connected to external copper pipes, drainage hoses and electric cable. Power and type of internal blocks can differ, and the power of external is the sum of capacities internal. Such systems allow to use one conditioner (the external block) at the same time for different rooms. They solve and placement problem on facade of periphericals as the N all room will be required only one external block.
Window conditioners consist of uniform monoblock and intend for average or small rooms. Cheap models only cool air, more expensive work from DU panels and can give the warmed-up air. In spite of the fact that this type of conditioners exists for a long time, it enjoys popularity, especially for small offices also now. Despite number of shortcomings, have also the advantages: unpretentiousness, simplicity of operation, ease of installation.
VRF and VRV systems — it is possible to compare them about Split systems, turning on several tens of internal blocks. Are controlled from the personal computer, between external and internal blocks there can be height difference up to 50 meters and distance up to 100 meters. The flexibility and high performance of VRV systems allows to save money and time, beginning from the first projecting phases.