Air conditioning is the creation and automatic maintenance (regulation) in closed rooms of all or individual parameters (temperature, humidity, cleanliness, air velocity) at a certain level in order to ensure optimal meteorological conditions that are most favorable for the well-being of people or the conduct of the technological process.
Fragment of the central air conditioner
Air conditioning is carried out by a set of technical means called an air conditioning system (ACS). The SCV includes technical means for air intake, preparation, i.e. imparting the necessary conditions (filters, heat exchangers, humidifiers or air dryers), movement (fans) and its distribution, as well as means of cooling and heat supply, automation, remote control and control. SLE of large public, administrative and industrial buildings are served, as a rule, by complex automated control systems.
Chiller Water Cooled Condenser
The automated air conditioning system maintains the specified air condition in the room regardless of fluctuations in environmental parameters (atmospheric conditions).
The main equipment of the air conditioning system for the preparation and movement of air is aggregated (assembled in a single housing) into an apparatus called an air conditioner. In many cases, all technical means for air conditioning are arranged in one block or in two blocks, and then the concepts of “SCR” and “air conditioning” are unambiguous.
Air Cooled Chiller
Before proceeding to the classification of air conditioning systems, it should be noted that the generally accepted classification of SCR still does not exist and this is due to the multivariance of the schematic diagrams, technical and functional characteristics, which depend not only on the technical capabilities of the systems themselves, but also on the objects of use (air-conditioned rooms ).
Fan coil unit floor type
Modern air conditioning systems can be classified according to the following criteria:
- by the main purpose (object of application): comfortable and technological;
- according to the principle of the location of the air conditioner in relation to the serviced premises: central and local;
- by the presence of its own (included in the design of the air conditioner) source of heat and cold: autonomous and non-autonomous;
- according to the principle of operation: direct-flow, recirculation and combined;
- according to the method of regulating the output parameters of conditioned air: with qualitative (one-pipe) and quantitative (two-pipe) regulation;
- by the degree of provision of meteorological conditions in the manned room: first, second and third class;
- by the number of serviced rooms (local zones): single-zone and multi-zone;
- according to the pressure developed by the fans of air conditioners: low, medium and high pressure.
In addition to the above classifications, there are various air conditioning systems serving special technological processes, including systems with time-varying (according to a certain program) meteorological parameters.
Fan coil unit of channel type
Comfortable SCRs are designed to create and automatically maintain temperature, relative humidity, cleanliness and air velocity that meet optimal sanitary and hygienic requirements for residential, public and administrative buildings or premises.
Typology of pumping stations
Technological SCRs are designed to provide air parameters that meet production requirements to the maximum extent. Technological air conditioning in rooms where people are located is carried out taking into account the sanitary and hygienic requirements for the state of the air environment.
Central SCRs are supplied from outside with cold (delivered by cold water or refrigerant), heat (delivered by hot water, steam or electricity) and electric energy to drive electric motors of fans, pumps, etc..
Typical layout of a split system with supply ventilation
Central SLE located outside the serviced premises and air conditioning one large room, several zones of such a room, or many separate rooms. Sometimes several central air conditioners serve one large room (production hall, theater hall, indoor stadium or ice rink).
Central SLE are equipped with central non-autonomous air conditioners, which are manufactured according to basic (typical) equipment layout schemes and their modifications.
Central SLE have the following advantages:
1) the ability to effectively maintain a given temperature and relative humidity in rooms;
2) concentration of equipment requiring systematic maintenance and repair, as a rule, in one place (utility room, technical floor, etc.);
3) the ability to provide effective noise and vibration damping. With the help of central SCRs, with proper acoustic treatment of air ducts, installation of noise and vibration dampers, it is possible to achieve the lowest noise levels in rooms and to serve rooms such as radio and television studios, etc..
Indoor unit of floor-standing (column) split-system, type
Despite a number of advantages of central SCVs, it should be noted that the large size and complex installation and construction work on the installation of air conditioners, laying air ducts and pipelines often lead to the impossibility of using these systems in existing buildings under reconstruction..
Local ACS are developed on the basis of autonomous and non-autonomous air conditioners, which are installed directly in the serviced premises..
The advantage of local SCRs is ease of installation and installation..
Such a system can be used in a large number of cases:
- in existing residential and administrative buildings to maintain a thermal microclimate in separate office premises or in living rooms;
- in newly constructed buildings for separate rooms, the mode of cold consumption in which differs sharply from that in most other rooms, for example, in server rooms and other rooms of office buildings saturated with heat generating equipment. In this case, the supply of fresh air and the removal of exhaust air are carried out, as a rule, by central supply and exhaust ventilation systems;
- in new buildings under construction, if maintaining optimal thermal conditions is required in a small number of rooms, for example, in a limited number of suites in a small hotel;
- in large areas of both existing and newly built buildings: cafes and restaurants, shops, project halls, auditoriums, etc..
Autonomous SCRs are supplied from outside with only electrical energy, for example, split-system air conditioners, cabinet air conditioners, etc..
Such air conditioners have built-in compression refrigeration machines, usually running on Freon-22.
Autonomous systems cool and dry the air, for which the fan blows recirculated air through surface air coolers, which are evaporators of refrigeration machines, and in transition and winter times they can heat the air using electric heaters or by reversing the operation of the refrigeration machine according to the so-called “thermal pump “.
The simplest option, representing decentralized provision of temperature conditions in rooms, can be considered the use of split-system air conditioners.
Non-autonomous SLE are subdivided into:
- air, when used, only air is supplied to the manned room. (Mini central air conditioners, central air conditioners);
- water-air, when using which air and water are supplied to the conditioned rooms, carrying heat or cold, or both together (chiller-fan coil systems, central air conditioners with local closers, etc.).
Single-zone central SLE are used to service large rooms with a relatively uniform distribution of heat, moisture release, for example, large halls of cinemas, auditoriums, etc. Such SCRs are usually equipped with devices for heat recovery (heat recovery units) or mixing chambers for use in serviced air recirculation rooms.
Indoor block of a wall-type split system
Multi-zone central SLE used to service large rooms in which the equipment is unevenly placed, as well as to service a number of relatively small rooms. Such systems are more cost effective than separate systems for each zone or each room. However, with their help, the same degree of accuracy in maintaining one or two set parameters (humidity and temperature) cannot be achieved as with autonomous SCR (split-system air conditioners, etc.).
Direct-flow SCV operate entirely on the outside air, which is processed in an air conditioner and then supplied to the room.
Recirculating SCR, on the contrary, they work without an inflow or with a partial supply (up to 40%) of fresh outside air or on recirculated air (from 60 to 100%), which is taken from the room and, after being processed in an air conditioner, is again supplied to the same room.
The classification of air conditioning according to the principle of operation for direct-flow and recirculation is mainly determined by the requirements for comfort, the conditions of the technological process of production or technical and economic considerations.
Central SLE with high-quality regulation of meteorological parameters represent a wide range of the most common, so-called single-channel systems, in which all the treated air at given conditions leaves the air conditioner through one channel and enters further into one or several rooms.
In this case, the control signal from the thermostat installed in the serviced room goes directly to the central air conditioner.
SCR with quantitative regulation cold and heated air is supplied to one or several rooms through two parallel channels. The temperature in each room is regulated by a room thermostat acting on local mixers (air valves), which change the ratio of cold and heated air flow rates in the supplied mixture.
Two-channel systems are used very rarely due to the complexity of regulation, although they have some advantages, in particular, the absence of heat exchangers, heat-cooling pipelines in the serviced premises; the ability to work together with the heating system, which is especially important for existing buildings, the heating systems of which can be preserved when two-channel systems are installed.
The disadvantage of such systems is the increased cost of thermal insulation of parallel air ducts supplied to each serviced room..
Two-channel systems, like single-channel systems, can be direct-flow and recirculation.
Air conditioning, according to SNiP 2.04. 05-91 *, according to the degree of provision of meteorological conditions, they are divided into three classes:
First class – provides the parameters required for the technological process in accordance with regulatory documents.
The second class – provides optimal sanitary and hygienic standards or required technological standards.
The third class – provides permissible norms if they cannot be provided by ventilation during the warm season without the use of artificial air cooling.
According to the pressure generated by the fans of central air conditioners, SCR are subdivided into low pressure systems (up to 100 kg / m2), medium pressure (from 100 to 300 kg / m2) and high pressure (above 300 kg / m2).
Types of air conditioners:
- Split systems (wall-mounted, floor-ceiling, column-type, cassette-type, multi-zone with variable refrigerant flow);
- Floor-standing air conditioners and split-system air conditioners with forced ventilation;
- Systems with chillers and fan coil units;
- Rooftop air conditioners;
- Cabinet air conditioners;
- Precision air conditioners;
- Central air conditioners.
What are the different types of air conditioning systems available and how do they differ from each other in terms of their functionality and effectiveness?