Classification of air conditioning systems and their features

Air conditioning systems, or SCR for short, are designed to create comfortable thermal conditions for a person or equipment in a room. They allow you to create a favorable microclimate both in hot and cold weather by using a refrigeration machine that runs on freon.

Comfort air conditioning includes essential air preparation: cooling, heating, dehumidification, humidification, filtration, ionization, etc. Maintaining the specified parameters is almost independent of the parameters of atmospheric air and their fluctuations. The only exceptions are cases of using SCR at unacceptable temperature values ​​outside, which were determined by the manufacturer of the equipment.

If we consider in more detail the purpose of air conditioning systems, then they can be divided into two groups:

• SLE comfortable - maintain basic air parameters (temperature, humidity, cleanliness) that meet sanitary and hygienic standards;
• Technological SCR - maintain the required air parameters in a particular production or technical room.

For example, one of the tasks of an air conditioning system for an apartment is to maintain a normal humidity level. The same 20% is the lower limit of the norm, upon reaching which the human skin and its mucous membranes dry, and 70% is the upper limit, at which the heat exchange of the body with the environment is significantly reduced, the work of the cardiovascular system deteriorates, headaches begin and lack of oxygen. The air conditioner maintains average humidity levels in both summer and winter - about 40-60%.

Technological SLEs create comfortable conditions for equipment in production. For example, the reliability of powerful computers will be ensured by precision systems capable of controlling temperature, humidity and air mobility with an accuracy of 0.5%.

Not everyone knows that the purpose of an air conditioning system is also to maintain an acceptable level of carbon dioxide in a room.

In children's hospitals, offices, shops and apartments, the indicators differ markedly, therefore, completely different types of air conditioning systems are installed in these institutions.

The normal gas composition of the air can be provided by air conditioners capable of carrying out a regular flow of oxygen into the room, that is, increasing the frequency of air exchange. Excess or lack of carbon dioxide in the body has a detrimental effect on health.

In general, the classification of SLE is very diverse. They can be divided according to different criteria:

• based on the principle of location relative to the serviced area - local and central;
• according to the principle of operation - recirculating, direct-flow and combined;
• by the number of serviced premises - single and multi-zone;
• by the number of regulators of outlet air parameters - one-pipe and two-pipe.

This is not a complete list of classifications. Many authors of thematic books hold different points of view on this issue and put forward their own versions of the division of SLE into classes.

Types and device of air conditioners

If we talk about the types of air conditioning systems, then there is a great variety, since there are devices for an apartment, and devices for office buildings, and units for industrial premises.Automation of air conditioning systems in this case is achieved by using additional equipment.

They can be made in the form of a monoblock or a two-component device - a split system. The first ones have in one case all the elements that ensure the movement of freon along the refrigeration circuit. In the latter, the noisier parts are taken out into the outdoor unit, which is located outdoors, and in the internal (room) unit there are filters, a fan, an evaporative radiator, sometimes a control board and other quiet parts.

The device of any SCR running on freon assumes the presence of such important elements as:

• a compressor that compresses and sucks the refrigerant;
• evaporative and condenser type heat exchangers, through which heat energy is transferred from freon to the environment;
• fans that provide blowing of heat exchangers;
• mechanical cleaning filters + often fine filters;
• control board responsible for the operation of all electronics;
• flow regulator (expansion valve or capillary tube) for metering the supply of liquid refrigerant from the condenser to the evaporator;
• 4-way valve in "warm" air conditioners, redirecting the refrigerant in the other direction.

The design of an industrial air conditioning system is much more complex. The same chiller may have multiple rows of fans or a number of 3-way valves that change the direction of water flow for a water cooled chiller.

The simplest schematic diagram of an air conditioning system is shown here. It reflects all the main components of the compression refrigeration cycle, together with the connecting communications.

In almost all SCRs, the circuit diagram is identical. The cooling cycle can also be represented graphically, as shown in the figure. Here, the left part of the curve is the state of the saturated liquid, the right is the state of saturated vapor. At the junction point, freon can be in any state.

Household SCV air conditioners

As already mentioned, there are air conditioning systems for residential premises - these are household split systems, and industrial - to meet the needs of production or other industrial and technological facilities. There are so-called semi-industrial or commercial systems that are installed in offices, shops, administrative buildings and other public facilities.

Air conditioning systems for an apartment include wall, floor-ceiling, cassette, duct and column split systems, as well as window and mobile monoblocks, which differ in the design of the indoor unit. They are also often used as semi-industrial devices, but only with an increased power range. The most popular household cooling appliance is the wall-mounted split, but its capacity is limited as the users of household appliances do not need a strong jet of cooled air.

In split systems, the compressor is located in an external unit, so the operation of such devices is completely silent. If there are several indoor units connected to external electrical wires and a freon line, then we are already talking about a multi-split air conditioning system. An outdoor unit can connect 2 to 9 indoor units.

VRV and VRF air conditioning systems

There are multi-zone systems that work with only one type of indoor unit - for example, wall-mounted, that is, all indoor modules must be exclusively of the same type. But modern manufacturers produce multi-split air conditioning systems with the ability to connect different types of indoor units to one outdoor unit, while for buildings that have a large number of rooms with different heat loads, multi-zone systems with a variable refrigerant flow have been created for several years.They have one external unit capable of providing dozens of internal ones.

For example, in MITSUBISHI ELECTRIC, the CITY MULTI series is designed for 16 internal modules of various types and completely different capacities. These inverter systems with variable capacity are equipped with a special thermostatic valve, which changes the power of the unit depending on the load and thereby regulates the freon consumption. Due to this, the temperature is maintained more accurately and there are no differences.

Indoor units of the multi-split air conditioning system, like that of MITSUBISHI ELECTRIC, can operate in different modes at the same time. This is provided by the BC controller, which distributes the freon between the units and separates it with a separator into high pressure vapor and liquid. Thanks to this separator, the design of this air conditioning system is simplified - the units are connected to the controller with just two pipes. Installation becomes cheaper and easier, the number of docking fittings decreases, the permissible pipeline length and height differences increase significantly.

As a rule, in simple multi-split systems, outdoor and indoor units are connected linearly, that is, a separate route is needed for each room module. In multi-zone ones, only one pair of tubes leaves the external block, which then branches out according to a tree-like principle with the help of refnets.

Refnet has different cross-sectional sizes. When combined with the pipe, it is cut along a line of a suitable diameter.

Multi-zone devices with variable refrigerant flow have another name - VRV-air conditioning systems or VRF. Their advantages are obvious:

• the length of a single pipeline system reaches 100 m or even more, the height differences between the blocks are up to 50 m, which allows the outdoor module to be placed in any convenient place;
• the number of indoor units connected to one external one reaches several dozen, while the productivity of the latter can be 30% less than the total productivity of the former;
• control can be carried out both from individual remote controls and from a central stationary console or computer - special software makes it possible to combine a computer network with an air conditioning network and control each air conditioner from a personal computer in different zones of the building.

There is practically no difference between the concepts of VRF air conditioning system and VRV. Initially, the creation of such a system belongs to DAIKIN, so other manufacturers use a different abbreviation, which does not change the meaning. It's just that different manufacturers endow the manufactured equipment with different technical capabilities (route length, the possibility of recuperation, etc.)

It is worth remembering that the operation of all units in different modes (cooling and heat) is possible only with a three-pipe connection system. A two-pipe VRF air conditioning system is able to provide different set air parameters, but only in one mode.

The outdoor unit of some VRV air conditioning systems may look like a semi-industrial two-fan unit or have a more serious design, as in the picture.

The disadvantage of air conditioning using a VRV system is the noticeable noise emitted by the flow valve. They try to hide it in a utility room or a false ceiling. There are also devices with a remote valve.

Design and calculation of air conditioning systems

When selecting the right refrigeration device for an apartment, an express method for calculating the SLE is often used, in which the approximate thermal load on the room is taken into account, in relation to which the closest standard size of the device is selected. The selection is made according to the nominal refrigerating capacity.

For 10 m², 1 kW of cold power is taken and added to the data obtained from 10 to 30% in the form of a reserve for incoming heat from household appliances, window and door openings, lighting fixtures, etc.

This method of calculating a suitable air conditioning system makes it possible to simplify the design work, but it allows inaccuracies if it is applied to systems with greater capabilities and a more complex device, for example, to multi-zone SCR. It is quite applicable when buying household split systems and window / mobile monoblocks.

What you need to know and consider when designing air conditioning systems with a complex device? First of all, they look at the initial data:

• regional location of the object and location relative to the cardinal points;
• construction drawings and floor plans;
• category of the object, taking into account fire safety standards;
• drawings showing the location of all building equipment;
• number of lighting fixtures;
• characteristics of energy carriers;
• data of already existing SLE.

After analyzing all the data provided, they proceed directly to the design of the SCR, which usually takes place in two stages.

At the first stage, a system is chosen with a technical justification why this particular type is better for this room. Here they calculate the air conditioning system by capacity, determine its location at the facility, prescribe the number of devices involved, determine the parameters of the area for installation and calculate the approximate cost of all work with the equipment.

The second stage involves the development of a working project, taking into account the building layout, thermal characteristics of building structures and a technological task. Be sure to calculate air exchange, thermal and heat-humidity balance of the room, carry out aerodynamic calculation of air networks and hydraulic calculation of fluid communications.

Further, everything is coordinated with the customer, SES, fire inspection and, if necessary, changes are made to the project. After that, the equipment is ordered and the working drawings are handed over to the installers.

Maintenance and repair of air conditioners

Any SCR requires regular maintenance, that is, cleaning and checking operating parameters, and in some cases, repair.

Standard SCR maintenance is the prevention of equipment breakdowns. It consists of:

• external cleaning of blocks;
• washing and disinfection of filters, fans, radiators;
• cleaning the drainage pipeline;
• checking the pressure in the system and the temperature of the outgoing air flows;
• broaching fasteners.

If necessary, it may be necessary to refuel or completely refill the circuit with freon.

Usually, the main purpose of cleaning an air conditioning system is to prevent the failure of parts such as the fan, four-way valve, compressor. If it is not carried out, then the efficiency of the device decreases, bacteria begin to multiply inside, when the device is turned on, an unpleasant odor appears, and the listed elements break.

Even if the air conditioning system is cleaned regularly, sometimes breakdowns are inevitable. Voltage drops lead to failure of the control board, which is the "brain" of the machine, and violation of the manufacturer's recommendations for its use within certain temperature limits leads to problems with the mechanical elements of the circuit.

An example of how air conditioning repairs may be required are given in the table.

Maintenance of industrial SCRs and repair and restoration work to eliminate malfunctions in them are carried out according to a more complex scheme and take more time. Timely identification of problems and their elimination helps to avoid stopping the entire workflow in production or any other large non-residential facility.

Preventive maintenance of household systems is recommended twice a year. Industrial installations need to be inspected and cleaned much more often - at least once a quarter, at most once a month. It all depends on the operating conditions and the location of the SCR.