Dew point humidity control principle. Persistent misconceptions about air conditioners. "Air conditioners disturb the interior"

Is it true that through the outdoor units that we see on the facades, fresh air enters the premises?

In fact, the outdoor units emit excess heat taken from the room into the street. The air conditioner does not ventilate the room, but works with the air that is there.

To quickly and energy-efficiently obtain the set temperature, it is necessary to ensure that windows and doors are tightly closed.

Only ducted air conditioners have the full function of fresh air supply. Ordinary wall-mounted split systems, if necessary, are used together with a separately purchased supply ventilation system.

Are you afraid of a cold? You won't get sick with "Chaos" ...

Is it true that air conditioning can cause a cold?

Of course, if, having come from the heat with a sweaty back, to sit directly under the directed flow of air-conditioned air, it is quite possible to catch a cold. Just like near an open window or in a draft.

But modern air conditioners have comfort modes that direct the flow of cooled air in the safest way. In all modern split systems, the dampers that control the air flow can automatically oscillate up and down, evenly dissipating cool air.

The "Chaos" technology allows to minimize the uncomfortable temperature difference along the height of the room and evenly distribute the conditioned air throughout the entire volume of the room.

And new air conditioners have a progressive airflow control system, or comfortable airflow distribution. This system is based on the Coanda effect (originally used in cooker hoods).

Horizontal blinds are programmed in such a way that in cooling mode they can direct the air flow upwards, and the air is distributed along the ceiling, gradually filling the room with a cool "shower". There is a soft cooling of the room without drafts and the danger of catching a cold.

The advanced airflow control system is used by Daikin, Sharp in their new models. Daikin's developers refer to this feature as Automatic Draft Elimination Mode.

And in the heating mode, the louvers of the air conditioner in the comfort air distribution mode are rotated so that the heated air descends along the wall, then spreads along the floor and, being lighter than cold air, rises up, providing gentle natural heating.

Warm air warms our feet first, helping to avoid colds.

Also, when heating with an air conditioner in the cold season, the temperature should not be set too high, so as not to reduce the body's resistance.

Why did legionnaires get sick?

Is it true that a conventional split system can spread "legionnaires' disease"?

A few decades ago, the whole world went around the information that during a meeting of veterans of a society organized in a New York hotel, the name of which contained the word “legionnaire” (now no one remembers the exact name), several participants in the meeting fell ill with a severe lung infection.

Soon the causative agent of this disease was identified and this bacterium was named legionella. The attack of the disease was associated with the air conditioning system that worked in the hotel, which allegedly contributed to the reproduction and spread of this pathogen throughout the building.

In fact, legionella has been fairly widespread in the past, and is present in domestic water systems, especially where older equipment is used. As long as the population of these bacteria is small, they do not pose a particular danger. But once in favorable conditions of humidity and temperature, contributing to their rapid reproduction, legionella from time to time causes focal outbreaks of this serious disease.

In the future, for many years, chilling publications appeared in the press about air conditioners that infect "legionnaires' disease." However, it is stubbornly silent that only some central air conditioning systems with cooling towers, where the very “unreliable” tap water circulates, can become a hotbed of infection.

There are practically no such systems in our country, and outbreaks of legionellosis have never been registered. And in split systems and window air conditioners, the conditions for the reproduction of legionella are completely unsuitable. Legionella need a water temperature of 30-35 ° C, while in household split systems, water exists only in the form of condensate, which has a temperature slightly above zero and is also immediately removed from the apparatus. There has never been a recorded case of legionnaires' disease in the world due to split systems and window air conditioners.

A good air conditioner will not miss the "dew point"

Is it true that the air conditioner dries out the air?

Humidity is a measure of the amount of water vapor in the air. We usually talk about relative humidity. This is the amount of water contained in the air at a given temperature compared to the maximum amount of water that can be contained in the air at the same temperature in the form of vapor.

Consequently, when the air is cooled by an air conditioner, the “dew point” shifts towards a decrease in relative humidity, and condensation of some of the water vapor from the air is indeed possible. But there is nothing wrong with that.

Modern air conditioners even have a separate “drying” function without air cooling, it is very useful for creating a comfortable microclimate.

Building codes and regulations (both Russian and foreign) clearly regulate the level of relative humidity in the room: from 30 to 60%.

In the cold season, the humidity of the air coming from the street during ventilation is really quite low, and we experience discomfort from this.

The operation of the central heating system and other heating devices also leads to overdrying of the air in winter. As a result, the relative humidity in apartments in winter can drop to 20 or even 15 percent.

But the air conditioner is not at all to blame for this winter dryness of the air. As a rule, it is not turned on at this time, and even more so in the cooling function.

Therefore, in summer, to create a comfortable microclimate, the air conditioner requires cooling of warm atmospheric air and at the same time dehumidifying it.

Our body primarily senses changes in temperature, not humidity. And if you only lower the temperature in the room, the increased humidity will be felt in the form of stuffiness, which is more difficult to bear than heat.

It turns out that when the temperature rises from 20 to 30 * C, the humidity of the air can almost double! At high temperatures, we suffer not so much from heat as from high humidity. And the percentage of oxygen in the air decreases due to an increase in the content of water vapor.

According to research by Daikin Corporation, it is enough to reduce the humidity in the room without lowering the temperature, and the conditions will become much more comfortable. This is what the air conditioner does in dry mode.

Achieving the optimal humidity value does not require significantly lowering the temperature, which means that there is no chance of catching a cold in a draft from a cool air flow. At the same time, you can also save energy, since air cooling costs 10% more per degree.

Comfort drying mode is provided as follows. In the indoor unit, the conventionally cooled air from the room is mixed with the warm outdoor air from the outdoor unit and then returned back to the room.

And in the automatic selection mode, the air conditioner itself will select the most comfortable ratio of temperature and humidity in the room, depending on the parameters of the air outside. This is Daikin's exclusive climate system.

You will not even hear how it will inflate ...

Is it true that air conditioners are very noisy - it's impossible to fall asleep?..

The maximum permissible noise level in residential premises according to official standards is 60 dB. The noise level, the source of which is a working air conditioner, usually does not exceed 45 dB.

Split systems are the least noisy. There are many models in which the noise level from a working indoor unit is 22-24 dB. This is below the noise level that happens in the library.

The sound level as sound pressure is measured not on the usual directly proportional, but on a logarithmic scale. This is due to the peculiarities of our perception of sounds: nature spares our hearing, and a threefold increase in sound pressure is perceived by us as an increase in volume by only 10 decibels. Therefore, for example, if the noise figure for one model is 25 dB, and for another 22 dB, this means: for our ear, the second model works 2 times quieter.

After all, it is mainly the air moving through the air ducts that makes noise, and the engines in air conditioners have been working almost silently for a long time. Fan designs are improving, allowing for more powerful airflow with smaller blades and well-designed blades, and at lower RPMs.

The thoughtful design of the front panel of the indoor unit and new elastic materials for the louver guides also contribute to reducing the noise level.

Wind as decoration in the interior

Is it true that air conditioners spoil the interior?

As for office premises, their design is most often carried out in the general traditions of "European-style renovation". In this design, which is based on modern finishing materials and simple style solutions, the indoor units of air conditioners fit perfectly.

As for living quarters, their interior has recently been often built on the contrast of old and modern, and then the air conditioner will take its rightful place among other “fancy” equipment.

If the interior of the dwelling gravitates towards the “antique” style, the air conditioner can be hidden, disguised. There are, for example, ducted air conditioners, which are located behind the false ceiling. When installing a duct air conditioner, it is not necessary to make suspended ceilings in all refrigerated rooms. You can hide all the equipment in the corridor by placing ventilation grills above the doorways.

Some firms try to take into account trends in residential interior design and offer original options both in form and in color.

Such, for example, is a very interesting series of air conditioners from LG Artcool. The indoor units of air conditioners have a rectangular design, and the color of the front panel can be matched to the interior.

Replaceable panels of air conditioners allow you to change the color of the device according to the color background of the room. If you want to change the color scheme of your home (change wallpaper, furniture upholstery), or you are tired of the appearance of the air conditioner, you can simply change its front decorative panel.

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P-IO-WH1-H-WC-WH2

- Outside temperature sensor

Defines the seasonal mode of operation. When the temperature threshold is set, the ACS automatically switches to the "Summer" or "Winter" modes. For liquid heaters, the preheating temperature is determined by the outside air temperature for faster reaching the specified temperature regime.

- Outside air damper

Prevents the entry of outside air when the ventilation system is off. This is especially necessary in the presence of a water heater, to protect it from freezing in winter. An electric drive is installed on the air damper shaft. When the “Start” command is received, the electric drive is energized and the damper opens.
The presence of a "return spring" (for the supply damper) allows, in the event of a power failure of the automation cabinet, to block the access of outside air to the room and the supply unit.

- Filter clogging control

The air filter is designed to clean the air from foreign particles. During operation, the filter material becomes clogged and needs to be cleaned. To control the degree of contamination of the filter, a differential pressure switch is used. This device, with the fan running, controls the pressure difference before and after the filter. In case of severe contamination, the pressure drop increases significantly, a mechanical relay is activated, and the ACS issues a warning. The signaling is displayed on the front panel of the shield by the yellow LED lamp "Filter".

- Water heater (works only in winter)

When a signal is given to turn on the system, the valve of the heat supply unit opens to 100%, the coolant, circulating through the heat exchanger, warms up the supply air duct channel.
If the system is turned on without warming up the water heater (heat exchanger), then at low outside air temperature, the antifreeze protection of the heat exchanger may be triggered by a signal from the capillary thermostat. When the temperature of the return heat carrier reaches the temperature of the supply heat carrier, the damper of the supply air duct opens and the supply fan turns on. Protection against freezing of the water heater in the operating mode is carried out by regulating the supply of the heat carrier according to the signals of the thermostat with a capillary tube and the temperature sensor on the return pipeline of the heat supply unit. The reason for the possible freezing of water in pipelines is its laminar movement at a negative outdoor temperature and water subcooling in the heat exchanger. When the velocity of the heat carrier in the center of the tube is less than 0.1 m/s, the velocity of the heat carrier near the tube wall is almost equal to zero.
Due to the low thermal resistance of the tube, the water temperature at the wall approaches the outside air temperature. The water in the first row of pipes on the outside air flow side is most susceptible to freezing. The risk of freezing is predicted by the air temperature after the heat exchanger being below the set value, measured by a capillary thermostat, or the return water temperature dropping below the set value, measured by the temperature sensor on the return pipe of the heat supply unit. When any of the specified values is reached, the control water valve of the water heater opens completely, the supply fan stops, and the supply air damper closes. In the event of a "fire" signal from the APS, the system is turned off, the circulation pump of the heat supply unit continues to operate. To protect against freezing, the automatic control system maintains the temperature of the return heat carrier at the set value by means of a valve of the heat supply unit and a pump. The water heater pump circulates the heat carrier preventing freezing. The pump in the "Winter" mode is always on.
The protection of the pump is provided by a motor-protective circuit breaker or a circuit breaker (depending on the pump version), which is activated when the rated current of the electric motor is exceeded. When the machine is triggered, the ACS generates a pump failure signal. In this case, the installation is switched off in the winter period until the causes of the accident are eliminated.

- Dew point humidity control

The supply air in winter is heated in the first air heater. Further, the air is humidified along the adiabatic. An average temperature sensor installed downstream of the humidifier regulates the output of the first air heater so that the air temperature after the humidifier stabilizes around the dew point.
Second heating air heater, installed behind the humidifier, heats the supply air to the required temperature, according to the readings of the air temperature sensor in the outlet duct.
Thus, indirect regulation of supply air humidity is carried out by thermostats without direct measurement of humidity.

- Water cooler

Designed for cooling. The automated control system, using a temperature sensor located in the supply air duct, maintains the air temperature, generating a direct control action on the three-way valve of the mixing unit of the cooler. For smooth and accurate regulation, a drive with analog control 0-10V is installed.

- Operation of the cooler in dehumidifying mode.

The air enters the heat exchanger of the cooler, where it is cooled. Excessive moisture in the air, falls in the form of condensate, as a result of which it is drained.
Humidity control is carried out indirectly, according to the readings of the average temperature sensor behind the cooler heat exchanger.
Further , according to the readings of the temperature sensor in the inflow channel at the outlet, the air is heated second heating air heater to the required temperature. A humidity sensor in the duct (room) is not required in this case.

- Fans

They are the main nodes in the air conditioning systems of the microclimate of buildings. The main purpose of the fan is to provide sanitary and hygienic conditions for a person to stay in the premises, as well as technological conditions for the normal functioning of technological processes in industrial premises. Ensuring sanitary and hygienic and technological conditions is achieved by removing polluted air from the premises and replacing it with fresh outdoor air, that is, maintaining the necessary air exchange.

- Frequency converters

At the moment of starting the electric motor, the starting current is several times higher than the nominal values, which negatively affects the operation of the electric motor itself, and can lead to failure of electrical equipment. To prevent high starting currents and the possibility of simplifying the air exchange attachment, a frequency converter is used. Starting the engine is carried out by smoothly changing the voltage and frequency. During the entire time, the motor current is maintained within the limit set by the inverter settings. The frequency converter allows you to set the required fan performance. Mandatory use at operating frequencies above 50 Hz. When using the emergency, there is no need to use the automatic combined motor protection.

In fact, the outdoor units emit excess heat taken from the room into the street. The air conditioner does not ventilate the room, but works with the air that is there. To quickly and energy-efficiently obtain the set temperature, it is necessary to ensure that windows and doors are tightly closed.

Only ducted air conditioners have the full function of fresh air supply. Ordinary wall-mounted split systems, if necessary, are used together with a separately purchased supply ventilation system.

"Air conditioning can catch a cold"

Some firms use the "Chaos" mode, or Chaos swing. This is a technology for distributing conditioned air by chaotic oscillation of the louvers of the indoor unit of the air conditioner and changing the opening angle of the louvers that supply air. The "Chaos" technology allows minimizing the uncomfortable temperature difference along the height of the room and uniformly distributing the conditioned air throughout the entire volume of the room.

And new air conditioners have a progressive airflow control system, or comfortable airflow distribution. This system is based on the Coanda effect (originally used in cooker hoods).

Horizontal blinds are programmed so that in cooling mode they can direct the airflow upwards, and the air is distributed along the ceiling, gradually filling the room with a cool "shower". There is a soft cooling of the room without drafts and the danger of catching a cold.

The most advanced airflow control system is used by Mitsubishi Electric. The air conditioners of the Deluxe FA series have an infrared sensor for remote measurement of the temperature of the surface of the floor and walls of the room.

If the sensor detects a warm or cold spot, it directs airflow to that spot using automatic vertical and horizontal louvers. This ensures a uniform temperature throughout the room, regardless of its size and, most importantly, the location of the indoor unit.

Interesting developments in air jet control from Daikin, Sharp. Daikin's developers refer to this feature as Automatic Draft Elimination Mode.

And one more piece of advice: when you come from the summer heat and turn on the air conditioner, do not set the temperature that differs from the street temperature by several degrees at once. First, set the difference to one or two degrees. By adapting, you can add another degree. Experts recommend that in summer the difference between the temperature in the street and in the room does not exceed 4-5 degrees. That is, at an outdoor temperature of 28 ° C, you should not set 18 ° C on the remote control, but it is better to limit yourself to 24 ° C.

Also, when heating with an air conditioner in the cold season, the temperature should not be set too high, so as not to reduce the body's resistance.

"Air Conditioning Spreads Legionnaires' Disease"

A few decades ago, the whole world went around the information that during a meeting of veterans of a society organized in a New York hotel, the name of which contained the word "legionnaire" (now no one remembers the exact name), several participants in the meeting fell ill with a severe lung infection. Soon the causative agent of this disease was identified and this bacterium was named legionella. The attack of the disease was associated with the air conditioning system that worked in the hotel, which allegedly contributed to the reproduction and spread of this pathogen throughout the building. In fact, legionella has been fairly widespread in the past, and is present in domestic water systems, especially where older equipment is used. As long as the population of these bacteria is small, they do not pose a particular danger. But once in favorable conditions of humidity and temperature, contributing to their rapid reproduction, legionella from time to time causes focal outbreaks of this serious disease.

In the future, for many years, chilling publications appeared in the press about air conditioners that infect "legionnaires' disease." However, it is stubbornly silent that only some central air conditioning systems with cooling towers, where the same "unreliable" tap water circulates, can become a hotbed of infection.

There are practically no such systems in our country, and outbreaks of legionellosis have never been registered. And in split systems and window air conditioners, the conditions for the reproduction of legionella are completely unsuitable. Legionella need a water temperature of 30-35 ° C, while in household split systems, water exists only in the form of condensate, which has a temperature slightly above zero and is also immediately removed from the apparatus. There has never been a recorded case of Legionnaires' disease in the world due to split systems and window air conditioners.

"The air conditioner is drying out the air"

As temperature changes, relative humidity changes without changing the amount of water vapor in the air. Because in physics there is such a thing - the dew point. This is the temperature to which air must be cooled at a given pressure in order for the vapor contained in it to reach saturation and begin to condense, that is, dew appears. Consequently, when the air is cooled by an air conditioner, the "dew point" shifts towards lower relative humidity, and condensation of some of the water vapor from the air is indeed possible. But there is nothing wrong with that.

Modern air conditioners even have a separate “drying” function without air cooling, it is very useful for creating a comfortable microclimate.

Building codes and regulations (both Russian and foreign) clearly regulate the level of relative humidity in the room: from 30 to 60%. In the cold season, the humidity of the air coming from the street during ventilation is really quite low, and we experience discomfort from this. The operation of the central heating system and other heating devices also leads to overdrying of the air in winter. As a result, the relative humidity in apartments in winter can drop to 20 or even 15 percent.

But the air conditioner is not at all to blame for this winter dryness of the air. As a rule, it is not turned on at this time, and even more so in the cooling function.

But in the summer months, the dew point shifts towards an increase in relative humidity. Warm outdoor air entering homes and offices becomes much more saturated with moisture, especially after rain. And then the relative humidity can reach 80-90%. Therefore, in summer, to create a comfortable microclimate, the air conditioner requires cooling of warm atmospheric air and at the same time dehumidifying it. Our body primarily senses changes in temperature, not humidity. And if you only lower the temperature in the room, the increased humidity will be felt in the form of stuffiness, which is more difficult to bear than heat.

It turns out that when the temperature rises from 20 to 30 C, the humidity of the air can almost double! At high temperatures, we suffer not so much from heat as from high humidity. And the percentage of oxygen in the air decreases due to an increase in the content of water vapor.

Moreover, Daikin Corporation is the first in the world to offer a comfort drying mode, which allows not only to reduce humidity, but also to increase it if necessary, selecting the most convenient microclimate parameters for each user. Achieving the optimal humidity value does not require significantly lowering the temperature, which means that there is no chance of catching a cold in a draft from a cool air flow. At the same time, you can also save energy, since air cooling costs 10% more per degree.

The value of relative air humidity can be set on the air conditioner control panel by analogy with air temperature. It is enough to set the humidity value from 40 to 60% by pressing the corresponding key. And in the automatic selection mode, the air conditioner itself will select the most comfortable ratio of temperature and humidity in the room, depending on the parameters of the air outside. This is Daikin's exclusive climate system.

"Air conditioners are noisy"

The maximum permissible noise level in residential premises according to official standards is 50 dB during the day and 40 dB at night. The noise level, the source of which is a working air conditioner, usually does not exceed 35 dB. Split systems are the least noisy. There are many models in which the noise level from a working indoor unit is 21-24 dB. This is below the noise level that happens in the library.

To achieve such good noise characteristics, air conditioner developers have done a lot. The design of the heat exchanger and the shape of the air ducts in the indoor unit of the air conditioner are constantly being improved so that the air flow is smoother. After all, it is mainly the air moving through the air ducts that makes noise, and the engines in air conditioners have been working almost silently for a long time. Fan designs are improving, allowing for more powerful airflow with smaller blades and well-designed blades, and at lower RPMs. The thoughtful design of the front panel of the indoor unit and new elastic materials for the louver guides also contribute to reducing the noise level.

"Air conditioners disturb the interior"

As for office premises, their design is most often carried out in the general traditions of "European-style renovation".

In this design, which is based on modern finishing materials and simple style solutions, the indoor units of air conditioners fit perfectly.

As for living quarters, their interior has recently been often built on the contrast of old and modern, and then the air conditioner will take its rightful place among other "fancy" equipment.

If the interior of the home gravitates toward the "antique" style, the air conditioner can be hidden, disguised. There are, for example, ducted air conditioners, which are located behind the false ceiling. When installing a duct air conditioner, it is not necessary to make suspended ceilings in all refrigerated rooms. You can hide all the equipment in the corridor by placing ventilation grills above the doorways.

Basic layout diagrams of central air conditioners Central air conditioners are non-autonomous air conditioners supplied with cold and heat from the outside. Central air conditioners can be divided into four classes:

straight-through;
with variable air flow;
with air recirculation;
with heat (cold) recovery.

The main parameters of central air conditioners are:

air consumption;
pressure created by the fan;
heat and cold performance;
degree of air filtration;
efficiency of heat recovery (in the presence of a heat recovery unit);
consumed electrical power;
the level of generated noise;
specific weight and size characteristics.

Central air conditioners are located near the serviced premises: on the roof (outdoor version of the unit), on technical floors, in basements. Air supply and exhaust to the air conditioner and to the premises is carried out by air ducts. Central air conditioners consist of sections, each of which performs certain functions: mixing air flows, filtering, heating, cooling or drying, humidification. To reduce the level of noise propagating through the duct system, silencers are built into the central air conditioners. Air conditioners are built on the basis of unified standard sections (modules), which are completed in various combinations depending on the requirements of the technical specifications.

Direct flow central air conditioners

Direct-flow central air conditioners consist of supply and exhaust parts. The inlet part includes air dampers, an inlet filter, a heating and cooling section, a ventilation section, and a silencer. The exhaust part consists of a fan and an air damper. Air dampers are multi-leaf with parallel blades, which are controlled by a servomotor synchronously: the amount of air entering the room must be equal to the amount of air removed.

The disadvantage of once-through central air conditioners is the need for large capacities of the heating and cooling sections, as well as the supply of air with the same temperature to all rooms. This drawback can be eliminated by using a direct-flow VAV (Variable Air Volume) system with variable air flow. In this case, separate temperature sensors are installed in each room, which control the dampers at the air inlet to each room.

The VAV system makes it possible to maintain the set temperature by changing the amount of heated (cooled) air supplied to the room. However, this is sometimes not consistent with the requirements of air flow standards. Therefore, air recirculation is organized in central air conditioners (mixing part of the exhaust air into the supply air).

Maintaining the temperature in the room is carried out by sensors located in the serviced room. Humidity can be regulated by the humidity of the air in the room (direct control) or by the dew point temperature of the air after the irrigation chamber (indirect control). When adjusting the humidity by the dew point temperature, it is necessary to install two heaters BH1 and BH2 in the air treatment line (Fig. 2).

The air is heated, brought in the irrigation chamber (OK) to parameters close to the dew point temperature of the supply air. The temperature sensor installed after the spray chamber regulates the output of the first air heater so that the air temperature after the spray chamber (≈ 95%) stabilizes around the dew point. The air heater of the second heating, installed after the irrigation chamber, brings the supply air to the required temperature.

Thus, indirect regulation of supply air humidity is carried out by thermostats without direct measurement of humidity. With combined regulation of air humidity, direct and indirect regulation are combined. This method is used in air conditioning systems that have a bypass (bypass) channel around the irrigation chamber, and is called the method of optimal modes.

On fig. 3 shows a thermodynamic model of a direct-flow air conditioning system. The blue color shows the annual limits of changes in outdoor air parameters. The lower (limiting) point of outdoor air during the cold period is designated Nzm, and for warm - Nl. The set of air states in the working area is indicated by the polygon Р1Р2Р3Р4 (zone Р), and the set of allowable states of the supply air - П1П2П3П4 (zone П).

During the cold period, the outside air with the parameters Nzm must be brought to one of the points of the set P. It is obvious that the minimum costs (the shortest path) will be if point P3 is selected from the set P3. In this case, the outside air must be heated in the heater of the first heating VP1 to the point Hzm, humidify adiabatically along the line Hzm Kzm at hkzm = const, and then heat the heater of the 2nd heating of VP2 to the temperature of point P3 (process Hzm Hzm Kzm P3). During the adiabatic humidification process, the air is humidified up to 95-98%.

The Kzm point, located at the intersection of the d3 line and the 95-98% relative humidity curve, is the dew point of the supply air P3. The maximum heat output of the air heater of the 1st heating VP1 should be:

QVP1 = G(hkzm - hzm), (1)

and the air heater of the second heating VP2:

QVP2 = G(hП3 - hkzm), (2)

As the outdoor air temperature rises, the intensity of heating of VP1 will decrease, but the sequence of air treatment will remain (H1 H1 Kzm P3). When the outside air reaches the enthalpy hn > hkzm, there is no need for a preheater for the first preheating BH1. In this case, the outside air only needs to be humidified and heated in BH2.

Obviously, the shortest air treatment path will be Hspm Kspm P3 or, for example, Hper Kperm P5. With a further increase in the outdoor temperature, point P5 will move along the line P3P2 P2P1 and reach point P1, which signals the need to switch to air treatment using the summer period technology . The range of outdoor air temperatures from hcm to hcl is a transitional period.

It is possible to exclude the second heating by mixing part of the heated outdoor air with humidified air after the spray chamber (Fig. 4). In this case, the outdoor air is heated to the point Hm, humidified in the irrigation chamber (Hm Km) to 95%, and then the heated air is mixed with humidified air in such a ratio that the mixture point coincides with point P3. This operation can be performed by a temperature sensor, or by a humidity sensor after the mixing chamber.

The easiest way to humidify is to use steam generators. In this case, heating is carried out by the first heater to point P3, and then it is moistened along the isotherm to point P3. However, the use of steam generators is economically unprofitable due to the high consumption of electricity. The use of a honeycomb humidifier gives a significant reduction in energy consumption. Thus, the power consumption for humidification is:

humidification in the irrigation chamber - 50 W;
steam humidification - 800 W;
honeycomb humidification - 10 watts.

In the warm period, the limiting parameters of the outside air are the Hl point. It is obvious that the minimum costs in the transition from the point Hl along the set of points P will be if you choose the end point P1. Air with parameters Hl must be subjected to cooling and dehumidification. This process can be implemented using a refrigeration machine (process Hl → P1) or an irrigation chamber. In the latter case, the air is cooled by the cold water of the irrigation chamber and dried along the line Hl → Kl, and then heated in VN2 along the line Kl → P1.

To implement all periods of operation of the air conditioner, it is necessary to install two temperature sensors after the irrigation chamber: one (T3) set to the dew point temperature of the cold period tcm, the second (T2) - to the dew point temperature tk of the warm period. Sensor T3, regulating the heat output of the heater VP1, during the cold period provides air heating up to enthalpy hcm, providing adiabatic humidification of the air in the irrigation chamber up to the moisture content of the supply air d3.

Temperature controller T4, the sensor of which is located in the room, stabilizes the temperature of the second air heater VP2, providing the supply air temperature equal to tP3. Thus, the joint action of the two temperature controllers T3 and T4 ensures the state of the supply air P3. During the transition period, the air heater VP1 is turned off. Outside air enters the air conditioner irrigation chamber and, according to the signals from sensor T3, the power of the heater VP2 is regulated, outputting the parameters of the supply air to point P5, located on the P3P2P1 line.

Adjustment of air parameters during the warm period is carried out using the T2 sensor installed after the irrigation chamber. This sensor, through the regulator, maintains the flow of cold water through the irrigation chamber in such a way that the water temperature in the irrigation chamber ensures the process Hl → Cl. The T4 regulator, located in the room, regulates the heater performance, heating the air up to tP1.

Thus, during the warm period, the required state of the supply air is achieved by thermostats T2 and T4. SLE with air recirculation. 5 shows a diagram of a central air conditioner with air recirculation. In order to reduce heat/cold losses, part of the removed air enters the mixing chamber (CC), where it mixes with fresh supply air. The temperature of the mixed air is determined by the temperature/amount of outside/exhaust air.

The amount of mixed/supply air is adjusted using three dampers: supply (PZ), exhaust (VZ) and recirculation (RZ). This allows you to implement any degree of recirculation from 0 to 100%. When the supply and exhaust dampers are fully open and the recirculation damper is fully closed, the system becomes a direct-flow system (recirculation rate 0%).

With the supply and exhaust dampers fully closed and the recirculation damper fully open, the recirculation rate will be 100%. The total air consumption Gb is determined by the estimated amount required for the assimilation of heat and moisture surpluses. The minimum amount of outdoor air Gн is determined by the calculation for the assimilation of harmful vapors and gases or to ensure sanitary standards.

Then the mass of recirculation air Gp is determined as Gp = Gb - Gn. In the cold period, the outside air Gn is mixed with the recirculation air, the resulting mixture is heated in the first heating air heater to the enthalpy hcm, then it is subjected to adiabatic humidification in the spray chamber to the state of Kzm and in the air heater VH2 it is brought to the temperature of point P3. The air treatment sequence is as follows Nzm + Uz = Snu Snu Kzm P3.

The humidity content of the air is regulated by the thermostat T3 (the sensor is installed after the irrigation chamber). The adjustment is made in such a way that the air at the outlet of the heater of the 1st heating has an enthalpy hcm. Adiabatic humidification brings the moisture content of the air to the state of Km. The TS4 thermostat, the sensor of which is located in the room, regulates the heat output of the second heating air heater, providing the supply air temperature tpz. Maximum heating capacity of the 1st heating air heater:

QT1 \u003d Gb (hkzm - hnu), (3)

and the air heater of the 2nd heating:

QT2 \u003d Gob (hP3 - hkzm). (4)

As the point H moves towards the isenthalpe hnu, the power of the heater of the first heating VH1 decreases. At the moment when the point H is on the line hnu, the need for VH1 disappears. The state of air from hzm to hnu is called the first cold mode. Reducing the power of the VH1 heater to zero is a signal for the transition to the second - cold mode, which is between the enthalpies hnu and hkzm.

During this period, the outside air is mixed with the exhaust air, the mixture is subjected to adiabatic humidification in the irrigation chamber to the state hzm, after which it is heated by the VN2 heater to the state P3 (process Nm2 + Uz = Сnu Kzm P3). after the irrigation chamber. The regulator acts on the air dampers that regulate the flow of outdoor and recirculation air, ensuring their proportions, at which the enthalpy of the mixture is equal to hcm.

In the scheme of Fig. 6 in principle, one sensor can be used instead of sensors T2, T3 and T5. As the point H moves towards the isenthalpe hkzm, the flow rate of the circulating air decreases. Complete closure of the first recirculation valve is a signal to transfer the system to a transient mode. The state of the outside air between the enthalpies hcm and hcl is a transition mode. During this period, the outside air (Нper) is humidified adiabatically and heated up in the VH2 heater.

The dew point temperature of the supply air varies from tcm to tcl. The supply air temperature changes along the P3P2P1 line. The moisture content of the supply air is determined by the condition of the outside air. The supply air temperature is controlled by the TC4 thermostat, which affects the performance of the air heater VH2. The first warm mode covers the state of the outside air between the isoenthalpies hcl and hU1.

This range uses only outside air without recirculation. Air treatment consists in cooling in the irrigation chamber, followed by heating in the VP2 heater (Hl1 Kkl P1 process). To cool the air to a state of Kcl, the thermostat T2 controls a valve that regulates the temperature of the water supplied to the irrigation chamber. This regulates the moisture content of the supply air. It is also possible polytropic cooling from point Hl1 to point P1 with the help of indirect cooling by a refrigeration machine.

If the enthalpy of the outside air becomes higher than the enthalpy of the recirculation air, then it is advisable to mix the outside air with the recirculation air. Air treatment in the enthalpy range from hU1 to hl is called the second summer mode. In this mode, the air treatment sequence is as follows: Hl + U1 = Snu Kl P1.SCR with heat recovery Despite the fact that SCR with heat recirculation is energy efficient, its use is limited by sanitary and hygienic standards.

If indoor air assimilates harmful substances, tobacco smoke, fat fumes, etc., its use for recycling is not allowed. In this case, cross-flow (recuperative) (Fig. 7, 8, 9) or rotating (regenerative) heat exchangers (Fig. 11) are used. Schemes with recuperative heat exchangers provide greater savings than recirculation, while maintaining a given proportion of fresh air in the inlet .

In the plate cross heat exchanger (Fig. 9), the supply and exhaust air flows are completely separated. Therefore, this scheme can be applied without restrictions. When using a rotary heat exchanger, part of the exhaust air is returned to the room. Therefore, despite the fact that the heat recovery efficiency of a rotating heat exchanger reaches 80%, its use is limited according to sanitary standards.

It should be noted that only recuperative heat exchangers absolutely separate the oncoming flows. Regenerative heat exchangers have a small amount of recirculation. The thermodynamic model of SCR with heat recovery is shown in fig. 8. It differs from TDM direct-flow SCR in that the recovered heat shifts the supply air temperature from the point Hfm to the point Hfm in winter and from the point Hl to the point Hl in summer.

The efficiency of heat recovery in the heating mode is defined as the part of the heat energy given to the supply air compared to that which could be transferred if this air were heated to the enthalpy of the air removed from the room:

where h21, (t21) is the enthalpy (temperature) of the supply air before the heat exchanger; h22, (t22) is the enthalpy (temperature) of the supply air after the heat exchanger; h11, (t11) is the enthalpy (temperature) of the removed air in front of the heat exchanger; h12, (t12) is the enthalpy (temperature) of the exhaust air behind the heat exchanger. The heat recovery efficiency of rotating regenerative heat exchangers is determined by the formulas −

in heating mode:

where d is moisture content, g/m3. The rotation speed of the regenerative heat exchanger depends on the outdoor air temperature: with a decrease in temperature, the rotation speed of the heat exchanger increases (1-15 min-1). In order not to clog the heat exchanger, air filters are installed in the circuit both in the supply and exhaust ducts, as well as periodic “scrolling” of the wheel of the recuperator not currently in use when the unit is running.

Functional devices of central air conditioners

Mixing chambers

Outside and recirculated air enters through the air channels into the mixing chamber of the air conditioner. The air quantity is controlled by air dampers consisting of parallel plastic or metal blades. The blades rotate around their axis synchronously (mechanically connected) with the help of an electric drive.

There can be three dampers in the system: outside air, return air and exhaust air. The angle of rotation of the blades of each of the three dampers is determined by the required amount of fresh and recirculated air. The electric damper drive is controlled by commands from the automatic air conditioning control system.

Air Filtration Sections

The filtration section is designed to clean the air from solid, liquid or gaseous impurities. Depending on the purpose of the premises served by the air conditioner, coarse, fine or ultra-fine filters can be used. Coarse filters (class EU1-EU4 according to Eurovent 4/5) are used in air conditioning systems with low requirements for indoor air purity.

These are usually technological premises. Fine filters (class EU5-EU9) are used in the second stage of cleaning after coarse filters. They are used for ventilation and air conditioning of administrative buildings, hotels, hospitals. Ultrafine cleaning is used in the pharmaceutical and semiconductor industries. Coarse filters that trap coarse dust, fatty vapors are made of metallized mesh.

Fine filters - made of synthetic fiber (pocket type). Ultrafine filters (Q, R, S) are made of glass submicron fibers with a hydrophobic coating (Fig. 14). Activated carbon filters are used for gas separation. Thus, the GEA company produces carbon filters for air conditioners that absorb hydrocarbons, hydrogen sulfide, and radioactive methyl iodide (see table).

Air cooling sections

The air flow is cooled in tubular heat exchangers with finned tubes. Refrigerated liquid or freon is used as a refrigerant. To obtain chilled water, water-cooling machines (chillers) and pumping stations are used. A direct expansion chiller may also be used with the condensing unit installed in an open area to provide cooling to the condenser.

The evaporator is located in the refrigeration section. In this case, the refrigeration capacity is adjusted by means of a thermostatic expansion valve and by changing the compressor capacity.

Air heating sections

In the air heating section, water, steam, electric and freon heaters can be used. Water and steam heaters use hot water or central heating steam. Electric heaters have from one to four power levels. The electric heater is controlled by the temperature of the air flow, as well as by the amount of flow: if the air volume drops below the permissible value, the supply voltage will be turned off.

Air humidification sections

Air humidification is carried out by direct contact of air with water or by adding steam to it. When air is moistened with water, the process on the d-h diagram follows the line h = const (adiabatic humidification), and with steam, along the line t = const (isothermal humidification). Irrigation nozzles, ultrasonic atomizers, etc., or steam generators are used. Spraying is carried out using spray nozzles, water supply is carried out by a pump.

To exclude the entrainment of water droplets, a drop catcher is installed at the outlet of the humidification section. The circulation pump is located in the water tray, which also functions as a water tank. As the water evaporates, the remaining evaporated water is periodically drained, and the pan is filled with fresh water.

The water level is controlled by a float that opens the feed pipe, and the circulating water is released by a ball valve on the discharge side of the pump. In some air conditioners, air humidification is carried out by dry superheated steam. Steam is supplied from the heating system and sprayed by injection nozzles. Such humidifiers have condensate traps, a steam filter, and a condensate level regulator. Steam humidification has several advantages:

high accuracy of air humidity maintenance;
dry superheated steam does not contain mineral salts and bacteria;
minimum operating costs.

Fan sections

In central air conditioners, air with a volume of 1,000 to 200,000 m3/h is processed. The speed of air flow in the free section of the installation should not exceed 5 m/s. The recommended speed during heating and ventilation is from 2.5 to 3 m/s, in cooling mode - from 2 to 2.5 m/s. During adjustment, special attention must be paid to the installation and tension of the fan belt: the drive pulleys must be strictly parallel, and the belt deflection must not exceed 10 mm with a pressing force on the belt in the middle between the pulleys with a force of 10 kg (specified according to the passport for the belt).

Silencing sections

The noise attenuation section consists of sound-absorbing plates, which are made of mineral wool reinforced with a glass fiber coating. Air dividers are installed in front of the noise-absorbing plates, which equalize the flow velocity in the channel cross section. Where noise requirements are high, soundproofing of air ducts is provided.

When choosing materials for sound attenuation sections, it must be taken into account that fiber separation can occur in mineral wool, which is dangerous to health (damage to the respiratory tract). Therefore, mufflers are chosen in which measures have been taken to eliminate this phenomenon (impregnation, material with an elastic protective film, etc.).

Page 2 of 6

1.2. Quality regulation of SCR

1.2.1. Automation of once-through SCR

In the technique of conditioning, quantitative and qualitative regulation is used. With quantitative regulation, the required air condition is achieved by changing the air flow rate at constant air parameters. Quantitative regulation is used in multi-zone systems, and in single-zone systems it is qualitative. Both of these methods can be used to obtain optimal SCR parameters.

The temperature is maintained by sensors located in the manned room. Humidity can be regulated by the humidity of the air in the room (direct regulation) or by the dew point temperature of the air after the irrigation chamber (indirect regulation).

When adjusting humidity according to the dew point temperature, it is necessary to install two heaters BH1 and BH2 in the air treatment line (Fig. 1.2). The air is heated, brought in the OK irrigation chamber to parameters close to the dew point temperature of the supply air. Temperature sensor T2, installed after the spray chamber, controls the power of the first air heater so that the air temperature after the spray chamber (ϕ= 95%) stabilizes around the dew point.

The air heater of the second heating, installed after the irrigation chamber, brings the supply air to the required temperature.

Thus, indirect regulation of supply air humidity is carried out by thermostats without direct measurement of humidity.

With combined regulation of air humidity, direct and indirect regulation are combined. This method is used in air conditioning systems that have a bypass channel around the irrigation chamber, and is called the method of optimal modes.

On fig. 1.3 shows a thermodynamic model of a direct-flow air conditioning system. The blue color shows the annual limits of changes in outdoor air parameters. The lower limit point of outdoor air during the cold period is designated Nzm, and for warm - Nl. Many States

air in the working area is indicated by the polygon P1P2P3P4 (zone P), and the set of permissible states of the supply air - P1P2P3P4 (zone P).

In the cold period, the outside air with the parameters Nzm must be brought to one of the points of the set P. It is obvious that the minimum costs (the shortest path) will be if In this case, the outside air needs to be heated in the first heating heater (VH1, Fig. 1.3) to the point H 'zm, humidify adiabatically along the line H 'zm→Kzm at hk zm = const, and then heat the heater of the second heating VN2 to the temperature of point P3 (process Hzm→H 'zm→Kzm→P3). During the adiabatic process of humidification, the air is humidified up to 95-98%. The Kzm point, located at the intersection of the d3 line and the 95-98% relative humidity curve, is the dew point of the supply air P3.

The maximum heat output of the first heating air heater VH1 must be

and air heater VH2

where G is the air consumption, kg/h.

As the outdoor temperature rises, the heating intensity of the HV1 will decrease, but the air treatment sequence will remain (H1→H ’1→Kzm→P3). When the outside air reaches the enthalpy hn > hk zm, there is no need for a preheater for the first heating VH1. In this case, the outside air only needs to be humidified and heated in BH2. Obviously, the shortest air treatment path will be H ’zm→Kzm→P3 or, for example, Hper→Kper→P5. With a further increase in the outdoor temperature, point P5 will move along the line P3P2P1 and reach point P1, which indicates the need to switch to air treatment using the warm period technology. The range of outdoor air temperatures within the limits of enthalpy change from hk zm to hcl is a transitional period.

It is possible to eliminate the second heating by mixing part of the heated outdoor air with humidified air after the irrigation chamber (Fig. 1.4).

In this case, the outside air is heated to the point H ''zm, humidified in the irrigation chamber (H ''zm → K ''zm) up to 95%, and then the heated air is mixed with humidified air in such a ratio that the mixture point coincides with the point P3. This operation can be performed by a temperature sensor, or by a humidity sensor after the mixing chamber.

The easiest way to humidify is to use steam generators. In this case, heating is carried out by the first heater to the point P '3, and then moistened along the isotherm to the point P3. However, the use of steam generators is economically unprofitable due to the high consumption of electricity. The use of a honeycomb humidifier gives a significant reduction in energy consumption. Thus, the power consumption for humidification in relative units is:

humidification in the irrigation chamber - 5;

steam humidification - 80;

honeycomb humidification - 1.

In the warm period, the limiting parameters of the outside air are the Hl point (Fig. 1.3). It is obvious that the minimum costs for the transition from the point Hl to the zone P will be if you choose the end point P1. Air with parameters Hl must be subjected to cooling and dehumidification. This process can be implemented using a refrigeration machine (Nl → P1 process) or an irrigation chamber. In the latter case, the air is cooled by the cold water of the irrigation chamber and dried along the line Nl → Kl, and then heated in VN2 along the line Kl → P1.

To implement all periods of operation of the air conditioner, it is necessary to install two temperature sensors after the irrigation chamber: one (T3) configured for the dew point temperature of the cold period tk zm, the second (T2) - for the dew point temperature tk of the warm period.

During the cold season, the T3 sensor, by regulating the heating capacity of the VN1 heater, provides air heating up to the enthalpy hk zm and adiabatic humidification of the air in the irrigation chamber up to the moisture content of the supply air d3. The temperature controller TC4, the sensor of which is located in the room, stabilizes the temperature of the second air heater VH2, providing the supply air temperature equal to tP3. Thus, the joint action of the two thermostats TC3 and TC4 ensures the state of supply air P3.

During the transitional period, the air heater VH1 is switched off. Outside air enters the irrigation chamber. Based on the T3 sensor signals, the power of the VN2 heater is controlled, which brings the supply air parameters to point P5, located on the P3P2P1 line.

Adjustment of air parameters during the warm period is carried out using the T2 sensor installed after the irrigation chamber. This sensor, through the regulator, maintains the flow of cold water through the irrigation chamber in such a way that the water temperature in the irrigation chamber ensures the process Nl→Kl. The TC4 regulator, located in the room, regulates the heater performance, heating the air up to tP1. Thus, during the warm season, the required state of the supply air is achieved by thermostats TC2 and TC4.

In the supply air dew point control mode, there is some fluctuation in air humidity. However, the temperature is maintained by the TC4 thermostat quite accurately.

1.2.2. Automation of SCR with air recirculation

On fig. 1.5 shows a diagram of a central air conditioner with air recirculation. In order to reduce heat (cold) losses, part of the removed air enters the mixing chamber (CC), where it mixes with fresh supply air. The temperature of the mixed air is determined by the temperature of the outside and exhaust air, as well as their quantity.

The amount of mixed and supply air is adjusted using three dampers: supply (PZ), exhaust (VZ) and recirculation (RZ). The dampers in the supply and exhaust ducts must operate in phase, and in the recirculation duct - out of phase with respect to the exhaust and supply ducts. This allows you to implement any degree of recirculation from 0 to 100%. When the supply and exhaust dampers are fully open and the recirculation damper is fully closed, the system becomes a direct-flow system (recirculation rate 0%). With the supply and exhaust dampers fully closed and the recirculation damper fully open, the recirculation rate will be 100%.

The total air consumption Gb is determined by the estimated amount required for the assimilation of heat and moisture surpluses. The minimum amount of outdoor air Gн is determined by the calculation for the assimilation of harmful vapors and gases or to ensure sanitary standards. Then the mass of recirculation air Gp is determined as Gp = Gb - Gn.

In the cold period (Fig. 1.6), the outside air Gн is mixed with the recirculation air, the resulting mixture is heated in the first heating air heater to the enthalpy hk zm, then it is subjected to adiabatic humidification in the spray chamber to the state Kzm and in the air heater VN2 it is brought to the temperature of point P3. The air treatment sequence is as follows: Hzm + Uz \u003d Cnu → C 'well → Kzm → P3. The humidity content of the air is regulated by the TC3 temperature controller, the sensor of which is installed after the irrigation chamber. The adjustment is made in such a way that the air at the outlet of the heater of the first heating has an enthalpy hk zm. Adiabatic humidification brings the moisture content of the air to the state Km.

The temperature controller TS4, the sensor of which is located in the room, regulates the heat output of the second heating air heater, providing the supply air temperature tpz. Maximum heat output of the first heating air heater

and the air heater of the second heating

As the point Нзм moves towards the isoenthalpe hн, the power of the heater of the first heating ВН1 decreases. At the moment when the point H is on the line hnu, the need for VH1 disappears. The state of air from hzm to hnu is called the first cold mode. Reducing the power of the VN1 heater to zero is a signal for the transition to the second cold mode, which is between the enthalpies hnu and hk zm. During this period, the outside air mixes with the exhaust air, the mixture is subjected to adiabatic humidification in the irrigation chamber to the state hzm, after which it is heated by the VN2 heater to the state P3 (process Hzm2 + Uz = C ''nu → Kzm → P3).

The moisture content of the supply air is regulated by the TC5 thermostat, whose sensor T5 is located after the irrigation chamber. The regulator acts on the air dampers that regulate the flow of outdoor and recirculation air, ensuring their proportions, at which the enthalpy of the mixture is equal to hk zm. In the scheme of Fig. 1.5, in principle, one sensor can be used instead of sensors T2, T3 and T5.

As the point Hcm moves towards the isoenthalpe hk cp, the flow rate of circulating air decreases. Complete closure of the recirculation valve is a signal to transfer the system to a transient mode. The state of the outside air between the enthalpies hk zm and hcl is a transition mode. During this period, the outside air (Нper) is humidified adiabatically and heated up in the VH2 heater. The dew point temperature of the supply air varies from tk zm to tkl. The supply air temperature changes along the P3P2P1 line. The moisture content of the supply air is determined by the condition of the outside air. The supply air temperature is controlled by the TC4 temperature controller, which affects the performance of the VH2 air heater.

The first warm regime covers the state of the outside air between the isenthalpies hpz and hU1. This range uses only outside air without recirculation. Air treatment consists in cooling in the irrigation chamber with subsequent heating in the VN2 heater (Hl1 → Kkl → P1 process). To cool the air to the state of Kcl, the TC2 thermostat controls a valve that regulates the temperature of the water supplied to the irrigation chamber. This regulates the moisture content of the supply air. It is also possible polytropic cooling from point Hl1 to point P1 with the help of indirect cooling by a refrigeration machine.

1.2.3. SCR automation with heat recovery

Despite the fact that SCR with air recirculation is energy efficient, its use is limited by sanitary and hygienic standards. If the indoor air assimilates harmful substances, tobacco smoke, fatty fumes, etc., its use for recycling is not allowed. In this case, cross-flow (recuperative) or rotating (regenerative) heat exchangers are used (Fig. 1.8).

It should be noted that only recuperative heat exchangers absolutely separate the oncoming flows. Regenerative heat exchangers have a small amount of recirculation.

The thermodynamic model of SCR with heat recovery is shown in fig. 1.7. It differs from TDM direct-flow SCR in that the recovered heat shifts the temperature of the supply air from the point Hfm to the point Hfl in winter and from the point Hl to the point Hl l in summer.

In SCR with a regenerative heat exchanger, the rotor speed is subject to adjustment, depending on the outside air temperature: with a decrease in temperature, the heat exchanger speed increases (1-15 min-1).

In order not to clog the heat exchanger, air purification filters are installed both in the supply and exhaust ducts, and periodic “scrolling” of the wheel of the heat exchanger that is not currently in use is ensured when the unit is running.

1.2.4. Automation of single-zone split systems

In residential and office premises, autonomous single-zone air conditioners (split systems) with the following features are widely used:

limited range of outdoor temperature - mainly manufacturers limit the use of split systems in winter and transitional periods of the year with a temperature not lower than minus (5-10) ° С;

 there are no humidification blocks;

 the heat exchanger of the internal block carries out functions of a cooler and a heater;

capacity adjustment is mainly carried out by starting-stopping the compressor or changing the amount of refrigerant supplied to the heat exchanger;

there are no bypass channels for air bypassing;

temperature control is carried out according to the temperature in the room, set by the user;

the temperature in the room is maintained in the heating mode (tset + 1) °C and cooling mode (tset - 1) °C;

The temperature of the refrigerant in the heat exchanger of the indoor unit is: in heating mode (40-45) °C; in cooling mode (5-7) °С.

The cooling mode can occur without changing the moisture content (dry cooling) or with a decrease in moisture content (cooling and dehumidification). For dry air cooling, the temperature of the heat exchange surface must be above the dew point of the cooled air (Fig. 1.9).

If the temperature of the heat exchange surface is below the dew point of the air, moisture will condense from the air, which in this case is not only cooled, but also dried. As a result of condensation, the air will interact with the damp surface of the air cooler. Air in a thin film near the water surface acquires parameters such as those of saturated water vapor at a temperature equal to the temperature of a given surface area.

The process of interaction of air with the humid surface of the air cooler is similar to the process in a contact type apparatus and is depicted on the dh diagram by a line directed from the point of the initial state Hl of the air to the intersection point of the isotherm corresponding to the average temperature tw of the air cooler surface, with the curve ϕ= 100% (Fig. 1.9 , HW line).

The air temperature at the outlet of the heat exchanger tк is determined by the air temperature at the inlet of the heat exchanger tн, the surface temperature of the heat exchanger tw and the efficiency coefficient of the heat exchanger Et (Fig. 1.10).

With a known temperature of the coolant at the inlet of the heat exchanger tw, the air temperature at the outlet tk can be determined by the formula:

where Et is the coefficient of heat transfer efficiency, showing the ratio of real heat transfer to the maximum possible in an ideal process.

For processes proceeding according to t = const

for processes proceeding according to d = const

Some manufacturers to evaluate the efficiency of surface heat exchangers in the technical documentation give a bypass factor value equal to the ratio:

For equipment, the bypass factor is 0.18-0.25.

On fig. 1.11 presents a thermodynamic model of processes in a single-zone split system, built taking into account the features discussed above.

During the warm period, the automatic air conditioning control system maintains the temperature (tset + 1), during the cold and transitional periods - (tset - 1).

In the cooling mode, the process proceeds from the point Hl along the line d = const to the intersection with the line ϕ= 100%, then along this line until the intersection with the line tout = tset + 1. It should be remembered that in reality the processes of cooling HlD and dehumidification DH occur simultaneously along a curve gradually approaching the line tset + 1 (process Hl1→Hl2→H2...).

Further, the automatic control system supports the process along the line tset + 1 with moisture condensation. The slope of the process is continuously changing along the lines KnHn. This process will continue until its direction coincides with the direction of the angular coefficient pom. So, if the angular coefficient is directed along the line pom, then the process in the room will stabilize along the line K3H3. If there is no moisture release in the room, the process will follow the K4H4 line at d = const.

In the cold and transitional periods of the year (heating mode), the process goes from the point Nzm vertically upwards (d = const) to the intersection with the line (tast - 1) °C. The lack of air humidification process can lead to dehumidification below comfortable conditions, which is a disadvantage of split systems in heating mode.