The system under consideration consists of two air conditioners "

the main one, in which the air is processed for the manned room, and the auxiliary one - the cooling tower. The main purpose of the cooling tower is air-evaporative cooling of water supplying the first stage of the main air conditioner during the warm season (surface heat exchanger PT). The second stage of the main air conditioner - the OK irrigation chamber, operating in the adiabatic humidification mode, has a bypass channel - B for regulating the air humidity in the room.

In addition to air conditioners - cooling towers, industrial cooling towers, fountains, spray pools, etc. can be used to cool water. In areas with hot and humid climates, in some cases, in addition to indirect evaporative cooling, machine cooling is used.

multistage systems evaporative cooling. The theoretical limit for air cooling using such systems is the dew point temperature.

Air conditioning systems using direct and indirect evaporative cooling have a wider range of applications) compared to systems that only use direct (adiabatic) evaporative air cooling.

Two-stage evaporative cooling is known to be most acceptable in

areas with dry and hot climates. With two-stage cooling, more low temperatures, lower air changes and lower relative humidity in rooms than with single-stage cooling. This property two-stage cooling caused a proposal to switch entirely to indirect cooling and a number of other proposals. However, all other things being equal, the effect of the action possible systems Evaporative cooling is directly dependent on changes in the condition of the outside air. Therefore, such systems do not always ensure the maintenance of the required air parameters in air-conditioned rooms during the season and even for one day. An idea of ​​the conditions and boundaries of the expedient use of two-stage evaporative cooling can be obtained by comparing the normalized parameters of the internal air with possible changes in the parameters of the external air in areas with a dry and hot climate.

the calculation of such systems should be performed with using J-d diagrams in the following sequence.

On the J-d diagram, points are plotted with the calculated parameters of the external (H) and internal (B) air. In the example under consideration, according to the design assignment, the following values ​​are accepted: tн = 30 ° С; tv = 24 ° C; fw = 50%.

For points H and B, we determine the value of the temperature of the wet thermometer:

tmn = 19.72 ° C; tmv = 17.0 ° C.

As you can see, the value of tmn is almost 3 ° C higher than tmw, therefore, for more cooling of the water and then the external supply air, it is advisable to supply the air removed to the cooling tower exhaust systems from office premises.

Note that when calculating a cooling tower, the required air flow may be greater than that removed from the air-conditioned rooms. In this case, a mixture of external and exhaust air must be supplied to the cooling tower and the temperature of the wet thermometer of the mixture must be taken as the design temperature.

From the calculated computer programs leading companies - manufacturers of cooling towers, we find that the minimum difference between the final water temperature at the outlet of the cooling tower tw1 and the temperature of the wet thermometer tвм of the air supplied to the cooling tower should be taken at least 2 ° С, that is:

tw2 = tw1 + (2.5 ... 3) ° С. (1)

To achieve a deeper air cooling in the central air conditioner, the final water temperature at the outlet from the air cooler and at the inlet to the cooling tower tw2 is not more than 2.5 higher than at the outlet from the cooling tower, that is:

tvk ≥ tw2 + (1 ... 2) ° С. (2)

Note that the final temperature of the cooled air and the surface of the air cooler depend on the temperature tw2, since with a cross flow of air and water, the final temperature of the cooled air cannot be lower than tw2.

Usually, the final temperature of the cooled air is recommended to be taken 1–2 ° C higher than the final temperature of the water leaving the air cooler:

tvk ≥ tw2 + (1 ... 2) ° С. (3)

Thus, when the requirements (1, 2, 3) are met, it is possible to obtain a relationship between the temperature of the wet thermometer of the air supplied to the cooling tower and the final temperature of the air at the outlet of the cooler:

tvk = tvm +6 ° С. (4)

Note that in the example in Fig. 7.14 the values ​​of tvm = 19 ° С and tw2 - tw1 = 4 ° С are accepted. But with such initial data, instead of the value of tvk = 23 ° С indicated in the example, it is possible to obtain the final air temperature at the outlet of the air cooler not lower than 26-27 ° С, which makes the whole scheme meaningless at tn = 28.5 ° С.

Ecology of consumption. The history of the creation of a direct evaporative cooling air conditioner. Differences between direct and indirect cooling. Variants of application of air conditioners of evaporative type

Cooling and humidifying the air by evaporative cooling is a completely natural process in which water is used as a cooling medium and heat is efficiently dissipated in the atmosphere. Simple patterns are used - when the liquid evaporates, heat is absorbed or cold is released. Evaporation efficiency - increases with increasing air speed, which provides forced circulation of the fan.

Dry air temperature can be significantly reduced by the phase transition of liquid water to steam, and this process requires significantly less energy than compression cooling. In very dry climates, evaporative cooling also has the advantage that when the air is conditioned it increases the humidity of the air, and this creates more comfort for the people in the room. However, unlike vapor compression cooling, it requires a constant source of water, and during operation it constantly consumes it.

The history of development

Over the centuries, civilizations have found original methods fight the heat in their territories. An early form of the cooling system, the "wind catcher", was invented many thousands of years ago in Persia (Iran). It was a system of windshafts on the roof that caught the wind, passed it through the water, and blew chilled air into indoor spaces... It is noteworthy that many of these buildings also had courtyards with large reserves of water, therefore, if there was no wind, then as a result of the natural process of water evaporation, hot air, rising upward, evaporated the water in the courtyard, after which the already cooled air passed through the building. Today, Iran has replaced wind catchers with evaporative coolers and is using them extensively, and the market, due to the dry climate, reaches 150,000 evaporators a year.

In the United States, the evaporative cooler has been the subject of numerous patents in the twentieth century. Many of whom, beginning in 1906, suggested using wood chips as a spacer for transferring a large number of water on contact with moving air, and maintaining intensive evaporation. The standard design, as shown in the 1945 patent, includes a water reservoir (usually equipped with a float valve to adjust the level), a pump to circulate water through gaskets from wood shavings, and a fan for supplying air through the spacers to the living quarters. This design and materials remain a staple in evaporative cooler technology in the Southwest United States. In this region, they are additionally used to increase humidity.

Evaporative cooling was common in aircraft engines of the 1930s, such as the engine for the Beardmore Tornado airship. This system has been used to reduce or eliminate a radiator that would otherwise create significant aerodynamic drag... In these systems, the water in the engine was kept under pressure by pumps that allowed it to heat up to over 100 ° C, since the actual boiling point was dependent on pressure. Superheated water was sprayed through a nozzle onto an open pipe, where it instantly evaporated, taking its heat. These pipes could be positioned below the surface of the aircraft to create zero drag.

External evaporative cooling devices have been installed on some vehicles to cool the interior. They were often sold as optional accessories. The use of evaporative cooling devices in automobiles continued until vapor compression air conditioning became widespread.

The principle of evaporative cooling is different from that on which vapor compression chillers operate, although they also require evaporation (evaporation is part of the system). In the vapor compression cycle, after the refrigerant has evaporated inside the evaporating coil, the refrigerant gas is compressed and cooled, condensing under pressure into liquid state... In contrast to this cycle, in an evaporative cooler, water evaporates only once. The evaporated water in the cooling device is discharged into the space with chilled air. In the cooling tower, the evaporated water is carried away by the air stream.

Evaporative Cooling Applications

There are direct, oblique, and two-stage (direct and indirect) evaporative air cooling. Direct evaporative air cooling is based on the isenthalpic process and is used in air conditioners during the cold season; in warm weather, it is possible only in the absence or insignificant moisture release in the room and low moisture content of the outside air. Bypassing the irrigation chamber somewhat expands the boundaries of its application.

Direct evaporative air cooling is advisable in dry and hot climates in the supply ventilation system.

Indirect evaporative air cooling is carried out in surface air coolers. An auxiliary contact apparatus (cooling tower) is used to cool the water circulating in the surface heat exchanger. For indirect evaporative cooling of air, it is possible to use devices of the combined type, in which the heat exchanger performs both functions simultaneously - heating and cooling. Such devices are similar to air recuperative heat exchangers.

The cooled air passes through one group of channels, inner surface the second group is irrigated with water flowing into the pan and then sprinkled again. Upon contact with the exhaust air passing in the second group of channels, evaporative cooling of the water occurs, as a result of which the air in the first group of channels is cooled. Indirect evaporative air cooling allows to reduce the performance of the air conditioning system in comparison with its performance with direct evaporative air cooling and expands the possibilities of using this principle, because the moisture content of the supply air is lower in the second case.

With two-stage evaporative cooling air use sequential indirect and direct evaporative cooling of air in the air conditioner. In this case, the installation for indirect evaporative cooling of air is supplemented with an irrigation nozzle chamber operating in the direct evaporative cooling mode. Typical spray chambers are used in evaporative air cooling systems as cooling towers. In addition to single-stage indirect evaporative air cooling, multistage air cooling is possible, in which deeper air cooling is carried out - this is the so-called compressorless air conditioning system.

Direct evaporative cooling (open cycle) is used to lower the air temperature using the specific heat of vaporization, changing the liquid state of water to a gaseous one. In this process, the energy in the air does not change. Dry, warm air replaced with cool and humid. The heat from the outside air is used to evaporate the water.

Indirect evaporative cooling (closed loop) is a process similar to direct evaporative cooling, but using a specific type of heat exchanger. In this case, moist, cooled air does not come into contact with the conditioned environment.

Two-stage evaporative cooling, or indirect / direct.

Traditional evaporative chillers use only a fraction of the energy required by vapor compression chillers or adsorption air conditioning systems. Unfortunately, they increase the humidity of the air to an uncomfortable level (except in very dry climatic zones). Two-stage evaporative chillers do not increase humidity levels as much as standard single-stage evaporative chillers.

In the first stage of a two-stage cooler, warm air is cooled indirectly without increasing humidity (by passing through a heat exchanger cooled by evaporation from the outside). In the direct stage, the pre-cooled air passes through the water-soaked pad, additionally cools and becomes more humid. Since the process includes a first, pre-cooling stage, less humidity is needed in the direct evaporation stage to achieve the required temperatures. As a result, according to manufacturers, the process cools air with relative humidity in the range of 50 - 70%, depending on the climate. For comparison traditional systems cooling increase air humidity up to 70 - 80%.

Appointment

When designing a central supply system ventilation, it is possible to equip the air intake with an evaporating section and thus significantly reduce the cost of cooling the air in the warm season.

During cold and transitional periods of the year, when the air is heated supply air heaters ventilation systems or indoor air by heating systems - the air heats up and its physical ability to assimilate (absorb) increases, with an increase in temperature - moisture. Or, the higher the air temperature, the more moisture it can assimilate into itself. For example, when the outside air is heated by an air heater by the ventilation system from a temperature of -22 0 С and a humidity of 86% (the parameter of outdoor air for HP in Kiev), up to +20 0 С - the humidity drops below the boundary limits for biological organisms up to unacceptable 5-8% air humidity. Low air humidity - negatively affects the skin and mucous membranes of a person, especially patients with asthma or lung diseases. Normalized air humidity for residential and administrative premises: from 30 to 60%.

Evaporative cooling of air is accompanied by the release of moisture or an increase in air humidity, up to a high saturation of air humidity of 60-70%.

Advantages

The amount of evaporation - and therefore the heat transfer - depends on the outside wet bulb temperature, which, especially in summer, is much lower than the equivalent dry bulb temperature. For example, in hot summer days When the dry bulb temperature is over 40 ° C, evaporative cooling can cool the water down to 25 ° C or cool the air.
Because evaporation removes much more heat than standard physical heat transfer, heat transfer uses up to four times less air flow than conventional air cooling methods, saving significant amounts of energy.

Evaporative cooling versus traditional ways air conditioning Unlike other types of air conditioning, evaporative air cooling (bio-cooling) does not use harmful gases (freon and others) that harm the environment as refrigerants. It also uses less electricity, thus saving energy, Natural resources and up to 80% of operating costs compared to other air conditioning systems.

disadvantages

Low efficiency in humid climates.
An increase in air humidity, which in some cases is undesirable - the exit is two-stage evaporation, where the air does not contact and is not saturated with moisture.

Principle of operation (option 1)

The cooling process is carried out by the close contact of water and air, and the transfer of heat to the air by evaporation of a small amount of water. The heat is then dissipated through the warm and moisture-laden air leaving the unit.

Principle of operation (option 2) - installation on the air intake

Evaporative Cooling Units

Exists Various types installations for evaporative cooling, but they all have:
- a section of heat exchange or heat transfer, constantly wetted with water by irrigation,
- fan system for forced circulation outside air through the heat exchange section,

In modern climatic technology, much attention is paid to the energy efficiency of equipment. This explains the recent increased interest in water-evaporative cooling systems based on indirect-evaporative heat exchangers(indirect evaporative cooling systems). Evaporative cooling systems can be an effective solution for many regions of our country, the climate of which is characterized by relatively low air humidity. Water as a refrigerant is unique - it has a high heat capacity and latent heat of vaporization, is harmless and available. In addition, water is well studied, which makes it possible to accurately predict its behavior in various technical systems.

Features of cooling systems with indirect evaporative heat exchangers

Main feature and the advantage of indirect evaporative systems is the ability to cool the air to a temperature below the wet bulb temperature. Thus, the technology of conventional evaporative cooling (in adiabatic humidifiers), when water is injected into the air stream, not only lowers the air temperature, but also increases its moisture content. In this case, the line of the process on the I d-diagram humid air goes along the adiabat, and the lowest possible temperature corresponds to point "2" (Fig. 1).

In indirect evaporative systems, the air can be cooled to point "3" (Fig. 1). The process in the diagram in this case goes vertically down the line of constant moisture content. As a result, the resulting temperature is lower, and the moisture content of the air does not increase (remains constant).

In addition, water evaporation systems have the following positive qualities:

• Possibility of joint production of cooled air and cold water.
• Low power consumption. The main consumers of electricity are fans and water pumps.
• High reliability due to the absence of complex machines and the use of a non-aggressive working medium - water.
• Environmental friendliness: low noise and vibration level, non-aggressive working fluid, low environmental hazard industrial production systems due to the low complexity of manufacturing.
• Simplicity structural performance and relatively low cost associated with the absence of strict requirements for the tightness of the system and its individual units, the absence of complex and expensive cars (refrigeration compressors), low overpressures in the cycle, low metal consumption and the possibility of widespread use of plastics.

Cooling systems that use the effect of absorbing heat by evaporating water have been known for a very long time. However, at the moment, water evaporative cooling systems are not widespread enough. Almost the entire niche of industrial and household systems cooling in the region of moderate temperatures filled with freon vapor compression systems.

This situation is obviously associated with the problems of operation of water evaporation systems at negative temperatures and their unsuitability for operation at high relative humidity of the outside air. It also affected the fact that the main devices of such systems (cooling towers, heat exchangers), which were used earlier, had large dimensions, weight and other disadvantages associated with working under conditions high humidity... In addition, they needed a water treatment system.

However, today, thanks to technical progress, highly efficient and compact cooling towers have become widespread, capable of cooling water to temperatures that are only 0.8 ... 1.0 ° C differing from the wet bulb temperature of the air flow entering the cooling tower.

The cooling towers of the companies should be noted here in a special way. Muntes and SRH-Lauer... So small temperature head managed to secure mainly original design cooling tower packing unique properties- good wettability, manufacturability, compactness.

Description of the indirect evaporative cooling system

In an indirect evaporative cooling system, atmospheric air from environment with parameters corresponding to point "0" (Fig. 4), it is blown into the system by a fan and cooled at constant moisture content in an indirect evaporative heat exchanger.

After the heat exchanger, the main air flow is divided into two: auxiliary and working, directed to the consumer.

The auxiliary flow simultaneously plays the role of both a cooler and a cooled flow - after the heat exchanger it is directed back towards the main flow (Fig. 2).

In this case, water is supplied to the channels of the auxiliary flow. The meaning of water supply is to "slow down" the rise in air temperature due to its parallel humidification: as you know, one and the same change in thermal energy can be achieved both by changing only the temperature, and by changing the temperature and humidity at the same time. Therefore, when the auxiliary stream is humidified, the same heat exchange is achieved with a smaller temperature change.

In indirect evaporative heat exchangers of another type (Fig. 3), the auxiliary flow is directed not to the heat exchanger, but to the cooling tower, where it cools the water circulating through the indirect evaporative heat exchanger: the water is heated in it due to the main flow and cools down in the cooling tower due to the auxiliary one. The movement of water along the circuit is carried out using a circulation pump.

Calculation of an indirect evaporative heat exchanger

In order to calculate the cycle of an indirect evaporative cooling system with circulating water, the following input data are required:

• φ OS is the relative humidity of the ambient air,%;
• t OS - ambient air temperature, ° С;
• ∆t х - temperature difference at the cold end of the heat exchanger, ° С;
• ∆t m - temperature difference at the warm end of the heat exchanger, ° С;
• ∆t wgr is the difference between the temperature of the water leaving the cooling tower and the temperature of the air supplied to it according to a wet bulb, ° С;
• ∆t min is the minimum temperature difference (temperature head) between the flows in the cooling tower (∆t min<∆t wгр), ° С;
• G p is the mass air flow required by the consumer, kg / s;
• η in - fan efficiency;
• ∆P in - pressure loss in apparatus and lines of the system (required fan pressure), Pa.

The calculation methodology is based on the following assumptions:

• Heat and mass transfer processes are assumed to be equilibrium,
• There are no external heat inflows in all sections of the system,
• The air pressure in the system is equal to atmospheric (local changes in air pressure due to its injection by a fan or passing through aerodynamic resistances are negligible, which makes it possible to use the I d diagram of humid air for atmospheric pressure throughout the calculation of the system).

The procedure for engineering calculation of the system under consideration is as follows (Figure 4):

1. According to the I d diagram or using the program for calculating humid air, additional parameters of the ambient air are determined (point "0" in Fig. 4): specific enthalpy of air i 0, J / kg and moisture content d 0, kg / kg.
2. The increment in the specific enthalpy of air in the fan (J / kg) depends on the type of fan. If the fan motor is not blown (cooled) by the main air flow, then:

If the circuit uses a duct-type fan (when the electric motor is cooled by the main air flow), then:

where:
η dv - efficiency of the electric motor;
ρ 0 - air density at the fan inlet, kg / m 3

where:
B 0 - barometric pressure of the environment, Pa;
R in - gas constant of air, equal to 287 J / (kg.K).

3. Specific enthalpy of air after the fan (point "1"), J / kg.

i 1 = i 0 + ∆i in; (3)

Since the process "0-1" occurs at a constant moisture content (d 1 = d 0 = const), then using the known φ 0, t 0, i 0, i 1 we determine the air temperature t1 after the fan (point "1").

4. The dew point of the ambient air t dew, ° C, is determined by the known φ 0, t 0.

5. Psychrometric difference in air temperatures of the main stream at the outlet of the heat exchanger (point "2") ∆t 2-4, ° С

∆t 2-4 = ∆t x + ∆t wgr; (4)

where:
∆t х is assigned based on specific operating conditions in the range of ~ (0.5 ... 5.0), ° С. It should be borne in mind that small values ​​of ∆t x will entail relatively large dimensions of the heat exchanger. To ensure low values ​​of ∆t x, it is necessary to use highly efficient heat transfer surfaces;

∆t wgr is selected in the range (0.8 ... 3.0), ° С; smaller values ​​of ∆t wgr should be taken if it is necessary to obtain the lowest possible temperature of cold water in the cooling tower.

6. We assume that the process of humidification of the auxiliary air flow in the cooling tower from the state "2-4", with sufficient accuracy for engineering calculations, proceeds along the line i 2 = i 4 = const.

In this case, knowing the value of ∆t 2-4, we determine the temperatures t 2 and t 4, points "2" and "4", respectively, ° C. To do this, we find such a line i = const so that between point "2" and point "4" the temperature difference is found ∆t 2-4. Point "2" is at the intersection of lines i 2 = i 4 = const and constant moisture content d 2 = d 1 = d OS. Point "4" is at the intersection of the line i 2 = i 4 = const and the curve φ 4 = 100% relative humidity.

Thus, using the diagrams given, we determine the remaining parameters at points "2" and "4".

7. Determine t 1w - water temperature at the outlet of the cooling tower, at the point "1w", ° С. In the calculations, the heating of water in the pump can be neglected, therefore, at the inlet to the heat exchanger (point "1w"), the water will have the same temperature t 1w

t 1w = t 4 + .∆t wgr; (5)

8.t 2w - water temperature after the heat exchanger at the inlet to the cooling tower (point "2w"), ° С

t 2w = t 1 - .∆t m; (6)

9. The temperature of the air discharged from the cooling tower into the environment (point "5") t 5 is determined by the graphical analytical method using the id diagram calculation used id diagram). The specified method is as follows (Fig. 5):

• point "1w", characterizing the state of water at the inlet to the indirect evaporative heat exchanger, with the value of specific enthalpy of point "4" is placed on the isotherm t 1w, spaced from the isotherm t 4 at a distance ∆t wgr.
• From the point "1w" along the isenthalp we lay off the segment "1w - p" so that t p = t 1w - ∆t min.
• Knowing that the process of heating the air in the cooling tower occurs according to φ = const = 100%, we build from the point "p" a tangent to φ pr = 1 and get the point of contact "k".
• From the point of contact "k" along the isenthalp (adiabat, i = const) we postpone the segment "k - n" so that t n = t k + ∆t min. Thus, the minimum temperature difference between the cooled water and the air of the auxiliary flow in the cooling tower is ensured (assigned). This temperature difference ensures that the cooling tower will operate as designed.
• Draw a straight line from the point "1w" through the point "n" to the intersection with the straight line t = const = t 2w. We get the point "2w".
• From the point "2w" draw a straight line i = const to the intersection with φ pr = const = 100%. We get point "5", which characterizes the air condition at the outlet of the cooling tower.
• Using the diagram, we determine the desired temperature t5 and the rest of the parameters of point "5".

10. We draw up a system of equations to find the unknown mass flow rates of air and water. Thermal load of the cooling tower by auxiliary air flow, W:

Q gr = G in (i 5 - i 2); (7)

Q wgr = G ow C pw (t 2w - t 1w); (8)

where:
С pw - specific heat capacity of water, J / (kg.K).

Heat load of the heat exchanger by the main air flow, W:

Q mo = G o (i 1 - i 2); (9)

Heat load of the heat exchanger by water flow, W:

Q wmo = G ow C pw (t 2w - t 1w); (10)

Material balance by air flow:

G o = G in + G p; (11)

Cooling tower heat balance:

Q gr = Q wgr; (12)

Heat balance of the heat exchanger as a whole (the amount of heat transferred by each of the streams is the same):

Q wmo = Q mo; (13)

Combined heat balance of the cooling tower and heat exchanger by water:

Q wgr = Q wmo; (14)

11. Solving together equations from (7) to (14), we obtain the following dependences:
mass air flow rate for auxiliary flow, kg / s:

mass air flow rate for the main air flow, kg / s:

G o = G p; (16)

Mass flow rate of water through the cooling tower according to the main flow, kg / s:

12. Amount of water required to make up the cooling tower water circuit, kg / s:

G wn = (d 5 -d 2) G in; (18)

13. The power consumption in the cycle is determined by the power consumed to drive the fan, W:

N in = G o ∆i in; (19)

Thus, all the parameters necessary for structural calculations of the elements of the indirect evaporative air cooling system have been found.

Note that the working flow of cooled air supplied to the consumer (point "2") can be additionally cooled, for example, by adiabatic humidification or in any other way. As an example, Fig. 4 denotes the point "3 *", which corresponds to adiabatic humidification. In this case, the points "3 *" and "4" coincide (Fig. 4).

Practical aspects of indirect evaporative cooling systems

Based on the practice of calculating indirect evaporative cooling systems, it should be noted that, as a rule, the auxiliary flow rate is 30-70% of the main flow and depends on the potential for cooling the air supplied to the system.

If we compare cooling by adiabatic and indirect evaporative methods, then from the I d-diagram it can be seen that in the first case air with a temperature of 28 ° C and a relative humidity of 45% can be cooled to 19.5 ° C, while in the second case - up to 15 ° С (fig. 6).

"Pseudo-indirect" evaporation

As mentioned above, an indirect evaporative cooling system achieves a lower temperature than a traditional adiabatic air humidification system. It is also important to emphasize that the moisture content of the desired air does not change. Such advantages in comparison with adiabatic humidification can be achieved due to the introduction of an auxiliary air flow.

There are few practical applications of the indirect evaporative cooling system at the moment. However, apparatuses of a similar, but slightly different principle of operation appeared: air-to-air heat exchangers with adiabatic humidification of the outside air (systems of "pseudo-indirect" evaporation, where the second flow in the heat exchanger is not some humidified part of the main flow, but another, absolutely independent circuit).

Such devices are used in systems with a large volume of recirculated air that needs cooling: in air conditioning systems for trains, auditoriums for various purposes, data centers and other facilities.

The purpose of their implementation is the maximum possible reduction in the duration of operation of energy-intensive compressor refrigeration equipment. Instead, for outdoor temperatures up to 25 ° C (and sometimes higher), an air-to-air heat exchanger is used, in which the recirculated room air is cooled with outdoor air.

For more efficient operation of the device, the outside air is pre-humidified. In more complex systems, humidification is also performed in the process of heat exchange (water injection into the channels of the heat exchanger), which further increases its efficiency.

Thanks to the use of such solutions, the current energy consumption of the air conditioning system is reduced by up to 80%. The total annual energy consumption depends on the climatic region of the system operation, on average it decreases by 30-60%.

Yuri Khomutsky, technical editor of the magazine "Climate World"

The article uses the methodology of the Moscow State Technical University. N.E.Bauman for calculating an indirect evaporative cooling system.

2018-08-15

The use of air conditioning systems (SCR) with evaporative cooling as one of the energy-efficient solutions in the design of modern buildings and structures.

Today, the most common consumers of heat and electricity in modern administrative and public buildings are ventilation and air conditioning systems. When designing modern public and administrative buildings to reduce energy consumption in ventilation and air conditioning systems, it makes sense to give special preference to lower capacity at the stage of obtaining technical specifications and reduce operating costs. Reducing operating costs is most important for property owners or tenants. Many ready-made methods and various measures are known - to reduce energy consumption in air conditioning systems, but in practice, the choice of energy-efficient solutions is very difficult.

Some of the many ventilation and air conditioning systems that can be classified as energy efficient are the evaporative cooled air conditioning systems discussed in this article.

They are used in residential, public and industrial premises. The process of evaporative cooling in air conditioning systems is provided by spray chambers, film, packed and foam devices. The systems under consideration can have direct, indirect, and also two-stage evaporative cooling.

Of the above options, the most economical equipment for air cooling are systems with direct cooling. They are supposed to use standard equipment without the use of additional sources of artificial cold and refrigeration equipment.

A schematic diagram of an air conditioning system with direct evaporative cooling is shown in Fig. 1.

The advantages of such systems include minimal maintenance costs of systems during operation, as well as reliability and design simplicity. Their main disadvantages are the impossibility of maintaining the parameters of the supply air, the exclusion of recirculation in the manned room and the dependence on external climatic conditions.

Energy consumption in such systems is reduced to the movement of air and recirculated water in adiabatic humidifiers installed in an AHU. When using adiabatic humidification (cooling) in AHUs, potable water must be used. The use of such systems may be limited in climatic zones with a prevailing dry climate.

The areas of application for air conditioning systems with evaporative cooling are objects that do not require precise maintenance of the thermal and humidity regime. Usually they are run by enterprises of various industries, where a cheap method of cooling the internal air is needed with a high thermal intensity of the premises.

Another option for economical air cooling in air conditioning systems is the use of indirect evaporative cooling.

A system with such cooling is most often used in cases where the parameters of the internal air cannot be obtained using direct evaporative cooling, which increases the moisture content of the supply air. In the “indirect” scheme, the supply air is cooled in a recuperative or regenerative heat exchanger in contact with an auxiliary air flow cooled by evaporative cooling.

A variant of the air conditioning system with indirect evaporative cooling and using a rotary heat exchanger is shown in Fig. 2. The SCR scheme with indirect evaporative cooling and the use of recuperative heat exchangers is shown in Fig. 3.

Air conditioning systems with indirect evaporative cooling are used when supply air is required without dehumidification. The required parameters of the air environment are maintained by the local closers installed in the room. The determination of the supply air flow rate is carried out in accordance with sanitary standards, or according to the air balance in the room.

Air conditioning systems with indirect evaporative cooling use either outdoor or extract air as auxiliary air. In the presence of local closers, the latter is preferred, as it increases the energy efficiency of the process. It should be noted that the use of exhaust air as an auxiliary air is not allowed in the presence of poisonous, explosive impurities, as well as a high content of suspended particles that pollute the heat exchange surface.

Outside air is used as an auxiliary flow when it is unacceptable for the extract air to flow into the supply air through leaks in the heat exchanger (i.e. heat exchanger).

The auxiliary air flow is cleaned in air filters before being fed for humidification. An air conditioning system with regenerative heat exchangers is more energy efficient and less expensive.

When designing and choosing schemes for air conditioning systems with indirect evaporative cooling, it is necessary to take into account measures to regulate heat recovery processes during the cold season in order to prevent freezing of heat exchangers. Provision should be made for heating the exhaust air in front of the heat exchanger, bypassing part of the supply air in the plate heat exchanger and regulating the speed in the rotary heat exchanger.

The use of these measures will eliminate the freezing of heat exchangers. Also, in calculations when using extract air as an auxiliary flow, it is necessary to check the system for operability during the cold season.

Another energy efficient air conditioning system is a two-stage evaporative cooling system. Air cooling in this scheme is provided in two stages: direct evaporative and indirect evaporative methods.

"Two-stage" systems provide for a more precise control of air parameters when leaving the central air conditioner. These air conditioning systems are used in applications where deeper cooling of the supply air is required compared to cooling in direct or indirect evaporative cooling.

Air cooling in two-stage systems is provided in regenerative, plate heat exchangers or in surface heat exchangers with an intermediate heat carrier using an auxiliary air flow - in the first stage. Air cooling in adiabatic humidifiers - in the second stage. The basic requirements for the auxiliary air flow, as well as for checking the operation of the SCR during the cold season are similar to those applied to the SCR schemes with indirect evaporative cooling.

The use of evaporative cooling air conditioning systems achieves better results that cannot be obtained with refrigeration machines.

The use of SCR schemes with evaporative, indirect and two-stage evaporative cooling allows, in some cases, to abandon the use of refrigerating machines and artificial cold, as well as significantly reduce the refrigeration load.

Energy efficiency of air handling is often achieved through the use of these three schemes, which is very important in the design of modern buildings.

Evaporative Air Cooling Systems History

Over the centuries, civilizations have found original methods of dealing with the heat in their territories. An early form of the cooling system, the "wind catcher", was invented many thousands of years ago in Persia (Iran). It was a system of windshafts on the roof that caught the wind, passed it through the water, and blew chilled air into the interior. It is noteworthy that many of these buildings also had courtyards with large reserves of water, therefore, if there was no wind, then as a result of the natural process of water evaporation, hot air, rising upward, evaporated the water in the courtyard, after which the already cooled air passed through the building. Today, Iran has replaced "wind catchers" with evaporative coolers and is widely using them, and the Iranian market, due to the dry climate, reaches a turnover of 150 thousand evaporators a year.

In the United States, the evaporative cooler was the subject of numerous patents in the 20th century. Many of them, beginning in 1906, suggested using wood shavings as a spacer, carrying a large amount of water in contact with moving air and supporting intense evaporation. The standard design from the 1945 patent includes a water reservoir (usually equipped with a float valve to adjust the level), a pump to circulate water through the wood chip spacers, and a fan to blow air through the spacers to the living quarters. This design and materials remain the mainstay of evaporative cooler technology in the Southwest United States. In this region, they are additionally used to increase humidity.

Evaporative cooling was common in aircraft engines of the 1930s, such as the engine for the Beardmore Tornado airship. This system was used to reduce or completely eliminate the radiator, which could otherwise create significant aerodynamic drag. External evaporative cooling devices have been installed on some vehicles to cool the interior. They were often sold as optional accessories. The use of evaporative cooling devices in automobiles continued until vapor compression air conditioning became widespread.

The principle of evaporative cooling is different from that on which vapor compression chillers operate, although they also require evaporation (evaporation is part of the system). In the vapor compression cycle, after the refrigerant has evaporated inside the evaporator coil, the cooling gas is compressed and cooled, condensing under pressure into a liquid state. In contrast to this cycle, in an evaporative cooler, water evaporates only once. The evaporated water in the cooling device is discharged into the space with cooled air. In the cooling tower, the evaporated water is carried away by the air stream.

1. Bogoslovsky V.N., Kokorin O. Ya., Petrov L.V. Air conditioning and refrigeration. - M .: Stroyizdat, 1985.367 p.
2. Barkalov B.V., Karpis E.E. Air conditioning in industrial, public and residential buildings. - M .: Stroyizdat, 1982.312 p.
3. Koroleva N.A., Tarabanov M.G., Kopyshkov A.V. Energy efficient ventilation and air conditioning systems for a large shopping center // AVOK, 2013. No.1. S. 24-29.
4. Khomutsky Yu.N. The use of adiabatic humidification for air cooling // Climate World, 2012. №73. S. 104-112.
5. P.V. Uchastkin Ventilation, air conditioning and heating at light industry enterprises: Textbook. manual. for universities. - M .: Light industry, 1980.343 p.
6. Khomutsky Yu.N. Calculation of an indirect evaporative cooling system // Climate World, 2012. №71. S. 174-182.
7. Tarabanov M.G. Indirect evaporative cooling of the supply air in the SCR with closers // AVOK, 2009. No. 3. S. 20–32.
8. Kokorin O. Ya. Modern air conditioning systems. - M .: Fizmatlit, 2003.272 p.

The invention relates to the technique of ventilation and air conditioning. The purpose of the invention is to increase the depth of cooling of the main air flow and reduce energy costs. Water-sprinkled heat exchangers (T) 1 and 2 for indirect evaporative and direct evaporative cooling of air are sequentially located along the air flow. T 1 has channels 3, 4 for general and auxiliary air flows. Between T 1 and 2 there is a chamber 5 for dividing air streams with a bypass channel 6 and a valve 7 placed in it per TiHpyeMbiM. A compressor 8 with a drive 9 is communicated by inlet 10 with the atmosphere, and outlet 11 - with channels 3rev (its air flow Valve 7 through the block control is connected to the indoor air temperature sensor Channels 4 of the auxiliary air flow are communicated by the outlet 12 with the atmosphere, and T 2 by the outlet 13 of the main air flow - with the room. Channel 6 is connected to channels 4, and the drive 9 has a speed controller 14 connected to If it is necessary to reduce the cooling capacity of the device, according to the signal from the room temperature sensor, valve 7 is partially closed through the control unit, and using the regulator 14, the speed of the blower is reduced, providing a proportional decrease in the total air flow by the amount of the auxiliary air flow reduction . 1 ill. (L to about 00 to

UNION OF SOVIET

SOCIALIST

REPUBLIC (51) 4 F 24 F 5 00

DESCRIPTION OF THE INVENTION

TO AUTHOR'S CERTIFICATE

USSR STATE COMMITTEE

ON CASES OF INVENTIONS AND DISCOVERIES (2 1) 4 166558 / 29-06 (22) 25.12.86 (46) 30.08.88. Vu.t, !! 32 (71) Moscow Textile Institute (72) O. Ya. Kokorin, M.l0, Kaplunov and S.V. Nefelov (53) 697.94 (088.8) (56) USSR author's certificate

263102, cl. F? 4G 5/00, 1970. (54) TWO-STAGE DEVICE

EVAPORATIVE AIR COOLING (57) The invention relates to ventilation and air conditioning techniques. The purpose of the invention is to increase the depth of cooling of the main air flow and reduce energy costs.

Water-sprinkled heat exchangers (T) 1 and 2 for indirect evaporative and direct evaporative cooling of air are sequentially located along the air flow. Т1 has channels 3, 4 for general and auxiliary air flows. Between Т1 and 2 there is a chamber 5 for dividing air flows with a crossover „SU“ 1420312 d1. inlet 6 and an adjustable valve 7 located in it.

8 with actuator 9 is communicated by input 10 with atmosphere, and output 11 - with channels

3 total air flows. Valve 7 through the control unit is connected to the room temperature sensor. Channels

4 of the auxiliary air flow are communicated by the outlet 12 with the atmosphere, and T 2 by the outlet 13 of the main air flow with the room. Channel 6 is connected to channels 4 and actuator 9 has a regulator

14 speed connected to the control unit. If it is necessary to reduce the cooling capacity of the device, according to the signal from the room air temperature sensor, valve 7 is partially closed through the control unit, and using the regulator 14, the number of revolutions of the blower is reduced, providing a proportional decrease in the total air flow rate by the amount of a decrease in the auxiliary air flow rate. 1 ill.

The invention relates to ventilation and air conditioning technology.

The aim of the invention is to increase the depth of cooling of the main air flow and reduce energy costs.

The drawing shows a schematic diagram of a device for two-stage evaporative air cooling. The device for two-stage evaporative air cooling contains sequentially located along the air flow, water-sprayed heat exchangers 1 and 2 of indirect evaporative air cooling, the first of which has channels 3 and 4 for general and auxiliary air flows. twenty

Between teploobmsngngkami 1 and 2 there is a chamber 5 1 for the separation of air flows with an overhead channel 6 and an adjustable kllgyn 7 located in it. driven

9 is communicated by the inlet 10 with the atmosphere, l by the outlet 11 - with channels 3 of the total flow ltna; ty;:; 3. an adjustable valve 7 is connected via a control unit to a room temperature sensor (HP is shown). The channels 4 of the auxiliary air flow are communicated by the outlet

12 with the atmosphere, and the heat exchanger 2 for direct evaporative cooling of the air by the outlet 13 of the main air flow - with the heat exchanger. The bypass channel 6 is connected to the valve 4 g3spg of the powerful air outlet, à the drive 9 of the blower 8 has a regulator 14 of the pressure of the pressure, which is connected to the control unit 4O (not yet: 3 ln. cooling "l303 is cold and works as follows.

Outside air through inlets 10 and 3-45 enters into the blower 8 and through outlet 11 ttartteT flows into the channels 3 of the general air flow to the heat exchanger of indirect evaporative cooling. With the passage of air in the channels 3 ilpo, its enthalpy ttpta decreases to a constant level of concentration, after which the total air flow enters the chamber 5 for the release of air pins.

From chamber 5, part of the pre-cooled air in where the auxiliary air flow through the bypass channel 6 enters the channels 4 of the auxiliary air flow irrigated from above, located in the heat exchanger 1 perpendicular to the direction of the total air flow, down the walls of the channels 4 films of water and at the same time cooling the general air flow passing through the channels 3.

The auxiliary air stream, which has increased its enthalpy and increased its enthalpy, is evacuated through outlet 12 to the atmosphere or can be used, for example, for ventilation of auxiliary rooms or cooling of building enclosures under construction. The main air flow comes from the chamber 5 for dividing air streams! 3 heat exchanger 2 of direct evaporative cooling, where the air is additionally cooled and reduced at constant enthalpy and at the same time is de-dried, after which it is cleaned. and the main air flow through outlet 13 is fed to the displacement. If necessary, reduce the tttc! TttIt Ttoëoltoïðelectricity of the tet ITT device according to the corresponding date signal and the room air temperature through the control unit (not shown) the adjustable cllpln 7 is partially covered, which leads to a decrease in tttteI «t about the auxiliary air flow cooling ”of the total air flow in the heat exchanger 1 of indirect evaporative cooling. Simultaneously with the cover

R. gys! Itpyentoro k: glplnl 7 with the use of the ItItett regulator 14 glst rotation!

tot:; the number of revolutions of the burner 8 is included with the provision of proportional.psh tt; t "flow rate of the total air flow and: Itу yy: t ng"

»Ep..tc1t ttãp! I first air sweat.

1 smullinventions of devices; for two-piece guggen cooling of the air, containing i oss. auxiliary air flows, a chamber for separating air flows between the heat exchangers with a bypass channel and a variable valve located in it;

Compiled by M. Rashchepkin

Tehred M. Khodanich Proofreader S. Shekmar

Editor M. Tsitkina

Circulation 663 Subscription

VNIIPI of the USSR State Committee for Inventions and Discoveries

113035, Moscow, Zh-35, Raushskaya nab., 4/5

Order 4313/40

Production and printing enterprise, Uzhgorod, st. Design, 4 swarm, and the outlet - with the channels of the general air flow, and the adjustable valve is connected through the control unit to the air temperature sensor in the room and the channels of the auxiliary air flow are communicated with the atmosphere, and the direct evaporative cooling heat exchanger - with the room, about t l This is due to the fact that, in order to increase the depth of cooling of the main air flow and reduce energy costs, the bypass channel is connected to the channels of the auxiliary air flow, and the pressure drive is equipped with a speed controller connected to the control unit.

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