In heating, ventilation and air conditioning systems, adiabatic evaporation is usually associated with humidification, but recently this process is becoming growing popularity in the most different countries The world is increasingly used for the "natural" cooling of air.
The evaporative cooling underlies one of the most definitely invented human cooling systems, where air cooling occurs due to the natural evaporation of water. This phenomenon is very common and occurs everywhere: one of the examples may be a feeling of cold, which you experience when water evaporates from the surface of your body under the influence of wind. The same thing happens with air, in which water is sprayed: Since this process occurs without an external energy source (this is the word "adiabatic"), the heat needed to evaporate water is taken out of the air, which, respectively, becomes colder.
The use of such a cooling method in modern systems Air conditioning provides high cooling capacity at low power consumption, since in this case the electricity is consumed only to maintain the process of water evaporation. At the same time, as a cooler instead chemical compositions Used ordinary waterWhat makes evaporative cooling more profitable economically and does not harm the ecology.
There are two basic evaporative cooling methods - direct and indirect.
Direct evaporative cooling
Direct evaporative cooling is the process of reducing the air temperature in the room with its immediate moisture. In other words, due to the evaporation of the sprayed water, cooling the ambient air occurs. At the same time, the distribution of moisture is carried out either directly in the room with the help of industrial humidifiers and nozzles, or by saturation of the air intake air and cooling it into the ventilation unit section.
It should be noted that in the conditions of direct evaporative cooling, a significant increase in the humidity of the supply air inside the room is inevitable, therefore, to assess the applicability of this method, it is recommended to take the formula as the basis of the temperature and discomfort. According to the formula, a comfortable temperature is calculated in degrees Celsius, taking into account humidity and temperature testimony over a dry thermometer (Table 1). Running forward, we note that the direct evaporative cooling system applies only in cases where street air in summer period Has high temperature values \u200b\u200bfor dry thermometer and low absolute humidity level.
Indirect evaporative cooling
To increase the effectiveness of evaporative cooling at high humidity of outdoor air, it is recommended to combine evaporative cooling with heat recovery. This technology is known as "indirect evaporative cooling" and is suitable for almost any country in the world, including countries with a very humid climate.
General scheme The operation of the supply and ventilation system with recovery is that the hot difts, passing through a special heat exchange cassette, is cooled due to cool air removed from the room. The principle of operation of indirect evaporation cooling is to install the system of adiabatic humidification in the exhaust channel of the supply and exhaust central air conditioners, followed by the transfer of cold through the recuperator of the supply air.
As shown in the example, due to the use of a plate recovery, street air in the ventilation system is cooled at 6 ° C. The use of evaporative cooling of exhaust air will increase the temperature difference from 6 ° C to 10 ° C without the growth of electricity consumption and humidity level. The use of indirect evaporative cooling is effective at high heat-flow, for example, in office and shopping centers, the centrals, production rooms etc.
The indirect cooling system with the use of the adiabatic humidifier Carel Humifog series:
| Conditions of calculation | |
| Street temperature and moisture content: | + 32ºС, 10.12 g / kg (indicators taken for Moscow) |
| Indoor air temperature: | +20 ºС. |
| Ventilation system: | 4 Implining and exhaust installations with a capacity of 30 000 m3 / h (air supply under sanitary standards) |
| Cooling system capacity with ventilation: | 2500 kW |
| Air supply air temperature: | +20 ºС. |
| Exhaust air temperature: | +23 ºС. |
| Efficiency of recovery on explicit heat: | 65% |
| Centralized cooling system: | Chiller-Fan Coil system with water temperature 7 / 12ºС |
Payment
* It is necessary to take into account that the cost of mounting the cooling system, taking into account all costs, is significantly higher compared to indirect cooling systems.
Capital expenditures
For analysis, we take the cost of equipment - chillers for the cooling system and humidification system for indirect evaporative cooling.
The cost of one rack of wetting Optimist produced by Carel (Italy) in the supply and exhaust installation is 7570 €.
The cost of chiller with a cooling capacity of 62.3 kW is approximately 12,460 €, based on the cost of 200 € per 1 kW of refrigeration. It should be borne in mind that the cost of mounting the cooling system, taking into account all costs, is significantly higher compared to indirect cooling systems.
Operating costs
For analysis we accept the cost water water 0.4 € per 1 m3 and electricity cost 0.09 € per 1 kW / h.
Water consumption by indirect cooling is 117 kg / h for one supply-exhaust installation, taking into account the loss of 10%, we will take it as 130 kg / h.
The power consumption of the humidification system is 0.375 kW for one sub-exhaust installation.
The final costs per hour are 0.343 € per 1 hour of operation of the system.
Refrigeration coefficient we take equal to 3 (ratio of cooling power to power consumed).
The final costs per hour are 7.48 € per 1 hour of operation.
The use of indirect evaporative cooling allows:
Reduce capital costs for cooling air intake air by 39%.
Reduce power consumption on the air conditioning systems with 729 kW to 647 kW, or 11.3%.
Reduce operating costs of air conditioning systems with 65.61 € / hour to 58.47 € / hour, or by 10.9%.
Thus, despite the fact that the cooling of fresh air is about 10-20% of the total need for cooling office and shopping centers, it is here that there are the greatest reserves in increasing the energy efficiency of the building without a significant increase in capital costs.
The article is prepared by the company's specialists to the publication in the journal on No. 6-7 (5) June-July 2014 (p. 30-35)
When building processes on the I - D diagram and selection technological scheme air treatment must strive for rational use Energy, providing economical spending cold, heat, electricity, water, as well as saving construction area occupied by equipment. For this purpose, it should be analyzed by saving artificial cold By applying direct and indirect evaporative air cooling, the use of the diagram with the regeneration of the heat of the air removed and the utilization of the warmth of secondary sources, if necessary, the use of the first and second recycling of air, the circuit with bypass, as well as controlled processes in heat exchangers.
Recycling is used in rooms with significant heat inspection when the consumption of supply air defined on the removal of excess heat is greater than the required external air consumption. In the warm year of the year, recycling makes it possible to reduce cold costs compared with the direct-flow scheme of the same performance if the outer air enthalpy is higher than the enthalpy of the air of the air, and also abandon the second heating. IN cold period - significantly reduce the cost of heat for heating the outer air. When using evaporative cooling, when the outer air enthalpy is lower than internal and removed, recycling is not appropriate. The movement of recycling air over the air duct network is always associated with additional electricity costs, it requires a construction volume to accommodate recycling air ducts. Recycling will be advisable if the costs of its device and functioning will be less than the resulting savings and cold savings. Therefore, in determining the flow air flow, it should always strive to bring it into the minimally necessary value of the outer air, taking the appropriate diagram of air distribution in the room and the type of air distributor and, accordingly, the direct-flow diagram. Recycling is also not compatible with the regeneration of heat removed air. In order to reduce the heat consumption on the heating of the outer air during the cold period of the year, it should be analyzed with the possibility of using secondary heat from low-precision sources, namely: heat of removed air, exhaust gas generators and technological equipment, heat of condensation refrigerators, heat of lighting fittings, warmth wastewater etc. The heat exchangers of the regeneration of the warmth of the removed air can also be somewhat reduced cold consumption in the warm season in areas with a hot climate.
To do right choiceIt is necessary to know possible air processing schemes and their features. Consider the best simple processes Changes in the condition of air and their sequence in central air conditioners serving one room large volume.
Typically, the determining mode for selecting the processing technological scheme and determining the air conditioning system is a warm period of the year. In the cold period of the year, they seek to preserve the consumption of supply air defined for the warm period of the year, and the air processing scheme.
The temperature of the wet thermometer of the main air flow after cooling in the surface heat exchanger of indirect evaporative cooling is of a lower value compared with the temperature of the wet thermometer of the outer air, as the natural limit of evaporation cooling. Therefore, upon subsequent processing of the main stream in the contact apparatus, the method of direct evaporative cooling can be obtained by lower air parameters compared to the natural limit. Such a sequential air treatment circuit of the main air flow by the method of indirect and direct evaporative cooling is called two-stage evaporative cooling. The layout of the central air conditioner equipment, corresponding to the two-stage evaporating air cooling, is presented in Figure 5.7 a. It is also characteristic of the presence of two streams of air: the main and auxiliary. Outer air having more low temperature On the wet thermometer than the inner air in the serviced room, enters the main air conditioner. In the first air cooler, it is cooled using indirect evaporative cooling. Next, it enters the adiabatic moisture unit, where it is cooled and moistened. The evaporative cooling of the water circulating through the surface air coolers of the main air conditioner is carried out during its spraying in the adiabatic humidification unit in the auxiliary stream. Circulation pump Picks the water from the pallet of the adiabatic humidification of the auxiliary stream and supplies it into the main stream air coolers and further - on spraying in the auxiliary stream. Water decreases from evaporation mainly and auxiliary stream is replenished through float valves. After two cooler steps, the air is fed into the room.
In modern climate machinery, much attention is paid to the energy efficiency of the equipment. This explains the interest in the recent interest in water acarbing cooling systems based on indirectly evaporating heat exchangers (indirectly evaporative cooling systems). Water acarbing cooling systems can be an effective solution for many regions of our country, whose climate is distinguished by relatively low air humidity. Water as the refrigerant is unique - it has a large heat capacity and hidden heat of vaporization, harmless and accessible. In addition, the water is well studied, which allows you to accurately predict its behavior in various technical systems.
In indirectly evaporative systems, the air can be cooled to the "3" point (Fig. 1). The process in the diagram in this case goes vertically down the line of constant moisture content. As a result, the temperature obtained turns out to be lower, and the air-containing air does not grow (remains constant).
In addition, water academic systems have the following positive qualities:
Cooling systems that use the effect of heat absorption during water evaporation are known for a very long time. However, at the moment, water acarbing cooling systems are not widely widespread. Almost all of the niche of industrial and household cooling systems in the region of moderate temperatures is filled with candidate paroxy systems.
Such a situation is obviously associated with the problems of operation of water acarbing systems when negative temperatures And their unsuitability of exploitation at high relative humidity of outdoor air. It also affected the fact that the basic devices of such systems (cooling towers, heat exchangers), used earlier, had large dimensions, mass and other disadvantages associated with work in high humidity. In addition, they needed water treatment system.
However, today, highly efficient and compact cooling towers, capable of cooling water to temperatures, are only 0.8 ... 1.0 ° C differ from the temperature of the air flow in a wet thermometer differing from technical progress.
Here, a special way to celebrate the cooling towers Muntes and SRH-Lauer. Such a small temperature pressure was able to provide mainly due to original design Hardery nozzles with unique properties - good wettability, manufacturability, compactness.
After the heat exchanger, the main air flow is divided into two: auxiliary and working, directed to the consumer.
The auxiliary stream simultaneously plays the role and cooler, and the cooled flow - after the heat exchanger, it is sent back, towards the main stream (Fig. 2).
At the same time, water is supplied to the channels of the auxiliary stream. The meaning of water supply is to "slow down" the growth of air temperature due to its parallel moisturizing: As is known, the same change in thermal energy can be achieved as a change in temperature only, as well as a change in temperature and humidity at the same time. Therefore, with moisturizing auxiliary stream, the same heat exchange is achieved by a smaller change in temperature.
In indirectly evaporative heat exchangers of another species (Fig. 3), the auxiliary stream is directed not to the heat exchanger, but to a cooling tower where the water is cooled, circulating through an indirect evaporative heat exchanger: water heats up in it due to the main flow and cools in the cooling towards the auxiliary. The movement of water along the contour is carried out using a circulation pump.
The calculation technique is based on the following assumptions:
The order of the engineering calculation of the system under consideration is as follows (Figure 4):
1. According to I D diagram or using a humid air calculation program, additional ambient air parameters are defined (point "0" in Fig. 4): Specific enthalpy of air I 0, J / kg and moisture content d 0, kg / kg.
2. The increment of the specific enthalpy of air in the fan (J / kg) depends on the type of fan. If the fan motor is not blown (not cooled) the main flow of air, then:
If the diagram uses a channel type fan (when the electric motor is cooled by the main air flow), then:
where:
η DV - electric motor efficiency;
ρ 0 - air density at the entrance to the fan, kg / m 3
where:
B 0 - barometric environmental pressure, PA;
R B is a gas constant of air equal to 287 J / (kg.k).
3. Specific air enthalpy after fan (point "1"), J / kg.
i 1 \u003d i 0 + Δi in; (3)
Since the process "0-1" occurs at constant moisture content (D 1 \u003d d 0 \u003d const), then according to the well-known φ 0, T 0, I 0, I 1, we determine the temperature of the air T1 after the fan (point "1").
4. The point of the surround air dew t Ros, ° C is determined by known φ 0, t 0.
5. The psychrometric difference of air temperature of the main flow at the outlet of the heat exchanger (point "2") Δt 2-4, ° C
Δt 2-4 \u003d Δt x + Δt WCR; (4)
where:
Δt x is assigned based on the specific working conditions in the range ~ (0.5 ... 5.0), ° C. It should be borne in mind that the small values \u200b\u200bof ΔT x will entail relatively large dimensions of the heat exchange apparatus. To ensure small values \u200b\u200bof Δt x, it is necessary to use highly efficient heat transfer surfaces;
ΔT WCR is selected in the range (0.8 ... 3.0), ° C; Smaller values \u200b\u200bof ΔT WCR should be taken if it is necessary to obtain the minimum possible temperature of cold water in the cooling towers.
6. We assume that the process of moisturizing the auxiliary air flow in the cooling towers from the state "2-4", with sufficient accuracy for engineering calculations, is based on the line i 2 \u003d i 4 \u003d const.
In this case, knowing the value Δt 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 \u003d const so that between the point "2" and the point "4" the temperature difference was found Δt 2-4. The point "2" is at the intersection of the lines I 2 \u003d i 4 \u003d const and constant moisture content D 2 \u003d D 1 \u003d D OS. The point "4" is on the intersection of the line I 2 \u003d i 4 \u003d const and the curve φ 4 \u003d 100% relative humidity.
Thus, using the diagrams given, determine the remaining parameters at the points "2" and "4".
7. Determine T 1w - the water temperature at the outlet of the cooling point, at the point "1W", ° C. In the calculations, you can neglect the heat of water in the pump, therefore, at the entrance to the heat exchanger (dot "1w ') water will have the same temperature T 1W
T 1W \u003d T 4 + .Δt WCR; (5)
8. T 2w - water temperature after heat exchanger at the inlet to the cooling tower (dot "2w"), ° C
t 2w \u003d T 1-Δt m; (6)
9. The air temperature emitted from the cooling towers in the environment (dot "5") T 5 is determined by the graph-analytical method using the diagram ID (a combination of Q T and I T diagrams can be used, but they are less common, so in this Calculation used ID diagram). The specified method is as follows (Fig. 5):
10. We compile a system of equations for finding unknown mass consumption of air and water. Thermal load of cooling towers on auxiliary air flow, W:
Q g \u003d g in (i 5 - i 2); (7)
Q WG \u003d G OW C PW (T 2W - T 1W); (8)
where:
With PW - the specific heat capacity of water, J / (kg.k).
Heat exchanger thermal load for main airflow, W:
Q Mo \u003d g O (i 1 - i 2); (9)
Heat exchanger thermal load, W:
Q wmo \u003d g OW C PW (T 2W - T 1W); (10)
Material Balance of Air Flows:
G O \u003d G in + g p; (11)
Heat balance by cooling towers:
Q g \u003d q wgr; (12)
The heat balance of the heat exchanger as a whole (the number of heat transmitted by each of the flows equally):
Q wmo \u003d q Mo; (13)
Joint thermal balance of cooling towers and heat exchanger on water:
Q ws \u003d q wmo; (14)
11. Deciding together equation with (7) software (14), we obtain the following dependencies:
Mass air flow over auxiliary stream, kg / s:
mass air flow by main airflow, kg / s:
G O \u003d G P; (16)
Mass flow of water through the mainstream cooling tower, kg / s:
12. The amount of water required to feed the water circuit of the cooling path, kg / s:
G wn \u003d (d 5 -d 2) g in; (18)
13. The power consumption in the cycle is determined by the power spent on the fan drive, W:
N B \u003d g o Δi in; (19)
Thus, all the parameters necessary for constructive calculations of the elements of the indirect air cooling system are found.
Note that the cooled air supplied to the consumer (point "2") can be additionally cooled, for example, adiabatic moisture or in any other way. As an example in Fig. 4 is indicated by the point "3 *", corresponding to adiabatic moisturizing. In this case, the points "3 *" and "4" coincide (Fig. 4).
If we compare cooling with adiabat and indirectly evaporative methods, then from the i d-diagram it can be seen that in the first case the 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 ° C (Fig. 6).
As mentioned above, an indirectly evaporative cooling system allows you to achieve a lower temperature than the traditional system of adiabatic air humidification. It is also important to emphasize that the moisture content of the desired air does not change. Such advantages Compared to adiabate moisture, it is possible to achieve due to the introduction of auxiliary air flow.
The practical applications of the system of indirect evaporation cooling at the moment are not enough. However, the devices of similar, but several other principles of operation appeared: air-air heat exchangers with adiabatic humidification of the outer air (the system of "pseudo-grade" evaporation, where the second stream in the heat exchanger is not some kind of moistened part of the main flow, and the other, an absolutely independent circuit).
Such devices are used in systems with a large amount of recycling air in need of cooling: in air conditioning systems of trains, visual halls of various purposes, data processing centers and other objects.
The purpose of their implementation is the maximum possible decrease in the duration of the energy-intensive compressor refrigeration equipment. Instead, with outer temperatures, up to 25 ° C (and sometimes higher), an air-air heat exchanger is used, in which the recycling air of the room is cooled by outer air.
For greater efficiency of the device, the outer air is pre-moistened. In more complex systems, moisturizing is carried out in the heat exchange process (water injection into the heat exchanger channels), which achieves an additional increase in its effectiveness.
Through the use of such solutions, the current power consumption of the air conditioning system is reduced by up to 80%. Calf-annual energy consumption depends on the climatic area of \u200b\u200bthe system operation, on average it decreases by 30-60%.
Yuri Khomutsky, technical editor of the magazine "World of Climate"
The article uses MSTU technique them. N. E. Bauman to calculate the indirectly evaporative cooling system.
For premises with large excess of explicit heat, where the main humidity of indoor air is required, air conditioning systems that use the principle of indirect evaporative cooling are applied.
The scheme consists of a system of processing the main flow of air and the evaporative cooling system (Fig. 3.3. Fig. 3.4). For cooling water, irrigation chambers of air conditioners or other contact apparatuses, spray pools, cooling towers and others can be used.
The water chilled by evaporation in the air flow, with a temperature, enters the surface heat exchanger - air conditioner air conditioner of the main air flow, where the air changes its condition from the values \u200b\u200bto the values \u200b\u200b(T.), the water temperature increases before. The heated water enters the coat unit, where it is cooled by evaporation to temperature and the cycle is repeated again. The air passing through the contact unit changes its state from the parameters to the parameters (T.). Passionate air, assimilating heat and moisture, changes its parameters to a state of t., And then to the state.
Fig.3.3. Scheme of indirect evaporation cooling
1-heat exchanger-air cooler; 2- contact apparatus
Fig.3.4. Diagram of indirect evaporation cooling
Line is a direct evaporative cooling.
If in the premises of excess heat make up, then with indirect evaporative cooling, the consumption of supply air will be
with direct evaporative cooling
Since\u003e, then<.
<), что позволяет расширить область возможного использования принципа испарительного охлаждения воздуха.
Comparison of processes shows that with indirect evaporative cooling, the performance of the SCP is lower than with direct. In addition, with indirect cooling, the moisture content of the supply air is lower (<), что позволяет расширить область возможного использования принципа испарительного охлаждения воздуха.
In contrast to the separate circuit of indirect evaporative cooling, a combined type apparatus was developed (Fig. 3.5). The device includes two groups of alternating channels separated by walls. Through a group of channels 1 passes auxiliary air flow. On the surface of the channel walls, water flows, supplied through the water distribution device. Some water is supplied to the water distribution device. When evaporation of water, the temperature of the auxiliary air flow decreases (with an increase in its moisture content), and the canal wall is cooled.
To increase the cooling depth of the main air flow, multistage schemes for processing the main flow, applying which theoretically, can be achieved by the temperature point temperature (Fig. 3.7).
The installation consists of air conditioning and cooling towers. The air conditioner produces indirect and direct isoentalpine cooling of the air of the served premises.
In the cooling, the evaporative cooling of water is occurring supplying the air conditioner surface air cooler.
Fig. 3.5. Diagram of the device of the combined apparatus of indirect evaporative cooling: 1,2-group of channels; 3- water distribution device; 4- pallet
Fig. 3.6. SCHE SPS two-stage evaporative cooling. 1-surface air cooler; 2-irrigation chamber; 3 - cooling time; 4-pump; 5-bypass with air valve; 6-fan
In order to unify equipment for evaporative cooling, irrigation chambers of typical central air conditioners can be used instead of cooling towers.
The outer air enters the air conditioner and at the first stage of cooling (air cooler) is cooled with constant moisture content. The second level of cooling is the irrigation chamber operating in isoenthalthalpy cooling mode. Cooling water supplying the surface of the water cooler is produced in the cooling towers. Water in this circuit circulates with a pump. Cooling is a device for water cooling atmospheric air. Cooling occurs due to evaporation of a part of water flowing through the rod under the action of gravity (evaporation of 1% water lowers its temperature by about 6).
Fig. 3.7. Chart with two-stage evaporative mode
cooling
The air conditioner irrigation chamber is equipped with a bypass channel with an air valve or has an adjustable process, which provides air regulation directed to the served room by the fan.
Ecology of consumption. The history of the creation of the air conditioner direct evaporative cooling. Differences direct and indirect cooling. Options for using evaporative air conditioners
Cooling and humidification by evaporative cooling is an absolutely natural process in which water is used as a cooling medium, and heat is effectively dissipated in the atmosphere. Simple patterns are used - during the evaporation of the fluid, the heat and selection of the cold occurs. Evaporation efficiency - increases with an increase in air velocity, which provides forced fan circulation.
The dry air temperature can be significantly reduced by the phase transition of liquid water into pairs, and this process requires significantly less energy than compression cooling. In a very dry climate, evaporative cooling also has the advantage that when air conditioning increases its humidity, and it creates more comfort for people in the room. However, in contrast to the parocompression cooling, it requires a constant source of water, and during operation it constantly consumes it.
History of development
Over the centuries of civilization, there were original methods of combating heat in their territories. The early form of the cooling system, the "wind catcher" was invented many thousands of years ago in Persia (Iran). It was a system of wind shafts on the roof, which captured the wind, passed it through water, and blinked the cooled air into the interior. It is noteworthy that many of these buildings also had yards with large water reserves, so if there was no wind, then as a result of the natural process of evaporation of water hot air, climbing up, evaporated the water in the courtyard, after which the cooled air passed through the building. Nowadays, Iran replaced the wind curls to evaporative coolers and use them widely, and the market due to dry climate - reaches turnover for the year in 150,000 evaporators.
In the US, the evaporative cooler in the twentieth century was the object of numerous patents. Many of which starting from 1906, offered to use wood chips, as a gasket carrying a large amount of water in contact with moving air, and supporting intensive evaporation. Standard design, as shown in Patent 1945, includes a water tank (usually equipped with a float valve to adjust the level), a pump for circulating water through wood chips, and a fan for supplying air through gaskets in residential areas. This design and materials remain basic, in the technology of evaporative coolers, in the south-west of the United States. In this region, they are additionally used to increase humidity.
The evaporative cooling was distributed in the aircraft engines of the 1930s, for example, in the engine for airship Beardmore Tornado. This system was used to reduce or completely eliminate the radiator, which otherwise could create significant aerodynamic resistance. In these systems, water in the engine was maintained under pressure using pumps that allowed it to heat up to a temperature of more than 100 ° C, since the actual boiling point depends on the pressure. Overheated water sprayed through the nozzle on the open pipe, where instantly evaporated, taking it heat. These pipes could be located under the surface of the aircraft to create zero resistance.
External evaporating cooling devices were installed on some cars for cooling the cabin. Often they were sold as additional accessories. The use of evaporative cooling devices in vehicles continued until there was no widespread air-conditioning air conditioning.
The principle of evaporation cooling differs from the on which the units of parocompression cooling work, although they also require evaporation (evaporation is part of the system). In the park compression cycle, after evaporation of the refrigerant inside the evaporative coil, the cooling gas is compressed and cooled, under pressure condensed into a liquid state. Unlike this cycle, in the evaporative cooler, the water evaporates only once. Steamed water in the cooling device is displayed in the cooled space. In the cooling edge, the evaporated water is carried out by air flow.
Options for applying evaporative cooling
The evaporative cooling of the air is direct, oblique, and two-stage (direct and indirect). Direct evaporative air cooling is based on isoentalpic process and is used in air conditioners during the cold season; In the warm time it is possible only in the absence of or minor moisture executions in the room and low moisture content of the outer air. Several expands the boundaries of its use bypassing the irrigation chamber.
Direct evaporative air cooling is advisable in dry and hot climate conditions in the supply ventilation system.
Indirect evaporative air cooling is carried out in surface air coolers. To cool the water circulating in the surface heat exchanger, use auxiliary contact apparatus (cooling tower). For indirect evaporative air cooling, you can use the combined type devices in which the heat exchanger performs both functions and cooling at the same time. Such devices are similar to air recuperative heat exchangers.
On one group of channels, the cooled air passes, the inner surface of the second group is irrigated with water flowing into the pallet, and then reprinted again. Upon contact with the emissions passing in the second group, the evaporative cooling of water occurs, as a result of which the air in the first group of channels is cooled. Indirect evaporative air cooling makes it possible to reduce the performance of the air conditioning system in comparison with its performance with direct evaporating air cooling and expands the possibilities of using this principle, because The moisture content of the supply air in the second case is less.
With two-stage evaporative coolingthe air use consistent indirect and direct evaporative air cooling in the air conditioner. In this case, the installation for indirect evaporation air cooling is complemented by an irrigation nozzle camera operating in direct evaporative cooling mode. Typical irrigation nozzle chambers are used in air evaporating cooling systems as cooling towers. In addition to single-stage indirect evaporative air cooling, it is possible a multistage, in which a deeper air cooling is carried out - this is the so-called uncompromising system of air conditioning.
Direct evaporative cooling (Open cycle) is used to reduce air temperature using the specific heat of evaporation, changing the liquid state of water to gaseous. In this process, the energy in the air does not change. Dry, warm air is replaced with cool and wet. Heat of external air is used to evaporate water.
Indirect evaporative cooling (closed cycle) Process similar to direct evaporative cooling, but using a certain type of heat exchanger. In this case, the wet, cooled air is not in contact with the air-conditioned medium.
Two-stage evaporative cooling, or indirect / direct.
Traditional evaporative coolers use only part of the energy with the necessary parocompressing cooling devices or adsorption air conditioning systems. Unfortunately, they increase the humidity of the air to the discomfort (except for very dry climatic zones). Two-step evaporative coolers do not increase the level of humidity as much as standard single-stage evaporative coolers do.
At the first stage of the two-stage cooler, warm air is cooled by indirect without increasing humidity (by passing through the heat exchanger, cooled by evaporation outside). In the straight stage, the pre-cooled air passes through water-soaked gasket, additionally cools and becomes more humid. Since the process includes the first, preventive stage, at the direct evaporation stage it is necessary less humidity to achieve the required temperatures. As a result, according to manufacturers, the process cools the air with a relative humidity within 50 - 70%, depending on the climate. For comparison, traditional cooling systems increase air humidity up to 70 - 80%.
Purpose
When designing a central ventilation system of ventilation, it is possible to equip the air intake of the evaporative section and so significantly reduce the cost of cooling air during the warm period of the year.
In the cold and transitional periods of the year, when air is heated with airborne carrier systems of ventilation or air indoor systems, air heating systems is heated and its physical ability to assimilate (absorb) to itself, with an increase in temperature - moisture. Or, the higher the temperature of the air - the more moisture it can assimilate. For example, when the outer air is heated by the calorifer of the ventilation system from the temperature -22 0 C and the humidity of 86% (the outer air parameter for HP G.Kiyeva), up to +20 0 C - the humidity falls below the boundary limits for biological organisms to an unacceptable 5-8% Air humidity. Low air humidity - negatively affects the human skin and mucous membranes, especially with asthma or pulmonary diseases. Normated for residential and administrative premises Air humidity: from 30 to 60%.
The evaporative air cooling is accompanied by the release of moisture or an increase in air humidity, up to high saturation of air humidity 60-70%.
Benefits
The volume of evaporation - and, accordingly, heat transfer - depends on the temperature of the outer air on the wet thermometer which, especially in summer, is much lower than the equivalent temperature of the dry thermometer. For example, in hot summer days, when the temperature of a dry thermometer exceeds 40 ° C, evaporative cooling can cool the water to 25 ° C or cool air.
Since evaporation removes much larger than the standard physical heat transfer, the heat transfer is used four times less air flow compared to conventional air cooling methods, which retains a significant amount of energy.
Evaporative cooling in comparison with traditional air conditioning methods Unlike other air conditioning types, the air cooling of the evaporative type (bio-cooling) does not use harmful gases as refrigerants (freon and others) that cause harm to the environment. It also consumes less electricity, thus saving electricity, natural resources and up to 80% of operational costs compared to air conditioning by other systems.
disadvantages
Low work efficiency in the wet climate.
Increasing air humidity, which in some cases undesirable - the yield of a two-stage evaporation, where the air does not contact and does not saturate.
Principle of operation (option 1)
The cooling process is carried out due to the close contact of water and air, and heat transfer into air by evaporating a small amount of water. Next, heat dissipates through the flowing and saturated air from the installation.
Principle of operation (option 2) - installation on the air intake
Installations of evaporative cooling
There are various types of installations for evaporative cooling, but they all have:
- section of heat exchange or heat transfer, constantly wetted by water by irrigation,
- a system of fans for forced circulation of outdoor air through the heat exchange section,
