In modern climate technology, much attention is paid to the energy efficiency of equipment. This explains the increased recent times interest in water evaporative cooling systems based on indirect evaporative heat exchangers (indirect evaporative cooling systems). Water evaporative cooling systems can be effective solution for many regions of our country, the climate of which is characterized by relatively low humidity. Water as a refrigerant is unique - it has a high heat capacity and latent heat of vaporization, is harmless and affordable. 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. So, the technology of conventional evaporative cooling(in adiabatic type humidifiers), when water is injected into the air stream, it not only lowers the temperature of the air, but also increases its moisture content. In this case, the process line on the I d-diagram of humid air goes along the adiabatic curve, 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 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 chilled air and cold water.
- Small 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 fluid - water.
- Ecological cleanliness: low noise and vibration level, non-aggressive working fluid, low environmental hazard industrial production systems due to the low labor intensity of manufacturing.
- Simplicity design and relatively low cost associated with the absence of strict requirements for the tightness of the system and its individual components, the absence of complex and expensive cars (refrigeration compressors), small excessive pressures in the cycle, low metal consumption and the possibility of widespread use of plastics.
Cooling systems that use the effect of heat absorption during the evaporation of water have been known for a very long time. However, on this 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 is filled with freon vapor compression systems.
This situation is obviously related to the problems of operation of water evaporation systems during negative temperatures and their unsuitability for operation at high relative humidity of the outside air. It was also affected by 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 operation in high humidity conditions. In addition, they needed a water treatment system.
However, today, thanks to technological progress, highly efficient and compact cooling towers have become widespread, capable of cooling water to temperatures that are only 0.8 ... 1.0 ° C different from the wet bulb temperature of the air flow entering the cooling tower.
Here, the cooling towers of the companies Muntes and SRH-Lauer. Such a small temperature difference was achieved mainly due to the original design of the cooling tower nozzle, which has 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 the point "0" (Fig. 4), is blown into the system by a fan and cooled at a 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 auxiliary flow channels. The meaning of water supply is to “slow down” the increase in air temperature due to its parallel humidification: as you know, the same change in thermal energy can be achieved both by changing only temperature, and by changing temperature and humidity at the same time. Therefore, when the auxiliary flow 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 not directed 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 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 needed:- φ oc - relative humidity environmental air, %;
- t os - ambient air temperature, ° С;
- ∆t x - 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 difference) between 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 the devices and lines of the system (required fan pressure), Pa.
The calculation methodology is based on the following assumptions:
- The processes of heat and mass transfer are assumed to be equilibrium,
- There are no external heat inflows in all parts of the system,
- The air pressure in the system is equal to atmospheric pressure (local changes in air pressure due to its injection by a fan or passing through aerodynamic resistances are negligible, which allows using the I d diagram of moist air for atmospheric pressure throughout the calculation of the system).
The order of 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 moist 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 increase in 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) 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 \u003d i 0 + ∆i in; (3)
Since the process "0-1" occurs at a constant moisture content (d 1 \u003d d 0 \u003d const), then according to 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 grew, ° С, is determined from the known φ 0, t 0.
5. Psychrometric air temperature difference of the main flow at the outlet of the heat exchanger (point "2") ∆t 2-4, °С
∆t 2-4 =∆t x +∆t wgr; (4)
where:
∆t x is assigned based on specific operating conditions in the range ~ (0.5…5.0), °C. In this case, it should be borne in mind that small values of ∆t x will entail relatively large dimensions of the heat exchanger. To ensure small 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 accept that the process of moistening the auxiliary air flow in the cooling tower from the state "2-4", with sufficient accuracy for engineering calculations, goes 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 will find such a line i=const, so that between the point "2" and the point "4" the temperature difference is the found ∆t 2-4. Point "2" is located at the intersection of the 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 above diagrams, we determine the remaining parameters at points "2" and "4".
7. Determine t 1w — the temperature of the water at the outlet of the cooling tower, at the point "1w", °C. In the calculations, we can neglect the heating of water in the pump, therefore, at the inlet to the heat exchanger (point "1w '"), the water will have the same temperature t 1w
t 1w \u003d 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 \u003d 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 i d diagram (with great convenience, a combination of Q t and i t-diagrams can be used, however, they are less common, therefore, in this i d diagram was used in the calculation). This 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 the 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 isenthalpe we set aside the segment "1w - p" so that t p \u003d t 1w - ∆t min.
- Knowing that the process of air heating in the cooling tower occurs according to φ=const=100%, we build a tangent to φ pr =1 from the point "p" and get the tangent point "k".
- From the point of contact “k” along the isoenthalpe (adiabatic, i = const), we set aside the segment “k - n” so that t n \u003d t k + ∆t min. Thus, the minimum temperature difference between the cooled water and the auxiliary flow air in the cooling tower is ensured (assigned). This temperature difference ensures that the cooling tower operates in the design mode.
- We 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 the point "5", which characterizes the state of the air at the outlet of the cooling tower.
- According to the diagram, we determine the desired temperature t5 and the remaining parameters of point "5".
10. We compose a system of equations for finding unknown mass flow rates of air and water. Thermal load of the cooling tower by auxiliary air flow, W:
Q gr \u003d G in (i 5 - i 2); (7)
Q wgr \u003d G ow C pw (t 2w - t 1w) ; (8)
where:
C pw is the specific heat capacity of water, J/(kg.K).
Heat load of the heat exchanger for the main air flow, W:
Q mo =G o (i 1 - i 2) ; (9)
Thermal load of the heat exchanger in terms of water flow, W:
Q wmo =G ow C pw (t 2w - t 1w) ; (10)
Material balance by air flow:
G o =G to +G p ; (11)
Thermal balance over the cooling tower:
Q gr =Q wgr; (12)
The heat balance of the heat exchanger as a whole (the amount of heat transferred by each of the flows is the same):
Q wmo = Q mo ; (13)
Combined heat balance of cooling tower and heat exchanger for water:
Q wgr =Q wmo ; (14)
11. Solving together the equations from (7) to (14), we obtain the following dependencies:
mass air flow in the auxiliary flow, kg/s:
mass air flow in the main air flow, kg/s:
G o =G p ; (16)
Mass flow of water through the cooling tower along the main flow, kg/s:
12. The amount of water required to feed the water circuit of the cooling tower, kg/s:
G wn \u003d (d 5 -d 2) G in; (18)
13. Power consumption in the cycle is determined by the power spent on the fan drive, W:
N in =G o ∆i in; (19)
Thus, all the parameters necessary for constructive calculations of the elements of the indirect evaporative air cooling system have been found.
It should be noted that the working stream of cooled air supplied to the consumer (point "2") can be additionally cooled, for example, by adiabatic humidification or by any other method. As an example, in fig. 4 shows the point "3*" corresponding 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 ability to cool 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, the indirect evaporative cooling system allows you to achieve a lower temperature than the traditional adiabatic air humidification system. It is also important to emphasize that the moisture content of the desired air does not change. Similar advantages compared to adiabatic humidification can be achieved by introducing an auxiliary air flow.
There are currently few practical applications of the indirect evaporative cooling system. However, devices of a similar, but somewhat different principle of operation have 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 moistened 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 to be cooled: in air conditioning systems of trains, auditoriums for various purposes, data centers and other facilities.
The purpose of their introduction 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 by the outside air.
For greater efficiency of the device, the outside air is pre-moistened. In more complex systems, humidification is also carried out in the process of heat exchange (injection of water 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 is reduced by 30-60%.
Yury Khomutsky, technical editor of the magazine "Climate World"
The article uses the methodology of Moscow State Technical University. N. E. Bauman for the calculation of an indirect evaporative cooling system.
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. Heat exchangers (T) 1 and 2 irrigated with water for indirect evaporative and direct evaporative air cooling are arranged in series along the air flow. T 1 has channels 3, 4 of the general and auxiliary air flows. Between T 1 and 2 there is a chamber 5 for separating air flows with a bypass channel 6 and a valve 7 placed in it per TiHpyeMbiM. control is connected to the temperature sensor of the air in the room Channels 4 of the auxiliary air flow are connected to the atmosphere by the outlet 12, and T 2 is connected to the room by the main air outlet 13. 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, at the signal of the air temperature sensor in the room, valve 7 is partially closed through the control unit, and using the regulator 14, the blower speed is lowered, ensuring a proportional reduction in the total air flow rate by the amount of reduction in the auxiliary air flow rate 1 ill. (L to about 00 to
UNION OF SOVIET
SOCIALIST
REPUBLIC (51)4 F 24 F 5 00
DESCRIPTION OF THE INVENTION
TO A8TOR'S CERTIFICATE
USSR STATE COMMITTEE
FOR INVENTIONS AND DISCOVERIES (2 1) 4 166558/29-06 (22) 25.12.86 (46) 30.08.88. Wu.t, !! 32 (71) Moscow textile institute (72) O.Ya. Kokorin, M.l0, Kaplunov and S.V. Nefelov (53) 697.94(088.8) (56) Author's certificate of the USSR
263102, class. F ?4 G 5/00, 1970. (54) A DEVICE FOR A TWO-STAGE
EVAPORATIVE AIR COOLING (57) The invention relates to ventilation and air conditioning technology. The purpose of the invention is to increase the depth of cooling of the main air flow and reduce energy costs.
Heat exchangers (T) 1 and 2 irrigated with water for indirect evaporative and direct evaporative air cooling are arranged in series along the air flow. T 1 has channels 3, 4 of general and auxiliary air flows. Between T 1 and 2 there is a chamber 5 for separating air flows with a switch SU„„ 1420312 d1. inlet channel 6 and an adjustable valve 7 placed in it. Supercharger
8 with drive 9 is connected by inlet 10 with the atmosphere, and output 11 - with channels
3 common air flow. Valve 7 is connected through the control unit to the air temperature sensor in the room. Channels
4 of the auxiliary air flow are connected by outlet 12 with the atmosphere, and T 2 by 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, at the signal of the air temperature sensor in the room, valve 7 is partially closed through the control unit, and using the regulator 14, the blower speed is reduced to ensure a proportional reduction in the total air flow rate by the amount of reduction in the auxiliary air flow rate. 1 ill.
The invention relates to ventilation and air conditioning technology.
The purpose 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 heat exchangers 1 and 2 irrigated with water for indirect evaporative air cooling, located in series along the air flow, the first part of which has channels 3 and 4 of the general and auxiliary air flows. twenty
Between the heat exchangers 1 and 2 there is a chamber 5 1 for dividing air flows with an overflow channel 6 and an adjustable valve 7 placed in it. driven
9 is connected by inlet 10 with the atmosphere, l by outlet 11 - with channels 3 of the total flow ltna; ty;:; 3. Regulating valve 7 is connected via a control unit to a room temperature sensor (HP shown) . Channels 4 of the auxiliary air flow are communicated with an output
12 with atmosphere, and heat exchanger 2 for direct air cooling with outlet 13 of the main air flow - with heating. The bypass channel 6 is connected to the 4 g3sgg auxiliary sweat air valves, and the drive 9 of the supercharger 8 has a speed controller 14, connected to the control unit 4O (not yet: 3ln? . device. cooling” l303 is stale; it works as follows.
Outside air through the inlet 10 and 3-45 enters the blower 8 and through the outlet 11 ttartteT flies into the channels 3 of the total air flow of the indirect evaporative cooling heat exchanger. With the passage of air in the channels 3 ilpo, its enthalpy ttpta decreases with a constant moisture content, after which the total air flow enters the chamber 5 of the air separation unit.
From chamber 5, part of the pre-cooled air in the area of 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 of the film of water and at the same time cooling the total air flow passing through the channels 3.
The auxiliary air flow, which has increased its enthal ITHIt3, is removed through the outlet 12 to the atmosphere or can be used, for example, for ventilation of auxiliary rooms or cooling of building fences. The main air flow comes from the air separation chamber 5! 3 direct evaporative cooling heat exchanger 2, where the air is further cooled and decompressed at a constant enthalpy and simultaneously supplied with fuel, after which it is processed. and the main air flow through outlet 13 is supplied to the bias. If necessary, reduce the tttc!tttIt Ttoëoltoïίίefficiency of the device tet ITT according to the corresponding signal from the room air temperature sensor through the control unit (not shown), the adjustable valve 7 is permanently closed, which leads to a decrease in the auxiliary air flow rate and a decrease in the degree cooling" of the total air flow in the heat exchanger 1 indirect evaporative cooling. Along with cover
R. gys!Itpyentoro k:gplnl 7 with the use ofItItett speed controller 14!
tot:;the number of turns of the blower 8 is included with the provision of a proportional.psh tt;t "flow rate of the total air flow and:
»en..tc1t ttãp!I I nogo sweat cl air.
1 srmullieacquisition of y.trists; for two-square experimen- tal air cooling, containing i os.heggo»l g erpo p,lñ!TOIT irrigated in the direction of air flow!30 auxiliary air flows, air flow separation chamber located between the heat exchanger with a bypass channel and an adjustable valve located in it, a blower with a drive, reporting Itttt ttt g3x
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 company, Uzhgorod, st. Design, 4 swarm, and the outlet - with channels of the general air flow, moreover, the adjustable valve is connected through the control unit to the room air temperature sensor and the channels of the auxiliary air flow are in communication with the atmosphere, and the direct evaporative cooling heat exchanger - with the room, from l in order to increase the cooling depth of the main air flow and reduce energy costs, the bypass channel is connected to the auxiliary air flow channels, and the blower drive is equipped with a speed controller connected to the control unit.
Similar patents:
For rooms with large surpluses of sensible heat, where it is necessary to maintain a high humidity of the indoor air, air conditioning systems using the principle of indirect evaporative cooling are used.
The scheme consists of a system for processing the main air flow and an evaporative cooling system (Fig. 3.3. Fig. 3.4). For cooling water, air conditioner spray chambers or other contact devices, spray pools, cooling towers, and others can be used.
Water, cooled by evaporation in the air stream, with temperature, enters the surface heat exchanger - the air cooler of the air conditioner of the main air duct, where the air changes its state from values to values \u200b\u200b(t.), The water temperature rises to. The heated water enters the contact apparatus, where it is cooled by evaporation to a temperature and the cycle is repeated again. The air passing through the contact apparatus changes its state from parameters to parameters (i.e.). The supply air, assimilating heat and moisture, changes its parameters to the state of t., and then to the state.
Fig.3.3. Scheme of indirect evaporative cooling
1-heat exchanger-air cooler; 2-pin device
Fig.3.4. diagram of indirect evaporative cooling
Line - direct evaporative cooling.
If the excess heat in the room is, then with indirect evaporative cooling, the supply air flow will be
with direct evaporative cooling
Since >, then<.
<), что позволяет расширить область возможного использования принципа испарительного охлаждения воздуха.
A comparison of processes shows that with indirect evaporative cooling, the performance of SCR is lower than with direct cooling. 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 scheme of indirect evaporative cooling, devices of a combined type have been developed (Fig. 3.5). The apparatus includes two groups of alternating channels separated by walls. Auxiliary air flow passes through channel group 1. The water supplied through the water distribution device flows down the surface of the channel walls. Some water is supplied to the water distribution device. When water evaporates, the temperature of the auxiliary air flow decreases (with an increase in its moisture content), and the channel wall also cools.
To increase the cooling depth of the main air flow, multistage main flow processing schemes have been developed, using which it is theoretically possible to reach the dew point temperature (Fig. 3.7).
The plant consists of an air conditioner and a cooling tower. In the air conditioner, indirect and direct isoenthalpic cooling of the air in the serviced premises is performed.
The cooling tower evaporatively cools the water that feeds the air conditioner's surface air cooler.
Rice. 3.5. Scheme of the device of the combined apparatus for indirect evaporative cooling: 1,2 - group of channels; 3- water distribution device; 4- pallet
Rice. 3.6. Scheme of SCR two-stage evaporative cooling. 1-surface air cooler; 2-irrigation chamber; 3- cooling tower; 4-pump; 5-bypass with air valve; 6-fan
In order to unify equipment for evaporative cooling, spray chambers of typical central air conditioners can be used instead of a cooling tower.
Outside air enters the air conditioner and is cooled in the first cooling stage (air cooler) with a constant moisture content. The second stage of cooling is the irrigation chamber operating in the isenthalpy cooling mode. Cooling of the water supplying the surface of the water cooler is carried out in the cooling tower. The water in this circuit is circulated by a pump. A cooling tower is a device for cooling water with atmospheric air. Cooling occurs due to the evaporation of part of the water flowing down the sprinkler under the action of gravity (evaporation of 1% of water lowers its temperature by about 6).
Rice. 3.7. diagram with two-stage evaporative mode
cooling
The air conditioner spray chamber is equipped with a bypass duct with an air valve or has a controlled process, which regulates the air sent to the serviced room by the fan.
Union of Soviet
Socialist
Republics
State Committee
USSR for Inventions and Discoveries (53) UDC 629. 113. .06.628.83 (088.8) (72) Inventors
V. S. Maisotsenko, A. B. Tsimerman, M. G. and I. N. Pecherskaya
Odessa Civil Engineering Institute (71) Applicant (54) TWO-STAGE EVAPORATION AIR CONDITIONER
COOLING FOR VEHICLE
The invention relates to the field of transport engineering and can be used for air conditioning in vehicles.
Air conditioners for vehicles are known, containing an air slotted evaporative nozzle with air and water channels separated from each other by walls of microporous plates, while the lower part of the nozzle is immersed in a tray with liquid (1)
The disadvantage of this air conditioner is the low efficiency of air cooling.
The closest technical solution to the invention is a two-stage evaporative cooling air conditioner for a vehicle, containing a heat exchanger, a tray with liquid in which the nozzle is immersed, a chamber for cooling the liquid entering the heat exchanger with elements for additional cooling of the liquid and a channel for supplying air from the external environment into the chamber , made tapering towards the inlet of the chamber (2
In this compressor, elements for additional air cooling are made in the form of nozzles.
However, the cooling efficiency in this compressor is also insufficient, since the limit of air cooling in this case is the temperature of the wet bulb of the auxiliary air flow in the sump.
10 in addition, the well-known air conditioner is structurally complex and contains duplicate units (two pumps, two tanks).
The purpose of the invention is to increase the degree of cooling efficiency and compactness of the device.
The goal is achieved by the fact that in the proposed air conditioner the elements for additional cooling are made in the form of a heat exchange baffle located vertically and fixed on one of the chamber walls with the formation of a gap between it and the chamber wall opposite to it, and
25, on the side of one of the surfaces of the partition, a reservoir is installed with liquid flowing down the said surface of the partition, while the chamber and the tray are made in one piece.
The nozzle is made in the form of a block of capillary-porous material.
In FIG. 1 shows a schematic diagram of an air conditioner, Fig. 2 raeeee A-A in Fig. one.
The air conditioner consists of two stages of air cooling: the first stage is cooling the air in the heat exchanger 1, the second stage is cooling it in the nozzle 2, which is made in the form of a block of capillary-porous material.
A fan 3 is installed in front of the heat exchanger, driven by a 4 ° electric motor. The heat exchanger 1 is installed on the pallet 10, which is made in one piece with the chamber
8. A channel adjoins the heat exchanger
11 for supplying air from the external environment, while the channel is made as a plan tapering towards the inlet 12 of the air cavity
13 chambers 8. Inside the chamber there are elements for additional air cooling. They are made in the form of a heat exchange partition 14, located vertically and fixed on the wall 15 of the chamber opposite the wall 16, relative to which the partition is located with a gap. The partition divides the chamber into two communicating cavities 17 and 18.
A window 19 is provided in the chamber, in which a droplet eliminator 20 is installed, and an opening 21 is made on the pallet. stream L
In connection with the implementation of the channel 11 tapering to the inlet 12 ! cavity 13, the flow rate increases, and outside air is sucked into the gap formed between the said channel and the inlet, thereby increasing the mass of the auxiliary flow. This flow enters the cavity 17. Then this air flow, having rounded the partition 14, enters the cavity 18 of the chamber, where it moves in the opposite direction to its movement in the cavity 17. In the cavity 17, towards the movement of the air flow, a film 22 of liquid flows down the partition along the partition - water from the reservoir 9.
When the flow of air and water come into contact, as a result of the evaporative effect, the heat from the cavity 17 is transferred through the partition 14 to the film 22 of water, contributing to its additional evaporation. After that, a stream of air with a lower temperature enters the cavity 18. This, in turn, leads to an even greater decrease in the temperature of the baffle 14, which causes additional cooling of the air flow in the cavity 17. Therefore, the temperature of the air flow will again decrease after rounding the baffle and entering the cavity
18. Theoretically, the cooling process will continue until its driving force becomes zero. In this case, the driving force of the evaporative cooling process is the psychometric difference -temperatures of the air flow after turning it relative to the partition and coming into contact with the water film in cavity 18. Since the air flow is pre-cooled in cavity 17 with a constant moisture content, the psychrometric temperature difference of the air flow in the cavity 18 tends to zero when approaching the dew point. Therefore, the limit of water cooling here is the dew point temperature of the outside air. The heat from the water enters the air flow n the cavity 18, while the air is heated, humidified and through the window 19 and the drop eliminator 20 is released into the atmosphere.
Thus, in chamber 8, the flow-through movement of heat-exchanging media is organized, and the separating heat-exchange partition allows indirect pre-cooling of the air flow supplied for cooling water due to the process of water evaporation. The cooled water flows down the partition to the bottom of the chamber, and since the latter is made in one whole with a pallet, then from there it is pumped into the heat exchanger 1, and is also spent on wetting the nozzle due to intracapillary forces.
Thus, the main air flow L .n, having been pre-cooled without changing the moisture content in the heat exchanger 1, enters the nozzle 2 for further cooling. without changing its heat content. Further, the main air flow through the opening in the pan
59 yes cools, while cooling the partition. Entering the cavity
17 of the chamber, the air flow, flowing around the partition, is also cooled, but without changes in moisture content. Claim
1. An air conditioner for a two-stage evaporative cooling for a vehicle, containing a heat exchanger, a liquid substation into which a nozzle is immersed, a chamber for cooling the liquid entering the heat exchanger with elements for additional cooling of the liquid, and a channel for supplying air from the external environment into the chamber, made tapering in direction to the camera inlet, different from the fact that, in order to increase the degree of cooling efficiency and the compactness of the compressor, the elements for additional air cooling are made in the form of a heat exchange baffle located vertically and fixed on one of the walls of the chamber with the formation of a gap between it and the opposite wall of the chamber, and on the side of one of On the surfaces of the partition, a reservoir is installed with liquid flowing down the said surface of the partition, while the chamber and the tray are made as one whole.
In HVAC systems, adiabatic evaporation is usually associated with air humidification, but in recent years this process has become increasingly popular around the world and is increasingly being used for "natural" air cooling.
WHAT IS EVAPORATIVE COOLING?
Evaporative cooling is the basis of one of the earliest man-made space cooling systems, where air is cooled by the natural evaporation of water. This phenomenon is very common and occurs everywhere: one example is the feeling of cold you experience when water evaporates from the surface of your body under the influence of wind. The same thing happens with the air in which water is sprayed: since this process occurs without an external source of energy (this is what the word "adiabatic" means), the heat needed to evaporate water is taken from the air, which, accordingly, becomes colder.
The use of this method of cooling in modern air conditioning systems provides high cooling capacity with low power consumption, since in this case electricity is consumed only to support the process of water evaporation. At the same time, ordinary water is used as a coolant instead of chemical compositions, which makes evaporative cooling more economical and environmentally friendly.
TYPES OF EVAPORATIVE COOLING
There are two main methods of evaporative cooling - direct and indirect.
Direct evaporative cooling
Direct evaporative cooling is the process of lowering the temperature of the air in a room by directly humidifying it. In other words, due to the evaporation of the atomized water, the surrounding air is cooled. In this case, the distribution of moisture is carried out either directly in the room using industrial humidifiers and nozzles, or by saturating the supply air with moisture and cooling it in the section of the ventilation unit.
It should be noted that under conditions of direct evaporative cooling, a significant increase in the humidity of the supply air inside the room is inevitable, therefore, to evaluate the applicability of this method, it is recommended to take as a basis the formula known as the “temperature and discomfort index”. The formula calculates the comfortable temperature in degrees Celsius, taking into account humidity and dry bulb temperature readings (Table 1). Looking ahead, we note that the direct evaporative cooling system is used only in cases where the outdoor air during the summer period has high dry bulb temperatures and low absolute humidity levels.
Indirect evaporative cooling
To improve the efficiency of evaporative cooling at high outdoor humidity, 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 very humid climates.
The general scheme of operation of the supply and ventilation system with recuperation is that hot supply air, passing through a special heat exchange cassette, is cooled by cool air removed from the room. The principle of operation of indirect evaporative cooling is to install an adiabatic humidification system in the exhaust duct of supply and exhaust central air conditioners, with subsequent transfer of cold through the heat exchanger to the supply air.
As shown in the example, by using a plate heat exchanger, the outdoor air in the ventilation system is cooled by 6 °C. The use of evaporative cooling of the exhaust air will increase the temperature difference from 6°C to 10°C without increasing electricity consumption and indoor humidity levels. The use of indirect evaporative cooling is effective at high heat inputs, for example, in office and shopping centers, data centers, industrial premises, etc.
Indirect cooling system using CAREL humiFog adiabatic humidifier:
Case: Estimating the cost of an indirect adiabatic refrigeration system versus chiller refrigeration.
On the example of an office center with a permanent stay of 2000 people.
| Terms of payment | |
| Outdoor temperature and moisture content: | +32ºС, 10.12 g/kg (indicators are taken for Moscow) |
| Air temperature in the room: | +20 ºС |
| Ventilation system: | 4 air handling units with a capacity of 30,000 m3/h (air supply according to sanitary standards) |
| The power of the cooling system, taking into account ventilation: | 2500 kW |
| Supply air temperature: | +20 ºС |
| Extract air temperature: | +23 ºС |
| Sensible heat recovery efficiency: | 65% |
| Centralized cooling system: | Chiller-fancoil system with water temperature 7/12ºС |
Calculation
- For calculation, we calculate the relative humidity of the air at the hood.
- At a temperature in the cooling system of 7/12 °С, the dew point of the exhaust air, taking into account internal moisture emissions, will be +8 °С.
- The relative humidity of the air in the exhaust will be 38%.
*It must be taken into account that the cost of installing a refrigeration 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 refrigeration system and humidification systems for indirect evaporative cooling.
- Capital cost for supply air cooling for an indirect cooling system.
The cost of one Optimist humidification rack manufactured by Carel (Italy) in an air handling unit is 7570 €.
- Capital cost for supply air cooling without indirect cooling system.
The cost of a chiller with a cooling capacity of 62.3 kW is approximately 12,460 €, based on a cost of 200 € per 1 kW of cooling capacity. It must be taken into account that the cost of installing a refrigeration system, taking into account all costs, is significantly higher compared to indirect cooling systems.
Operating costs
For analysis, we take the cost of tap water 0.4 € per 1 m3 and the cost of electricity 0.09 € per 1 kWh.
- Operating costs for supply air cooling for an indirect cooling system.
Water consumption for indirect cooling is 117 kg/h for one air handling unit, taking into account losses of 10%, we will take it as 130 kg/h.
The power consumption of the humidification system is 0.375 kW for one air handling unit.
The total cost per hour is 0.343 € for 1 hour of system operation.
- Operating costs for supply air cooling without indirect cooling system.
We take the coefficient of performance equal to 3 (the ratio of cooling power to power consumption).
The total cost per hour is 7.48 € for 1 hour of operation.
Conclusion
The use of indirect evaporative cooling allows:
Reduce capital costs for supply air cooling by 39%.
Reduce energy consumption for building air conditioning systems from 729 kW to 647 kW, or by 11.3%.
Reduce the operating costs of the building's air conditioning systems from 65.61 €/h to 58.47 €/h, or by 10.9%.
Thus, despite the fact that fresh air cooling accounts for approximately 10-20% of the total cooling demand of office and shopping centers, it is here that there are the greatest reserves in improving the energy efficiency of a building without a significant increase in capital costs.
The article was prepared by TERMOCOM specialists for publication in ON magazine No. 6-7 (5) June-July 2014 (pp. 30-35)
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