Schematic diagram of an air conditioning system using two-stage evaporative cooling. Air conditioner two stage evaporative cooling for vehicle 25 evaporative cooling direct indirect two and multi stage
In modern climate control technology Much attention is paid to the energy efficiency of equipment. This explains the increased Lately interest in water evaporative cooling systems based on indirect evaporative heat exchangers (indirect evaporative cooling systems). Water evaporative cooling systems may be 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 accessible. In addition, water has been well studied, which makes it possible to fairly 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 humidifiers), when water is injected into the air flow, it not only lowers the air temperature, but also increases its moisture content. In this case, the process line on the I d-diagram humid air follows an adiabatic path, and the minimum 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 along 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 combined 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 fluid - water.
- Environmentally friendly: low noise and vibration levels, non-aggressive working fluid, low environmental hazard industrial production systems due to low manufacturing complexity.
- Simplicity of 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 machines ( refrigeration compressors), low excess 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 water evaporation 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 domestic cooling systems in the region of moderate temperatures is filled with refrigerant vapor compression systems.
This situation is obviously related to the problems of operating water evaporation systems at subzero 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), previously used, had large dimensions, weight and other disadvantages associated with working in conditions of high humidity. In addition, they required 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 it is worth special mentioning the cooling towers of the companies Muntes and SRH-Lauer. Such a low temperature difference was achieved mainly due to original design cooling tower nozzles with 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), is pumped 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).
At the same time, water is supplied to the auxiliary flow channels. The point of supplying water is to “slow down” the rise in air temperature due to its parallel humidification: as is known, the same change in thermal energy can be achieved either by changing only the temperature or by changing temperature and humidity simultaneously. Therefore, when the auxiliary flow is humidified, the same heat exchange is achieved by 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 cooled in the cooling tower due to the auxiliary one. Water moves along the circuit using a circulation pump.
Calculation of indirect evaporative heat exchanger
In order to calculate the cycle of an indirect evaporative cooling system with circulating water, the following initial data are required:- φ os — relative humidity ambient air,%;
- t ос — ambient air temperature, ° C;
- ∆t x - temperature difference at the cold end of the heat exchanger, ° C;
- ∆t m—temperature difference at the warm end of the heat exchanger, °C;
- ∆t wgr - the difference between the temperature of the water leaving the cooling tower and the temperature of the air supplied to it according to the wet thermometer, ° C;
- ∆t min - minimum temperature difference (temperature difference) between the flows in the cooling tower (∆t min<∆t wгр), ° С;
- G r — 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:
- Heat and mass transfer processes are assumed to be equilibrium,
- There are no external heat inflows in all areas 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 resistance 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. Using 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 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 — electric motor efficiency;
ρ 0 — air density at the fan inlet, kg/m 3
Where:
B 0 — ambient barometric pressure, Pa;
R in is the 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 “0-1” process 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 from the known φ 0, t 0.
5. Psychrometric temperature difference of the main flow air at the outlet of the heat exchanger (point “2”) ∆t 2-4, °C
∆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. 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), °C; Lower values of ∆t wgr should be taken if it is necessary to obtain the minimum possible cold water temperature in the cooling tower.
6. We accept that the process of humidifying the auxiliary air flow in the cooling tower from 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 will find a line i=const such that between point “2” and 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 located 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 water temperature at the outlet of the cooling tower, at point “1w”, °C. In the calculations, we can neglect the heating of water in the pump, therefore, at the entrance 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”), °C
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 graphic-analytical method using an i d diagram (with great convenience, a set of Q t and i t diagrams can be used, but they are less common, therefore in this i d diagram was used in the calculations). The specified method is as follows (Fig. 5):
- point “1w”, characterizing the state of water at the inlet to the indirect evaporation heat exchanger, with the specific enthalpy value of point “4” is placed on the t 1w isotherm, separated from the t 4 isotherm at a distance ∆t wgr.
- From the point “1w” along the isenthalp we plot 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 at φ = const = 100%, we construct a tangent to φ pr = 1 from point “p” and obtain the tangent point “k”.
- From the point of tangency “k” along the isenthalpe (adiabatic, i=const) we plot the segment “k - n” so that t n = t k + ∆t min. Thus, a minimum temperature difference between the cooled water and the auxiliary air in the cooling tower is ensured (assigned). This temperature difference guarantees the operation of the cooling tower in the design mode.
- We draw a straight line from point “1w” through point “n” until it intersects with the straight line t=const= t 2w. We get point “2w”.
- From point “2w” we draw a straight line i=const until it intersects with φ pr =const=100%. We get point “5”, which characterizes the state of the air at the outlet of the cooling tower.
- Using the diagram, we determine the desired temperature t5 and other parameters of point “5”.
10. We compose 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:
C pw is the specific heat capacity of water, J/(kg.K).
Thermal load of the heat exchanger along the main air flow, W:
Q mo =G o (i 1 - i 2); (9)
Thermal 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)
Heat balance for cooling tower:
Q gr =Q wgr; (12)
The heat balance of the heat exchanger as a whole (the amount of heat transferred by each flow is the same):
Q wmo =Q mo ; (13)
Combined thermal balance of the cooling tower and water heat exchanger:
Q wgr =Q wmo; (14)
11. Solving equations from (7) to (14) together, we obtain the following dependencies:
mass air flow along the auxiliary flow, kg/s:
mass air flow along 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 recharge the water circuit of the cooling tower, kg/s:
G wn =(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 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 any other method. As an example in Fig. 4 indicates the point “3*”, corresponding to adiabatic humidification. In this case, 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 cooling ability of 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°C (Fig. 6).
"Pseudo-indirect" evaporation
As mentioned above, an indirect evaporative cooling system can achieve lower temperatures than a traditional adiabatic 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 through the introduction of an auxiliary air flow.
There are currently few practical applications of indirect evaporative cooling systems. However, devices of a similar, but slightly different operating principle 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 humidified part of the main flow, but another, completely 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 processing centers and other facilities.
The purpose of their implementation is to reduce the operating time of energy-intensive compressor refrigeration equipment as much as possible. Instead, for outside 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-humidified. In more complex systems, humidification is also carried out during the heat exchange process (water injection into the heat exchanger channels), 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%. Annual energy consumption depends on the climatic region of operation of the system; on average, it is reduced by 30-60%.
Yuri Khomutsky, technical editor of Climate World magazine
The article uses the methodology of MSTU. N. E. Bauman for calculating the indirect evaporative cooling system.
The system under consideration consists of two air conditioners"
the main one, in which air is processed for the serviced premises, and the auxiliary one - the cooling tower. The main purpose of the cooling tower is air-evaporative cooling of water feeding the first stage of the main air conditioner during the warm season (surface heat exchanger PT). The second stage of the main air conditioner - irrigation chamber OK, operating in adiabatic humidification mode, has a bypass channel - bypass B to regulate 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 a hot and humid climate, 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 than systems that use only direct (adiabatic) evaporative cooling.
Two-stage evaporative cooling is known to be most suitable in
areas with dry and hot climates. With two-stage cooling, lower temperatures, fewer air changes and lower relative humidity in rooms can be achieved than with single-stage cooling. This property of two-stage cooling has led to a proposal to switch entirely to indirect cooling and a number of other proposals. However, all other things being equal, the effect of possible evaporative cooling systems directly depends on changes in the state of the outside air. Therefore, such systems do not always ensure the maintenance of the required air parameters in air-conditioned rooms throughout the season or even one day. An idea of the conditions and boundaries of the appropriate use of two-stage evaporative cooling can be obtained by comparing the normalized parameters of indoor air with possible changes in the parameters of outdoor air in areas with a dry and hot climate.
the calculation of such systems should be performed using the J-d diagram in the following sequence.
Points with the calculated parameters of external (H) and internal (B) air are plotted on the J-d diagram. In the example under consideration, according to the design specifications, the following values are accepted: tн = 30 °С; tв = 24 °С; fв = 50%.
For points H and B, we determine the value of the wet thermometer temperature:
tmn = 19.72 °C; tmv = 17.0 °C.
As you can see, the value of tmn is almost 3 °C higher than tmv, therefore, for greater cooling of water and then external supply air, it is advisable to supply air removed by exhaust systems from office premises to the cooling tower.
Note that when calculating a cooling tower, the required air flow may be greater than that removed from the conditioned rooms. In this case, a mixture of external and exhaust air must be supplied to the cooling tower and the wet thermometer temperature of the mixture must be taken as the calculated temperature.
From the calculation computer programs of leading cooling tower manufacturers, we find that the minimum difference between the final water temperature at the outlet of the cooling tower tw1 and the wet thermometer temperature twm of the air supplied to the cooling tower should be taken to be at least 2 °C, that is:
tw2 =tw1 +(2.5...3) °C. (1)
To achieve deeper air cooling in the central air conditioner, the final water temperature at the outlet of the air cooler and at the inlet to the cooling tower tw2 is taken to be no more than 2.5 higher than at the outlet of the cooling tower, that is:
tвк ≥ tw2 +(1...2) °С. (2)
Please note that the final temperature of the cooled air and the surface of the air cooler depend on the temperature tw2, since with a transverse flow of air and water, the final temperature of the cooled air cannot be lower than tw2.
Typically, the final temperature of the cooled air is recommended to be 1–2 °C higher than the final water temperature at the outlet of the air cooler:
tвк ≥ tw2 +(1...2) °С. (3)
Thus, if the requirements (1, 2, 3) are met, it is possible to obtain a relationship connecting the wet thermometer temperature of the air supplied to the cooling tower and the final temperature of the air leaving the cooler:
tвк =tвм +6 °С. (4)
Note that in the example in Fig. 7.14 the values taken are tbm = 19 °C and tw2 – tw1 = 4 °C. But with such initial data, instead of the value tin = 23 °C 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 °C, which makes the whole scheme meaningless at tn = 28.5 °C.
For rooms with large excesses of sensible heat, where it is necessary to maintain high humidity in the internal air, air conditioning systems are used that use the principle of indirect evaporative cooling.
The circuit consists of a main air flow processing system and an evaporative cooling system (Fig. 3.3. Fig. 3.4). To cool water, irrigation chambers of air conditioners or other contact devices, spray pools, cooling towers and others can be used.
Water, cooled by evaporation in the air flow, with a temperature, enters the surface heat exchanger - the air cooler of the air conditioner of the main air flow, where the air changes its state from values to values (t.), the water temperature rises to. The heated water enters the contact apparatus, where it is cooled by evaporation to 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 t., and then to the state.
Fig.3.3. Indirect evaporative cooling circuit
1-heat exchanger-air cooler; 2-contact device
Fig.3.4. indirect evaporative cooling diagram
Line - direct evaporative cooling.
If there is excess heat in the room, then with indirect evaporative cooling the supply air flow rate 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 SCR productivity 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 (Figure 3.5). The device includes two groups of alternating channels separated by walls. An auxiliary air flow passes through channel group 1. The water supplied through the water distribution device flows along the surface of the channel walls. A certain amount of 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, multi-stage schemes for processing the main air flow have been developed, using which it is theoretically possible to achieve the dew point temperature (Fig. 3.7).
The installation consists of an air conditioner and a cooling tower. The air conditioner produces indirect and direct isenthalpy cooling of the air in the serviced premises.
In the cooling tower, evaporative cooling of the water that feeds the surface air cooler of the air conditioner occurs.
Rice. 3.5. Diagram of the design of a combined indirect evaporative cooling apparatus: 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 standardize evaporative cooling equipment, the spray chambers of standard central air conditioners can be used instead of a cooling tower.
Outside air enters the air conditioner and is cooled at the first cooling stage (air cooler) with a constant moisture content. The second stage of cooling is the irrigation chamber, operating in isenthalpy cooling mode. Cooling of the water feeding the surfaces of the water cooler is carried out in a cooling tower. The water in this circuit is circulated by a pump. 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 influence of gravity (evaporation of 1% of water lowers its temperature by about 6).
Rice. 3.7. diagram with two-stage evaporation mode
cooling
The air conditioner's irrigation chamber is equipped with a bypass channel with an air valve or has an adjustable process, which ensures regulation of the air directed into the room served by the fan.
In heating, ventilation and air conditioning systems, adiabatic evaporation is usually associated with air humidification, but recently the process has become increasingly popular around the world and is increasingly being used to “naturally” cool air.
WHAT IS EVAPORATIVE COOLING?
Evaporative cooling is the basis of one of the very first space cooling systems invented by man, where air is cooled due to the natural evaporation of water. This phenomenon is very common and occurs everywhere: one example would be the feeling of cold you experience when water evaporates from the surface of your body due to the influence of the wind. The same thing happens with the air in which water is atomized: since this process occurs without an external source of energy (this is what the word “adiabatic” means), the heat necessary to evaporate the water is taken from the air, which, accordingly, becomes colder.
The use of this cooling method 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, instead of chemical compounds, ordinary water is used as a coolant, which makes evaporative cooling more economically profitable and does not harm the environment.
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 reducing the temperature of the air in a room by directly humidifying it. In other words, due to the evaporation of atomized water, the surrounding air is cooled. In this case, moisture is distributed either directly into the room using industrial humidifiers and nozzles, or by saturating the supply air with moisture and cooling it in a section of the ventilation unit.
It should be noted that in conditions of direct evaporative cooling, a significant increase in the humidity of the supply air indoors is inevitable, therefore, to assess 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 in the summer has high dry bulb temperatures and low absolute humidity levels.
Indirect evaporative cooling
To increase the efficiency of evaporative cooling when outdoor air humidity is high, 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 operating scheme of a 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 operating principle 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 recuperator to the supply air.
As shown in the example, due to the use of a plate heat exchanger, the street 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 energy consumption and indoor humidity levels. The use of indirect evaporative cooling is effective for high heat fluxes, for example in office and shopping centers, data centers, industrial premises, etc.
Indirect cooling system using the CAREL humiFog adiabatic humidifier:
Case: Estimating the costs of an indirect adiabatic cooling system compared to cooling using chillers.
Using the example of an office center with a permanent residence of 2000 people.
| Payment terms | |
| Outdoor temperature and humidity content: | +32ºС, 10.12 g/kg (indicators taken for Moscow) |
| Room temperature: | +20 ºС |
| Ventilation system: | 4 supply and exhaust units with a capacity of 30,000 m3/h (air supply according to sanitary standards) |
| Cooling system power including ventilation: | 2500 kW |
| Supply air temperature: | +20 ºС |
| Extract air temperature: | +23 ºС |
| Sensible heat recovery efficiency: | 65% |
| Central cooling system: | Chiller-fan coil system with water temperature 7/12ºС |
Calculation
- To make the calculation, we calculate the relative humidity of the exhaust air.
- At a temperature in the cooling system of 7/12 °C, the dew point of the exhaust air, taking into account internal moisture releases, will be +8 °C.
- The relative humidity in the exhaust air 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 a humidification system for indirect evaporative cooling.
- Capital cost of 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 costs for supply air cooling without an 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 assume the cost of tap water is 0.4 € per 1 m3 and the cost of electricity is 0.09 € per 1 kW/h.
- Operating costs for supply air cooling for an indirect cooling system.
The water consumption for indirect cooling is 117 kg/h for one supply and exhaust 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 € per 1 hour of system operation.
- Operating costs for supply air cooling without an indirect cooling system.
We take the cooling coefficient equal to 3 (the ratio of cooling power to power consumption).
The total cost per hour is 7.48 € per 1 hour of operation.
Conclusion
Using indirect evaporative cooling allows you to:
Reduce capital costs for supply air cooling by 39%.
Reduce energy consumption for the building's air conditioning systems from 729 kW to 647 kW, or by 11.3%.
Reduce operating costs for building air conditioning systems from 65.61 €/hour to 58.47 €/hour, or by 10.9%.
Thus, despite the fact that fresh air cooling accounts for approximately 10–20% of the total cooling needs of office and shopping centers, it is here that there are the greatest reserves for increasing the energy efficiency of a building without a significant increase in capital costs.
The article was prepared by TERMOKOM specialists for publication in ON magazine No. 6-7 (5) June-July 2014 (pp. 30-35)
For servicing individual small rooms or their groups, local air conditioners with two-stage evaporative cooling, based on an indirect evaporative cooling heat exchanger made of aluminum rolling tubes, are convenient (Fig. 139). The air is purified in filter 1 and supplied to fan 2, after the discharge hole of which it is divided into two flows - main 3 and auxiliary 6. The auxiliary air flow passes inside the tubes of the indirect evaporative cooling heat exchanger 14 and provides evaporative cooling of the water flowing down the inner walls of the tubes. The main air flow passes from the fin side of the heat exchanger tubes and transfers heat through their walls to the water, cooled by evaporation. Recirculation of water in the heat exchanger is carried out using pump 4, which takes water from pan 5 and supplies it to irrigation through perforated tubes 15. The indirect evaporative cooling heat exchanger plays the role of the first stage in combined two-stage evaporative cooling air conditioners.
