Evaporative condenser: The principle of evaporative condenser is to use the evaporation of part of the water to take away the heat released by the condensation process of gas refrigerant. Its shell is a rectangular box of thin steel plate, which contains condensing coil group, water sprinkling device, water retaining fence, water collecting tray at the bottom, circulating water pump outside the box, centrifugal fan or axial fan on the top or side of the box. In addition, there is a float valve in the water tray. When the water is continuously evaporated and the water level in the water tray is too low, the float valve will automatically open to replenish cooling water. Refrigeration system cycle: Compressor exhaust Evaporative cooling condenser Throttling Evaporator Compressor suction

External environment

Water-cooled condenser: After the circulating cooling water is cooled by the cooling tower, it is pumped into the condenser to cool the high-temperature refrigerant, and then returned to the cooling tower for cooling. Refrigeration system cycle: compressor exhaust water-cooled condenser throttling evaporator compressor suction

Water-cooled cooling tower

2 External environment Evaporative cooling and the external environment are primary heat exchange, and water-cooled condenser and the external environment are secondary heat exchange, so evaporative cooling can obtain a smaller heat exchange temperature difference.

2. Advantages and disadvantages analysis

Advantages:

1. Compared with water-cooled condensers, evaporative cooling does not have secondary heat exchange, so the design condensation temperature can be 3~5 degrees lower. Under the design working conditions, the efficiency difference is 3-5%. The energy-saving effect of evaporative cooling is related to the local climate humidity. When the air humidity is high, the power of water vaporization is not strong and the cooling effect is limited; only in places with dry climates can the energy-saving effect be significant. 2. It saves the circulating water system and saves space.

3. It saves the power consumption of the circulating water pump;

In general, the significant advantage of evaporative cooling is energy saving. Disadvantages:

1. Large initial investment in equipment. Compared with the price of evaporative cooling and water cooling (including cooling tower + water pump + condenser) of the same quality, the price of evaporative cooling is about 2.5 times that of water cooling. The evaporative cooling all-in-one machine places all the equipment outdoors, and the protection level of the unit needs to be improved (especially for electrical instruments). The cost and maintenance cost of the whole machine must be increased.

2. High installation cost of evaporative cooling. There are a large number of heat exchange tubes inside the evaporative cooling, which are very heavy. The cost of evaporative cooling hoisting and positioning is significantly increased.

3. High installation cost of intermediate pipelines of refrigeration units. Since evaporative cooling is installed on the roof, the compressor exhaust pipeline is very long and contains high-temperature and high-pressure refrigerant. Therefore, the requirements for installation and construction are very high, and all welds must be inspected.

4. High cost of unit commissioning. Usually, the unit needs to be pressure tested and vacuum tested on site. For evaporative cooling units, the refrigerant pipeline is relatively complex, and the workload of leak detection and repair will be greatly increased.

5. Civil construction cost of the machine room In addition to the weight of the evaporative cooling system, a large amount of circulating water is also filled in it during normal operation. The combined impact of the two on the building is very large. This part of the impact must be considered when designing the machine room, and the civil construction cost investment must be increased.

6. The system safety is not high, and the unit operation stability is low. The possibility of refrigerant leakage in the evaporative cooling system is very high. Evaporative cooling is a one-time heat exchange. Any environmental fluctuation will affect the exhaust pressure of the compressor, causing the compressor to make frequent adjustments. The water buffer in the middle of the water cooling system can filter out some fluctuations, so that the unit can run more smoothly.

7. Picky about refrigerants Due to different physical properties, the pipeline pressure loss of refrigerants during flow is very different. The core of evaporative cooling energy saving is to reduce the condensing temperature to reduce the compressor exhaust pressure, thereby saving energy. The exhaust pipeline of the evaporative cooling system is long. If the pressure drop of the exhaust pipeline is too large, the compressor will be forced to increase the exhaust pressure to overcome the pipeline resistance, which will greatly reduce the energy saving effect.

4 We usually see that systems that use evaporative cooling use ammonia as the refrigerant, precisely because ammonia has very low flow resistance. Fluorine refrigerants have poor fluidity, so the energy-saving effect of using evaporative cooling will be greatly reduced.

8. Very sensitive to non-condensable gases The refrigeration system will inevitably infiltrate non-condensable gases (especially negative pressure systems), and non-condensable gases will eventually gather on the high-pressure side. For evaporative cooling, they will gather in the heat exchange coil, which will greatly occupy the heat exchange area, causing the exhaust pressure to rise and increase power consumption. In extreme cases, gas blockage will occur, completely making evaporative cooling unable to work. Therefore, an exhaust system must be configured.

9. Descaling The unit will be scaled during operation. If it is not removed, the heat exchange efficiency will be greatly reduced, thereby increasing the power consumption of the unit. Water-cooled condensers will scale on the inside of the heat exchange tubes, and generally need to be cleaned every 1 to 2 years (open the end cover for cleaning). However, the evaporative cooling scale is on the outside of the tube and the evaporative cooling heat exchange tubes are serpentine coils stacked together, which means that it is difficult to clean and it is impossible to judge the internal situation. For the cleaning of evaporative cooling, there is basically only one method, chemical cleaning, but the operation is very difficult and demanding. Incorrect or uneven concentration ratio will corrode the heat exchange tubes, and the cleaning effect is very general. Customers often complain that the new unit is very energy-saving in the first two years, but then it gets worse and worse. This is the reason.

10. Corrosiveness After the water in the evaporative cooling water pan evaporates, impurities will remain in the water pan. Long-term concentration will make the water in the water pan become strongly acidic or alkaline, thereby corroding the water pan and the shell, and such water spraying

5 on the heat exchange tube will accelerate the corrosion of the heat exchange tube. 11. Maintainability After the water-cooled heat exchanger is piped, it can be used normally again by simply plugging the pipe. The heat exchange tube of the evaporative cooling is made of very long straight pipes bent. Once leaking, the entire evaporative cooling coil needs to be replaced.

Points to note when using evaporative cooling

1. Since the heat exchange tubes are exposed outdoors, electric heating systems must be added in cold areas in winter to prevent the water pan from freezing;

2. Choose a full coil heat exchange method; some evaporative cooling manufacturers will use the heat exchange coil + PVC filler method to reduce costs. In fact, part of the heat exchange coil is replaced by PVC filler, and evaporative cooling becomes a combination of 0.5 evaporative cooling + 0.5 water cooling, which has a much worse energy-saving effect. In addition, PVC fillers need to be replaced regularly every year, which is both troublesome and expensive.

3. The heat exchange of evaporative cooling is all through the vaporization of water, and the water consumption is relatively large, so the water baffle is very important. The floating water rate of a good brand is basically the same as that of a closed cooling tower.

4. Considering all aspects, evaporative cooling must choose a good brand to make sense.

III. Summary

The evaporative condenser replaces the secondary heat exchange of water cooling with a primary heat exchange, which saves energy significantly. However, the application of any technology has its applicability and limitations. The market is the best test tool. The market share of evaporative cooling is less than 10%, and the mainstream is water cooling. In dry areas, ammonia is used as the refrigerant and a good brand is selected. Evaporative cooling can save energy significantly. The payback period of the additional initial investment is generally within 5 years (annual operation time is 8,000 hours), which is a very cost-effective choice. However, in humid climate areas, fluorine refrigerants have an initial investment cycle of about 5 to 10 years. Considering the maintenance and repair costs, the investment payback period may be more than 10 years. For normal temperature units, evaporative cooling has no advantages, and water cooling is recommended.