How to accurately choose air-cooled and water-cooled chillers？
The air-cooled chiller uses a shell and tube evaporator to exchange heat between water and refrigerant. The refrigerant system absorbs the heat load in the water. After the cooling water produces cold water, the heat is transferred to the finned condenser through the action of the compressor to dissipate heat. The fan is lost to the outside air (wind cooling).
The water-cooled chiller uses the shell evaporator to exchange heat between water and refrigerant. The refrigerant system absorbs the heat load in the water. After the cooling water generates cold water, the heat is transferred to the shell condenser through the action of the compressor, and the refrigerant and water are used. After heat exchange, the water absorbs the heat and then heats it to the external cooling tower through the water pipe.
In fact, the two types of chillers use a refrigerant cycle for cooling, which was introduced in the previous article, so I won’t repeat them here. Under normal circumstances, the two are compatible with each other. The difference is that water-cooled units generally use shell and tube condensers with water as the cooling medium; air-cooled units use finned condensers, which directly use air as the cooling medium. Because the air-cooled unit is directly cooled by air, there is no need for related cooling water devices in the system, including cooling towers, cooling water pumps, valve systems, etc., so it is especially suitable for making cooling towers and valve systems.
For the above two types of chillers, the main comparisons are as follows:
1. Performance comparison:
The heat transfer temperature difference of the condenser of a water-cooled unit is generally 4~8℃, while the heat transfer temperature difference of an air-cooled unit is generally 8~15℃. At the same outdoor ambient temperature, the water temperature of the cooling circulating water is lower than the outdoor air temperature. Therefore, the condensing temperature of the air-cooled unit in normal operation is much higher than that of the water-cooled unit, which makes the air-cooled unit consume more power than the water-cooled unit under the same cooling capacity.
2. Comparison of initial equipment investment:
Since the heat exchange efficiency of water is much greater than that of air, air-cooled condensers have larger equipment volume, use more materials, and high manufacturing costs than water-cooled types with the same heat exchange capacity. Since the nominal power of the equipment of the air-cooled unit is greater than the nominal power of the water-cooled unit, the increase in power capacity and the cost of electrical control equipment are also high.
3. Comparison of computer room equipment:
Air-cooled chiller is an outdoor machine that can be placed on the roof of a building or on the outdoor ground. Its chilled water circulating pump can also be placed with the unit without occupying the machine room. For water-cooled chillers, a computer room should be provided to ensure the normal operation and service life of the equipment including chillers, chilled water circulating pumps, and cooling water circulating pumps, and cooling tower equipment should be installed on the roof or outdoor ground of the building. It can be seen that when the building cannot provide a computer room, it should be a more feasible way to choose an air-cooled chiller.
4. Operating cost comparison:
Since the water-cooled unit operates at a lower condensing temperature, the cooling efficiency is high, and the power consumption of the unit is small. Generally speaking, compared with air-cooled chillers with the same cooling capacity, the total power consumption of water-cooled chillers (including cooling pumps and cooling tower fans) is only 70% of that of air-cooled chillers.
5. Maintenance comparison:
The shell and tube condenser used in the water-cooled unit has a small impact on the heat exchange efficiency within a certain range of dirt accumulation, so the performance of the unit decreases with the generation of dirt to a small extent, the cleaning cycle is long, and the relative maintenance cost is low. Moreover, the heat exchange efficiency of the finned condenser used in the air-cooled unit is greatly affected by the accumulation of dirt. A dust filter must be installed in front of the finned tube for heat dissipation, and it must be cleaned frequently. Due to the high operating pressure of air-cooled units, they are generally installed outdoors and the operating environment is relatively poor. They are not as good as water-cooled units in terms of maintenance and reliability.
Through the above, because of the different functional composition, different operating conditions of air cooling and water cooling are also created. Generally, air-cooled chillers are used in general laboratories, but more water-cooled chillers are used in large-scale industrial production.
