I. Selection of Cold Source for Purification Air Conditioning System
1. Comparison and selection of centralized refrigeration station and dispersed independent refrigeration source.
The centralized installation of refrigeration stations in large-scale production plants is beneficial to construction investment and operation management. However, due to the difference of temperature and humidity requirements, cooling parameters are quite different; for clean workshops with different operation rules and operation time, on the basis of centralized refrigeration station, scattered, independent and dedicated refrigeration units are installed nearby, which is of great benefit to saving energy, guaranteeing parameters and facilitating operation and management.
2. Refrigerant using frozen water or direct evaporation of freon.
It is more advantageous for large factories to supply chilled water from centralized refrigeration stations as refrigerant for purifying air conditioning systems. Because of the convenience of chilled water transportation, the cold loss in the process of transportation is relatively small. Moreover, the use of chilled water as refrigerant is also beneficial to the control, regulation and maintenance management of the parameters of purified air conditioning system. However, small independent and decentralized refrigeration units can use water-cooled chillers or air-cooled direct evaporation refrigeration units. This depends on the specific circumstances of the specific project.
3. Compression refrigerator or direct-fired lithium bromide absorption refrigerator.
Piston type, centrifugal type and screw type refrigerators are all compressed refrigerators. Centrifugal type and screw type refrigerators are the most commonly used compressed refrigerators in the design of purification air conditioning. Because of its low investment and convenient operation and management, but its operation consumes high power. The cooling water supply temperature of the compressed refrigeration unit can be adjusted, and the lowest water supply temperature can be 4 C. However, in areas where power supply is tight and gas and coal supply is more convenient, especially when waste heat and steam can be used, it is more economical to use direct-fired lithium bromide absorption chiller, especially when the chiller can provide heat as well as cooling.
4. The determination of the temperature of the chilled water in the purified air conditioning system.

When chilled water is used as refrigerant to purify air conditioning system, the initial temperature of chilled water (the inlet temperature of chilled water in surface cooler) should be at least 3.5 C lower than the final temperature of treated air (determined in design calculation); if the purpose of air treatment system is to dehumidify and cool by refrigeration, the final temperature of chilled water should be at least 3.5 C lower. The outlet temperature of chilled water in surface cooler should be 0.7 C lower than the final temperature of treated air, and the initial temperature (inlet temperature) of chilled water used as dry cooling coil should be at least 2 C higher than the dew point temperature of clean indoor air.

Selection of Heat Sources for Purification Air Conditioning System
1. In order to prevent freezing in winter, the heater of fresh air preheater should be heated by electricity or steam, but not by hot water, so that the preheater itself may be in danger of being frozen.
2. Heat medium of heater in air conditioning unit can be heated by hot water, steam or electricity. The electric heating control is flexible and convenient, and the temperature control accuracy is high, but the operation cost is expensive. Electric heating is usually used in places where there is no hot water and steam supply. When hot water is used as heat medium, not only the regulation and management is convenient, but also the control accuracy is high. It is the most commonly used heat medium for heaters, and steam can be used as heat medium for heaters when the accuracy of temperature is not high (e.g. temperature).
3. When the precision of temperature is very high (e.g. temperature), it is a feasible method to install an electric heater with micro-adjustment of temperature precision on the branch pipe fed into the clean room.
4. It is convenient, feasible, economical and reliable to humidify air-conditioning system by using superheated steam (> 0.2MPa) as heat medium, dry steam humidifier or electrothermal or electrode humidifier. When the accuracy of relative humidity is not high and the humidification amount is large, it is advisable to use water to humidifier.