The high-precision constant temperature and humidity air conditioning refrigeration system consists of four main components: compressor, evaporator, condenser, and expansion valve.
1) Compressor
Compressors are divided into three categories according to their structure: open type, semi-enclosed type, and fully enclosed type. At present, most of the high-precision constant temperature and humidity air conditioning refrigeration systems dedicated to computer rooms use fully enclosed compressors.
A fully enclosed refrigeration compressor is a compressor and an electric motor installed in a sealed iron shell to form a whole. From the outside, there are only the suction and exhaust pipe joints of the compressor and the wires of the motor; the compressor shell is divided into upper and lower parts. After the compressor and the motor are installed, the upper and lower iron shells are welded into one.
Among the fully enclosed refrigeration compressors, there are piston compressors and scroll compressors.
In the currently produced computer room dedicated air conditioning systems, the compressors used are all fully enclosed scroll refrigeration compressors. Its structure mainly consists of the following items: rotary inlet and outlet valves; pressure gauge interface; built-in overload protection; elastic machine base; crankcase heater; built-in lubricating oil pump.

The biggest advantages of scroll refrigeration compressors are:

1. Simple structure: The compressor body only needs two parts (moving plate and fixed plate) to replace multiple accessories in the piston compressor, so the failure rate is very low.

2. High efficiency: The suction gas and the conversion process gas are separated to reduce the heat transfer between the suction and the process, which can improve the efficiency of the compressor. The scroll compression process and the conversion process are very quiet.

(II) Evaporator

1. Classification of evaporators: Evaporators can be divided into two categories according to the type of medium to be cooled: evaporators for cooling liquids (dry evaporators) and evaporators for cooling air (surface cooling evaporators). The evaporators used in air conditioning systems are generally evaporators for cooling air.

2. A-type evaporator: The advantage of the "A" type structure evaporator is that the structure has a larger windward area and a lower wind speed to prevent water from being carried against the wind. The evaporator is equipped with 1/2" copper tube aluminum fins and stainless steel condensate pan to facilitate better heat transfer. The evaporator coil is divided into multiple entry and staggered arrangement, so that each refrigeration system can be spread on the windward side of the coil. When a single refrigeration system is running, the sensible heat cooling capacity can reach 55%-60% of the total cooling capacity.
(III) Condenser Condensers can be divided into three types according to their cooling form: water-cooled, air-cooled, evaporative and water-spraying.
① Water-cooled: In a water-cooled condenser, the heat released by the refrigerant is taken away by the cooling water. The cooling water can flow through once or be recycled. When using circulating water, a cooling water tower or cold water pool is required. Water-cooled condensers have shell and tube type, sleeve type, immersion type and other structural forms.
② Air-cooled: In an air-cooled condenser, the heat released by the refrigerant is taken away by the air. Its structural form is mainly composed of several groups of copper tubes. Since the heat transfer performance of air is very poor, fins are usually added to the outside of the copper tube to increase the heat transfer area on the air side. At the same time, a ventilator is used to accelerate the air flow and force the air to convect to increase the heat dissipation effect.
③ Evaporative and water-spraying: In this type of condenser, the refrigerant condenses in the tube, and the outside of the tube is cooled by water and air at the same time.
At present, the type of high-precision constant temperature and humidity air conditioning refrigeration system specially used for imported computer rooms is mainly air-cooled.
(IV) Thermal expansion valve 1. The structure of the thermal expansion valve: The top of the expansion valve is composed of a sealed box cover, a corrugated film temperature-sensing package and a capillary tube to form a closed container, which is filled with Freon to form a sensing mechanism. The refrigerant filled in the sensing mechanism can be the same as that of the refrigeration system, or different. For example, if the refrigeration system uses R-22, the temperature-sensing package can be filled with R-12. The temperature-sensing package is used to sense the superheated steam temperature at the outlet of the evaporator. The capillary tube is used as a connecting pipe between the sealed box and the temperature-sensing package to transfer pressure to the diaphragm, which is stamped from a thin alloy sheet. It has good elasticity after being stressed. The adjusting rod is used to adjust the opening superheat of the expansion valve. It is used to adjust the elastic force of the spring during the debugging process. When the adjusting rod is rotated inward, the spring is compressed. When the adjusting rod is rotated outward, the spring is relaxed. The transmission rod is pressed between the valve needle seat and the transmission disk to transmit pressure. The valve needle seat is equipped with a valve needle to open or close the valve hole.
2. Working principle of thermal expansion valve: The expansion valve senses the change of superheat at the outlet of the evaporator through the temperature-sensing package, causing the pressure change of the material filled in the temperature-sensing system and acting on the transmission diaphragm. The diaphragm is forced to move up and down, and then the force is transmitted to the transmission rod through the transmission plate to push the valve needle up and down, so that the valve is closed or opened, which plays a role of pressure reduction and throttling and automatic adjustment. The refrigerant supply of the evaporator maintains a certain superheat at the outlet of the evaporator, so as to ensure the full utilization of the heat transfer area of ​​the evaporator and reduce the occurrence of wet compression and cylinder flushing.
3. Types of expansion valves: The pressure acting on the lower part of the transmission diaphragm in the thermal expansion valve body is the evaporation pressure after throttling (this pressure enters the space under the diaphragm through the gap between the transmission rod and the transmission plate). This structure is called an internal balanced expansion valve. The pressure acting on the lower part of the transmission diaphragm in the thermal expansion valve body is not the evaporation pressure after throttling, but the valve that introduces the pressure at the outlet of the evaporator into the space structure under the transmission diaphragm through an external balance pipe is called an external balanced thermal expansion valve.