1. The structure and working principle of high-precision constant temperature and humidity air conditioner
High-precision constant temperature and humidity air conditioner is mainly composed of compressor, condenser, expansion valve and evaporator. Generally speaking, the refrigeration process of air conditioner is as follows: the compressor compresses the refrigerant gas that absorbs heat energy after passing through the evaporator into high-pressure gas, and then sends it to the condenser of the outdoor unit: the condenser releases the heat energy of the high-temperature and high-pressure gas into the surrounding air through the fan, so that the high-temperature and high-pressure gas refrigerant condenses into liquid again, and then sends it to the expansion valve; the expansion valve cools the liquid refrigerant sent from the condenser pipeline into a liquid and gas mixed refrigerant, and then sends it to the evaporator circuit; the evaporator evaporates the liquid and gas mixed refrigerant into gaseous refrigerant by absorbing the heat in the machine room environment, and then sends it back to the compressor to repeat the previous process.
1. The difference between high-precision constant temperature and humidity laboratory air conditioners and ordinary computer room air conditioners: 
A. High-precision constant temperature and humidity laboratory air conditioners must have high-precision temperature and humidity sensors, and the sensor accuracy is required to be: ±1.5%RH, ±0.3℃ (at 23±2℃) 
Repeatability: better than 0.5%RH and 0.1℃ 
Stability: better than 1.0%RH and 0.1℃ per year. 
The sensor accuracy of ordinary computer room air conditioners is ±3%RH, ±1℃. 
B. High-precision constant temperature and humidity laboratory air conditioners have higher requirements for air volume 
. In theory, the larger the air volume, the smaller the air supply enthalpy difference, and the more uniform the temperature and humidity; but the larger the air volume, the smaller the dehumidification capacity, or even completely lost. Therefore, high-precision constant temperature and humidity air conditioners require as large an air volume as possible on the basis of ensuring dehumidification capacity, and the design of air volume is very strict, while ordinary computer room air conditioners have lower requirements. 
C. High-precision constant temperature and humidity laboratory air conditioners require adjustable 
heating, cooling, humidification, and dehumidification capacity. Due to the accuracy requirements, high-precision constant temperature and humidity laboratory air conditioners require adjustable heating, cooling, humidification, and dehumidification capacity. 
※ For heating, according to the temperature difference, a multi-stage heating method is used for adjustment. When the temperature difference is small, only the first stage of heating is turned on. When the temperature difference is slightly larger, the 1st and 2nd stage heating are turned on at the same time. When the temperature difference is larger, the 1st, 2nd, and 3rd stage heating are turned on at the same time. For humidification, a proportional display method is used to control the humidification amount according to the humidity difference.