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    Room 508,Building 12,Lefu Zhihuiyuan,No.30 ,Xiangyuan Road,Gongshu District, Hangzhou,Zhejiang,China.
  • benny@hzgreeme.com

Working Principle of Constant Temperature and Humidity Machine

With the demand of the market and the prosperity of manufacturing industry, China has introduced many advanced test systems from abroad in recent years, which has played an important role in the development of China's environmental test industry. However, due to its complexity, many problems appear in the operation of the test box, which affects the development of the product. The reason for these phenomena is that the working principle of the comprehensive test is not known. For this reason, we have made some brief expositions on the basic working principle of the system of constant temperature and humidity machine. The working principle and working process of several main systems are described below.

1. Refrigeration system
Refrigeration system is one of the key parts of constant temperature and humidity machine. Generally speaking, the refrigeration methods are mechanical refrigeration and auxiliary liquid nitrogen refrigeration. Mechanical refrigeration uses steam compression refrigeration. They are mainly composed of compressor, condenser, throttle mechanism and evaporator. If the temperature of our experiment is -55 C, the single stage refrigeration is difficult to meet the requirements, so the refrigeration mode of constant temperature and humidity machine usually adopts cascade refrigeration. The refrigeration system of constant temperature and humidity machine consists of two parts, called high temperature part and low temperature part, and each part is a relatively independent refrigeration system. The evaporation of the refrigerant in the high temperature part absorbs heat from the refrigerant in the low temperature part and vaporizes; the evaporation of the low temperature part absorbs heat from the cooled object (air in the test machine) to obtain cooling capacity. The high temperature part and the low temperature part are connected by an evaporative condenser, which is not only the condenser of the high temperature part, but also the condenser of the low temperature part.

2. Heating system
The heating system is relatively simple compared with the refrigeration system. It mainly consists of high-power resistance wires. Because of the high heating rate required by the test, the heating system power is relatively large, and there is also a heater on the bottom of the test machine.

3. Control System
The control system is the core of the comprehensive test box, which determines the heating rate, accuracy and other important indicators of the test machine. Nowadays, most of the controllers of the test machine adopt PID control, and a few of them adopt the combination of PID and fuzzy control. Because the control system basically belongs to the category of software, there generally will be no problems during the usage of the part.

4. Humidity system
The temperature system is divided into two subsystems: humidification and dehumidification.
Generally, steam humidification method is adopted, that is, low pressure steam is directly injected into the test space to humidify. This humidification method has the advantages of high humidification capacity, fast speed and sensitive humidification control. Especially in the case of cooling, it is easy to realize forced humidification.
There are two ways of dehumidification: mechanical refrigeration dehumidification and drying dehumidification. The dehumidification principle of mechanical refrigeration dehumidification is to cool air below dew point temperature, so that water vapor with more than saturated moisture content condenses out, reducing humidity. Desiccant dehumidifier is to use air pump to extract the air from the test box and inject the dry air into it. At the same time, the wet air is sent to the recyclable drying for drying. After drying, it is sent to the test box again and again for dehumidification. Now most of the comprehensive test boxes adopt the former dehumidification method and the latter one, which can make the dew point temperature reach below 0 ℃. It is suitable for occasions with special requirements, but it is expensive.

5. Sensor System
Sensors mainly include temperature and humidity sensors. Temperature sensors are mostly used in platinum cells and thermocouples. There are two methods to measure humidity: dry-wet bulb thermometer and solid-state electronic sensor. Because of the low accuracy of wet and dry bulb method, the constant temperature and humidity box is gradually replacing wet and dry bulb with solid sensor to measure humidity.

6. Supply air circulation system
The air circulation system is generally composed of centrifugal fans and electric machinery driving their operation. It provides the circulation of air in the test machine.

Hangzhou Greeme Environmental Co., Ltd. Constant Temperature and Humidity Machine has seven humanized designs:
1. Control accuracy of constant temperature and humidity machine. To meet the harsh requirement of temperature and humidity in special environment, the temperature control precision is (±1 C) and the humidity control precision is (±5% RH).
2. The cycle runs steadily for 365 days at a time. The usage rate of constant temperature and humidity machine is higher than that of ordinary household air conditioner. The equipment runs continuously for 365 days a year, 24 hours a day. The product reliability design, rigorous testing, high efficiency compressor, stable performance, durable endurance, good quality  meet the needs of low constant temperature and humidity in special places.
3. Stainless steel sheet for fuselage. The fuselage is made of stainless steel sheet metal with beautiful appearance and anti-corrosion, which effectively increases the service life of the product.
4. Function = refrigeration + heating + dehumidification + humidification. This machine has the functions of refrigeration, heating, dehumidification and humidification. Users can choose one function according to their needs, which can not only meet the requirements of temperature and humidity, but also achieve the effect of energy saving.
5. Accessories = all adopt international famous brands. Compressor and main parts operate normally in different environments through scientific and reasonable design of refrigeration system. It overcomes the shortcomings of insufficient refrigeration capacity and dehumidification capacity of domestic same industry models and high failure rate of frequent start-up products of units. At the same time, it also improves the service life of the product.
6. Control = Intelligent PLC Touch Controller. Intelligent PLC touch controller is adopted in the unit. Air temperature and humidity are displayed. The temperature and humidity that need to be controlled are set well. When the temperature and humidity are set, the unit will stop automatically, and when the temperature and humidity are higher than the setting, the unit will start automatically to realize automation. It can start and stop automatically according to the relative temperature and humidity set by users, with high accuracy, good reliability, beautiful appearance and easy operation.
7. Protection = Fault Display Function. The unit has the functions of temperature and humidity display and fault display. It is equipped with overload, short circuit, phase absence, overheating, high voltage, low voltage, etc.

Hangzhou Greeme Environmental Co., Ltd. can be used according to your area and different environments, and scientific and reasonable configuration options can be provided to you to solve your humidity problem!

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