High- and low-temperature thermal monitoring rooms are the best-selling products in the current research equipment. In the market, the temperature and humidity of this type of laboratory is constant. Most of them adopt temperature control, that is, the temperature of the heater compensates the cold volume of the evaporator to achieve a balance of temperature and humidity. Cooling control is that the PID controller calculates the closing time of the solenoid valve in one cycle according to the condition of the equipment and controls the amount of refrigerant entering the system through the closing of the solenoid valve. Compared to the temperature control mode, the cold control mode has obvious energy saving advantages.
- Presentation of resources
Then use the high and low humidity test room developed as an example that brings him the performance of the equipment.
1) Inner volume: W 600mm x H 850mm x D 800mm;
2) Temperature range: -70~+150℃;
3) Relative humidity: 20% – 98%;
4) Temperature uniformity: ±2℃;
5) Temperature change: ≤±2.0℃;
6) Temperature change: ±0.5℃;
7) Humidity change: when humidity > 75% RH, ≤± 3.0% RH, when humidity ≤75% RH, ≤± 5.0% RH;
8) Heating rate: 25 ~ + 85 ℃, the average temperature change rate is about 3 ℃ / min (average in the whole process, no-load);
9) Cooling rate: 25 ~ -70 ℃, the average rate of temperature change is about 1 ℃ / min (average in the whole process, no-load).
- Infrastructure design and service standards
Equipment is divided into the following sections: main building, air conditioning, refrigeration and electrical control. Its structure and working principles are as follows:
a) Main part of the box
The main box is made of polyurethane plate + glass wool (thickness: 100mm), the inner box wall is SUS 304 stainless steel (thickness: 10mm), and the outer box wall is steel plate. Plastic spray (top color: camel). ).
Gate. One door has a door opening of W 600mm x H 850mm. The inner door is stainless steel and the upper surface is plastic sprayed metal in the same color as the surface of the box. Heating wires are placed around the door and in the middle of the door. The opening of the heating wires is automatically opened by the equipment according to different working conditions, to ensure that the door of the equipment will not be covered and locked in low temperature conditions.
b) Air circulation section
This section is an important part of the license for unity, logic and other indicators of equipment, mainly consisting of the following: centrifugal fan. The fan is the power source to mix the air in the box. The fan mixes the mixed air in the box through the evaporator and the heater, and then sprays it in the channel to spread the air in the box evaporator properly. The cooling element inside the box is the element that converts the energy between the cooling energy of the refrigerator and the hot air inside the box. Electric wire heater. It is the main heating element for the equipment, providing the necessary heat to heat the equipment and to control the cold and hot temperature. Humidifier water heaters are used to heat water and liquids to provide the necessary humidity for equipment.
c) Refrigeration unit
The refrigeration unit is the main part of the cold water produced by the equipment, providing the cooling power required for cold, low temperature, constant temperature and heating of the equipment.
Since the low temperature of the test room is -70 ℃, the refrigeration system adopts cascade refrigeration. Working Principle a four-stage refrigerator consists of two single-unit refrigeration systems that use different refrigerants. Usually, R404A environmental refrigerant with high boiling point is used in high temperature system, and R23 environmental refrigerant with low boiling point is used in low temperature system. Each becomes a cooling system using the same refrigerant. The evaporation of the refrigerant in the high temperature system is used to make the refrigerant in the low temperature system. The refrigerant in the low temperature system absorbs heat from the air during evaporation, so the temperature in the box can reach -70 ℃. A cascade system connects the upper and lower levels by means of heated air. In a super heater, the air of the high-temperature system makes the high-temperature air condense into a liquid, and the high-temperature system transfers temperature and environment (air or water).
The PID controller of the refrigeration system calculates the time to open the solenoid valve in the outgoing cycle according to the actual condition of the appliance, and controls the amount of refrigerant enters the evaporator through the solenoid valve switch. Valve, so that it reaches a constant state of equilibrium and temperature. In this system, the heater does not need to be turned on, and the constant temperature is completely maintained by the refrigeration system itself.
d) Electrical control unit
Electrical control includes temperature and humidity control systems and protection systems. A temperature and humidity system controller can understand the program with specific benefits. The controller is a color LCD touch screen, which can understand the conversation of the crowd, with a friendly interface and convenient operation. The controller compares the temperature and humidity value in the box measured by the temperature sensor with the temperature and humidity value set by the user, and performs the PID function according to the same set of rules that the controller uses identify and determine the operating conditions of each production area. The stop volume and humidity of the solenoid valve is controlled by the generator port that allows the temperature and humidity in the box to change as needed.
The protection system includes a circuit breaker, overheat protection, compressor overpressure protection and compressor overheat protection. When the fault occurs, a sound will be sent to the fire alarm and the corresponding electricity will be cut off to ensure the safety of workers, equipment, samples and the environment.
The temperature and humidity data in the controller can be transferred to the U disk through the USB function, and the data can be read and changed on the PC through special software. A standard RS485 interface is also provided and the user can monitor the device via PC.
- Conclusion
Cold control technology can effectively create and achieve temperature control effects through the opening and closing of the solenoid valve. The whole process of cooling and keeping the temperature under the temperature does not require the installation of a heater, which is very different from the temperature control system that is commonly used today. Also, its saving effect is obvious, and energy saving is more than 30%.
