Constant-temperature cold water unit and control method thereof

Abstract

The invention provides a constant-temperature cold water unit and a control method thereof. The constant-temperature cold water unit comprises a water tank, a refrigerating unit, a controller, a water tank temperature sensor and a water tank temperature controller, wherein the refrigerating unit is a closed water tank refrigerating loop consisting of a compressor, a condenser, an expansion vale and an evaporator sequentially; the compressor, a second solenoid valve and a gas-liquid separator are sequentially composed to be a closed idle loop; the compressor, the condenser, a third solenoid valve, a capillary tube and the gas-liquid separator are sequentially composed to be a closed spray liquid cooling circuit. The constant-temperature cold water unit further comprises a heater; and the water tank temperature controller comprises two PID (Proportion Integration Differentiation) temperature controllers. According to the invention, when the temperature of the water tank is constant, the compressor and the gas-liquid separator are configured to be the idle loop, so that the energy consumption is saved; when the temperature of the compressor exceeds a set value, the spray liquid cooling circuit can be opened for cooling the compressor. In the constant-temperature cold water unit, two PID temperature controllers are adopted, therefore, the water temperature is ensured to be constant, and the water temperature stability of plus or minus 0.1 DEG C can be reliably ensured.

Description

technical field [0001] The invention belongs to constant temperature equipment, in particular to a high-end fixed-frequency chiller with a water temperature stability of ±0.1°C. Background technique [0002] The temperature stability of the constant temperature chiller depends not only on the system's real-time follow-up ability to external system load changes, but also largely on the shape and capacity of the water tank and the insulation effect. At present, similar units in the market adopt hot gas bypass condenser or compressor motor frequency conversion technology. With the change of load, the opening of bypass valve or motor frequency is adjusted by single PID control. Heating, that is, only strengthening the real-time follow-up ability of the stand-alone system. When the load changes, the above-mentioned heat bypass and frequency conversion methods all need to be adjusted in the intermediate transition section, and the response speed is slow. The heat pump method has ...

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Problems solved by technology

When the load changes, the above-mentioned heat bypass and frequency conversion methods all need to be adjusted in the middle transition section, and the response speed is slow. The heat pump method has poor adaptability to low temperature heating. At the same time, due to the positive and negative actions of cooling, heating and load changes, the effect of single PID control mode is unstable.

For the hot side mode, it is generally equivalent to artificially generating a cooling load effect, which is introduced before the evaporator to ensure that the return air temperature of the compressor is normal, and the compressor works continuously at 100% load, which increases energy consumption unnecessarily; especially with multiple evaporators For use, it is also necessary to use a superheated cooling expansion valve and a bypass valve, which are introduced after the evaporator to prevent the return air temperature from being lower than the safety limit and damage the unit; since the return air pipe is directly mixed with gas and liquid, the requirements for the gas-liquid separator are high, which undoubtedly causes The system is complex, which increases investment and maintenance costs; for the frequency conversion mode, hot gas bypass is also required when the load is 30% low, and the power consumption of the frequency converter is as high as 15%. The temperature rise of the motor is high, the insulation level is high, and the investment is larger, the maintenance is more difficult, and the application range is more limited

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