Screw chiller is named screw chiller because its key component-compressor adopts screw type. The unit is made up of gas refrigerant in the state of evaporator. After adiabatic compression by the compressor, it becomes a high temperature and high pressure state. The compressed gas refrigerant is cooled and condensed at equal pressure in the condenser. After condensation, it becomes a liquid refrigerant, and then expands to low pressure through a throttle valve to become a gas-liquid mixture. Among them, the liquid refrigerant at low temperature and low pressure absorbs the heat of the cold substance in the evaporator and becomes a gaseous refrigerant again. The gaseous refrigerant re-enters the compressor through the pipeline to start a new cycle. These are the four processes of the refrigeration cycle and the main working principle of the screw chiller.

Key points of product selection

The main control parameters of screw chillers are refrigeration performance coefficient, rated refrigeration capacity, input power and refrigerant type.

The selection of chillers should be considered according to the cooling load and use. For the refrigeration system with low load operating conditions for a long time, multi-head piston compressor unit or screw compressor unit should be selected for easy adjustment and energy saving.

3. When selecting chillers, give priority to units with higher performance coefficient values. According to statistics, the general chiller annual running time under 100% load accounted for about 1/4 of the total running time. The proportion of operating time of 100, 75, 50 and 25 percent of the total operating time is roughly 2.3, 41.5, 46.1 and 10.1 percent. Therefore, in the selection of chillers should give priority to the efficiency curve is relatively flat models. At the same time, the adjustment range of the load of the chiller should be considered in the design selection. Multi-head screw chiller part load performance is excellent, can be selected according to the actual situation.

4. When selecting chillers, pay attention to the conditions of nominal working conditions. The actual cooling capacity of the chiller is related to the following factors:

a) Outlet temperature and flow of cold water;

B) Inlet temperature, flow rate and fouling coefficient of cooling water.

5. When selecting a chiller, pay attention to the normal working range of the unit, mainly the current limit of the main motor is the current value of the shaft power under the nominal working condition.

6. Attention should be paid in the design selection: under the nominal working condition flow, the outlet temperature of cold water should not exceed 15 ℃, and the outdoor dry bulb temperature of air-cooled unit should not exceed 43 ℃. If it is necessary to exceed the above range, it should be understood whether the use range of the compressor is allowed and whether the power of the main motor is sufficient.