First, the working principle of screw chiller
Screw chiller is named after its key component-compressor adopts screw, and the unit is made of gaseous refrigerant from evaporator. After adiabatic compression by the compressor, it becomes a high temperature and high pressure state. The compressed gas refrigerant is cooled and condensed into the same pressure in the condenser, and becomes a liquid refrigerant after condensation, and then expands to a low pressure through the throttle valve to become a gas-liquid mixture. Among them, the liquid refrigerant with low temperature and low pressure absorbs the heat of the cooled substance in the evaporator and becomes a gaseous refrigerant again. The gaseous refrigerant re-enters the compressor through the pipeline and starts a new cycle. These are the four processes of the freezing cycle. It is also the main working principle of screw chiller.
Second, the selection points of screw chillers
1. The main control parameters of screw chiller are refrigeration performance coefficient, rated refrigeration capacity, input power and refrigerant type.
2. The selection of water chillers should be considered according to the cooling load and use. For the refrigeration system with long working time under low load, it is advisable to choose multi-head piston compressor or screw compressor, which is convenient to adjust and save energy.
3. When selecting water chillers, give priority to units with higher performance coefficient. According to statistics, the running time of general water chillers under 100% load accounts for less than 1/4 of the total running time. In the total running time, the running time ratio of 100%, 75%, 50% and 25% load is approximately 2.3%, 4 1.5%, 46. 1% and1. Therefore, when selecting water chillers, the model with relatively flat efficiency curve should be given priority. At the same time, the adjustment range of chiller load should be considered in the design and selection. Multi-head screw chiller has excellent part-load performance and can be selected according to the actual situation.
4. When selecting water chillers, attention should be paid to the conditions of rated working conditions. The actual cooling capacity of water chillers is related to the following factors:
A) cold water outlet temperature and flow;
B) Inlet water temperature, flow rate and fouling coefficient of cooling water.
5. When selecting a water chiller, attention should be paid to the normal working range of this type of unit, mainly because the current limit of the main motor is the current value of the shaft power under rated working conditions.
6. During the design and selection, it should be noted that the outlet temperature of cold water should not exceed 65438 05℃ and the outdoor dry bulb temperature of air cooling unit should not exceed 43℃ under the rated working condition flow. If it is necessary to exceed the above range, you should know whether the applicable range of the compressor is allowed and whether the power of the main motor is sufficient.
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