Parameters and Analysis of the Eight Systems of the Chiller!

I. Evaporation Pressure and Evaporation Temperature
The pressure and temperature of the refrigerant in the evaporator are the saturated pressure and saturated temperature of the refrigerant, which can be measured by the corresponding instruments or gauges installed on the evaporator. Among these two parameters, if one is measured, the other can be found from the thermodynamic property table of the corresponding refrigerant.
The evaporation pressure and evaporation temperature are closely related to the heat brought into the evaporator by the chilled water:
When the cooling load of the air conditioner increases: The return water temperature of the chilled water in the evaporator rises, causing the evaporation temperature to rise, and the corresponding evaporation pressure also rises.
When the cooling load of the air conditioner decreases: The return water temperature of the chilled water decreases, and both its evaporation temperature and evaporation pressure decrease.
Generally, the refrigeration capacity of the chiller must be slightly larger than the designed cooling load of the air conditioner it bears. Otherwise, a satisfactory air conditioning effect cannot be achieved during operation.
According to the provisions of China's JB/T7666 95 standard (General Provisions for Nominal Operating Conditions of Refrigeration and Air Conditioning Equipment), the nominal operating condition of the chiller is that the outlet temperature of the chilled water is 7°C, and the return water temperature of the cooling water is 32°C.
Other corresponding parameters are that the return water temperature of the chilled water is 12°C, and the outlet water temperature of the cooling water is 37°C. Since increasing the outlet temperature of the chilled water is very beneficial to the economy of the chiller, the outlet temperature of the chilled water should be increased as much as possible during operation while meeting the requirements of air conditioning use.
Generally, the evaporation temperature is often controlled within the range of 3°C to 5°C, which is 2°C to 4°C lower than the outlet temperature of the chilled water.

An excessively high evaporation temperature often makes it difficult to achieve the required air conditioning effect, while an excessively low evaporation temperature not only increases the energy consumption of the chiller but also easily causes the evaporation pipeline to freeze and crack.
II. Condensing Pressure and Condensing Temperature
The cooling medium used in the condenser has an important influence on the condensing temperature and condensing pressure of the chiller. The condensing temperature of the chiller changes with the temperature of the cooling medium. The condensing temperature of a water-cooled unit is generally 4°C to 8°C higher than the outlet water temperature of the cooling water. If it is higher than 8°C, it is necessary to check whether the copper pipes in the condenser are scaled and need to be cleaned; the condensing temperature of an air-cooled unit is generally 5°C to 10°C higher than the outlet air temperature.
As the condensing temperature rises, the power consumption increases. Conversely, when the condensing temperature decreases, the power consumption decreases accordingly. When air exists in the condenser, the temperature difference between the condensing temperature and the outlet of the cooling water increases, while the temperature difference between the inlet and outlet of the cooling water decreases instead. At this time, the heat transfer effect of the condenser is not good, and the shell of the condenser feels hot to the touch.
In addition, the scaling and silt on the water side of the condenser tubes also play a considerable role in affecting heat transfer. Therefore, when the chiller is in operation, attention should be paid to ensuring that the indicators such as the temperature, flow rate, and water quality of the cooling water are within the qualified range.
III. The Pressure and Temperature of the Cooling Water
When the chiller operates under the nominal operating condition, the inlet water temperature of the condenser is 32°C, the outlet water temperature is 37°C, and the temperature difference is 5°C. Under the nominal operating condition, the pressure drop of the inlet and outlet water of the condenser is generally about 0.07MPa. The method of adjusting the pressure drop is also to adjust the opening degree of the outlet valve of the cooling water pump and the opening degree of the inlet and outlet pipes of the condenser.
There are also two principles to follow: First, the outlet water of the condenser should have sufficient pressure to overcome the resistance in the cooling water pipeline; second, when the chiller operates under the designed load, the temperature difference of the cooling water entering and leaving the condenser is 5°C.
It should also be noted that the practice of randomly opening the cooling water valve excessively, increasing the cooling water flow to reduce the condensing pressure and trying to reduce the energy consumption will only backfire and have the opposite effect.
IV. The Suction Temperature of the Compressor
The suction temperature refers to the temperature of the refrigerant gas in the suction cavity of the compressor. The suction temperature not only affects the exhaust temperature but also has an important impact on the volumetric refrigeration capacity of the compressor. When the suction temperature of the compressor is high, the exhaust temperature is also high, and the specific volume of the refrigerant when it is sucked in is large. At this time, the unit volumetric refrigeration capacity of the compressor is small. On the contrary, when the suction temperature of the compressor is low, its unit volumetric refrigeration capacity is large. However, if the suction temperature of the compressor is too low, it may cause the refrigerant liquid to be sucked into the compressor, resulting in the compressor experiencing a "liquid slugging" phenomenon.
In order to ensure the normal operation of the compressor, its suction temperature needs to be slightly higher than the evaporation temperature, that is, it should have a certain degree of superheat. For a reciprocating chiller, its suction superheat is generally 5°C to 10°C. If a dry evaporator is used, the magnitude of the superheat can be adjusted by adjusting the adjusting screw of the thermal expansion valve. In addition, attention should be paid to the fact that the length of the suction pipeline of the compressor and the performance of the insulating material wrapped around it will have a certain impact on the superheat.
V. The Discharge Temperature of the Compressor
The discharge temperature of the compressor is the temperature of the high-pressure superheated vapor of the refrigerant when it reaches the discharge cavity of the compressor after compression. Since the refrigerant discharged by the compressor is superheated vapor, there is no corresponding relationship between its pressure and temperature, and it is usually measured by a thermometer installed in the discharge cavity of the compressor.
The direct influencing factor of the discharge temperature is the suction temperature of the compressor, and the two are in a direct proportion relationship.

In addition, the discharge temperature is also related to the type of refrigerant and the level of the compression ratio. Under the air conditioning working condition, due to the small compression ratio, the discharge temperature is not very high. When the suction and discharge valve plates of the reciprocating compressor are not tight or broken, causing leakage (internal leakage), the discharge temperature will rise significantly.
VI. Oil Pressure Difference, Oil Temperature and Oil Level Height
The lubricating oil system is an essential part of the normal operation of the chiller, which provides lubrication and cooling conditions for the moving parts of the unit. From the composition characteristics of the lubrication systems of various chillers, except that the lubricating oil of the reciprocating unit is stored in the crankcase of the compressor and attached to the refrigeration system, both the centrifugal and screw units have independent lubricating oil systems, their own oil storage devices, and oil coolers specially used to reduce the oil temperature.
VII. The Operating Current and Voltage of the Main Motor
During the operation of the main motor, it relies on a certain input current and the specified voltage to ensure the power required for the operation of the compressor. Generally, the rated power supply voltage required by the main motor is 400V, three-phase, 50Hz, and the instability rate of the average phase voltage of the power supply is less than 2%.
In actual operation, the operating current of the main motor increases or decreases with the size of the refrigeration capacity in the energy regulation when the inlet and outlet water temperatures of the chilled water and cooling water of the chiller remain unchanged.
The current value is an important parameter that changes with the load of the motor. When the chiller is in operation, attention should be paid to frequently comparing it with the ammeter in the main power distribution room. At the same time, attention should be paid to the swing of the pointer (because there are inevitably some small swings usually). Under normal circumstances, due to the phase imbalance of the three-phase power supply or the voltage change, the pointer of the ammeter will swing periodically or irregularly and significantly.
When the load of the compressor changes, this phenomenon will also occur. During operation, it is necessary to pay attention to strengthening the monitoring to maintain the normal state of the current and voltage values.