When a refrigeration system malfunctions, its operating status is generally understood by looking, listening, and touching. When the system's operating pressure and temperature exceed the normal range, aside from deterioration due to indoor and outdoor environmental temperatures, there must be a problem; this is an important basis for determining the root cause of the fault.
The pressure in the refrigeration
system can be divided into high and low pressure parts during operation. The high-pressure section extends from the discharge port of the compressor to the expansion valve, which is called the high pressure. The pressure at the suction port of the compressor is called the suction pressure, and the suction pressure is close to the evaporation pressure; the difference between the two is the flow resistance of the pipeline.
For convenience, the evaporation pressure and condensation pressure of the refrigeration system are both measured at the suction and discharge ports of the compressor. These are commonly referred to as the suction and discharge pressures of the compressor. The purpose of measuring the suction and discharge pressures of the refrigeration system is to obtain the evaporation temperature and condensation temperature of the refrigeration system, thereby understanding the operating condition of the system.
Temperature of the refrigeration system
The temperature in the refrigeration system covers a wide range, including the evaporation temperature, suction temperature, condensing temperature, and discharge temperature. The operating conditions of the refrigeration system are mainly determined by the evaporation temperature and condensing temperature.
Evaporation Temperature
It refers to the temperature at which the liquid refrigerant boils and vaporizes in the evaporator. Example: The evaporating temperature of an air conditioning unit is 5~7 degrees, which is considered the optimal evaporating temperature for the unit. This means that the design evaporating temperature of the air conditioning unit is between 5~7 degrees. When an air conditioning unit is tested after maintenance, if the evaporating temperature does not reach 5~7 degrees, the cause should be identified.
Since the evaporating temperature cannot be directly measured, it can only be obtained by measuring the corresponding evaporating pressure and then referring to the saturated temperature-pressure chart of the refrigerant. The common saturated temperature-pressure charts for refrigerants are freely available on our Refrigeration and Air Conditioning Technology public account. Those who need it can obtain it for free through the menu in the public account.
Condensation Temperature
It is the temperature at which the superheated vapor of the refrigerant releases heat and condenses into a liquid in the condenser. The condensation temperature cannot be measured directly; it can only be obtained by measuring the corresponding condensation pressure and then referring to the refrigerant's saturation temperature-pressure chart. When the condensation temperature is high, its condensation pressure relatively increases, and they correspond to each other. If the condensation temperature is excessively high, the unit's load is heavy, the motor is overloaded, which is unfavorable for operation, the cooling capacity correspondingly decreases, and the power consumption increases, so it should be avoided as much as possible.
Exhaust Temperature
Refers to the temperature at the compressor exhaust port (including the temperature of the exhaust port connecting pipe). Monitoring the exhaust temperature requires a temperature measuring device, which is generally not installed on small units. For temporary measurement, a semiconductor spot thermometer can be used, but the error is relatively large. The exhaust temperature is affected by the suction temperature and the condensation temperature. When the suction temperature or condensation temperature rises, the exhaust temperature also increases accordingly. Therefore, it is necessary to control the suction temperature and condensation temperature to stabilize the exhaust temperature.
Suction Temperature
Refers to the gas temperature at the compressor suction connection pipe. Measuring the suction temperature requires a temperature measuring device. Generally, small units do not have a temperature measuring device, and during maintenance and commissioning, it is usually estimated by touch. The suction temperature of air conditioning units is generally required to be controlled around 15 degrees. Exceeding this value can have a certain impact on the cooling effect.
