The condensing pressure is the pressure at which the refrigerant condenses into a liquid in the condenser. Since the pressure inside the condenser in the refrigeration system cannot be measured, in reality, the pressure drop of the refrigerant in the exhaust pipe and the condenser is actually small. Therefore, regardless of design debugging or overhaul, it is generally considered that the exhaust pressure is approximately equal to the condensing pressure.

The condensation temperature and the condensing pressure correspond one-to-one, that is, the saturation temperature at the time of condensation, and the condensation temperature is not equal to the temperature of the cooling medium, and there is also a heat transfer temperature difference between the two.

So how is the condensation temperature determined?

According to experience, the system's condensation temperature = ambient temperature + (10 ~ 15 ° C); we take the summer ambient temperature of 35 ° C air conditioning as an example.

In the summer air conditioning outdoor environment temperature of about 35 degrees, we can estimate the condensation temperature at this time: condensation temperature = 35 + (10 ~ 15 ° C) = 45 ° C.

The pressure corresponding to the condensing temperature is the condensing pressure (can be queried by the temperature gauge provided by the refrigeration encyclopedia public number). If the exhaust pressure of the refrigeration system is lower than this pressure, please consider whether the refrigerant charge is less or less;

If the exhaust pressure of the system is higher than this pressure, please consider whether the refrigerant charge is excessive, whether the condenser heat transfer is sufficient, and whether the expansion valve opening is too small.

Second, the evaporation temperature

The evaporation temperature is the temperature at which the liquid refrigerant boils. When the refrigerant flow rate is constant, the lower the evaporation pressure, the lower the evaporation temperature. However, by continuously reducing the evaporation temperature of the system, the refrigeration capacity of the refrigeration compressor is also continuously reduced, the refrigeration speed is not necessarily fast, and the lower the evaporation temperature, the lower the refrigeration coefficient of the system. .

So, how to judge whether the evaporation pressure of the system is normal?

According to experience, the evaporation temperature of the air conditioning system = ambient temperature - (10 ~ 15 ° C); we take the summer (set temperature in the room 22 ° C) air conditioning as an example:

In summer, the temperature of the air conditioner indoor unit is 22 degrees, we can estimate the evaporation temperature at this time: evaporation temperature = ambient temperature - (10 ~ 15 ° C); that is, evaporation temperature = 22 - (10 ~ 15 ° C) ≈ 12 ° C;

The pressure corresponding to the evaporation temperature is the evaporation pressure (can be queried by the temperature pressure gauge provided by the refrigeration encyclopedia public number). If the evaporation pressure of the refrigeration system is lower than this pressure, please consider whether the heat transfer of the evaporator has a problem and the expansion valve is open. Is the degree too low?

If the evaporation pressure of the system is higher than this pressure, please consider whether the refrigerant charge is too high, the expansion valve opening is too large, and so on.

Third, the inhalation temperature

The suction temperature is the temperature of the refrigerant at the compressor suction valve or at the compression button. In order to ensure the safe operation of the compressor and prevent the liquid hammering phenomenon, it is required that the suction temperature is slightly higher than the evaporation temperature, that is, the refrigerant vapor becomes a superheated gas.

Whether the suction temperature is normal or not, can directly feedback whether the opening of the expansion valve is appropriate. Many people know the inhalation superheat, and also know that the inspiratory superheat* is 5~7°C;

But many novices don't know the actual meaning of this parameter; knowing the inhalation superheat, we can calculate the normal inspiratory temperature of the system.

Inspiratory temperature = inspiratory superheat + evaporating temperature, such as:

We know that the evaporation temperature of a refrigeration system is 12 ° C; the suction superheat according to * is 5 ~ 7 ° C; we can calculate that the inhalation temperature of the system * is about 17 ° C;

We can determine whether the inhalation temperature at this time is normal according to the temperature of the hand. For example, if the suction pipe is iced at 17 ° C, we can judge that the opening of the expansion valve is large or the refrigerant charge is large. If the suction temperature is hotter than 17 ° C, the expansion valve can be determined at this time. The opening is small or the refrigerant charge is small.

If the suction pipe does not condense, the intake air temperature is too high. Check if the refrigerant charge is small or the expansion valve opening is small. If the suction pipe is frosted (icing), the intake air temperature is low. Check if the refrigerant charge is high or the expansion valve opening is large.

Fourth, the exhaust temperature

The exhaust temperature is the temperature at which the exhaust gas is discharged after the compressor is working, and can be measured from the exhaust pipe by a thermometer. The temperature of the exhaust gas is proportional to the pressure ratio and the intake air temperature. The higher the pressure ratio, the higher the suction temperature, the higher the exhaust temperature

Many of the peers have not heard of the "exhaust superheat" concept, "exhaust superheat": the difference between the compressor's exhaust pipe (or condenser inlet temperature) and the saturation temperature corresponding to the condensing pressure.

A normal refrigeration system has a superheat of 20 to 30 °C. Therefore, we can judge whether the exhaust temperature is normal according to this empirical value; for example, the air conditioner whose condensation temperature is 45 °C, the normal value of the exhaust temperature at this time should be:

Exhaust temperature = exhaust superheat + condensation temperature = 25 + 45 = 70 ° C;

Five, operating current

There are many factors affecting the operating current of the compressor, such as:

Bad heat dissipation of the external unit;

The external power supply voltage is abnormal;

The refrigeration system has air;

Poor oil return, resulting in high housing / internal temperature;

Impurities in the system, too much moisture,

In addition, let's talk about the effects of refrigerant and compression ratio on current:

How much compressed refrigerant

Degree of compression of the refrigerant (compression ratio)

In fact, it is well understood. For *: The more refrigerant compressed by the compressor, the harder it is for the compressor to compress and the current will be larger. For the second one: the higher the degree of compression of the refrigerant (the greater the compression ratio), the more work the compressor does, and the corresponding current is greater.

Therefore, the operating current of the compressor can largely reflect whether the refrigeration charge of the refrigeration system is normal. Generally, there is a current value on the nameplate of the refrigeration equipment.

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