Estimation of Temperature and Pressure in the Refrigeration System

The balance pressure, high-pressure, and low-pressure are important parameters in air conditioner maintenance. These three pressures are the pressures corresponding to the refrigerant at different positions during its circulation in the air conditioner pipeline.

Since the refrigerant circulates and changes between the gas and liquid states, accompanied by heat absorption and heat release, the temperature of the external environment has a significant impact on it. Generally, when the ambient temperature is high, the pressure value increases, and when the ambient temperature is low, the pressure value decreases.

The balance pressure refers to the pressure when the high and low pressures are balanced when the compressor is not in operation; the high-pressure refers to the discharge pressure or condensing pressure; the low-pressure refers to the suction pressure or evaporation pressure. The measurements of these three pressures are all taken at the process port of the gas valve of the outdoor unit. During the cooling operation, it is the low-pressure, during the heating operation, it is the high-pressure, and when not in operation, it is the balance pressure.

Condensing Pressure and Condensing Temperature:
The condensing temperature refers to the saturation temperature when the refrigerant vapor in the condenser condenses under a certain pressure. The condensing temperature is not equal to the temperature of the cooling medium, and there is also a heat transfer temperature difference between the two.
The condensing pressure is the pressure at which the refrigerant condenses from a gas to a liquid in the condenser. Since the pressure inside the condenser in the refrigeration system cannot be measured, and in fact, the pressure drop of the refrigerant in the exhaust pipe and the condenser is actually very small, so whether it is in the design, debugging, or maintenance process, it is generally considered that the discharge pressure is approximately equal to the condensing pressure.

The Relationship between Condensing Temperature and Condensing Pressure:
The condensing pressure and the condensing temperature correspond to each other; the lower the condensing pressure (high pressure), the lower the condensing temperature; the higher the condensing pressure (high pressure), the higher the condensing temperature.

Estimation of Condensing and Evaporation Temperatures
When debugging refrigeration equipment, we often need to know the condensing temperature, and then further calculate the condensing pressure (high pressure or discharge pressure). Then, according to the actual pressure, we can determine whether there is a problem with the refrigeration system.
Reference of Empirical Estimation Values: Condensing temperature = Ambient temperature/Water temperature + (10~20℃);
Example: For a water chiller, given that the outlet water temperature of the cooling tower is 25 degrees, then the condensing temperature of the refrigeration system at this time: Condensing temperature = 25 + (10~20) = 40℃. According to the temperature-pressure comparison table, it is easy to find that the condensing pressure at this time is 14.2bar (using R22 refrigerant);
When the ambient temperature is high, subtract the higher value (20 or 15); when the ambient temperature is low, subtract the lower value (10℃);

The Relationship between Condensing Temperature and Power
When the condensing temperature increases, with the evaporation temperature remaining unchanged, the compression ratio of the compressor increases. And the power of the compressor is directly proportional to the compression ratio, that is, as the compression ratio increases, the power of the compressor also increases.
It can be simply understood as follows: The power required for the compressor to compress 5 kilograms of refrigerant to 15 kilograms is definitely less than the power required for the compressor to compress 5 kilograms of refrigerant to 25 kilograms.

The Relationship between Condensing Temperature and Refrigeration Capacity
When the condensing temperature rises, the refrigeration capacity of the system will also decrease.

The reason is that due to the increase in the condensing temperature, the unit refrigeration capacity of the refrigerant will decrease. Under the same mass flow rate of the refrigerant, the refrigeration capacity of the system decreases.

The Relationship between Heat Load and Condensing Pressure
Under a constant working condition (refrigerant flow rate), the greater the heat load, the higher the condensing pressure, and vice versa. We can imagine that when the condenser you designed is small (the heat load is relatively large), the refrigeration system is very likely to trigger a high-pressure alarm.

Analysis of the Reasons for Abnormal Condensing Temperature
Low Condensing Temperature: There are many reasons for the low condensing temperature. The mechanism leading to the low condensing temperature is that there is less refrigerant in the evaporator or the throttling effect of the throttle valve is not good. The following are listed:

How to Control the Condensing Temperature:
By controlling the inlet pressure of the condenser, the condensing pressure of the condenser can be controlled, because the pressure drop of the condenser is actually very small, and it can be approximately regarded that the inlet pressure is equal to the condensing pressure. So how to control the inlet pressure?
Methods: