Condensing units – definition and classification

Condensing units - definition and classification

Definition of a condensing unit

The condensing unit is a compact and high-pressure part of the refrigeration system. Its purpose is to perform compression and condensation processes to obtain liquid refrigerant at the outlet. Its design provides an easy connection to the evaporators of external refrigeration and freezing devices such as cabinets, counters, racks, chambers, etc. It consists of several main components: suction separator, compressor, oil separator, condenser with fan, liquid receiver, filter drier, sight glass, valves, sensors, and an electrical box that controls the unit’s operation. These elements are usually placed inside a metal housing suitable for safe mounting on the ground or wall. Two copper pipes lead out of the basic unit housing: the suction line and the liquid line. Depending on the application, condensing units can vary in design, size, and capacity. They are used mainly in refrigeration systems, but also in heating, ventilation, and air-conditioning installations.

How does a condensing unit work?

The principle of operation of the condensing unit is shown in the animation. The refrigerant enters the unit at low pressure and temperature, flowing through the suction line. In the suction separator, the possible liquid phase of the refrigerant is separated to ensure the safe operation of the compressor. After compression, the oil is recovered from the high temperature and pressure gas and returned to the compressor crankcase, while the oil-free refrigerant flows to the condenser, passing the check valve. During the condensation in the heat exchanger, excess heat is rejected to the environment by the air flow from the fan. On the outlet of the condenser, the liquid refrigerant is stored in the liquid receiver and flows out from it to the filter drier. The purpose of the filter drier is to absorb moisture and remove solid contaminants from the refrigerant. The last element through which the liquid refrigerant flows is the sight glass with a moisture indicator. It allows observation of the presence and flow condition of the refrigerant, which exits the liquid line on the outlet of the unit. The liquid line must be finally connected with the inlet pipe of one or even several external evaporators on which the expansion valve is installed. After the cooling effect is produced inside the refrigeration device or chamber, the superheated refrigerant returns to the condensing unit through the suction line.

Classification of condensing units

Condensing units can be classified according to the temperature level of the application, the working medium type, construction, location of unit installation, cooling method of the condenser, and the compressor type. The classification of condensing units is shown in the table.

Condensing units
Application type Refrigerant type Construction
Low temperature

Medium-high temperature

High temperature

CO2 (R744)



With housing

Without housing

Location of operation Cooling method Compressor type






Current trends in the refrigeration industry

Currently, the trend in the refrigeration industry is the development and production of eco-friendly, highly-efficient condensing units working with natural refrigerants, especially with CO2. Unlike HFCs (hydrofluorocarbons), natural refrigerants do not harm the ozone layer and have a minimal impact on the global warming.

Significant growth in the commercial refrigeration market is expected in the coming years. Therefore, the aspect of sustainability is becoming more and more important. Powerpack (multi-compressors) systems are more commonly being replaced by decentralized cooling systems, resulting in more precise regulation and increased operational safety. In addition to this, the refrigeration industry is undergoing an energy-efficiency transformation towards inverter technology, gradually moving away from the on-off technology. Inverter condensing units provide lower energy consumption and ensure a longer lifetime of compressors.

Modern condensing units should also be compact and low-noise featured. An excellent example of this type of condensing unit that follows all the modern trends in the refrigeration industry is our iCOOL CO2.

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