How Refrigeration Condensers and Compressors Work

Refrigeration Condensers and Compressors

The condenser is charged to expel heat from the refrigeration system. During this process, the refrigerant condenses into a liquid state inside the condenser.

Historically, water was the first medium used to absorb heat in condensers. Coolants deliver most of this condensation heat, allowing the refrigerant to condense to 5 °C above the temperature of the condensation medium in water-cooled systems.

Types of Water-Cooled Condensers

• Shell and tube
• Shell and coil
• Tube-in-tube (coaxial)

Cleaning and Maintenance

Proper maintenance is essential for efficiency:

• Mechanical cleaning: Suitable for tube-in-tube and shell-and-tube designs (where tubes have internal flanges).
• Chemical cleaning: Primarily used for tube-in-tube and shell-and-coil systems.
• Always consult the manufacturer for specific instructions on how to clean the condenser.

Condenser Operation and Subcooling

The primary function of the condenser is the de-superheating of hot gas flowing from the compressor. Once the refrigerant transitions into a liquid and cools further below the condensation temperature, it undergoes subcooling.

When the condenser is cold enough to reduce the discharge pressure to a point where the expansion valve is underfed, a discharge pressure regulator must be used. These regulators utilize mechanisms such as fan cycle regulation, shutters, and condenser flooding.

In air-cooled systems, the refrigerant condenses at 15 °C above the temperature of the air entering the condenser. This absorbed heat can be reclaimed to heat water or add warmth to a conditioned space.

Water-Cooled Equipment and Cooling Towers

Water-cooled systems are highly efficient. This equipment rejects heat either into water drainage systems or directly into the atmosphere using cooling towers.

Cooling Tower Types:

• Evaporative condensers
• Natural draft towers
• Forced draft towers

Water-recirculating systems are used to assist the evaporative cooling process. As water evaporates, the concentration of minerals increases; to prevent scaling, additional fresh water must be introduced.

Refrigeration Compressors

The compressor acts as a vapor pump. It cannot compress liquid refrigerant. Its primary job is to raise the low-pressure gas from the suction side to the high-pressure discharge side, adding heat to the gas in the process. On a hot day, the discharge of a compressor can reach up to 95 °C.

Industrial refrigeration relies on two main types of compressors: rotary screw and reciprocating (alternative) compressors.

Screw Compressors

A screw compressor compresses vapor between interlocking screw gears. These are typically utilized in large-scale industrial installations.

Reciprocating Compressors

Reciprocating compressors consist of crankshafts, connecting rods, an oil pump, pistons, valve plates, heads, and a housing. Most are cooled by suction gas, though some are air-cooled. They are categorized into two main types:

• Hermetic compressors: These feature the motor at one end and the compressor at the other. They can be welded (requiring the casing to be cut open in specialized workshops for repairs) or accessible/semi-hermetic.
• Open compressors: The motor is located externally, separate from the compressor housing.

If a reciprocating compressor's cylinder is filled with liquid or gas that cannot be evacuated, a severe mechanical breakdown will occur.

Compressor Protection Devices

To prevent damage, compressors utilize internal overload protection devices:

• Internal surge protection: Directly interrupts the power feed stream. Without this device, the compressor motor would burn out.
• Pilot-type internal device: Interrupts the control voltage, allowing for the installation of additional external protection systems.