Our glossary for climate & cooling

The air volume—also known as the airflow rate—indicates how much air the fan of a fan or ventilation unit moves per hour in m³/h. It depends on the rotational speed, blade size, design, and back pressure. The correct airflow is essential, as too little air results in poor heat dissipation and can lead to pressure problems or icing, while too much air leads to unnecessary power consumption.

In refrigeration technology, there are two main airflow configurations for fan units: forced-draft (the fan is located before the heat exchanger and pushes air through the fan motor toward the fan blades) and induced-draft (the fan is located after the heat exchanger and draws air in through the fan wheel and then through the motor).

The condensing temperature is the temperature at which a gaseous refrigerant condenses under a specific pressure, i.e., transitions from a gaseous to a liquid state. Key points: The condensing temperature depends directly on the pressure in the condenser: Higher pressure → higher condensing temperature. It is generally higher than the ambient temperature so that the refrigerant can release the transported heat to the surroundings. It is an important operating parameter because it provides information about the system’s efficiency. An unnecessarily high condensing temperature leads to higher energy consumption by the compressor. In short: The condensing temperature describes the thermodynamic conditions under which the refrigerant in the condenser can release the absorbed heat and return to a liquid state.

A compressor is a central component of a refrigeration system or air conditioning unit that compresses the refrigerant, thereby setting the refrigeration cycle in motion. Through compression, the compressor increases the pressure and temperature of the gaseous refrigerant, turning it into a liquid before it expands in the evaporator and thereby generates cooling. The compressor ensures that the refrigerant is transported through the cycle and enables heat to be released in the evaporator. Based on their design, compressors are classified as fully hermetic or semi-hermetic. Fully hermetic: scroll compressors, rotary vane compressors, small-stroke reciprocating compressors. Semi-hermetic: reciprocating compressors, screw compressors, two-stage reciprocating compressors.

See Compressor.

A condenser is a key component of a refrigeration unit or air conditioning system that cools the gaseous refrigerant from the evaporator before it returns to the compressor. In this process, the refrigerant releases the heat it has absorbed into the surrounding environment. Key features and functions: The refrigerant condenses in the condenser, i.e. it changes from a gaseous to a liquid state. Heat is dissipated via air (air-cooled condenser) or water (water-cooled condenser). This is critical to the efficiency of the refrigeration or air conditioning system, as the condensation temperature and heat transfer affect the compressor’s workload. The condenser is thus the heart of heat dissipation in refrigeration systems, returning the refrigerant to its liquid state.

A condensing unit is a pre-assembled technical assembly used in refrigeration and air conditioning systems that combines the central components of a refrigeration machine. Its function is to compress, cool, and liquefy the refrigerant circulating in the refrigeration cycle so that the absorbed heat can be released into the environment. Typically, a condensing unit comprises the following components: Compressor(s) Condenser Fan for the condenser Manifold Fan for the condenser Depending on the configuration, high-pressure/low-pressure pressure switches All elements are mounted on a common frame and matched to the respective compressor size. This compact design simplifies both the sizing and installation of a chiller, as the essential components do not need to be procured or adapted individually.

Refrigeration capacity refers to the amount of energy transferred by a cooling system during a cooling process. It serves as a measure of how much heat is removed from a medium per unit of time. It is typically expressed in watts (W), and less commonly in joules (J). Refrigeration capacity is calculated based on the change in energy transferred during the cooling process. It is a key parameter for evaluating the efficiency of cooling systems and for sizing air conditioning units, refrigerators, and other refrigeration systems. It also allows for the comparison of the performance of different systems. A higher cooling capacity usually indicates a greater amount of energy transferred per unit of time—and thus a greater cooling capacity of the unit. The cooling capacity can only be specified in relation to the refrigerant and the evaporation temperature! An example: A cold room is to be operated with the refrigerant R134a and cooled down to 0°C. The design calculation resulted in a cooling requirement of 1 kW. Therefore, a condensing unit with 1 kW of cooling capacity at an evaporation temperature of -8°C / -10°C (always approx. 7 to 10 K lower than the cold room temperature) is required. Only by specifying the evaporation temperature can a condensing unit with the correct cooling capacity be determined.

CSIR stands for “Capacitor Start – Induction Run” and refers to the starting method of a single-phase compressor motor. Along with CSR, it is the most common starting method for compressors. CSIR refers to a so-called soft start with a starting capacitor but without an operating capacitor. The electrical components include a starting capacitor, a starting relay, and thermal protection (Klixon). Compared to RSIR, it has a higher starting torque. In addition to CSR and RSIR, PSC is another starting method.

CSR stands for “Capacitor Start – Capacitor Run” and refers to the starting method of a single-phase compressor motor. Along with CSIR, it is the most common starting method for compressors. The electrical components include a starting capacitor, a running capacitor, a starting relay, and thermal protection (Klixon). This is a so-called heavy-duty start with high efficiency, as operation is carried out using two capacitors: one for starting and one for continuous operation. Other starting methods include RSIR and PSC.

Current consumption refers to the amount of electrical current a device draws from the power grid during operation. It is measured in amperes (A). The higher the current consumption, the more electrical power the device requires during operation. This value is important for accurately assessing the load on wiring, fuses, and components and ensuring safe, reliable operation.

Door panel thickness refers to the thickness of the door panel in a cold room or freezer room. It is critical for: Thermal insulation: Thicker door panels reduce heat loss and improve the energy efficiency of the cold room. Mechanical stability: Increased door panel thickness ensures greater stability and a longer service life, especially for heavy doors. Sound insulation and robustness: Thicker door panels offer better protection against mechanical impacts and reduce noise transmission. Typical door panel thicknesses in cold and freezer rooms: 60–80 mm: Standard refrigeration: 100 mm: Deep-freeze: >100 mm: Special applications or energy-efficient cold rooms. The door panel thickness must be selected in coordination with hinges, door frames, gaskets, and overlaps to ensure optimal sealing, ease of use, and energy efficiency. The cold room latch must also always be matched to the thickness of the door panel.

The evaporation temperature is the temperature at which the refrigerant in the evaporator, at a
specific pressure, evaporates—that is, changes from a liquid to a gaseous state. It is
directly determined by the saturation pressure of the refrigerant used. It depends on the refrigerant,
system pressure, superheat, and the load on the evaporator.

Cold-sealing gaskets are used on refrigerated display cases, refrigerated and frozen storage rooms to prevent air and cold air loss. Gaskets are available by the meter or, very often, as welded frames. The outer dimension refers to the outermost measurement of a gasket’s frame. It is very important that the frame has the correct dimensions and the seal has the correct height, as these factors influence the pressure on the door seal, the compression during closing, and thus the airtightness and energy efficiency of the cold storage room or refrigeration unit. An incorrect outer dimension causes the gasket to seal suboptimally and may cause it to protrude, or, in the case of magnetic gaskets, the magnet may not sit in the intended position. In addition to the outer dimension, the insertion dimension should be measured for so-called insert gaskets.

The term “fully hermetic” refers to the design of a compressor. A distinction is made between fully hermetic and semi-hermetic compressors. In a fully hermetic compressor, the motor and the compressor are housed in a sealed, welded casing. One of the advantages is that it requires no maintenance. In the event of a malfunction, the unit must be replaced. Fully hermetic compressors include, in particular, scroll compressors, rotary piston compressors, and small-stroke piston compressors. Typical applications: household refrigeration appliances, small commercial systems, air conditioning systems, heat pumps, etc.

See oil compensation connection

HBP stands for “High Back Pressure” and describes the application range of compressors,
condensing units, and chillers. Equipment in the HBP range is designed for high-pressure applications
with high evaporation temperatures (high systems) and is used in chillers, dehumidifiers,
air dryers, air conditioning systems, and heat pumps. Depending on the refrigerant, evaporation temperature, and cooling capacity, some compressors can also
cover mixed ranges and
combinations of MBP & HBP and LBP & MBP.

Refrigeration gaskets are used in refrigeration and freezer rooms to prevent air and cold air loss. For welded frame gaskets with snap-in profiles (featuring a snap-in tab at the bottom), the snap-in dimension is required to manufacture the frame to fit the designated groove in the door into which the gasket is inserted. An incorrect insertion dimension will result in the seal frame being manufactured too small or too large, making installation impossible. The insertion dimension is relevant exclusively for plug-in seals; all other seals are measured using the outer dimension.

LBP stands for “Low Back Pressure” and describes the application range of compressors,
condensing units, and refrigeration units. Units in the LBP range are designed for low
evaporation temperatures and are used in the low-pressure range in deep-freezing applications
(freezer chests, deep-freezer cabinets, and preservation units) with evaporation temperatures ranging from
approx. -45°C to -10°C. Typical applications include deep-freeze chambers, deep-freeze rooms,
deep-freeze cabinets, and ice storage rooms. Depending on the refrigerant,
evaporation temperature, and cooling capacity, some units can also cover mixed ranges and combinations of MBP & HBP
and LBP & MBP.

MBP stands for “Medium Back Pressure” and describes the application range of compressors, condensing units, and refrigeration units. Equipment from the MBP range is often used in the medium-pressure range for standard refrigeration with an evaporation temperature of approximately -10°C to +5°C. However, this temperature range is only a rough guide, as it can vary significantly depending on the refrigerant. Typical applications include natural gas-cooled cold rooms, refrigerated display cases, beverage coolers, and self-service counters. Depending on the refrigerant, evaporation temperature, and cooling capacity, some units can also cover mixed ranges and combinations of MBP & HBP and LBP & MBP.

NTC sensors, also known as NTC resistors, are thermosensitive components whose resistance decreases as the temperature rises, unlike PTC sensors. This property makes NTC sensors ideal for precise temperature measurements.

The number of poles in an electric motor describes the number of its magnetic poles (north and south poles), which occur in pairs, and significantly determines its speed and torque: A higher number of poles results in greater torque at lower speeds, while a lower number of poles means higher speeds with less torque. It is generated by the windings in the stator and is decisive for the synchronous speed, which is calculated from the mains frequency and the number of pole pairs (e.g., at 50 Hz: 3000 rpm for one pole pair, 1500 rpm for two pole pairs). The number of poles in an electric motor determines how fast the fan rotates. Typical speeds for 50 Hz applications and their differences are, for example: 2 -pole approx. 2800 rpm High airflow, louder, compact design 4-pole approx. 1400 rpm Standard for condensers & evaporators 6-pole approx. 900 rpm Quieter operation, lower air pressure 8-pole approx. 700 rpm Very quiet, low airflow As a general rule: The higher the number of poles, the slower and quieter the motor—but also the lower the air pressure. The choice of pole count depends on the application (e.g., 2-pole motors for high speeds, multi-pole motors for high torque)

The oil-leveling connection (referred to as the “Gemini” configuration for Embraco compressors) is one of the possible connection types for compressors, alongside the suction, discharge, and service connections. This connection is designed for and necessary for the parallel operation of two (or more) compressors of the same design. The compressors’ oil reservoirs are hydraulically connected via a specially designed oil equalization line. A prerequisite is that both compressors are of the same design, mounted on the same base plate, horizontally, and at the same height. The line must not run upward and must be flexible enough to accommodate compressor movements. Only in this way does the oil level remain uniform in both compressors, ensuring reliable oil transport. Purpose: To ensure a uniform oil supply during parallel operation to guarantee lubrication and operational safety. Important: Use is permitted only with approved, identical compressors and in accordance with the manufacturer’s installation guidelines. Incorrect installation or the combination of different types will result in a loss of oil balance.

A running capacitor is an electrical component used in single-phase AC motors, such as those found in compressors, fans, or pumps. The capacitor is permanently connected to the auxiliary winding circuit. It generates an artificial rotating field that enables the motor to start and ensures smooth, efficient continuous operation. The running capacitor improves torque, lowers current draw, and reduces vibrations as well as motor heating. Capacitor capacities are specified in microfarads (µF). Running capacitors are designed for continuous operation and have lower capacities compared to starting capacitors. Typical malfunctions manifest as starting problems or erratic motor operation. A defect often causes the motor to fail to start, hum, or shut down due to overload protection. Maintenance tip: Check the capacitor if you have motor problems—it’s often the cause!

The term “pressure-type” refers to the airflow direction in fans or fan wheels. In this configuration, air is drawn into the fan unit from the motor side and forced through the fan wheel and the heat exchanger. This creates higher air pressure, which is better suited for “deep” registers. In addition to pressure-type units, there are also suction-type fan units.

PSC stands for “Permanent Split Capacitor” and refers to the starting method of a single-phase compressor motor. This involves a running capacitor that remains connected at all times. PSC motors offer a simple, quiet solution. Other starting methods include CSIR, CSR, and RSIR.

PTC sensors, also known as PTC resistors, are thermosensitive components in which the
resistance increases as the temperature rises, unlike NTC sensors. This makes them
particularly useful for preventing overheating.

A reciprocating compressor is a positive-displacement compressor that compresses refrigerant through the
reciprocating motion of a piston in a cylinder. Compression occurs
when the piston draws in the gas, compresses it, and expels it through a discharge valve.
Reciprocating compressors are among the most widely used designs in refrigeration technology.
They operate with one or more cylinders and use intake and exhaust valves to
control the gas flow. These compressors are robust, easy to maintain, and available in
fully hermetic, semi-hermetic, and open configurations. They are suitable for a wide
range of capacities, from small refrigeration systems to industrial refrigeration applications, and are also
available in two-stage or multi-stage designs, particularly for low-temperature applications.
Key features:

Displacement principle with piston-cylinder system
High pressure ratios and wide operating limits
Good serviceability (especially semi-hermetic/open)
Versatile: from commercial to industrial refrigeration
In addition to reciprocating compressors, a distinction is also made—depending on the design—between rotary piston, small-stroke piston, scroll,
screw compressors, and two-stage reciprocating compressors.

Unlike reciprocating compressors, fully hermetic rotary compressors feature a rotating piston that compresses gases such as refrigerants. This eccentrically mounted piston divides the working chamber into at least two sections. While the refrigerant is drawn into one section, it is compressed in the other. Due to their high power density and robustness, these compressors are used in air conditioning systems, heat pumps, and transport refrigeration, among other applications. In addition to rotary piston compressors, a distinction is also made—depending on the design—between reciprocating piston, small-stroke piston, scroll, screw, and two-stage reciprocating piston compressors.

Rising and non-rising hinges describe the path of movement of the door leaf when opening and closing cold storage or freezer room doors. Rising hinge: When the door is opened, the door leaf lifts slightly upward. This helps the door seal close properly, prevents contact with the floor, and makes it easier to handle heavy doors. Non-rising hinge: The door leaf remains in a fixed horizontal plane during movement. Advantages include easier installation and simple adjustment; disadvantages may include reduced seal pressure or floor contact with heavy doors. The choice of hinge type affects the seal, door operation, and longevity of the cold room.

The overlap refers to the portion of the door leaf that extends beyond the door frame on cold storage or freezer doors, created by the design of the door hinge. It ensures that when the door closes, the door leaf, frame, and gasket align correctly, thereby achieving a tight seal to prevent air leakage. The overlap is critical for: minimizing heat loss, the energy efficiency of the cold storage room, and the longevity of the door seal. An overlap that is too small can lead to leaky doors, while an overlap that is too large causes closing problems or excessive seal wear.

Along with soldered connections, Rotalock connections (screw-on connections) are among the most commonly used
types of connections for compressors. This is a screw-on connection in which a
Rotalock valve with a gasket is screwed into place. The pipe can be attached to the Rotalock valve either
by soldering or with a union nut.

RSIR stands for “Resistive Start – Induction Run” and refers to the starting method of a single-phase
compressor motor. It is a simple single-phase motor with a starting winding and
starting resistor without a starting capacitor. It is frequently used in hermetic refrigeration compressors (e.g.,
in refrigerators) to limit the starting current and enable efficient operation,
since only a main winding and a starting winding used for a short time are present.
Other starting methods include CSIR, CSR, and PSC.

A screw compressor is a semi-hermetic compressor in which, instead of pistons, two counter-rotating intermeshing screws transport and compress the refrigerant within the housing through rotation. In addition to screw compressors, a distinction is also made—depending on the design—between rotary piston, short-stroke piston, reciprocating piston, scroll, and two-stage reciprocating piston compressors.

A scroll compressor is a highly efficient, fully hermetic refrigerant compressor that operates using two spiral-shaped discs (“scrolls”). One disc remains stationary while the other moves in a circular path. The spirals themselves are separated by a minimal distance, which enables oil-free compression. This motion compresses the refrigerant particularly quietly, smoothly, and efficiently. In addition to scroll compressors, other types—depending on the design—include rotary vane compressors, small-stroke reciprocating compressors, reciprocating compressors, screw compressors, and two-stage reciprocating compressors.

The term “semi-hermetic” refers to the design of a compressor. A distinction is made between semi-hermetic and fully hermetic compressors. In a semi-hermetic compressor, the housing is bolted together and can be opened. The motor is usually housed in the same casing as the compressor, which allows for maintenance and replacement of individual parts. Semi-hermetic compressors are predominantly reciprocating or screw compressors, as well as two-stage reciprocating compressors.

A small-stroke reciprocating compressor is a compact, fully hermetic reciprocating compressor that operates with a small displacement per piston stroke. Due to its design, it is particularly suitable for small to medium cooling capacities and applications where reliable, simple, and cost-effective operation is a priority. Despite their small size, small-stroke reciprocating compressors deliver stable performance, are robust, easy to maintain, and can be used in many areas—for example, in refrigerated display cases, small commercial refrigeration systems, or in air conditioning systems. In addition to small-stroke reciprocating compressors, a distinction is also made—depending on the design—between rotary piston, reciprocating, scroll, screw compressors, and two-stage reciprocating compressors.

Along with the Rotalock connection (screw connection), the brazed connection is one of two
possible connection types for compressors. In this method, the pipes are brazed directly to the
compressor’s connection ports. Among the advantages is the direct and secure
connection. Caution is required when soldering and replacing connections involving flammable refrigerants.
Proper handling by the refrigeration technician and adherence to
safety measures are absolutely essential.

A starting capacitor is an electrical component used to temporarily increase the
starting torque in single-phase induction motors in refrigeration and air conditioning systems,
particularly in compressors that are difficult to start. It is connected only during the starting phase
of the motor.

Due to its significantly higher capacitance compared to the running capacitor, the
starting capacitor creates a strong phase shift between the main and auxiliary windings, thereby achieving a
high starting torque. Activation and deactivation are controlled by starting relays,
centrifugal switches, or electronic starting systems.

Start-up capacitors are not suitable for continuous operation. Typical failure symptoms include
failure of the motor to start, humming noises, and the tripping of motor protection or
overcurrent protection devices.

Displacement is the volume of gas that a compressor piston theoretically draws in and expels with each stroke. It is usually measured in cm³. This determines the displacement flow rate (air volume per unit of time, e.g., l/min) that a compressor can draw in, based on the displacement and the rotational speed. A larger displacement means that the compressor can move more gas and thus generate more cooling capacity. Important: Displacement is not the same as the actual flow rate. How much gas the compressor actually moves depends on pressure conditions, valve losses, backflow, and speed.

The term “inlet-type” refers to the direction of airflow in fans. In this configuration, air is drawn in through
the grille (from the fan blade toward the motor). Inlet-type fans are often quieter and therefore
better suited for noise-sensitive environments. Alternatively, a discharge-type fan can be used.

The rated voltage specifies the electrical voltage (volts, “V”) at which electronic devices operate. The European standard is 230V, though a deviation of +/- 10% is permitted to ensure that older devices can still be used. These are labeled as 220V or 240V. In addition, there are higher voltages of 400V for devices with higher power requirements.

A two-stage reciprocating compressor is a semi-hermetic refrigerant compressor that compresses the gas in two consecutive stages. It features two cylinders of different sizes: The larger cylinder handles the first compression stage in the low-pressure range, while the smaller cylinder further compresses the pre-compressed refrigerant in the high-pressure range. Thanks to this optimized design, the compressor operates particularly efficiently, reduces thermal load, and ensures reliable performance even at low temperatures. Two-stage reciprocating compressors are frequently used in deep-freeze systems, industrial process cooling, and wherever high performance and operational reliability are required. In addition to two-stage reciprocating compressors, a distinction is also made—depending on the design—between rotary vane, small-stroke reciprocating, reciprocating, scroll, and screw compressors.

Viscosity is a measure of an oil’s flowability, e.g., ISO VG 32, 68, or 100. It determines
how easily an oil flows between moving parts
of a system under load or at certain temperatures.

Low number → lower viscosity, suitable for smaller compressors or lower temperatures.
High number → higher viscosity, e.g., for slow-running reciprocating compressors.
The correct viscosity ensures optimal lubrication, energy efficiency, and service life of
refrigeration compressors and other system components. It must be suitable for the design and application of the
compressor. The viscosity or oil grade for compressors is always specified by the respective
manufacturer.