BTEB Refrigeration & AC Exam key terms

A fluid used in a refrigeration cycle that absorbs heat by evaporating at low pressure and releases heat by condensing at high pressure, carrying heat from one place to another.

Heat added to or removed from a substance that changes its temperature without changing its state, such as warming air from 25 to 30 degrees Celsius.

Heat absorbed or released when a substance changes state at constant temperature, such as boiling liquid refrigerant into vapour or melting ice into water.

The amount of heat needed to raise the temperature of one kilogram of a substance by one kelvin, expressed in kilojoules per kilogram-kelvin.

The fixed link between a refrigerant's saturation pressure and saturation temperature, allowing technicians to find evaporating or condensing temperature by reading a gauge.

The temperature at which a refrigerant boils or condenses at a given pressure; both liquid and vapour phases coexist at this temperature during a state change.

The number of degrees a vapour is above its saturation temperature at the measured pressure; useful for checking that the evaporator is properly fed with refrigerant.

The number of degrees a liquid is below its saturation temperature at the measured pressure; indicates how much liquid refrigerant has been cooled after condensing.

The total heat content of a refrigerant per unit mass, combining internal energy and flow work; used with pressure-enthalpy charts to calculate cycle performance.

A diagram plotting refrigerant pressure against enthalpy that shows the evaporation, compression, condensation and expansion processes, used to analyse system capacity and efficiency.

The pump of a refrigeration system that draws low-pressure vapour from the evaporator and compresses it to a higher pressure and temperature so it can reject heat.

A heat exchanger where hot high-pressure refrigerant vapour gives up heat to air or water and condenses into a liquid before entering the expansion device.

A heat exchanger where low-pressure liquid refrigerant boils and absorbs heat from the surrounding air or product, producing the cooling effect.

A metering device that drops refrigerant pressure from condensing to evaporating level and regulates the flow of liquid into the evaporator.

A modulating metering device that uses a sensing bulb to control refrigerant flow and maintain a set superheat at the evaporator outlet.

A fixed-bore metering device made of a long narrow tube that restricts refrigerant flow and creates the pressure drop between condenser and evaporator.

A vessel on the suction line that traps liquid refrigerant and oil, allowing only vapour to reach the compressor and preventing slugging damage.

A device in the liquid line containing desiccant and a screen that removes moisture and solid particles from the refrigerant to protect the system.

The pipe carrying low-pressure refrigerant vapour from the evaporator back to the compressor inlet; it is normally insulated to limit heat gain.

A sight-glass device in the liquid line with a colour-changing element that shows whether the refrigerant contains excess moisture and whether liquid flow is full.

The ordinary air temperature measured by a thermometer exposed to the air but shielded from radiation and moisture, indicating sensible heat level only.

The lowest temperature air can reach by evaporative cooling, measured with a wetted thermometer; together with dry bulb it defines air humidity.

The ratio of the actual water vapour in the air to the maximum it could hold at that temperature, expressed as a percentage.

The rate of heat removal required to keep a space at a chosen temperature, made up of heat from people, equipment, solar gain, conduction and infiltration.

Heat entering a conditioned space from outside or generated inside, including conduction through walls, solar radiation, infiltration and internal sources.

A cooling capacity unit equal to the heat absorbed by melting one tonne of ice in 24 hours, approximately 3.5 kilowatts.

A system with an indoor unit containing the evaporator and an outdoor unit containing the compressor and condenser, connected by refrigerant piping.

An assembly of compressor, condenser, fan and controls mounted together, often outdoors, that supplies high-pressure refrigerant to the indoor evaporator.

A machine that cools water or another secondary fluid, which is then circulated to air-handling units or fan coil units to cool building spaces.

An indoor terminal device containing a coil and fan that cools or heats room air using chilled or hot water supplied from a central plant.

A large factory or site-assembled unit with fans, coils, filters and dampers that conditions and distributes air through ductwork in a building.

A pump used during installation to remove air and moisture from refrigerant piping and the evaporator before charging, preventing acid and ice formation.

The process of pulling a deep vacuum on a sealed refrigeration circuit to boil off moisture and prove the system is leak-free and dry.

The amount of refrigerant added to a system, measured by weight or determined by superheat and subcooling readings, needed for correct operation.

The practice of finding refrigerant leaks using electronic detectors, soap bubbles, pressure tests or dye, essential for efficiency and environmental safety.

A check in which dry nitrogen or another gas is used to pressurise a circuit and confirm it holds pressure without leaks before charging.

Scheduled servicing such as cleaning coils, checking belts, tightening electrical terminals and measuring pressures to prevent breakdowns and maintain efficiency.

A safety procedure that isolates electrical or mechanical energy sources and attaches warning tags so equipment cannot be started while being serviced.

Safety gear such as gloves, goggles, and respirators worn to protect against refrigerant frostbite, chemical splashes and electrical hazards during service work.