Glossary
The terms you will see in surveys, quotes and service reports.
Air conditioning terms explained
Short definitions of the terms that come up in surveys, quotes, service reports and compliance paperwork.
- Air conditioning energy inspection
- A periodic inspection of air conditioning systems over 12 kW by an accredited assessor to check efficiency; often called a TM44 inspection.
- Air curtain
- A unit above a doorway that blows a stream of air across the opening to reduce heat exchange while the door is open.
- Air handling unit (AHU)
- A central unit that filters, heats, cools and moves air through ductwork, often with heat recovery.
- Air-to-air heat pump
- A heat pump that moves heat between outdoor air and indoor air — the same equipment as reverse-cycle air conditioning.
- ASHRAE
- A US-based engineering society whose data-centre guidance sets widely used temperature ranges for IT equipment.
- Automatic leak detection
- A system that monitors for refrigerant leaks and raises an alarm; it can extend F-gas leak-check intervals and is mandatory at 500 tonnes CO2e.
- BMS
- Building management system: central software and controllers that monitor and control building services such as heating, cooling and ventilation.
- Branch selector box
- A component on heat recovery VRF systems that switches individual indoor units between heating and cooling.
- BS 4142
- The British Standard method for rating and assessing industrial and commercial sound, often used to assess outdoor plant noise.
- BS EN 378
- The standard covering safety and environmental requirements for refrigerating systems and heat pumps, including refrigerant charge limits in occupied rooms.
- Ceiling cassette
- An indoor unit fitted into a suspended ceiling that blows air in up to four directions.
- CIBSE
- The Chartered Institution of Building Services Engineers, publisher of design guides and the TM44 inspection methodology.
- Close control unit
- A precision air conditioning unit for server rooms and data centres that controls temperature and humidity tightly.
- CO2 equivalent (CO2e)
- Refrigerant charge in kg multiplied by its GWP, divided by 1,000, giving tonnes of CO2 equivalent. Used for F-gas thresholds.
- Commissioning
- Setting up and testing a new system to confirm it works as designed, with results recorded.
- Compressor
- The pump in the outdoor unit that circulates refrigerant and raises its pressure and temperature.
- Condensate
- Water removed from the air as it is cooled, which must be drained away from the indoor unit.
- Condensate pump
- A small pump that lifts condensate water to a drain where it cannot flow away by gravity.
- COP
- Coefficient of performance: heat delivered divided by electricity used, at given conditions.
- Defrost cycle
- A short reverse cycle a heat pump runs to clear ice from its outdoor coil in cold, damp weather.
- Diversity
- Allowance for the fact that not every room reaches its peak load at the same time.
- Ducted unit
- An indoor unit hidden above a ceiling that delivers air through ducts and grilles.
- EC motor
- Electronically commutated fan motor; more efficient and controllable than older AC motors.
- Evacuation
- Removing air and moisture from new pipework with a vacuum pump before charging with refrigerant.
- F-gas
- Fluorinated greenhouse gases, including HFC refrigerants such as R32 and R410A.
- F-gas company certificate
- Certification a business needs to install, service or decommission F-gas equipment for others.
- Fan coil unit (FCU)
- A terminal unit that heats and cools a room by blowing air over coils fed with chilled and hot water.
- GWP
- Global warming potential: how much a gas warms the climate compared with the same mass of CO2.
- HCFC
- Hydrochlorofluorocarbon refrigerants such as R22, phased out because they damage the ozone layer.
- Heat load
- The amount of heat a cooling system must remove from a space, in kW.
- Heat recovery VRF
- A VRF system that can cool some zones while heating others, moving heat around the building.
- HFC
- Hydrofluorocarbon refrigerants such as R410A and R32, subject to the F-gas phase-down.
- HFC phase-down
- The stepped reduction in the quantity of HFCs that can be placed on the market.
- Indoor unit
- The part of an air conditioning system inside the room — wall-mounted, cassette, ducted or floor-standing.
- Inverter
- Variable-speed compressor control that adjusts output continuously instead of switching on and off.
- kW
- Kilowatt: the unit used for heating and cooling capacity.
- Leak check
- An inspection of a refrigerant system for leaks, required at set intervals for equipment at or above 5 tonnes CO2e.
- Low-ambient kit
- Controls that let a cooling system keep running when it is cold outside, needed for server rooms.
- Multi-split
- One outdoor unit connected to two to five indoor units.
- MVHR
- Mechanical ventilation with heat recovery: fresh air supply and extract through a heat exchanger.
- N+1
- A resilience arrangement with one more unit than the load needs, so one can fail without loss of cooling.
- Operator
- Under F-gas rules, the person or business with actual control over the equipment.
- Outdoor unit
- The part of a split or VRF system outside the building, containing the compressor and condenser coil.
- PPM
- Planned preventive maintenance: scheduled service visits at set intervals.
- Pressure test
- Testing new pipework with nitrogen at pressure to prove it is leak-tight before charging.
- R22
- An HCFC refrigerant that cannot be used for servicing in the UK since 1 January 2015.
- R32
- An HFC refrigerant with a GWP of 675, now standard in most new small split systems.
- R410A
- An HFC refrigerant with a GWP of 2,088, common in systems installed from the 2000s to the early 2020s.
- Refrigerant recovery
- Removing refrigerant from a system into certified cylinders so it is not released to the air.
- SEER
- Seasonal energy efficiency ratio: a measure of cooling efficiency over a typical season.
- Split system
- An air conditioning system with separate indoor and outdoor units connected by refrigerant pipework.
- TM44
- The CIBSE methodology for air conditioning energy inspections, used as the common name for the inspection.
- VRF / VRV
- Variable refrigerant flow: a multi-zone system where shared outdoor plant serves many individually controlled indoor units. VRV is a manufacturer trademark.
- WEEE
- Waste electrical and electronic equipment: rules for disposing of old units responsibly.