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Glossary of HVAC Terms

At Air Options, we understand that some of the language used in our industry can be confusing. As such, we’ve created a handy glossary of HVAC terms which covers all of the most commonly used terms & phrases.

  • AC – An abbreviation of Air Conditioning.
  • Air Con – A further abbreviation of Air Conditioning
  • AHU – An abbreviation of Air Handling Unit and is similar to the above albeit on a larger and more centralised scale often serving smaller FCU’s.
  • AIR CONDITIONER or AIR CONDITIONING – A common term for a system that offers cooling whether it be a wall mount, ceiling suspended or otherwise. It is a confused term given the evolution of the products and often misunderstand to describe cooling only systems of yesteryear. Given most systems now also heat (see HEAT PUMP), it is more likely to be used as a global term covering all.
  • AIR SOURCE HEAT PUMP or ASHP – A term for a heat pump system which heats and can cool via a DX unit using refrigerant as a medium. This proves to be very energy efficient as the heating is created by removing heat from the external ambient via an ‘air to air’ heat exchanger as opposed to being reliant upon electric heaters, or removing heat from another medium as a GSHP does below.
  • CASSETTE UNIT –  A term for an internal fan coil unit located within the ceiling void/ recessed within a grid, although in modern times are often on display complete with services. Cassettes are fitted with a 2 or 4 way blow fascia discharging conditioned air into the space.
  • CEILING SUSPENDED – A term for an internal fan coil unit located underneath the ceiling and capable of long air throws via a single outlet.
  • CHASSIS UNIT – A term for an internal fan coil unit located at low level just above the floor. The unit is not of a finished appearance and requires boxing in or enclosing. The chassis unit is generally fitted with duct and grilles to complete and distribute the air onto the space.
  • CHW – An abbreviation of chilled water and is often used when referring to water chiller style solutions.
  • CU or CONDENSING UNIT – CU is an abbreviation of Condensing Unit. This plant is generally located externally or within a plant room and the component of the system where the heat rejection/ absorption is carried out with ambient. The CU is nearly always coupled with an AHU or FCU dependent upon the style of system offered.
  • DUCTED UNIT – A term for an internal fan coil unit located within the ceiling void/ above a grid and generally cannot be seen, although once again in modern times are often on display complete with services to suit aesthetics. Ducted units require custom ductwork and grilles fitted to distribute air to corresponding areas and can come is some very large capacities.
  • DX – Direct expansion is a system concept where refrigerant gas is utilised as the cooling medium and water is not utilised /circulated.
  • ECA – Enhanced Capital Allowances are attracted as a consequence of good system design, equipment selection and government incentive. ECA’s allow the purchasing party to offset part or all of the installation costs against company corporation tax in year one as opposed to the normal depreciation term. Full details available from the HMRC or your accountant and are in addition to standard capital allowances.
  • FCU – An Abbreviation of Fan Coil Unit which is a generic name for the internal system which creates the cooling or heating effect, whether it be wall, ceiling, void mounted or otherwise.
  • GROUND SOURCE HEAT PUMP or GSHP – A term for a system which heats by using water as a medium, and then uses heat pump technology to increase the temperature of this water. This proves to be very energy efficient as the heating is created by removing heat naturally stored in the ground via a ‘ground to water’ heat exchanger or matrix, as opposed to removing it from the ambient air as per ASHP.
  • HEAT PUMP – A generic term for a system which heats and cools via a single unit, whether it be Water Chilled or a DX system. This proves to be very energy efficient as the heating cycle is created by heat exchange as opposed to the heat being created by electric heaters or otherwise.
  • HRV or HEAT RECOVERY VENTILATION – This is a relatively modern term for an energy efficient ventilation system. Heat is removed from the extracted air via a thermal wheel or recuperator making for a very efficient and effective package.
  • HVAC – An industry abbreviation for Heating, Ventilation & Air Conditioning which is used to refer to products or services of a general nature.
  • LOW LEVEL or FLOOR MOUNTED UNIT – This is much the same as a chassis unit albeit is of a finished appearance from the factory and complete with its own discharge grille. These units generally sit upon the floor and resemble a storage heater in appearance.
  • LPHW – An abbreviation for Low Pressure Hot Water and really is self-explanatory in the fact that low pressure hot water is pumped/ circulated around a coil within an FCU/ AHU to heat the area served.
  • PAC or CRAC – Precision Air Conditioning or Computer Room Air Conditioning. This is a term for system installed within temperature sensitive environments such as computer rooms and data centres.
  • VENTILATION – The term ventilation is used to explain a system which introduces fresh air and extracts stale air from an area such as an office for example. Ventilation systems are in addition to air conditioning, HVAC or heat pump packages and are not designed to offer accurate temperature control of the space served. That said air conditioning and ventilation packages should be designed to work in harmony with each other.
  • VRV or VRF – An industry abbreviation for the type of system concept offered. In this case it stands for Variable Refrigerant Volume /Flow. These systems are of an energy efficient nature whilst retaining extremely small footprints and reduced noise levels.
  • WALL MOUNT – This is a very generic term, although when directed at the style of air conditioning or heat pump system installed, a ‘wall mount’ is a unit mounted and fixed to an internal wall at high level with one point of discharge, normally at the bottom. In most cases this is the most cost-effective method of unit.
  • WATER CHILLER – This system concept utilises refrigerant as a cooling medium in addition to recirculating water to deal with heat rejection/ absorption.