Heating ventilation and air conditioning HVAC

'HVAC' refers to Heating Ventilation and Air Conditioning, which can be used in buildings to:

  • Maintain internal air quality.
  • Regulate internal temperatures.
  • Regulate internal humidity.

It is sometimes extended to include refrigeration (HVACR), for example in CIBSE Guide B. Heating, Ventilating, Air Conditioning and Refrigeration.

  • Internal air quality can be maintained by a combination of introducing 'fresh' air into the building, extracting 'stale air' and by filtration. Ventilation may be natural, mechanical, or mixed mode (a hybrid system). See ventilation form more information.
  • Internal temperatures can be regulated by heating and cooling. Typically this is achieved by heated water (or sometimes steam) and chilled water that is generated by boilers and chillersand then used in heating coils and cooling coils as part of the ventilation system.
  • Humidity can be regulated by ventilation, dehumidification and humidification. Dehumidification is often provided alongside cooling as cooling air reduces the amount of moisture it is able to 'hold', resulting in condensation and so dehumidification.
  • NB CIBSE Guide B defines refrigeration as 'the process of removing heat' and heat rejectionas 'the discharge of heat to waste or atmosphere or to a system permitting reclaim or recovery'.

Very broadly, HVAC systems can be centralised in a building, or local to the space they are serving, or a combination of both (for example local air handling units supplied by centrally-generated cooling). They may also be connected to a wider district heating or cooling network.

They may be integrated, with heating, ventilation and air conditioning provided by a single system, for example, air handling units connected to ductwork, or they may be a combination of separate systems, for example mechanical ventilation but with radiators for heating and local comfort cooling units.

They may also include passive or 'natural' systems such as natural ventilation.

In mechanically ventilated commercial developments HVAC is often provided by air handling unitsconnected to ductwork that supplies air to and extracts air from internal spaces. Air handling unitstypically comprise an insulated box that might include some, or all of the following components; filter racks or chambers, a fan (or blower),

heating elements, cooling elements, dehumidification, sound attenuators and dampers. Air handling units that consist of only a fan and a heating or cooling element, located within the space they are serving, may be referred to as fan coil units(FCU). See Air handling units for more information.

HVAC can consume large amounts of energy, and where possible, demand should be reduced and passive systems adopted.

Extracting internal air and replacing it with outside air can increase the need for heating and cooling. This can be reduced by re-circulating a proportion of internal air, or by heat recovery ventilation (HRV) that recovers heat from extract air and to pre-heat incoming fresh air.

It is important that HVAC systems are considered together during the design process, even where they consist of independent systems. This is because of the interaction between heating, cooling, humidity control and ventilation. This is particularly complicated when other elements of environmental behaviour are considered such as solar gain, natural ventilation, thermal mass and so on.

The design of HVAC systems is generally a specialist task, undertaken by a building services engineer, and because of its interaction with other elements of the building it is important that it is considered from the outset, as a fundamental part of the design process, and not an 'add on' at the end.

HVAC may be controlled by a building management system to maximise occupant comfort and minimise energy consumption.

Regular inspection and maintenance is necessary to ensure that systems are operating optimally.

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