Here heating and cooling is carried out in a central plant room and conveyed by ductwork. Examples include:
Constant volume (CV) systems : Relatively low cost and easy to install. Separate systems may be required for different zones. This system is often used to provide fresh air in partially centralised air/water systems.
Variable air volume (VAV) systems : Zone control is provided by varying the volume of air at a constant temperature. Costs can be reduced by operating supply and extract fans at reduced speeds, reducing the volume for part of the year. Popular in buildings needing all year cooling.
Displacement ventilation systems : Low level cool air is provided by a central plant at low speeds but unable to remove large heat gains. Mainly used to provide ventilation in conjunction with chilled beams/ceilings.
Centrally cooled or heated air further heated or cooled on entry to rooms. Variations include:
Centralised air systems : A central air supply is provided either at constant or variable volume and then further heated or cooled to individual room requirements by additional heating or cooling coils. This gives greater control in constant volume systems and can also improve variable systems in areas where loads vary.
Four-pipe fan coil units : This system usually involves a fan, heating and cooling coils and air filters. Fresh air and heated or chilled water are provided to each unit and the air is heated or cooled just prior to entry into a space. Fan coil units are mounted either at the building perimeter or at high level, often above a suspended ceiling.
Chilled ceilings and beams : Consists of ceiling mounted panels of pipes that are cooled by cool water. Cold air sinks through a space or is radiated downwards. Fan energy is saved by using water. These units should be avoided in areas where significant moisture is present as condensation may occur.
With this air conditioning system, all operations are performed locally. Typical examples are:
Split systems: Comprise of two main components – an indoor room cooling unit and an outdoor refrigeration (condensing) unit linked by pipes transporting refrigerant. In some systems heating can be provided by reversing the process. These are popular air conditioning systems in shops, restaurants and offices and are ideal for relatively small spaces. Installation and servicing should be conducted by specialist maintenance contractors.
Variable refrigerant flow (VRF) systems : These are sophisticated split systems providing heating or cooling (using refrigerants or water) on an individual basis. Useful in office blocks, hotels and large retail stores around places like York, Coventry and Derby, etc, which may require cooling in some areas and heating in others. The outside condensing units of a VRF air conditioning system can be dispersed, making them particularly useful for refurbishment projects in Glasgow or Edinburgh. Installation and servicing should be conducted by specialist maintenance technicians.