MASTERCLASS – AIR CONDITIONING TECHNOLOGY

VOL 51 – Airside Control Fan Coil Units

 

In last month’s article we looked at the need to specify various elements of a Fan Coil Unit based system together with the precautions and considerations the specifier / contractor / manufacturer must bear in mind if a successful installation is to be achieved. We now continue in more detail with these important criteria in mind in our coverage of this increasingly popular and important approach to comfort conditioning.

Airside Control Fan Coil Units

Airside control fan coil units have been available for many years offering an alternate control method to the more traditional waterside control fan coil unit.

Although utilising this alternate method of controlling the units’ cooling or heating output to the space or zone to be conditioned, this type of unit is available in similar model types, ranges and capacities as its waterside counterpart. These could include Vertical or Horizontal orientated units and either basic chassis or cased models as required (the latter for vertical units only). This also applies to the range of application variations and accessory options too.

In basic terms, the difference in control equipment is that the Airside unit typically utilises an actuator motor coupled to either a gear drive assembly or a linkage arrangement. These in turn move damper equipment that in turn controls the path of the air to initiate heating or cooling as opposed to the valves that are used on a waterside control machine.

The following stages describe and illustrate the cooling, bypass (ventilation only) and heating operations of Airside control more clearly:

Heating Mode:

Airside control fan coil units – Cooling damper closed, Heating damper in the open / control mode. This means the air being re-circulated is passing predominantly over either the heating coil or through the bypass channel depending on the amount of heating required.

Bypass Mode:

Airside control fan coil units – Cooling damper closed, Heating damper closed. All the air being re-circulated is passing through the bypass channel and is not affected by the cooling or heating coils at all.

 Cooling Mode:

Airside control fan coil units – Cooling damper open / control mode, Heating damper closed. This means the air being re-circulated is passing over the Cooling coil or through the bypass channel depending on the amount of cooling required.

This is of course a very simplistic illustration. In point of fact, with the controls equipment available in today’s marketplace, the control of the air to the space is much more responsive to the demands made. They are equally subtle in providing the appropriate air treatment by virtue of the fact that the mode dampers modulate, to allow mixing to take place within the unit, and thereby more closely match specific demand and supply.

 DISCLAIMER:

Whilst every effort is made to ensure absolute accuracy, Business Edge Ltd. will not accept any responsibility or liability for direct or indirect losses arising from the use of the data contained in this series of articles.