FAN COIL UNITS
Fan coil insights
Barry Trewhitt, president of HEVAC, part of the Federation of Environmental Trade Associations (FETA), gives an overview of how to get the best out of fan coil units throughout the life of your building.
Particular attention should be paid to the positioning of sensors, and to ensure that localised draughts from other fan coil units or other services are kept to a minimum.
G
etting the best out of fan coil units starts with the design of the building. Units should be sized correctly for the space they are serving. Undersized units may struggle to
maintain desired temperatures, while oversized units can lead to temperature fl uctuations causing reduced effi ciency and uneven comfort levels.
As the output of a fan coil unit is intrinsically linked to the water temperatures, ensure that all the terminal unit equipment, not just the fan coil units, are selected based on realistic and achievable water temperatures, not just arbitrarily chosen design values.
Fan coil units should be properly positioned to address local heat gains or losses from external sources such as direct sunlight, exterior walls, or windows. Units with higher cooling demands (IT rooms, higher occupancy offi ces) will require larger units to meet the demands. Estimated heating and cooling loads should be calculated from industry guidance such as CIBSE Guide B or BSRIA Rules of Thumb. Control strategies should be structured to complement the
operation of the fan coil unit, rather than hinder it. By using variable speed fans and larger heat exchangers, fan coil units can be used to quickly heat, or cool areas compared to other heating systems like underfl oor heating, and this should capitalise on energy and carbon savings.
Occupancy detection
Occupancy detection using widely, and commercially available PIR sensors or CO2 monitoring can be integrated with modern access control systems to build up an accurate picture of who is in a building. Less frequented areas can then use a wide-ranging setback temperature as thermal comfort becomes less important. Areas that are occupied infrequently can have even wider ranging setpoints focused more on protecting the building’s fabric or contents. Integration into the building’s ventilation system should be
defi ned to allow for free cooling and indoor air quality. Fan coils are typically just recirculation devices, and by integrating with AHUs, the fan coil can add better localised thermal comfort as required. In addition, fan coil units are used to aid air distribution around spaces more evenly. Fan coil units with EC motors are now deemed an industry
standard due to the Specifi c Fan Power (SFP) requirements in UK Building Regulations Part L. Beyond improved SFPs, they also allow for variable speed control of the fan. Unit controls from either the fan coil manufacturer or a systems integrator should make use of this and ensure that the fan speeds can ramp up or down to suit the duty requirements of the space.
26 February 2025 •
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