Walk onto almost any office floor in London and you’ll find fan coil units (FCUs) in the ceiling void. A single floor can have dozens; a large building can have hundreds. Each one uses only a little energy, but small inefficiencies multiplied across a whole building add up to a large share of the HVAC bill. The good news: most FCU waste comes from controls, not hardware, so it can usually be fixed without replacing plant.
What is a fan coil unit?
A fan coil unit is a small terminal unit containing a fan, a heating and/or cooling coil, a filter and control valves. Chilled and hot water from central plant flows through the coils, and the fan blows air across them to heat or cool the space. Each FCU is normally controlled by its own controller connected to the Building Management System (BMS).
Where fan coil units waste energy
- Conditioning empty space: with hybrid working, many floors are half empty on any given day, but FCUs run to full occupancy schedules.
- Fighting units: neighbouring FCUs with different setpoints — one heating, one cooling — in the same open-plan space.
- Narrow deadbands: units flipping between heating and cooling with no neutral zone.
- Blocked filters: fans working harder and delivering less air, leading to complaints and lower setpoints.
- Passing or stuck valves: chilled or hot water flowing when it shouldn’t, wasting central plant energy.
- Faulty sensors: a return-air sensor reading wrong drives the unit to heat or cool unnecessarily.
Six ways to cut fan coil unit energy use
1. Occupancy-based control
Linking FCUs to occupancy (from PIR sensors, lighting control or wireless sensors) lets unoccupied zones set back automatically. This is usually the single biggest saving available.
2. Group and align setpoints
Grouping FCUs that serve the same open-plan area and giving them a common setpoint stops units fighting each other.
3. Widen deadbands
A sensible gap between heating and cooling setpoints prevents constant switching while keeping occupants comfortable.
4. Tighten schedules and optimum start
Run FCUs only during real occupied hours, and use optimum start so they switch on only as early as needed to reach temperature.
5. Monitor filter condition
Changing filters on condition rather than on a fixed calendar keeps airflow up and fan energy down.
6. Use BMS data to find faulty units
Trend logs reveal units that are always at 100% valve, constantly heating in summer, or never reaching setpoint. Those are the units with stuck valves, failed sensors or balancing problems — and fixing a handful often solves the complaints on a whole floor.
Do you need to replace the fan coil units?
Usually not. Most of the measures above are changes to controls and programming. Where controllers are old or closed-protocol, they can often be replaced with modern BACnet controllers — such as Distech Controls — and integrated into a Niagara 4 supervisor, while the FCU hardware stays in place.
Fan coil optimisation in London and the South East
Parsek Group helps facilities management companies and building owners reduce HVAC energy through FCU control strategies, sensor testing and BMS optimisation. We start with the data your BMS already has, find where energy is being wasted, and fix it — typically one floor first, then the rest of the building.
Want to know how much your fan coil units could save? Contact Parsek Group to discuss a pilot on one floor.