What is an FCU?

What is an FCU?

• A stand-alone HVAC unit that heats or cools a single room.
• Pulls room air in → moves air across a coil → supplies conditioned air back to the room.
• Unlike an AHU, an FCU does not require ductwork and serves individual spaces.

FCU vs AHU

FCU	AHU
Serves single rooms / localized control	Serves multiple rooms / entire buildings
Small, room-based, decentralized	Large, centralized (roof/basement/mechanical room)
Recirculates air within a space (no duct system needed)	Delivers conditioned air via ductwork

 Main Components of an FCU

• Blower - Draws in room air & pushes it across the coil.
• Motor - Powers the blower for air circulation.
• Coils (Cooling / Heating)
  • Cooling coil uses chilled water from a chiller.
  • Heating coil uses hot water from a boiler or electric heating.
• Filter – Traps dust, insects, and debris; protects the coil.
  •  Must be replaced regularly to maintain efficiency.
• Drain / Condensate Pan – Collects water that forms on the cooling coil, preventing damage and mold.
• Actuator Valve – Controls water flow through the coil → regulates temperature.
• Thermostat – Adjusts temperature, operation mode (cool/heat), and fan speed (low/medium/high).
• Air Vents (Return & Supply)
  • Return: Air intake to the FCU
  • Supply: Conditioned air discharged back to the space

Where FCUs Are Commonly Used

• Hotels
• Apartments / Condominiums
• Small offices
• Any building requiring individual room temperature control

How an FCU Operates (Process Flow)

1. Blower pulls room air through the return vent.
2. Air passes across the cooling or heating coil.
3. Air temperature changes based on chilled water / hot water / electric coil.
4. Conditioned air is supplied back into the room via the supply vent.
5. This cycle repeats until set temperature is reached.
6. FCUs can be two-pipe or four-pipe, which determines cooling/heating changeover capability (covered in the next lesson).

FCU Mounting Configurations

1. Ceiling-Mounted Concealed FCU
   • Common in offices with drop ceilings
   • HVAC components hidden above ceiling tiles
   • Supply/return air via ceiling grilles & ducts
   • Quiet operation, less visible → good for aesthetics
2. Ceiling-Mounted Exposed FCU
   • Found in open-ceiling, modern/loft-style offices
   • Mechanics remain visually exposed as part of design
   • Air may be delivered via ducts or directly from unit
   • More noise due to exposed structure
     → must consider acoustic impact
3. Wall or Floor-Mounted FCU
   • Typical in hotels, apartments & small living spaces
   • Bottom grille = return air intake
     Top grille = conditioned air discharge
   • Pros: Easy access, simple maintenance & inspection
     Cons: Occupies wall/floor space
4. Floor-Mounted Concealed / Underfloor FCU
   • Less common; mostly used in data centers
   • Provides flexible spot-cooling for IT equipment racks
   • Uses floor grilles and ducts for airflow distribution

Two-Pipe vs Four-Pipe FCU Systems

Two-Pipe System (Single Loop)

• Coil handles either cooling OR heating at a time
• Requires seasonal changeover (heating ↔ cooling)
• Lower installation and piping cost
• Less flexibility in mixed-season conditions

Four-Pipe System (Dual Loop)

• Two loops: Chilled water + Hot water
• Can heat and cool simultaneously, no seasonal switch needed
• Higher complexity and higher installation cost
• Best comfort performance → independent temperature control year-round

Installation Codes & Regulatory Standards

• FCU installs must comply with national, state, and local codes
• Key governing standard: NEC (National Electric Code)
• Final compliance checked by AHJ (Authority Having Jurisdiction)
• Following code ensures safety, performance, and reliability

Advantages of FCUs

1. Easy to retrofit / add to existing spaces
   • No ductwork required → lower installation cost
   • Minimal disruption when adding cooling to a room
2. Simple maintenance & replacement
   • Serviceable without shutting down building systems
   • Straightforward operation → easier troubleshooting
3. Individual room control
   • Each space can be set to a preferred temperature
   • Example: Office cooler for focus vs home warmer for comfort
4. Energy savings
   • May reduce heating/cooling cost up to ~20%
   • Only conditions occupied rooms → avoids wasted energy
5. Improved air quality
   • Filters capture dust/pollen → helps reduce allergy symptoms

Disadvantages of FCUs

1. High long-term maintenance burden
   • Each FCU needs regular service
   • Filter changes, actuator replacement, condensate pan repairs
   • More units → higher cumulative maintenance cost
2. Maintenance often occurs in occupied rooms
   • Work has to be done inside offices, hotel rooms, meeting rooms
3. Proper sizing is critical
   • Undersized unit → runs harder → more energy use
   • Oversized unit → short cycling → temp swings & inefficiency
4. Possible temperature imbalance
   • Uncoordinated FCUs may conflict with each other
   • Hot/cold zone differences increase energy use
5. No fresh air supply
   • Recirculates room air only
   • A separate ventilation system is required for outdoor air
6. Noise concerns
   • Can disrupt quiet environments
   • Causes: improper install, old motors, unbalanced fan blades, speed changes