Fan Coils, Cab Heaters, and Unit Vents
Lesson 2.5
Fan Coil Unit (FCU)
A self-contained box with a fan and a coil. Can heat, cool, or both. Common in hotels, apartments, healthcare, perimeter offices. Two-pipe systems have one coil that switches between hot and chilled water seasonally. Four-pipe systems have separate HW and CHW coils and can heat and cool independently year-round. Typical points: zone temp (AI), HW valve (AO), CHW valve (AO), fan enable or speed (DO or AO).
Cabinet Unit Heater (Cab Heater)
A fan blowing over a heating coil. Heating only. Simple. Common in vestibules, lobbies, warehouses. If zone temp is below setpoint, open the HW valve and run the fan. Above setpoint: close the valve, stop the fan. Typical points: zone temp (AI), HW valve (DO or AO), fan enable (DO).
Unit Ventilator (Unit Vent)
A fan coil with an outdoor air damper built in. Built for classrooms. The OA damper modulates based on outdoor conditions and occupancy. Typical points: zone temp (AI), return air temp (AI), outdoor air temp (AI), occupancy (BI), OA damper (AO), HW valve (AO), fan enable (DO).
Radiant Panels
No fan, no noise. Heats or cools by radiation from ceiling or floor surfaces. Water flows through tubing embedded in the ceiling, floor, or wall. Response time is slower; the zone may take 30-60 minutes to respond to a setpoint change. A DOAS unit handles ventilation separately. Typical points: zone temp (AI), HW or CHW valve (AO).
Baseboard and Perimeter Heat
The simplest terminal unit there is. A heating element along the wall. Electric baseboard: a thermostat switches power to the resistance element. Hot water baseboard: a zone valve opens when there is a call for heat. Typical points: zone temp (AI), heat enable (DO).
Exhaust Fan
Remove air from a space when a condition is met. Often the simplest sequence you will write. The classic electrical room sequence: if room temperature rises above setpoint (often 85-90 degrees F), enable the exhaust fan. Typical points: room temp (AI), fan enable (DO).
# AIR HANDLING SYSTEMS