Temperature sensors are mounted on the outside or top of AHU units with rods extending inside the unit to measure air temperature at various points (e.g., at heating coil inlet); these measurements are sent to control systems to dictate how coils should operate.

An HVAC system's primary function is to supply heated, ventilated, and air-conditioned air to building spaces while ensuring correct temperature, humidity, CO2 levels, and freshness of air to keep occupants comfortable.

Bag filters are the second line of defense in an AHU after panel filters; they have jagged/pleated edges extending back a certain distance that increase surface area for capturing dirt that passes through panel filters.

Air intake contains surprising amounts of dirt and muck including pollen, skin debris, tire rubber from roads, and automotive emissions that must be filtered before reaching building coils and occupants.

The plant room in a building contains all mechanical and electrical assets that control power and air conditioning, and is typically an area where occupants in offices never go or have knowledge of its existence.

An intake mesh grill on the outside of an AHU prevents large debris, animals, and other foreign material from entering the system, protecting fans and internal components from damage; this grill must be cleaned periodically as it accumulates debris.

Filter material thickness determines how much dirt and germs it captures; thicker filter material captures more contaminants, but requires the fan to work harder, increasing electricity costs.

Pressure differential sensors are installed on filter panels to measure the pressure drop across the filter, indicating how dirty it has become; marking clean and dirty reference points on these gauges allows maintenance staff to determine when filter replacement is needed during walk-around inspections.

Chilled water should enter cooling coils at the base and exit at the top (counterflow to gravity) to maximize heat transfer efficiency, because gravity assists the water's rise and gives it extra time to shed heat; if water enters from the top, gravity's momentum causes it to move too quickly through the coil without giving up all its heat.

Some cooling coils use refrigerant systems with thermal expansion valves instead of chilled water; refrigerant lines split and branch to multiple coils with thermal bulbs at the bottom to meter refrigerant flow and control cooling.

Drain lines under coils must be installed on an incline and include a bend (trap) to prevent water from flowing backward and air from being sucked in; water condensing from the air on cooling coils drains through these lines into the building's drainage system.

Belt drives connecting motors to fans wear out and can break over time; a properly functioning BMS system will detect a sudden loss in motor speed and stop the motor, though preventative maintenance should be planned to avoid belt failure.

Induction motors powering HVAC fans have data plates listing electrical specifications (kilowatts, amps); variable frequency drives (VFDs) or variable speed drives (VSDs) can control motor speed by changing the frequency (e.g., from 50/60 Hz down to 40 Hz), which reduces fan revolutions and volume of air delivered to the space.

HVAC systems include electrical isolator switches that can cut power to fans and motors; these isolators must be switched off before entering or working on an AHU because rotating fans can cause serious injury (loss of arm or finger).

Humidifiers in AHUs add moisture to air by spraying fine water mist (or in some systems using steam) to increase the water content of the air, maintaining indoor humidity levels for comfort and to control static electricity in offices.

Fresh air velocity can be measured and converted to volume flow rate if ductwork size is known, allowing BMS systems to calculate and monitor the volume of fresh air being supplied to the building.

A frost protection sensor detects if incoming air temperature drops to around 5°C and triggers electric heating to warm the air; this prevents pipes within coils from freezing and bursting, which would leak fluid into the air stream.

Fins on heating and cooling coils dramatically increase effective surface area compared to bare pipes, allowing air rushing across the coil to absorb or release thermal energy instead of bypassing gaps between pipes.

100% fresh air (no recirculation) requires full conditioning of all supply air through heating, cooling, and humidification coils, making it energy-intensive compared to recirculation strategies.

Minimum fresh air intake is typically around 10% of total air supply, required by building standards to maintain occupant health and indoor air quality despite energy costs.