Engineering: One System, Multiple Design Variables An AHU is not just a box with a fan and cooling coil. A small design mistake can increase: ✗ Fan power ✗ Pressure drop ✗ Noise ✗ Operating cost ✗ Maintenance frequency 1. Typical AHU Air Path Fresh Air → Louver → pre-Filter → Heat Recovery → Cooling/Heating Coil → Fan → Silencer → Supply Air Return/exhaust air paths must also be considered, especially where heat recovery, pressure control and IAQ are important. 2. Airflow Sizing The basic relationship is: Q = A × V Where: • Q = Airflow (m³/s) • A = Face area (m²) • V = Air velocity (m/s) Example: 20,000 m³/h = 5.56 m³/s At 2.5 m/s face velocity: Required area ≈ 2.22 m² Lower face velocity generally means a larger AHU footprint but can reduce component pressure drop and fan energy. ASHRAE notes that designers should not automatically default to 2.5 m/s; lower coil/filter velocities can provide energy benefits. (ASHRAE Handbook) 3. Pressure Drop = Hidden Energy Cost Typical AHU res...
HVAC Duct Air Leakage Test — MEP Engineer Handover
For HVAC ductwork, air-leakage testing is an important quality-control activity before final handover. It confirms that the duct system is properly sealed and can maintain the required airflow and pressure.
Typical testing process:
1. Review approved Shop Drawing, Method Statement and ITP.
2. Inspect duct joints, flanges, flexible connections and access doors.
3. Isolate the test section and seal all openings.
4. Connect the duct leakage test fan/unit.
5. Pressurize the duct to the specified test pressure.
6. Measure the actual air leakage using calibrated instruments.
7. Compare the result with the approved allowable leakage criteria.
8. Rectify leakage points and repeat the test if required.
9. Record results in the test report/WIR and submit for inspection.
Equipment commonly used:
Duct Leakage Test Unit / Fan
Calibrated Pressure Gauge or Manometer
Flow Meter / Orifice Plate
Anemometer where applicable
Smoke pencil or smoke generator for locating leakage
Calibrated measuring instruments
Common standards:
SMACNA HVAC Air Duct Leakage Test Manual
DW/143 — Ductwork Leakage Testing
ASHRAE standards/guidelines where specified
Project specifications and approved Method Statement always take priority.
The important point is not only “test passed.” During handover, the engineer should verify the approved design, test results, calibration certificates, inspection records, drawings, O&M documents and final as-built information.
Good testing + proper documentation = reliable HVAC system + smooth FM handover.
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