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...
BOILER SAFETY: A HIGH-ENERGY EQUIPMENT RISK THAT CANNOT BE IGNORED
Boilers are high-energy systems containing pressurized steam/hot water and fuel. Poor operation, inadequate maintenance, or failure of safety devices can result in fire, explosion, pressure release, burns, and serious equipment damage.
Key Boiler Safety Controls
1. Pressure Protection
- Ensure safety/relief valves are correctly sized, tested, and maintained.
- Never bypass or isolate safety devices.
- Monitor operating pressure continuously.
2. Water-Level Control
- Maintain the correct boiler water level.
- Test low-water cut-off devices regularly.
- Low water can cause severe overheating and tube failure.
3. Combustion & Fuel Safety
- Verify proper burner operation and flame detection.
- Maintain fuel trains, valves, regulators, and interlocks.
- Ensure adequate combustion and ventilation air.
- Investigate abnormal flame, smoke, or combustion conditions immediately.
4. Boiler Controls & Interlocks
Critical protections should include:
- High-pressure cut-off
- Low-water cut-off
- Flame-failure protection
- Fuel shut-off
- High-temperature protection
- Emergency shutdown
5. Inspection & Maintenance
- Conduct periodic inspection of pressure vessels and associated equipment.
- Check tubes, refractory, burners, valves, gauges, pumps, and controls.
- Maintain accurate maintenance and testing records.
6. Lockout/Tagout (LOTO)
Before maintenance, isolate and verify:
Fuel + Electrical + Steam/Pressure + Water + Other Stored Energy
Never rely solely on a closed valve or electrical switch—verify zero energy before work begins.
🚨 Golden Rule
Never operate a boiler with a defective safety device, uncontrolled pressure, abnormal water level, or suspected combustion problem.
A strong boiler safety program combines competent operators, preventive maintenance, functional safety interlocks, periodic inspection, emergency procedures, and strict compliance with applicable codes and regulations.
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