How to calculate AHU CFM To calculate AHU CFM (Cubic Feet per Minute), you determine the airflow required based on either the room volume and air changes per hour (ACH), or by using thermal load and temperature difference. Both methods are widely used in HVAC design and commissioning. 🧩 Methods of Calculating AHU CFM 🔹 Method 1 – Room Volume & ACH This is the most common method for ventilation design. C F M = R o o m V o l u m e × A C H 60 Room Volume = Length × Width × Height (ft³) ACH (Air Changes per Hour) = Number of times air is replaced per hour Example: Room size = 20 ft × 15 ft × 10 ft = 3,000 ft³ ACH = 6 (typical for offices) C F M = 3000 × 6 60 = 300 C F M ➡️ The AHU must supply 300 CFM to meet ventilation requirements. 🔹 Method 2 – Thermal Load (BTU/hr) Used when sizing AHUs for cooling/heating loads. C F M = B T U / h r 1.08 × Δ T BTU/hr = Heat load of the space ΔT = Temperature difference between supply and return air Example: Heat loa...
🔥 Fire Triangle and Fire Tetrahedron A professional and detailed explanation of the Basic Fire Triangle and Fire Tetrahedron, written for safety engineers and facility managers: 🔹 Fire Triangle The fire triangle is the simplest model explaining the three essential elements required for fire ignition and continuation: Fuel – combustible material (wood, paper, chemicals, gases). Heat – sufficient energy to raise the fuel to ignition temperature. Oxygen – typically from air, supporting combustion. ➡️ Removing any one of these elements will extinguish the fire. 🔹 Fire Tetrahedron The fire tetrahedron expands the triangle into a four‑sided model, adding the chemical chain reaction : Fuel Heat Oxygen Chemical Chain Reaction – the self‑sustaining process of free radicals that keeps combustion going. ➡️ Fire suppression methods often target this chain reaction (e.g., halon or clean agent systems). 🔹 Practical Applications Firefighting Strategies: Remove fuel (isolation, firebre...