CFM = Sensible Heat Load (Btu/hr) / (1.08 * ΔT)
Store a friction loss vs. CFM vs. diameter table. Use INDEX/MATCH or linear interpolation to find the nearest duct diameter for a given CFM at your target friction rate. hvac design calculations excel
=B2/(1.08*20) – assuming B2 holds the sensible heat load. 3. Duct Sizing (Equal Friction Method) Using the equal friction method (e.g., 0.08 to 0.12 in. w.g./100 ft), you can size ducts using a friction chart approximation. CFM = Sensible Heat Load (Btu/hr) / (1
Or for heating: GPM = Btu/hr / (500 * ΔT) Use INDEX/MATCH or linear interpolation to find the
Where ΔT is the temperature difference between supply and return air (typically 20°F for cooling).
Velocity (FPM) = CFM / Area (ft²) . Add conditional formatting to highlight if velocity exceeds 1,500 FPM (noise risk) or 2,500 FPM (erosion risk). 4. Water Pipe Sizing (Hydronic Systems) For chilled or hot water systems, use: