Skip to main content
Speclore

Surface Roughness Ventilation Ducts

Reference data and engineering information about surface roughness ventilation ducts for hvac systems applications.

surfaceroughnessventilationducts

Overview

Engineering reference data for Surface Roughness Ventilation Ducts in HVAC systems.

Key Formulas

Sensible Heat

Q=m˙cpΔTQ = \dot{m} c_p \Delta T

Heat causing temperature change.

Latent Heat

Q=m˙hfgΔωQ = \dot{m} h_{fg} \Delta\omega

Heat causing moisture change.

COP (Cooling)

COP=Qc/WCOP = Q_c / W

Coefficient of performance.

Variables

Symbol Description Unit
QQ Heat transfer W
m˙\dot{m} Mass flow rate kg/s
cpc_p Specific heat of air J/(kg·K)
ΔT\Delta T Temperature difference K

Surface Roughness Coefficients

Relative Roughness

Relative roughness is the ratio between absolute roughness and the hydraulic diameter of the pipe or duct. It is a critical parameter when calculating pressure loss using the Colebrook Equation for turbulent flow.

r=kdhr = \frac{k}{d_h}

Where:

  • rr = relative roughness (dimensionless)
  • kk = absolute roughness of the duct surface (m, ft)
  • dhd_h = hydraulic diameter (m, ft)

Duct Material Selection Guide

Material Typical Applications
Galvanized Steel Most common material for comfort air conditioning systems; standard fabricated ductwork
Aluminum Clean room applications, moisture-laden air, special exhaust systems, ornamental duct systems
Stainless Steel Kitchen exhaust, moisture-laden air, fume exhaust systems
Carbon Steel (Black Iron) Flues, stacks, hoods, high-temperature industrial systems, special coating requirements
Copper Chemical exhaust systems, visual/architectural ductwork
Fibreglass Reinforced Plastic (FRP) Chemical exhausts, scrubbers, underground systems — corrosion resistant, self-insulating, excellent sound attenuation
PVC Chemical exhaust, fumes, underground duct systems — corrosion resistant, lightweight, easy to modify
Fabric (Textile) Applications requiring even air distribution
Flex Duct Equipment connections (inner liner supported by helix wire coil)

For turbulent flow in ducts, the friction coefficient depends on both the Reynolds Number and the surface roughness. As surfaces degrade over time (e.g., rust formation on steel), roughness values can increase significantly — rusted steel can reach roughness values up to 100× greater than new commercial steel.

References