Chilled Water Pipe Sizing & Hazen-Williams Engine
Sizes Schedule 40 carbon steel / GI chilled water supply and return headers using the Hazen-Williams formulation ($C=120$). Enforces ASHRAE 90.1 dual screening criteria for maximum velocity ($\le 8.5\text{ FPS}$) and head loss rate ($\le 4.0\text{ ft / 100 ft}$).
Governing Engineering Standards & Calculation Model (Hazen-Williams & ASHRAE 90.1)
1. Thermodynamic Water Flow Rate Equation
Based on the specific heat of chilled water ($1.0 \text{ BTU/lb}\cdot^\circ\text{F}$) and standard density ($8.33 \text{ lb/gal}$):
Q (GPM) = (Capacity × 24.0) / ΔT
Flow (L/s) = Q × 0.06309
Flow (m³/h) = Q × 0.2271
2. Hazen-Williams US Customary Frictional Head Loss
The head loss per 100 feet of pipe is determined using the Hazen-Williams empirical equation with roughness coefficient C = 120 (standard commercial schedule 40 mild steel and galvanized pipe in closed hydronic loops):
Velocity V = (0.408 × Q) / (d_i)² (FPS)
Where Q is fluid flow in US Gallons per Minute (GPM) and d_i is actual inside diameter in inches.
This calculation provides preliminary engineering screening and pipe diameter selection for initial spatial layout, shaft clearance, and pumping preliminary estimates. Detailed hydraulic distribution networks require dynamic balancing valve calculations, 3D piping thermal expansion loop analysis per ASME B31.9, chiller evaporator minimum flow rate validation, and hydraulic network simulation verified by a licensed mechanical engineer.