HVAC Chilled-Water Loops
Chilled-water loops circulate chilled water between a chiller plant and AHU coils. Friction is dominated by long horizontal runs + many fittings; static head is typically zero (closed loop). VFDs are standard for variable-volume loops to track building load.
Target industries
Commercial HVAC Data center cooling District energyRecommended calculation methods
- Darcy-Weisbach (precision required for low ΔT designs)
- Hazen-Williams (legacy designs)
Key design factors
- Closed-loop static head ≈ 0 — TDH = friction only
- Coil + valve + fitting losses dominate; pipe friction often < 30% of TDH
- Variable-volume control via 2-way valves + VFD primary pump
- Air separation + expansion tank sizing
Common pitfalls
- Constant-volume design with 2-way valves → starved coils at part load
- Underestimating fitting K-values in tight mechanical rooms
- Missing low-flow protection on chiller evaporator side