💧 HVAC

Pump Head Calculator (Total Dynamic Head)

Calculate total dynamic head (TDH), pump power and motor sizing for HVAC chilled water, condenser water and plumbing systems. IS 9137.

📐 Standard: IS 9137 / HI
✅ Free to use
📄 PDF export
📱 Mobile friendly

ℹ️ About This Calculator

Total Dynamic Head (TDH) is the total resistance a pump must overcome to move fluid through a piping system. It combines static head (elevation difference), friction head (pipe and fitting losses), and pressure head (differential between suction and discharge vessels). TDH directly determines the pump power requirement and motor selection.

For HVAC chilled water systems, the typical TDH range is 15–30m for small systems and 30–60m for large central plant systems. Condenser water systems are typically 20–35m. The system curve (TDH vs. flow) intersects the pump curve at the operating point. Always ensure the pump operates within 70–110% of its BEP (best efficiency point) to avoid excessive vibration and premature wear. IS 9137 governs centrifugal pump testing and rating in India.

📐 TDH and Pump Power Formulas

IS 9137 / HI

TDH = H_static + H_friction + H_velocity + H_pressure

H_friction (Darcy-Weisbach):
  hf = f × (L/D) × (v²/2g)
  f = Moody friction factor (from Colebrook equation)

H_friction (Hazen-Williams for water):
  hf = 10.67 × L × Q^1.852 / (C^1.852 × D^4.87)

Pump Power:
  P_shaft (kW) = ρ × g × Q × TDH / (1000 × η_pump)
  P_motor (kW) = P_shaft / η_motor

Motor selection: next standard size above P_motor × 1.1

❓ Frequently Asked Questions

What is the typical pump efficiency for HVAC centrifugal pumps? +
Modern HVAC centrifugal pumps typically achieve 70–80% efficiency at their best efficiency point (BEP). Smaller pumps (below 5 kW) may be 55–65% efficient. Always select a pump that operates near its BEP at design conditions to maximize efficiency and lifespan.
How do I calculate friction head for a piping system? +
Use the Darcy-Weisbach equation: hf = f × (L/D) × v²/2g. For water systems, the Hazen-Williams method is simpler: use a C value of 130–150 for new steel pipe, 120 for older steel, 150 for copper and plastic. Account for fittings by adding equivalent pipe length — a gate valve adds ~0.5× pipe diameter, an elbow adds ~30× pipe diameter in equivalent length.
What pump speed should I use for chilled water systems? +
Most HVAC chilled water pumps run at 1450 RPM (2-pole, 50Hz) or 960 RPM (4-pole, 50Hz). Variable speed drives (VSDs) are now mandatory for pumps above 7.5 kW in ECBC-compliant buildings. VSDs can reduce pump power by up to 50% at part-load conditions, as power varies with the cube of speed (affinity law).
What is the difference between static head and dynamic head? +
Static head is the height difference between the pump centerline and the highest point of the system — it is constant regardless of flow rate. Dynamic head (friction head) increases with flow rate squared. Total dynamic head (TDH) is the sum of both. For closed loop HVAC systems (chilled water), the static head is zero since the system is pressurized — only friction head applies.
What safety factor should I apply to TDH? +
Standard practice is to add 10–15% to the calculated TDH and flow before selecting the pump. This accounts for fouling of pipes over time, additional future connections, and calculation uncertainties. Do not oversize by more than 25% — an oversized pump runs at a high flow far from BEP, causing excessive noise, vibration, and motor overload.

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⚠️ Disclaimer: For preliminary engineering design only. Verify all results with a licensed engineer before use. Full disclaimer →

💧 Pump Head Calculator
Reference: IS 9137 / HI