💧 HVAC

Pump Head Calculator – Total Dynamic Head (TDH) & Pump Power

Free pump head calculator: total dynamic head (TDH), friction loss and pump power by Darcy-Weisbach for water-supply and HVAC pumps. No sign-up.

📐 Standard: IS 9137 / HI
✅ Free to use
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Pump Head Calculator Calculator
Reference: IS 9137 / HI
💧 HVAC
Free pump head calculator: total dynamic head (TDH), friction loss and pump power by Darcy-Weisbach for water-supply and HVAC pumps. No sign-up.
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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

🧮 Worked Example

Example: A chilled water booster pump must deliver 20 L/s (72 m³/hr) to an overhead tank 25 m above the sump, through piping with an estimated friction loss of 8 m and negligible pressure head. TDH = 25 + 8 + 0.5 (velocity head) = 33.5 m. Shaft power = ρ×g×Q×TDH/(1000×η_pump) = 1000×9.81×0.02×33.5/(1000×0.72) ≈ 9.13 kW. With motor efficiency 90%, P_motor = 9.13/0.90 ≈ 10.14 kW. Adding a 10% margin, the next standard size 11 kW motor is selected.

📊 Pump Head & Velocity Reference (IS 9137 / HI)

Total Dynamic Head (TDH) is the sum of the static lift (vertical rise), the friction loss in pipe and fittings, and any residual pressure needed at the outlet. Keeping pipe velocities in the recommended band controls both friction loss and noise, and is the first thing to check when a pump runs hot or noisy.

Recommended Water Velocities

Pipe dutyVelocity (m/s)Note
Pump suction0.9 – 1.5Low, to protect NPSH
Pump delivery1.5 – 2.5Economic range
General distribution1.0 – 2.0Noise limit ~2.4 m/s
Long risers / mains1.2 – 2.0Watch friction loss

Pump Power

Shaft power P (kW) = (ρ × g × Q × H) / (1000 × ηpump), where Q is flow in m³/s, H is TDH in metres and η is pump efficiency (0.6–0.8 typical). Divide by motor efficiency and add a 10–15% margin, then round up to the next standard motor rating. Undersizing the margin is the usual cause of a pump that cannot meet duty on a hot day.

Velocities are indicative for cold water; verify against the pipe material's friction data and the pump manufacturer's curve.

❓ 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.
How do I calculate pump head for a building? +
Add the static lift (height from the pump to the highest outlet or tank), the friction loss through the pipe and fittings on that route, and the residual pressure required at the top outlet. The total is the Total Dynamic Head. This calculator computes friction by the Darcy-Weisbach method and adds it to your static and residual figures.
What is a good water velocity for pipe sizing? +
Keep suction velocity around 0.9-1.5 m/s to protect NPSH, and delivery velocity around 1.5-2.5 m/s for an economic balance of pipe cost and friction. Staying below about 2.4 m/s also keeps flow noise acceptable in occupied buildings.
How do I size a pump motor in kW? +
Calculate shaft power from flow, head and pump efficiency, divide by the motor efficiency, add a 10-15% margin, then select the next standard motor rating (e.g. 2.2, 3.7, 5.5, 7.5 kW). Always check the duty point against the pump curve rather than sizing on head alone.

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