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Total Dynamic Head (TDH) Calculator for Pumps
Add static lift, required pressure head, and friction losses to calculate pump TDH.
Method record
What this calculator measures
Total dynamic head is the energy per unit weight the pump must add at the design flow. Friction is flow-dependent, while static elevation is not.
TDH = static lift + (PSI × 2.31) + friction loss Use it correctly
Calculation steps
- Define suction and discharge reference points.
- Convert required pressure to head.
- Add friction at design flow.
Applicability
Use the model within its limits
Include suction losses, velocity head, equipment losses, and pressure differences where the system requires them.
What this result represents
- System
- Pump
- Formula
- TDH = static lift + (PSI × 2.31) + friction loss
- Review
- Verify safety-sensitive work with qualified guidance.
Worked Field Example
Worked Example: Commercial Cooling Tower Circulation TDH
Field Scenario: Calculating Total Dynamic Head for an open-loop cooling tower circulating pump discharging 250 GPM through a chiller condenser.
Given Input Parameters
Step-by-Step Mathematical Solution
- Static Lift h_static = 28.0 ft.
- Discharge Pressure Head h_press = 15.0 PSI × 2.307 = 34.6 ft.
- Total Friction & Equipment Loss h_friction = 2.4 + 16.8 + 12.0 = 31.2 ft.
- Total Dynamic Head: TDH = 28.0 + 34.6 + 31.2 = 93.8 ft (40.6 PSI).
93.8 feet TDH (40.6 PSI total operating head).
Professional Guidance: Select a centrifugal pump whose Best Efficiency Point (BEP) matches 250 GPM at 94 ft TDH.
Quick Answer & Key Principles
How to Calculate Total Dynamic Head (TDH) for Pumps
Direct Answer: Total Dynamic Head (TDH) is the total equivalent vertical height in feet that a pump must push liquid against. Calculate TDH by summing static lift, required operating pressure head, and friction loss.
TDH = Static Elevation Head (ft) + Pressure Head (PSI × 2.31) + Friction Head Loss (ft) - Static Elevation Head: The vertical distance in feet from liquid source level to the highest discharge elevation.
- Pressure Head: Operating pressure required at the system end, converted: Head (ft) = PSI × 2.31.
- Friction Head Loss: Energy loss from fluid drag along pipe walls and fittings (via Hazen-Williams).
- Velocity Head: Fluid kinetic energy (V² / 2g), which is negligible (<1-2 ft) in standard low-velocity piping.
Engineering FAQs
Frequently Asked Questions
What is the exact formula for Total Dynamic Head (TDH)?
TDH = h_static + h_pressure + h_friction + h_velocity. In closed recirculating loops where the pump discharges back into the same closed circuit, static lift cancels out (h_static = 0), and TDH consists solely of friction losses through pipe, fittings, and heat exchangers.
Why is velocity head often neglected in preliminary TDH calculations?
Velocity head (h_v = v² / 2g) represents kinetic energy. In water distribution systems where velocities are maintained between 4 and 8 ft/s, velocity head is only 0.25 to 1.0 foot of head, which is usually well within standard engineering design margins.
How does overestimating TDH harm a pumping system?
Specifying a pump designed for excessive TDH causes the pump to operate far to the right of its Best Efficiency Point (BEP) at lower actual head, drawing excessive motor amperage, causing motor overload trips, and risking cavitation.