How To Fill Simplified Tdh Calculation Worksheet Example

Calculate your Total Dynamic Head (TDH) with this interactive tool. Follow our expert guide below to understand how to properly fill out the simplified TDH calculation worksheet.

Comprehensive Guide: How to Fill Simplified TDH Calculation Worksheet

The Total Dynamic Head (TDH) calculation is a critical component in designing and operating pumping systems. It represents the total resistance that a pump must overcome to move fluid through a system. This guide will walk you through each step of filling out a simplified TDH calculation worksheet, explaining the key components and providing practical examples.

Understanding the Components of TDH

TDH consists of four main components that must be calculated and summed:

1. Elevation Head (H_e): The vertical distance the fluid must be lifted
2. Friction Head (H_f): The resistance caused by fluid moving through pipes and fittings
3. Pressure Head (H_p): The pressure difference between the suction and discharge points
4. Velocity Head (H_v): The energy required to maintain the fluid’s velocity (often negligible in most systems)

The total TDH is calculated as: TDH = H_e + H_f + H_p + H_v

Step-by-Step Guide to Filling the Worksheet

1. System Information Section

Begin by documenting basic information about your pumping system:

• Fluid Type: Specify whether you’re pumping water, fuel, chemical solutions, or other fluids. Different fluids have different viscosities and specific gravities that affect calculations.
• Flow Rate: Enter the required flow rate in gallons per minute (GPM) or liters per minute (LPM). This is typically determined by your system requirements.
• Pipe Material: Document the material of your piping system (PVC, steel, copper, etc.). Different materials have different roughness coefficients that affect friction losses.
• Pipe Diameter: Record the internal diameter of your pipes in inches or millimeters. Larger diameters generally result in lower friction losses.

2. Elevation Head Calculation

Elevation head is typically the easiest component to calculate. It represents the vertical distance between the fluid source and its destination.

1. Measure the vertical distance from the water surface at the source to the water surface at the destination
2. If pumping uphill, this value is positive. If pumping downhill, it can be negative (though pumps still need to overcome system resistance)
3. For multi-level systems, calculate the net elevation change by summing all vertical rises and falls

Scenario	Elevation Change	Elevation Head
Ground-level tank to rooftop tank (50 ft height difference)	+50 ft	50 ft
Basement sump to ground-level discharge	+12 ft	12 ft
Reservoir to lower treatment plant	-25 ft	0 ft (pump still needs to overcome friction)

3. Friction Head Calculation

Friction head represents the energy lost due to fluid moving through pipes, fittings, and valves. This is typically the most complex part of TDH calculation.

Pipe Friction: Use the Hazen-Williams equation for water or the Darcy-Weisbach equation for other fluids. Most engineers use published friction loss tables or software for these calculations.

The basic formula for pipe friction is:

H_f = (K × Q^1.85) / (C^1.85 × D^4.87)

Where:

• H_f = Friction head loss (feet per 100 feet of pipe)
• K = Conversion constant (1.318 for US units)
• Q = Flow rate (GPM)
• C = Hazen-Williams roughness coefficient
• D = Inside diameter of pipe (inches)

Pipe Material	Hazen-Williams C Factor
New steel pipe	140
New cast iron pipe	130
PVC pipe	150
HDPE pipe	150
Copper tubing	140
Old steel pipe (corroded)	100

Fitting and Valve Losses: Each fitting and valve in the system creates additional friction. These are typically expressed as equivalent lengths of straight pipe or as loss coefficients (K factors).

Common equivalent lengths for fittings (in feet of straight pipe):

• 45° elbow: 1-2 ft
• 90° elbow (standard): 3-5 ft
• 90° elbow (long radius): 2-3 ft
• Tee (straight through): 1-2 ft
• Tee (branch flow): 4-6 ft
• Gate valve (fully open): 1-2 ft
• Globe valve (fully open): 10-15 ft
• Check valve: 5-10 ft

4. Pressure Head Calculation

Pressure head accounts for any pressure differences between the suction and discharge points of the system.

1. Determine the pressure at the suction point (P_s)
2. Determine the required pressure at the discharge point (P_d)
3. Calculate the difference: ΔP = P_d – P_s
4. Convert pressure to head: H_p = (ΔP × 2.31) / SG
   • 2.31 converts psi to feet of head for water
   • SG = Specific gravity of the fluid (1.0 for water)

Example: If your system requires 30 psi at the discharge and you have 5 psi at the suction with water (SG=1.0):

H_p = ((30 – 5) × 2.31) / 1.0 = 57.75 feet

5. Velocity Head Calculation

Velocity head is usually negligible in most pumping systems but should be calculated for completeness:

H_v = v² / (2g)

Where:

• v = fluid velocity (ft/s)
• g = gravitational acceleration (32.2 ft/s²)

For a system with water moving at 10 ft/s:

H_v = (10)² / (2 × 32.2) = 1.55 feet

Common Mistakes to Avoid

• Ignoring minor losses: Fittings, valves, and other components can contribute significantly to total head loss, especially in systems with many turns or control valves.
• Using incorrect pipe diameters: Always use the internal diameter, not the nominal pipe size. Schedule 40 and Schedule 80 pipes of the same nominal size have different internal diameters.
• Forgetting about specific gravity: When pumping fluids other than water, always account for the specific gravity in your calculations.
• Neglecting system changes over time: Pipe roughness increases with age and corrosion, so your TDH will increase over the life of the system.
• Miscounting elevation changes: Always measure from water surface to water surface, not from pipe to pipe or tank bottom to tank bottom.

Practical Example: Residential Water Boosting System

Let’s work through a complete example for a residential water pressure boosting system:

System Parameters:

• Flow rate: 20 GPM
• Pipe: 1″ copper (ID = 1.025″)
• Total pipe length: 150 ft
• Elevation change: +25 ft (from basement to second floor)
• Fittings: 8 standard 90° elbows, 3 gate valves
• Required discharge pressure: 40 psi
• Suction pressure: 20 psi

Step 1: Elevation Head

H_e = 25 ft (direct from measurement)

Step 2: Friction Head

First, calculate pipe friction using the Hazen-Williams equation:

For copper pipe, C = 140

H_f = (1.318 × 20^1.85) / (140^1.85 × 1.025^4.87) = 1.85 ft per 100 ft

Total pipe friction = (1.85/100) × 150 = 2.78 ft

Now add fitting equivalents:

• 8 × 90° elbows = 8 × 4 ft = 32 ft equivalent
• 3 × gate valves = 3 × 1.5 ft = 4.5 ft equivalent
• Total equivalent length = 32 + 4.5 = 36.5 ft

Friction for equivalent length = (1.85/100) × 36.5 = 0.675 ft

Total H_f = 2.78 + 0.675 = 3.46 ft

Step 3: Pressure Head

ΔP = 40 psi – 20 psi = 20 psi

H_p = (20 × 2.31) / 1.0 = 46.2 ft

Step 4: Velocity Head

First calculate velocity:

Area = π × (1.025/12)²/4 = 0.00573 ft²

Velocity = (20 GPM × 0.002228 ft³/s per GPM) / 0.00573 = 7.75 ft/s

H_v = (7.75)² / (2 × 32.2) = 0.93 ft

Step 5: Total Dynamic Head

TDH = H_e + H_f + H_p + H_v = 25 + 3.46 + 46.2 + 0.93 = 75.59 ft

For this system, you would need a pump capable of delivering 20 GPM at 76 feet of head (rounding up for safety).

Advanced Considerations

For more complex systems, consider these additional factors:

• Viscosity effects: High-viscosity fluids require adjustments to friction loss calculations
• Temperature effects: Fluid viscosity changes with temperature, affecting friction losses
• Cavitation risks: Ensure Net Positive Suction Head Available (NPSHa) exceeds NPSH Required (NPSHr)
• System curves: Plot the system curve to understand how TDH changes with flow rate
• Parallel/series operations: For multiple pumps, calculate combined performance characteristics

Tools and Resources

While manual calculations are valuable for understanding, several tools can simplify TDH calculations:

• Pipe friction calculators: Online tools that compute friction losses based on pipe characteristics
• Pump selection software: Programs like Pump-Flo or manufacturer-specific tools
• CFD software: For complex systems, Computational Fluid Dynamics can model flow patterns
• Mobile apps: Many pump manufacturers offer TDH calculator apps

Remember that while these tools are helpful, understanding the underlying principles is crucial for verifying results and troubleshooting system issues.

Maintenance and Re-evaluation

TDH isn’t a “set and forget” calculation. Regular maintenance and system checks are essential:

1. Annual inspections: Check for pipe corrosion, scale buildup, or other changes that could increase friction
2. Performance monitoring: Track pump performance over time to detect increases in required TDH
3. System modifications: Any changes to the piping system (new branches, additional fittings) require TDH recalculation
4. Fluid changes: If the pumped fluid changes (different viscosity or specific gravity), recalculate TDH

By regularly reviewing your TDH calculations, you can identify potential issues before they become serious problems, ensuring your pumping system operates efficiently throughout its lifespan.

Authoritative Resources on TDH Calculations

U.S. Department of Energy – Pumping System Assessment Tool Hydraulic Institute – Pump Standards EPA – Pumping System Assessment Tool Sourcebook