Tecnobosque Wildfire Knowledge Graph · Water Systems
Reference Concept · v1.0Definition → relationship → calculation → evidence context
Total Dynamic Head (TDH) is the total head a pump must overcome at a specified flow, combining elevation change, friction and minor losses, and any required residual discharge pressure.
TDH
What is total dynamic head (tdh)?
TDH is an energy-per-unit-weight representation of everything the pump must overcome. Because friction loss rises strongly with flow, TDH is not one fixed property of a hose system.
Pump operating flow is found where the system requirement meets the pump performance curve. Quoting only a pump’s headline maximum flow or maximum head can therefore be misleading.
Why it matters
For independent wildfire-preparation water systems, pump flow and head must be evaluated together. A pump’s maximum flow at zero head is not the flow it will deliver through a real hose network.
A pump does not only lift water uphill. It must also overcome energy losses through hose, fittings and valves and still deliver useful pressure at the sprinkler or nozzle.
H_TDH = H_static + h_f + Σh_minor + H_pressureAll terms must be expressed as compatible head units, such as metres or feet of water. Pump selection then uses the manufacturer’s performance curve at the required flow.
Elevation difference between source and discharge.
Distributed energy loss along hose or pipe.
Losses through fittings, valves, entrances and other local components.
Head equivalent of the residual pressure needed at the outlet.
Simplified pump-head requirement
A system requires 12 m of elevation lift, 8 m of hose/fitting loss at the target flow and 20 m of residual pressure head.
TDH = 12 + 8 + 20TDH = 40 mSelect a pump that can deliver the required flow at about 40 m head, using its performance curve.If the flow changes, friction loss changes and the operating point must be recalculated.
What controls or changes this quantity?
Friction loss generally increases rapidly as flow rises.
Larger internal diameter can sharply reduce friction loss for the same flow.
Longer runs increase distributed friction loss.
Static lift and required sprinkler/nozzle pressure add directly to system head.
Engineering context
Elevation component independent of friction.
Flow-dependent friction and fitting losses.
Useful pressure that must remain at the discharge device.
Manufacturer relationship between delivered flow and head.
How to interpret it correctly
- Calculate TDH at the intended operating flow, not just at zero flow.
- Use internal hose diameter and realistic length/fitting assumptions.
- Match the resulting duty point to a pump curve.
- Keep a safety margin for real installation losses without substituting arbitrary oversizing for calculation.
Use the calculator as a transparent technical aid and keep its assumptions explicit.Open Wildfire Water Pump Sizing Calculator →
Why it matters in wildfire analysis
A pump advertised at a high maximum flow can deliver far less when lifting water uphill through long small-diameter hose. TDH makes that difference visible.
Tecnobosque links TDH to hose friction and sprinkler runtime so storage, pump and distribution are sized as one system.
Limitations and boundaries
- Simple calculators may not reproduce transient pressure, pump priming, cavitation or complex branched networks.
- Manufacturer pump curves and actual hose characteristics should govern final equipment selection.
- A wildfire-preparation water system must not be assumed to provide firefighter protection or safe manual operation during evacuation conditions.
Total Dynamic Head (TDH) FAQ
What is Total Dynamic Head?
It is the total head a pump must overcome at a specified flow, including elevation, friction, fittings and required discharge pressure.
Is TDH the same as elevation lift?
No. Elevation is only the static component; real systems also have dynamic losses and outlet-pressure requirements.
Why does TDH change with flow?
Because hose and fitting friction losses depend on flow rate.
How do I select a pump from TDH?
Find a pump whose performance curve delivers the required flow at the calculated TDH.
Total dynamic head: avoid a common pump-sizing error
Total dynamic head (TDH) is the head the pump must overcome at a specified operating flow. In a simplified system it includes the static elevation difference, friction losses in hose and fittings, and the required delivery pressure expressed as head. It is not just the physical height between a tank and a sprinkler.
Worked example: suppose the outlet is 12 m above the pump, frictional losses at the intended flow correspond to 9 m of water head, and a nozzle requires another 20 m of pressure head. Ignoring inlet-side complications and other losses, the pump must provide roughly 41 m of total head at the required flow. A pump advertised as capable of 41 m only at zero flow would not meet this duty point.
Flow and head must be read together on the manufacturer’s pump curve, including efficiency and the available suction conditions. For temporary wildfire protection, such calculations are planning aids; actual system design needs a qualified installer and adherence to local water, electrical and fire-safety requirements.
Use the water-pump sizing calculator to test transparent assumptions.