A bore pump can run for long periods and still be a poor candidate for a variable speed drive. The important question is not whether a drive can slow the motor. It is whether the system needs materially less hydraulic work at lower demand, while the pump, motor and controls can operate safely across that range.
That distinction matters when electricity cost is part of the decision. Variable speed drives for bore pumps can support changing flow or pressure requirements, but they also introduce losses and operating constraints. A drive fitted to a fixed or unsuitable duty may add complexity without delivering meaningful bore pump energy savings.
Start with a verdict rather than a product preference. There are three defensible outcomes: an energy case where measured demand variation and the system curve support a saving model; a control case where pressure, surge or operating behaviour improves but energy benefit is limited; or no clear case, where a different pump, tank arrangement or operating strategy deserves attention first. Published Hydrovar variable-speed controls are a product pathway, not evidence that any bore system should use one.
Begin With a Measured Operating Baseline
Before modelling a new control method, establish what the existing arrangement actually does. A useful baseline separates each meaningful duty condition, such as high demand, reduced demand, tank refill, irrigation-zone change or a fixed transfer period. A single monthly energy bill cannot show whether the pump spends time throttled, cycling, bypassing flow or already operating close to one stable point.
For each condition, record the measured flow, pressure or head at identified points, electrical power and operating hours. Note the control state and the system response as well: valve position, bypass operation, tank level, pressure switching and the reason the duty changes. If readings are not taken at the same time, under comparable source and demand conditions, they are much less useful for a savings comparison.
The bore itself needs its own evidence record. Sustainable bore yield and drawdown set what the source can provide. They are not substitutes for total dynamic head, or TDH, which is the head the system requires at a given flow. Likewise, a pump curve is a separate check on how the selected pump performs, while water chemistry remains a component-compatibility issue. Published HydroTouch VSD controls provide a multi-pump control pathway, but not proof that the category fits the installed bore system. Keeping these questions separate prevents a drive from being treated as a remedy for a source or pump-selection problem.
The current submersible bore pump range is the appropriate starting point when the pump and motor family need to be identified. The exact pump and motor documentation is then needed to confirm the approved operating range and the control compatibility for that installed equipment.
Map the System Head Across the Required Duty Range
A speed change affects a pump and a system together. To see whether lower speed can reduce input energy, break the system requirement into the parts that stay relatively constant and the parts that change with flow.
Static head is the elevation or pressure component that remains necessary even when flow falls. Friction head is the resistance in pipework, fittings, valves and other components, and it changes as flow changes. An open discharge with substantial elevation lift may therefore retain much of its head requirement at low flow. A system where friction forms a larger share can have more scope for head to fall as demand reduces.
Build a system curve from the measured or calculated head requirement over the actual operating range, rather than relying on the pump’s nominal duty. Include the relevant pipe paths, pressure requirements, control valves, tanks and changing discharge conditions. If different operating modes use different paths or setpoints, each may require its own curve or clearly stated case.
This is why a statement such as “demand is lower at night” does not establish an energy case. The decision depends on how far the operating point can move, how often it moves and how much of the original head is static. A drive may still be useful for control, but a high static-head component can restrict the reduction in pump power available from slowing the system.
Test Reduced Speed Against the Whole System
Pump affinity laws are useful relationships for interpreting how a centrifugal pump changes with speed. They are not a complete energy calculation for a bore installation. Applying them without the full system curve can make the benefit appear larger than it is, especially where static head remains a substantial part of the duty.
The first check is hydraulic. For each proposed speed and control target, locate the revised operating point against the pump curve and the relevant system curve. Confirm that the resulting flow and pressure meet the actual requirement. Then assess whether minimum and maximum flow conditions, pressure stability and the bore’s sustainable output remain acceptable. A pump operating point above sustainable bore yield is not made suitable by a control system.
The next check is time. Model the annual duty profile using the measured hours spent at each condition, not a convenient snapshot. Compare the baseline input energy with the predicted input energy for the proposed speed and operating time. Electricity cost can then be added to a bounded payback model, together with the installed scope and other documented costs. Without those inputs, an assumed payback period is only a sales figure. The broader APT Water information pathway can help place those measurements within a pump-and-control discussion without turning a published product into final design approval.
For systems with several pumps or a changing lead-lag arrangement, that control category still depends on the pump configuration, the control objective and the required compatibility review.
Account for What the Drive Changes Electrically and Mechanically
The energy model is incomplete if it stops at the water. An external drive has its own losses and heat. Motor efficiency and motor heating can change with operating point, while the quality of the drive output, cable arrangement, output filtering, harmonics and electromagnetic compatibility requirements may affect the design. These are equipment- and installation-specific checks, not universal drive settings.
Submersible motor cooling also deserves separate attention. Water moving past the motor can be part of the cooling arrangement in a bore. At lower flow, there may be less cooling flow, so the motor manufacturer’s documentation and the installation arrangement must be checked. A cooling sleeve may be relevant in some installations, but it cannot be assumed from a general article. Neither lower speed nor a reduced number of starts automatically proves a longer motor life.
Control tuning is another constraint. A poorly configured pressure-control loop can hunt or create excessive pressure variation, which defeats the operating objective. Protection functions, fault handling, source-level behaviour and commissioning responsibilities should be defined before installation.
Compare the Drive With Other Ways to Meet the Objective
An energy decision improves when the alternative is explicit. If the pump is oversized for a steady duty, correct pump selection may address the underlying mismatch more directly than continuous speed reduction. If demand changes between a small number of predictable conditions, a tank, pressure-switch arrangement or operating schedule may deserve comparison. Where throttling is the present control method, the opportunity may be stronger, but it still has to be measured against the actual head profile and the proposed operating range.
Separate the objective before comparing options. Constant pressure, reduced pressure surges, fewer starts, a smaller tank requirement, a changing irrigation flow and lower energy input are not the same objective. A VSD can have a sound control case even when the direct energy model is weak. Equally, an attractive energy estimate may not proceed if motor cooling, output requirements, the bore source or control stability cannot be resolved.
For Perth and wider Western Australian bore applications, the same discipline applies across residential, commercial, irrigation and industrial contexts. Locality does not turn a variable demand profile into proof of savings. The duty record, pipework and source conditions must do that work.
Commissioning Must Be Able to Prove the Result
The commissioning plan should be written before the expected saving is presented. Its purpose is to compare the new arrangement with a defined baseline under comparable conditions, then explain any difference rather than merely reporting a lower power reading at one instant.
At commissioning, confirm the measured flow, pressure or head, real electrical power, speed or control state, and operating time for each agreed duty condition. Record source conditions that can affect the comparison, including drawdown where relevant. Confirm that the control reaches the required target without unstable cycling, and retain the manufacturer-approved pump and motor information used for the setup. The result should also confirm that electrical, cooling and protection requirements have been addressed by the responsible project personnel.
After an agreed operating period, compare energy per delivered outcome across matching duty conditions. A reduced kW reading is not enough if the system is also delivering less flow, lower pressure or fewer operating hours. Conversely, an energy increase may be justified by a different control objective, but that should be named rather than hidden inside a savings claim.
Frequently Asked Questions
Do VSDs Always Save Energy on Bore Pumps?
No. Savings depend on the demand profile, system curve, static-head component, pump and motor behaviour, drive losses and the control objective.
Why Does Static Head Reduce the Savings Opportunity?
Static head remains part of the required head even when flow falls. With less head available to reduce, slowing the pump may change total input power less than expected.
Can a VSD Help Even if Energy Savings Are Limited?
Yes. It may support a variable control objective, reduce pressure surges or change tank and start-stop behaviour, subject to system and equipment checks.
How Should Savings Be Verified?
Compare measured flow, head or pressure, power and operating time for equivalent duty conditions after commissioning, using a documented baseline.
Make the Decision Package Evidence-Ready
The strongest case for a drive is a documented match between changing demand, a system curve with room to reduce friction head, compatible pump and motor operation, and a measured annual duty profile. If that evidence does not support bore pump energy savings, the control benefits may still be valuable, or another system change may be more appropriate.
Before you contact APT Water, prepare measured duty points, operating hours, pressure or head records, pump and motor curves, current control details, source information and any electrical constraints. That package supports a focused review of the energy case, the control case and the measurements needed after commissioning, without assuming a selected product or final project outcome.