A fan-upgrade calculation starts with a question: what electrical energy did the system use while delivering a defined air duty, and what would it have used under the same conditions after the change? A motor nameplate, a catalogue efficiency claim or a single speed setting cannot answer that question. The video shows a measurement and verification workflow; its numbers are teaching values, not a LONGWELL test result or customer saving.
Before replacing a fan, decide which loads you will meter, how operating conditions will be matched, and which records will remain available for review. That plan is more useful than assuming a fixed percentage saving from a change to EC control.
Draw the electrical measurement boundary first
Record whether the meter includes the motor, variable-speed drive, EC controller, control transformer and any auxiliary load. Use the same boundary for the old and new arrangements. If a component is added or removed, show it as a separate line instead of silently changing what “fan power” means. Meter true electrical power in kilowatts; current alone does not account for voltage and power factor.
Also record delivered airflow, static-pressure boundary, fan command, damper position and relevant operating state for each interval. A lower power reading alongside lower required airflow is not automatically an efficiency gain. The drawing below is a measurement plan, not a wiring or product test diagram.
Capture a baseline before the old fan disappears
Log enough intervals to represent the operating modes that materially affect annual energy use. The required duration depends on the site’s schedule and variability; a universal one-week window is not a substitute for seasonal evidence. Keep timestamped meter data, operating hours, airflow or pressure observations, weather or production variables where relevant, and a record of sensor location and calibration.
The baseline must describe the service the system provided. A filter change, damper adjustment, altered occupancy or different process load may change fan power independently of the new fan. Document these conditions before removal, then define how the reporting period will be matched or adjusted. The US Department of Energy measurement and verification guidance describes how project savings are quantified under a stated measurement plan.
Integrate measured power into energy
For each logged interval, multiply average real power by its duration. Sum those interval values to obtain kilowatt-hours. If the system has different operating modes, retain them rather than collapsing a month into one guessed average. Confirm that missing meter data and outliers have an explicit treatment. An annual estimate can then use documented operating schedules and representative conditions; label it an estimate until post-installation data are available.
Fan laws can help screen a proposed speed change, but the simple cubic relation applies to comparable conditions along a system curve. Installed losses, control method and motor or drive efficiency can change the result. A damper-controlled baseline does not necessarily have the same part-load power profile as a speed-controlled system. Use the selected model’s current curve and a system calculation to form a forecast, then meter the installed system to verify it. The DOE fan-systems resources provide a broader framework for assessing the whole system.
Make every baseline adjustment visible
Compare reporting-period energy with the baseline adjusted to equivalent service and operating conditions. State each adjustment’s sign, size, reason and source data. Keep the unadjusted measurement as well so a reviewer can reproduce the bridge. If the duty changed too much to compare credibly, call the result a modeled estimate and describe its uncertainty.
The video illustrates the arithmetic with an adjusted baseline of 17,400 kWh and reporting energy of 12,900 kWh. The difference is 4,500 kWh, or 25.9% of the adjusted baseline. Its illustrative uncertainty range is 3,800–5,200 kWh. None of these values is a measured LONGWELL fan rating, customer case or savings guarantee.
Evaluate the fan at its actual duty point
The company’s EC250 catalogue identifies LWBE3G250 variants and their model-specific curves and drawings; those documents establish candidate hardware and selection inputs, not an upgrade’s energy saving. The LONGWELL EC backward-curved fan family is a place to identify options for an engineering review. Match the exact suffix, voltage, control interface, airflow, static pressure, installation geometry and current revision before comparing a selected fan with an existing installation.
A photograph or family page cannot show the installed operating point. Ask for the specific curve, drawing and electrical data, then test the proposed arrangement at the service duty. For a related discussion of why site conditions dominate a generic percentage, see the EC fan savings guide.
Report a result that someone else can audit
Retain the before-and-after meter extracts, interval calculations, airflow and pressure checks, adjustment log, excluded data, and assumptions about annual operation. Present energy in kWh separately from cost. Apply the site’s tariff only after energy is established, and treat demand charges, maintenance or cooling effects as separate analyses supported by their own evidence. State uncertainty or a range when measurement and operating conditions warrant it.
The useful output is a workbook and measurement plan that another engineer can reproduce. Where the baseline is missing or the delivered duty cannot be matched, report a forecast with those limits clearly shown rather than a verified saving.
