Maximum Demand Monitoring for Malaysian Commercial and Industrial Facilities

A TNB bill shows the recorded Maximum Demand, but the bill alone does not tell the facility team which operating event created it. A demand-monitoring system fills that gap by recording the 30-minute demand, the time of the monthly maximum and the daily trend behind the result.

First, understand what TNB is measuring

TNB records Maximum Demand (MD) in kilowatts. Its published definition is twice the largest number of kilowatt-hours supplied during any consecutive 30 minutes in the month. Put simply, TNB is not looking only at a momentary spike on a meter display. It is the highest half-hour demand interval that matters.

If a facility uses 450 kWh during its highest 30-minute interval, the corresponding demand is 900 kW. Monthly kWh tells the plant manager how much electricity was consumed. MD shows how much load was placed on the supply system during the busiest interval. The two figures answer different questions.

The time of the peak matters

Under the current Time-of-Use (TOU) schedule for Peninsular Malaysia, effective from 1 July 2025, the Peak Period is 2:00 pm to 10:00 pm, Monday to Friday. The weekday period from 10:00 pm to 2:00 pm the following day, together with the whole of Saturday and Sunday, is Off-Peak.

For a non-domestic medium- or high-voltage customer billed under a TOU category, the relevant Maximum Demand for capacity and network charges is the highest 30-minute demand recorded during the Peak Period. A high load at 11:00 am and the same load at 3:00 pm therefore do not have the same MD cost implication under TOU.

Why Maximum Demand needs to be monitored

On a real site, the peak is rarely caused by one machine alone. For a Malaysian TOU customer, the period after 2:00 pm deserves particular attention. Production may already be at full output while chillers and ventilation systems are carrying the afternoon cooling load. If another compressor, oven, pump or production line starts in that same half-hour, it may establish the billable MD for the month.

Without a recorded curve and timestamp, the facility team may know that the MD was high but still be unable to identify the cause. Monitoring turns a monthly billing figure into operational evidence that can be checked against production and equipment records.

What a useful monitoring system should show

Start at the incoming supply

The safer starting point is a load study. Check the monthly MD trend, the time each peak occurred, the production shift and the equipment operating at that time. The main incomer shows the total demand, but it does not explain the cause. Sub-metering on production feeders, chillers, compressors, pumps or refrigeration circuits makes the discussion much more useful.

Record the value and the time together

A maximum-demand value is much more useful when it includes a timestamp. The facility team can match the time against production records, shift changes, equipment start-up or an HVAC schedule. A configurable demand alarm can also notify operators when the monitored value approaches an internal threshold.

Add branch meters where the total is not enough

From monitoring data to a reduction opportunity

Suppose a TOU customer’s bill shows 1,200 kW MD during the 2:00 pm–10:00 pm Peak Period. The load study finds that a 150 kW auxiliary load can be moved before 2:00 pm, after 10:00 pm or staggered so that it does not overlap with the afternoon production peak. The working target would be 1,050 kW.

The calculation shows why the data is worth collecting; it is not a guaranteed saving. First use the demand report to confirm whether the same 150 kW overlap repeats and which equipment contributes to it. Only then should the site evaluate scheduling, alarms or a separate control project using the actual TNB tariff and operating constraints.

Acrel Maximum Demand monitoring architecture

Acrel provides the field meter and reporting platform needed to see the incoming demand, trace contributing feeders and retain the records for review. The core scope here is monitoring: APM521 calculates demand at the electrical point, while the IoT EMS Platform centralises the monthly report and daily curve.

APM521 for 30-minute Maximum Demand monitoring

The Acrel APM521 multifunction power meter can be installed at the incoming feeder or another agreed monitoring point. It measures real-time demand and records monthly maximum demand with a timestamp for active, reactive and apparent power. The meter also supports demand alarms and Modbus communication, allowing the demand value to be brought into an energy-management platform or the site’s PLC/BMS.

For the comparison to be meaningful, the CT ratio, wiring, meter clock, demand period, sliding-window width, reset date and monitoring point must be commissioned correctly. The APM521 is a customer-side monitoring meter in this application; it does not replace TNB’s revenue meter, and its recorded value should not be presented as the official billing value. During commissioning, compare both readings over several billing intervals and investigate any consistent difference.

Demand reports in the Acrel IoT EMS Platform

For a single incoming meter, the operator can check demand locally or through communication. When a factory has several incomers, transformers or important feeders, the Acrel IoT EMS Platform brings the records into one place. Its Demand Analysis module provides two practical views:

• Maximum Demand Report: queries the maximum demand for each month and shows the time at which it occurred. The facility team can compare different months and trace a peak back to the relevant shift or operating event.
• Demand Monitoring: shows the selected meter’s demand throughout the day. Users can switch between a trend chart and tabular data, select the date and circuit, and export the records for further review.

For a Malaysian TOU customer, the daily view helps the engineer focus on the 2:00 pm–10:00 pm Peak Period. If the monthly report shows that MD occurred at 3:40 pm, the engineer can open that day’s curve, check which feeders increased at the same time and discuss a specific operating change with production. This is more useful than waiting for the next bill and trying to reconstruct the event from memory.