Finding Wasted Energy With Building Meter Data

Room-level meter data helps identify electricity use that needs checking. Compare 15-minute readings with booking schedules and building needs. Consumption in an empty room may be an AC unit left on, but it may also support security or maintenance. Confirm the cause, fix unnecessary operation, then measure the result again.

A walkthrough, equipment inventory, and lighting survey help explain the readings. Use measurements and site observations together so findings can be tested.

Why can't the electricity bill show you the waste?

Because the bill is one number, for one month, from one meter at the building's incoming supply. It tells you that you spent. It cannot tell you where, or when.

Take a set of multipurpose halls rented out by the event — a campus auditorium, a community hall, a hotel function room. Air conditioning and lighting are switched on by a staff member before the event and switched off by whoever remembers. Ask the manager what one wedding costs in electricity and you get a shrug. Ask what the halls draw on a Tuesday with no bookings and you get a guess.

The manager's instinct is usually right: the AC gets left on. But an instinct cannot be put in a budget, cannot be added to a rental rate, and cannot be defended when the finance director asks why the bill went up 18%. A number can do all three.

That is the whole gap this article is about. Not "does the building waste energy" — almost every building does. The question is how much, in which room, during which hours, and what it costs at your tariff.

What do you measure, and at what resolution?

Two things, at two levels of detail.

Per space, not per building. One digital power meter on the supply to each rented hall or each floor. A building-level meter averages your problem rooms together with your well-behaved ones until the problem disappears into the mean.

Interval data, not monthly totals. An interval reading is simply a consumption snapshot taken on a fixed clock — every 15 minutes, or every minute if the meter and network allow. A 30-day month of 15-minute readings gives 2,880 data points per meter. A monthly bill is one.

From those two, three numbers fall out:

The second row is the finding. The first row is what makes the finding sellable to the owner, because it turns the audit into pricing work rather than a lecture about the environment.

One more note on resolution. Fifteen minutes is enough to see a hall left on overnight. One minute is what you want if you are chasing compressor cycling or a motor that restarts every few minutes. Start at 15 and go finer only on the meter that looks wrong.

What does the data actually reveal?

The same handful of findings show up in building after building. Here is what to look for, without assuming the same cost ranking at every site:

The last row is worth its own sentence. When the sum of your sub-meters — the extra meters installed downstream of the utility's meter — falls 8% short of the building's incoming meter month after month, investigate unmetered circuits, meter accuracy, measurement timing, and losses. These findings can affect installation drawings and billing calculations. Meters used to bill tenants also have to meet applicable transaction-measurement requirements. More on that below.

Here is the data path that produces those rows:

Nothing exotic. Meters speak Modbus over a two-wire RS-485 loop — the plain serial cabling that building automation has used for thirty years — a small local server collects and stores the readings, and the booking calendar supplies the other half of the answer. Much of the analysis comes from joining those two datasets with database queries before changing the control system.

If you want the deeper version of the metering-to-invoice path, I wrote it up in Metering to Invoice. For the case where the meter is an old mechanical dial with no output at all, there is Reading Legacy Utility Meters With ESP32-CAM.

Which fix pays first?

Schedule first. Then setpoints — the target temperatures you ask the air conditioning to hold. Equipment last. Confirm the priority from the site's measurements.

Scheduling is the cheapest lever and the biggest one. A US Department of Energy study by Pacific Northwest National Laboratory (PNNL-25985, 2017) modelled fourteen commercial building types and found that fully applying building controls — mostly correcting schedules, setpoints and operating sequences, not replacing hardware — could cut national commercial building energy use by 29%. The measures that carried the most weight were the boring ones: turn things off when the space is unoccupied, stop running equipment outside its needed hours.

Setpoints come second. Test a change from 20°C to 24°C if measurements and room conditions suggest overcooling. Verify comfort and operational needs; electricity readings alone do not establish that a temperature change is suitable.

Equipment last. Replacing a chiller — the central plant that makes the cold water your air handlers blow over — or relamping to LED is real money with a real payback, and it should be argued from a measured baseline: the before-number you can point back to a year later. Otherwise you buy efficient equipment and keep running it on the same broken schedule.

One design rule sits above all three: the manual override has to survive. Events run late. The committee wants the lights on for teardown. A schedule needs a safe manual-control route for authorised staff when an event runs late. Have a qualified installer design the Auto/Manual controls for each zone, define who may use them, and log each manual operation with its start time and duration. The log is what keeps the report honest without turning the operator into a suspect.

What does Indonesian regulation require?

Two separate regimes touch this work, and they are easy to confuse.

Energy management, if the building is large enough. Permen ESDM No. 8 of 2025 on Energy Management was set on 7 March 2025 and promulgated on 13 March 2025, replacing Permen ESDM 14/2012 (JDIH BPK record). Building operators consuming at least 500 TOE per year fall under a mandatory energy management obligation. TOE — tonnes of oil equivalent — is the standard unit regulators use to compare fuels; 500 TOE works out to roughly 5.8 GWh of electricity a year, about 485,000 kWh a month. That catches large malls, hospitals, integrated campuses and hotel complexes. The obligations are a certified energy manager, a written conservation programme, periodic energy audits and an annual performance report.

Below the threshold, distinguish these specific energy-management duties from other requirements that may still apply to the building. The method in this article does not change — you just run it because it pays, not because you were told to.

Legal metrology for billing meters. UU 2/1981 and Permendag 24/2024 are references for instrument verification. Check the meter type, use, valid verification status, and re-verification interval with the local metrology authority. Do not apply one interval to every meter model or accuracy class.

Rebilling electricity to tenants. Check distribution and resale requirements with PLN and the competent energy authority. Do not assume a no-margin arrangement is automatically exempt from licensing, or that one rule authorises disconnection. Record the basis for unit charges, common-area costs, and allocation in the agreement.

The practical distinction: audit meters and billing meters have different purposes. Audit meters still need suitable measurement and safe installation. Billing meters need the applicable transactional-measurement requirements. Store meter identity and verification evidence with the readings.

How do you run this without instrumenting the whole building?

You do not need a hundred meters to start. You need one month of honest data from the few points that matter.

1. Pick 3–5 points, not 50. The biggest rented spaces, the chiller supply, and the common-area lighting board. These points might cover 60–75% of the bill in an initial estimate; verify the site's actual load distribution.
2. Get one month of interval data. Permanent meters if the budget is there; clamp-on loggers — meters that clip around an existing cable and need no rewiring — rented for a month if it is not. Select loggers that measure the relevant electrical quantities accurately; current alone is not a complete energy measurement.
3. Get the booking schedule for the same month. This is the half that audits skip, and it is the half that makes the data mean something. A spreadsheet of start and end times per room is enough.
4. Compute the split. kWh inside booked hours versus kWh outside them, per room, per day. Publish it as a single ratio — "41% of the halls' electricity was drawn during hours with no booking" identifies a pattern whose cause still needs investigation.
5. Convert to rupiah at the actual tariff, then rank. Use the customer’s tariff class and bill for the period being examined, including applicable time-of-use rates, reactive-power charges, taxes, and other fees. Rank findings by rupiah per month, never by percentage — a 40% saving on a small load loses to a 5% saving on the chiller.
6. Fix the schedule, then re-measure the same way. Same meters, same interval, same overlay, 30 days later.

Step six is the one that gets dropped, and dropping it is what makes energy projects unfalsifiable. Comparable before-and-after measurements make a savings claim reviewable. Account for changes in bookings, weather, and operating conditions too.

What you hand over at the end

Four things, and none of them is a slide deck:

• A baseline. kWh per room per month, split into booked and unbooked hours, for a stated month.
• A ranked finding list. Each line with a rupiah figure per month at the building's own tariff, and the intervention that removes it.
• A control change that actually shipped. Schedules loaded, zones wired to contactors, Auto/Manual selectors in place, manual operations logged.
• A re-measure date. On the calendar, with the same method written down so a different person can repeat it.

If you also want per-room enforcement — cutting supply on non-payment, not just measuring it — the device class for that is covered in Room-Level Energy Control With Smart Breakers.

We are good at costing hardware down to the last rupiah and terrible at costing the hours our buildings run empty. The hall that cooled itself all Sunday did not do anything unusual. It did exactly what it was told, by a schedule nobody had looked at in four years — and the only reason anyone found out is that somebody finally put a meter on it and read the numbers by the hour.