Fazley Rabbi"The electricity bill went up again, and I have no idea which part of the factory is responsible." The main meter tells you the total for the month. It does not tell you whether the compressor, the dyeing section, the office ACs or the pumps on the roof are behind the increase. Without that, every saving effort is a guess: switch off some lights, tell staff to be careful, and hope.
Sub-metering means measuring electricity on individual circuits, so you can see where it actually goes.
What sub-metering involves
A sub-meter is an energy meter installed on one circuit or distribution board rather than on the whole supply. Many digital energy meters can report their readings over a data connection. Where that is not possible, clamp-on current sensors around the cables can estimate usage. A small gateway collects readings from all the meters and sends them to a dashboard over Wi-Fi or mobile data.
On the dashboard you see usage by circuit, by hour and by day. That is where the useful questions come from.
Where to put the first meters
You do not need a meter on every socket. Start where the big loads are:
- large motors, compressors, chillers and pumps
- each floor or production section
- air conditioning, which in offices and shops is often the biggest load in the hot months
- lighting and general sockets, as one group
If you run a generator during load-shedding, ask your electrician whether the meters can tell grid supply and generator supply apart, so the two are not mixed up in your reports.
Getting started, step by step
- Collect a few months of bills so you know the pattern you are trying to change.
- List your main loads with your electrician, using the distribution board layout.
- Choose four to six circuits that you suspect use the most.
- Have a qualified electrician install the meters or sensors. This is work inside live distribution boards, not a do-it-yourself job.
- Collect data for a few weeks, covering normal working days, holidays and nights.
- Review it together with your production or facilities manager and pick one change to try.
- Measure again after the change, so you know whether it worked.
What to look for in the data
- Night and holiday usage. When nobody is working, usage should drop sharply. If it does not, something is running that should not be: an AC, a compressor, a pump, the lights in a store room.
- Idle running. Machines left on between batches or during the lunch break.
- Everything starting at once. Many loads switching on together at the start of a shift can push demand up. Staggering start-up may help; your electrician can tell you whether it matters for your connection.
- A load that creeps up over weeks. A motor or compressor slowly using more than before can be a sign that it needs maintenance.
- Power factor. Some commercial and industrial connections are charged extra for poor power factor. Ask your electrician or electricity provider whether this applies to you before buying correction equipment.
Honest limits and trade-offs
Monitoring by itself saves nothing; savings come from the changes you make after seeing the data. Clamp-on sensors are quicker to fit but less accurate than proper meters, which is fine for finding waste but not for billing anyone. If you need to divide a bill between tenants in an apartment or commercial building, use proper meters and agree the method with everyone first.
What you can do yourself, and where to get help
You can read your bills, walk the floor at night to see what is running, and decide which changes are acceptable for production. An expert helps with choosing meters, building the gateway and dashboard, and turning raw readings into a clear weekly report. See IoT device development.
A small first step
Meter your main incoming supply plus your three or four largest loads for one month. That is often enough to show where to look first. The IoT pilot project page explains how to keep the trial small and useful, and you can contact me if you would like help planning it.