Sub-metering and energy monitoring in commercial buildings

What a bill cannot tell you

A bill tells you the building used a certain amount in a month. It cannot tell you that the heating comes on at four in the morning, that something substantial runs all weekend, that one tenant uses four times what another does, or that the saving you were promised last year never materialised.

Half-hourly data and a handful of sub-meters tell you all of those within weeks, and the first three are so common that finding at least one of them is close to routine.

The out-of-hours baseline is the classic finding

Look at consumption at three on a Sunday morning, when the building is empty. Whatever it is using then, it is using every hour of every day, and most of it is doing nothing useful.

That single number is the cheapest piece of energy analysis available, it needs no new hardware if you have half-hourly data already, and in a lot of buildings it is startling.

Where sub-metering earns its money

• Multi-let buildings, where landlord and tenant consumption need separating before anyone can argue about who pays for what.
• Buildings with a large single process or plant item, where you want to know what it actually costs to run.
• Before and after a major measure, so the saving can be demonstrated rather than claimed.
• Where a service charge apportions energy and the apportionment is being questioned.

The honest limitation

Monitoring only saves money if somebody looks at it and then does something. Plenty of buildings have dashboards nobody opens, reporting that goes to an inbox nobody reads, and alarms that were switched off because they were noisy.

Before installing monitoring, it is worth being clear about who will look at it, how often, and what they are empowered to change. Without that it is a capital cost with no return, which is the one thing this measure cannot afford to be.