Before renovating, an owner typically looks at the energy certificate first. A reasonable instinct — except the certificate doesn’t say what most people assume it says.
What the certificate calculates, and what it doesn’t
An energy certificate is built on standardised assumptions: average occupancy, standard climate data, typical operating hours, nominal equipment efficiencies. That’s a fine basis for comparing buildings — but it isn’t a description of how this specific building actually runs, day to day.
In reality, a building’s consumption is shaped by:
- actual occupancy and daily scheduling,
- the real, maintained-or-neglected condition of the plant,
- control faults — a badly set schedule or a stuck valve can go unnoticed for years,
- and how the system responds to real weather, not standard climate data.
The “performance gap”
The literature calls this the energy performance gap: multiple studies find actual consumption can deviate from the certificate’s calculated value by 30-50% or more, in either direction. Some buildings look good on paper and run poorly; others are the opposite.
The certificate tells you how the building is supposed to perform. Measurement tells you how it actually performs.
What real-time measurement shows that paper doesn’t
When you measure continuously by zone and by system — not just aggregate building consumption, but heating, ventilation, lighting, and cooling separately — patterns become visible that a certificate says nothing about:
- heating or cooling running while the building is unoccupied,
- one zone systematically overheated while its neighbour is underheated,
- ventilation scheduling that doesn’t track actual occupancy,
- a piece of equipment whose consumption creeps up gradually without ever registering as a hard fault.
We go into more detail on these patterns, and how to flag them automatically, in another post.
Red flags only measurement reveals
- Overnight or weekend heating/cooling load while the building is unused.
- A zone temperature that never stabilises over several hours.
- A baseline load that creeps up gradually with no explanation (the “never switched off” load).
- A significant gap between two zones with an otherwise similar use pattern.
What should an owner actually do?
We’re not suggesting the certificate is worthless — it’s still needed for regulatory compliance. What we’d suggest is getting real data before committing to a renovation budget: a few weeks of zone-level measurement often points at the spend far more precisely than a static document ever could.
If you’re curious what measurement would show in your building, get in touch — let’s talk about where the fastest payback is.