Knowledge baseEN ISO 52120-1
classes A to D, and why class B is the benchmark
EN ISO 52120-1:2022 (which replaced EN 15232-1) classifies building automation and control systems by how much they contribute to a building's energy performance. Bisly delivers class B functions as standard and class A on request, with a function-by-function table for tenders.
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The four classes
What each class means
| Class | Description | Typical use |
|---|---|---|
| A | High energy performance BACS and technical building management (TBM): demand-driven control throughout, with active optimisation | Buildings targeting top certification levels |
| B | Advanced BACS with some specific TBM functions: room-level control communicating with the central system, demand-controlled ventilation, monitoring and alarms | New non-residential buildings; German GModG § 56 benchmark |
| C | Standard BACS — the reference class for energy calculations | Minimum in most existing buildings |
| D | Non-energy-efficient BACS | To be upgraded |
Class descriptions summarised from EN ISO 52120-1:2022.
In practice
What a class B building does every day
01
Room by room
Each room controls its own temperature and communicates with the central system, so setpoints follow schedules and occupancy.
02
Plant follows demand
Heat generation, distribution and ventilation adapt to the real load instead of running on fixed curves.
03
Air on demand
Ventilation driven by CO₂ or occupancy per zone.
04
Light on demand
Presence detection and daylight dimming; blinds by sun position.
05
Watched continuously
Energy monitoring, fault detection and alarms, with data kept for benchmarking.
Why it matters
Class B in regulation and tenders
The EPBD defines what a BACS must be able to do; EN ISO 52120-1 is the standard engineers use to specify how well it does it. German law (GModG § 56) uses class B functions as the benchmark, and tenders across the Greater Region increasingly ask for a function-by-function class declaration.
Because Bisly is configured rather than programmed, class B functions come as standard settings rather than custom engineering — one reason the system costs less than conventional automation at the same class.
Questions