A building can be well-designed and well-equipped : without smart control, it wastes energy continuously. The BMS (Building Management System) is the brain that runs the HVAC equipment at the right time, at the right output. Properly tuned, it is one of the most cost-effective energy levers there is — and it is now becoming mandatory in tertiary buildings.
BMS, BAS : what are we talking about ?
A BMS (in France, GTB) centrally supervises and controls a building's technical equipment : heating, ventilation, air conditioning, lighting, sometimes energy and security. A BAS / GTC focuses on one technical system (often HVAC). In practice, it decides when an air-handling unit starts, what temperature is maintained, and raises an alert when something drifts.
How a BMS lowers the bill
The savings don't come from a single setting, but from stacking several levers :
- Time scheduling — no heating or cooling at night, at weekends or in unoccupied zones ;
- Setpoint and heating-curve optimisation — producing exactly what's needed, based on outdoor temperature ;
- Free cooling — cooling for free with outside air whenever possible ;
- Demand-controlled ventilation — adjusting airflow to real occupancy (CO₂ sensors) ;
- Anti-overlap — preventing simultaneous heating and cooling ;
- Drift detection — spotting a faulty sensor, a stuck valve, equipment running non-stop ;
- Consumption monitoring — measuring to target the biggest energy users.
What the standards say
The EN ISO 52120-1 standard (which replaced EN 15232) classifies buildings into four automation classes (A to D) and quantifies their energy impact. For offices, moving from standard control (class C) to high-performance control (class A) typically means :
The classes :
- Class A — high-performance BMS, fine and continuous control ;
- Class B — advanced BMS ;
- Class C — standard control (the baseline) ;
- Class D — non energy-efficient (the most wasteful).
👉 The order of magnitude : a well-designed and properly commissioned BMS can save close to a third of a tertiary building's thermal energy, without major works — purely by intelligently controlling the existing installations.
Now an obligation : the BACS decree
The French BACS decree (Building Automation & Control Systems) requires a building automation and control system in many tertiary buildings fitted with HVAC systems, depending on their power :
- existing buildings, systems > 290 kW → by 1 January 2025 ;
- existing buildings, systems > 70 kW → by 1 January 2030 ;
- new buildings, systems > 70 kW → mandatory since 8 April 2024.
The BACS decree is the logical companion to the French tertiary decree (Éco Énergie Tertiaire), which mandates a 40% consumption cut by 2030 : those targets are hard to reach without finely controlling your installations.
🖥️ At Clim Froid Services, we work on BMS commissioning support, point-to-point checks against the functional analysis, control-scenario testing, fault diagnosis and strategy optimisation. Because a BMS only saves energy if it is genuinely commissioned. Let's talk about your installation.
Sources
- EN ISO 52120-1 (replaces EN 15232-1) — Energy performance of buildings — Contribution of building automation, controls and building management (efficiency classes A–D and impact factors).
- Decree no. 2020-887 of 20 July 2020 ("BACS decree") and its amending texts — building automation and control systems for tertiary buildings. Official up-to-date timetable : rt-re-batiment.developpement-durable.gouv.fr
- Éco Énergie Tertiaire scheme (tertiary decree), French Ministry for Ecological Transition — ecologie.gouv.fr
The percentages cited are orders of magnitude from the standard's efficiency factors for office buildings ; actual savings depend on each building and its use.