BMS, supervision, hypervision, BACS: the building-operations glossary

Building-operations vocabulary mixes three registers that are almost never told apart: legal terms (BACS is defined in the French construction code), normative terms (control classes come from an ISO standard), and commercial terms each vendor defines its own way — « hypervision », « BOS », « smart building ».

That confusion has a real cost: it makes people buy the wrong thing. The most expensive example in the French market is the « class B » the BACS Decree never required (see below).

Each definition below states its status: legal, normative, industry consensus, or marketing vocabulary. Where sources diverge, we say so instead of picking a side.

BACS — legal term. Building Automation and Control System. Article R175-1 of the French construction and housing code defines it as any system comprising all the products, software and engineering services able to support the energy-efficient, economical and safe operation of a building's technical systems. It is a transposition of the European EPBD definition. It is the only one of these five terms with an enforceable definition.

GTB — dominant French usage. Gestion Technique du Bâtiment: the computerised system that regulates and supervises technical installations (heating, ventilation, cooling, DHW, lighting). The official BACS Decree application guide states the equivalence itself: a BACS « corresponds to a building technical management system (GTB) ». In practice GTB and BACS name the same thing — one in the trade's language, the other in the law's.

GTC — term with no primary source. Gestion Technique Centralisée. Two readings coexist among serious sources: either a narrower scope (a single technical lot, with the GTB aggregating several GTCs), or an earlier generation of equipment limited to status reporting. No regulation, no official guide and no standard uses the term. Any confident claim about GTC is commercial usage, not definition.

BMS / BAS — English commercial usage. Building Management System and Building Automation System: the common English equivalents of GTB, with no normative definition of their own. One trap: ISO 52120-1 formally separates automation and control (BAC) from technical building management (TBM). A scope advertised as « BAS » may therefore cover only part of what the law calls BACS.

Classes A to D come from NF EN ISO 52120-1 (2022, which replaced EN 15232-1). They rank the control functions present, use by use — heating, cooling, DHW, lighting, auxiliaries. D covers non-performing systems, C standard functions, B advanced functions, A high-energy-performance functions.

The received wisdom. Almost all French commercial content — installers, brokers, BMS vendors — states that « the BACS Decree requires class B ». That is false.

Neither decree no. 2020-887, nor decree no. 2023-259, nor articles R175-1 to R175-3 of the construction code cite any class or any standard. The decree mandates functionalities: continuously tracking and analysing consumption per functional zone at hourly resolution, benchmarking the building's efficiency against reference values, detecting efficiency losses, being interoperable with technical systems, and allowing manual shutdown.

The ministry's application guide (version 2, January 2026) is explicit: BACS categorised in class C are deemed to meet all regulatory requirements.

So where does « class B » come from? From the BAT-TH-116 energy-savings-certificate (CEE) scheme, which conditions a subsidy on class A or B. That is a funding condition, not a compliance one. Confusing the two leads to over-scoping a project — or wrongly rejecting a compliant installation.

Two nuances that matter: the same guide calls class C a minimum and invites operators to assess investing in A or B; and a class describes functions present, never measured performance. A poorly commissioned class-A system guarantees no savings.

Supervision — established usage. Real-time operation of technical installations: acquiring measurements, visualising them, handling alarms, issuing commands. The term is old, shared with industrial computing (SCADA) and cybersecurity, and its meaning is stable.

Hypervision — marketing vocabulary. Used in the French-speaking market for a software layer sitting above several supervision systems or BMS, aggregating their data into a single interface.

We sell a tier that carries this name. So here is what verification actually returns:

• The term has no normative or regulatory definition. It appears in neither NF EN ISO 52120-1, nor the ISO 16484 series, nor the BACS Decree texts, nor the ISA-95 hierarchy, nor France's ANSSI « security supervision » guides.
• Sources diverge on the very axis of the distinction. For some, hypervision means multi-site (a portfolio). For others, multi-domain on a single site (BMS + security + fire). The same product therefore qualifies under one definition and not the other.
• It has circulated in the French trade press since 2014 without stabilising.
• It is French-specific: the international equivalent is closer to PSIM or « single pane of glass ».
• In IT, « hypervisor » means virtualisation. To a CIO, the word evokes VMware first.

What this means for a buyer: do not judge a tool on the word. Ask about the capability — does it consolidate several sites? several systems? does it correlate their data, or merely juxtapose them in tabs? That is verifiable; the word is not.

BOS — Building Operating System. A software layer that centralises and normalises building data so third-party applications can use it. In the Smart Buildings Alliance doctrine, the BOS is « the heart of the BIS », the conductor of data governance. A structuring term in the French industry, but with no normative definition.

BIS — Building Information System. Still in SBA doctrine: the overall architecture of a building's information system — applications, systems and data flows — organised around the BOS.

R2S (Ready2Services) — label. French connected-building label, a reference framework published by the Smart Buildings Alliance and awarded by Certivéa. It assesses a tertiary building's ability to host services, around foundations such as independent layered architecture, interoperability, IP as a standard, data openness and security.

BOS or BMS? They are not competitors but layers: the BMS regulates equipment, the BOS exposes data above it. A vendor presenting its BOS as a BMS replacement is conflating the two.

BIM — Building Information Modelling. The process of producing and structurally managing information about an asset across its life cycle. The ISO 19650 series sets the concepts and information-management requirements. BIM is a process, not a file.

IFC — Industry Foundation Classes. The open, vendor-neutral exchange format for BIM, developed by buildingSMART International and standardised as ISO 16739-1 (2024 edition). This is what you import to get a model usable independently of the design tool.

Digital twin — a digital representation of a real-world entity, synchronised with it, allowing it to be observed and acted upon. ISO/IEC 30173 (2023) frames the term, but commercial usage stretches it a long way: a 3D model without live data is not a digital twin, it is a 3D model.

ANSI/ISA-18.2 — standard. « Management of Alarm Systems for the Process Industries » (2016 edition). It defines a full alarm-system life cycle: philosophy, identification, rationalisation, design, operation, maintenance, monitoring and change management. It also defines an alarm's states — normal, unacknowledged, acknowledged, RTN unacknowledged, shelved, suppressed, out of service.

EEMUA 191 — the British reference guide on alarm-system design and management, often cited alongside ISA-18.2.

What this changes in practice: an alarm following that life cycle is an object with a state, an owner and an audit trail, not a threshold email that gets lost. It is the difference between a control room and an inbox.

Tertiary Decree — the Éco Énergie Tertiaire scheme (decree no. 2019-771). Final-energy reduction for tertiary buildings above 1,000 m²: −40% by 2030, −50% by 2040, −60% by 2050, in relative or absolute terms. Our dedicated page covers duties, deadlines and penalties.

BACS Decree — a separate obligation (decrees no. 2020-887 and no. 2023-259) to fit tertiary buildings with an automation and control system. In force since 1 January 2025 above 290 kW; postponed to 1 January 2030 for the 70–290 kW band in existing buildings.

OPERAT — the public platform run by ADEME where the annual consumption filing for tertiary buildings takes place.

EFA — entité fonctionnelle assujettie, the scheme's declaration unit: premises hosting a single activity, operated by a single regulated party. Splitting a portfolio into EFAs is what sinks the most filings.

HDD / DJU — heating degree days (degrés-jours unifiés). A climate indicator summing the gaps between a reference temperature and outdoor temperature. It corrects heating consumption for weather so two years can be compared — without it, a mild winter looks like an energy saving.