Office BMS: control your HVAC consumption and secure compliance
BACS decree and the 70 kW threshold: what applies to you in 2025
Your HVAC bills absorb 45% of the floor’s consumption, and you’re discovering the BACS deadline of 1 January 2025 a few months late. On the office floors of more than 500 sq m that we audit, manual or basic regulation remains very common, which represents a significant source of savings from the first months of operation. Kytom has been integrating BMS solutions since 2006 on open BACnet and KNX protocols, and delivers a compliant installation in 12 weeks including audit, on the 850 sq m that make up our average project area. Our reading of the market contrasts with the dominant integrator narrative: a BMS is not a global IT project, it’s a tool for compliance with the framework arising from the ELAN law article 175, which requires a reduction in energy consumption of 40% by 2030, 50% by 2040 and 60% by 2050 relative to the reference of the 2010 decade, and a facility management tool, calibrated as tightly as possible to stay under a 5-year ROI. The BACS decree (order of 7 April 2023) and the tertiary decree (-40% final energy consumption by 2030, -50% by 2040, -60% by 2050, art. R.174-22 Construction Code) set the course; we translate these obligations into technical architecture, auditable sub-metering and regulatory proof. Here is how we proceed.
the framework
The BACS decree (order of 7 April 2023, JORF no. 0084) makes a building management system mandatory for any tertiary building equipped with HVAC installations exceeding 70 kW. Two deadlines structure your timeline: 1 January 2025 above 290 kW, 1 January 2027 between 70 and 290 kW. The framework combines with a separate regulatory obligation that imposes, for the tertiary stock, measurable reduction trajectories through to 2050.
A BMS acts where energy is lost in the tertiary sector:
| Item | Share of consumption |
|---|---|
| Heating, ventilation, air conditioning | 45% |
| Lighting | 20 to 25% |
| Office equipment and auxiliaries | 15 to 20% |
A BMS’s performance is measured in four classes (A, B, C, D), a reference used in the BAT-TH-116 CEE sheets. Class A targets -30% relative to class D regulation.
In practice at Kytom, BACS compliance does not require class A. Class B is legally sufficient and represents a significantly lower investment than class A, which makes it the default choice for most tertiary projects. We only recommend class A if the targeted reduction trajectory for 2030 remains out of reach in class B, which is determined by an energy audit, not by a commercial default.
your gains
Turning your BMS into auditable proof
The annual declaration (art. R.174-31 Construction Code) requires proof of a reduction trajectory relative to a reference year (2010 to 2019, of your choosing). A poorly exploited BMS provides raw data, not proof: your consumption remains attributed to the global meter, without granularity by lot.
We secure your declaration against three measurable requirements:
- Sub-metering by regulatory use (HVAC, lighting, DHW, others), meters compliant with the MID directive class 2, a condition for producing a verifiable file in the event of an inspection.
- Automated export from the BMS interface, which eliminates manual re-entry and the discrepancies it usually introduces between entry and raw data.
- Historical archiving for at least 10 years of time-stamped consumption, a duration aligned with the commitment and the NF EN 16247-2 energy audit.
The cost of non-compliance is heavy: a fine of EUR7,500 per legal entity (art. L.174-1), publication on the regulatory platform, and corrective works estimated at between 80 and 200 EUR/sq m over 5 years to catch up with the -40% trajectory. In concrete terms, the real ROI of a BMS for a subject entity incorporates this avoided cost of forced compliance: 60 to 120 EUR/sq m more over 10 years that a strictly energy-based analysis ignores.
when not to go ahead
The cases where a BMS is not the right answer
We turn down BMS projects that make no economic sense. Three situations should lead you to postpone or abandon the investment.
Below 70 kW of nominal HVAC power (typically floors under 600 sq m with a dedicated heat pump), the BACS decree does not apply and the ROI exceeds 8 years. The right answer: local regulation via programmable thermostats and a lighting timer, for an investment 5 to 10 times lower.
On a building destined for demolition or heavy restructuring within 5 years, a BMS loses its relevance: the depreciation will not have time to run. It is better to secure compliance with temporary sub-metering and concentrate the trade-offs on the restructuring project.
On a new floor delivered shell & core, the BMS integrates directly into the initial HVAC lot via the fluids technical specifications; our 5-step sequencing becomes redundant and invoices the same service twice. We then direct you towards a technical specification mission, shorter and less costly.
Conversely, on floors occupied 24/7 (call centres, local data centres), the deployment must be spread over 16 to 20 weeks with night interventions, which raises the project cost by 25 to 35%. We tell you this during the audit phase, not at the end of the works.
Method
- Technical audit
We survey your HVAC, lighting and blind equipment, analyse your consumption over a rolling 12 months and identify the 3 to 5 priority lots. Duration: 1 to 2 weeks. Deliverable: audit report with a quantified savings potential and a BACS class recommendation (B or A). - Technical design
We choose the appropriate protocol (KNX, BACnet, Modbus, LoRaWAN), size the network architecture and the controllers, define the 20 to 80 measurement points depending on the area (ratio of 1 point per 25 to 40 sq m). Duration: 2 weeks. Deliverable: validated design file. - Costing and planning
We provide a detailed quote by lot, a works schedule coordinated with the other trades, and the qualification of our integrator partners. You make decisions on a clear scope, with no budget surprises during the works. - Site deployment
We install the local controllers, configure the time-based scenarios, integrate the web or mobile interface and run non-regression tests. Duration: 4 to 6 weeks. Coordination with your facility teams and the other technical lots. - Commissioning and follow-up
We train your facility teams, adjust the setpoints after 4 then 3 months of operation, deliver a monthly consumption report and provide a 8am-6pm hotline with intervention within 4h on a blocking incident. Follow-up included for 12 months.
Frequently asked questions
At what threshold does a BMS become mandatory?
The BACS decree (order of 7 April 2023, JORF no. 0084) requires a building management system for any HVAC installation exceeding 70 kW. Two deadlines pace the obligation: 1 January 2025 for power exceeding 290 kW, 1 January 2027 for power between 70 and 290 kW. Below 70 kW, a BMS is not regulatorily required and the ROI exceeds 8 years: we then recommend local regulation via programmable thermostats, which is far more economically relevant.
What ROI can be expected from a BMS on a typical tertiary floor?
On the BMS projects we support, the return on investment is generally between 4 and 7 years for a well-sized installation, with significant HVAC savings as a result. Inadequate sizing noticeably extends this timeframe and reduces the energy gains, whereas a BMS adjusted to the right scope generates 15 to 25% HVAC savings. For a subject entity, the calculation incorporates the avoided cost of forced compliance, i.e. 60 to 120 EUR/sq m more over 10 years that a strictly energy-based analysis ignores.
