Most buildings with newly installed technical systems end up with three to four separate control systems that do not communicate with each other. The reason is structural: BACS are considered late in the tender process – as an add-on to the specialist contracts – instead of being the starting point, against which all other specialist contracts are dimensioned. The result is buildings that are expensive to operate, impossible to maintain, and do not meet EPBD requirements.
| 3-4 Separate control systems in a typical newly built Danish commercial building | 20% Building energy consumption is due to incorrectly configured or fragmented control systems | 30% A building without a cohesive BACS uses more energy compared to one with an integrated system. | 25 years Typical lifespan of building services installations — and thus the duration of operating costs |
The building as a fragmented system
Imagine a 5,000 m² office building, newly constructed with modern facilities. The ventilation system is from supplier A with its own DDC controller. The lighting system is from supplier B with DALI control in its own system. The solar shading is from supplier C with its motor and timer. A fourth system attempts to integrate it all as a master BMS.
Fire systems. Fire interfaces. Fire service agreements. All have done exactly what they were asked to do. No one has done what is necessary for the system to function as a whole. This is not a hypothetical scenario – it is everyday life in the Danish and Scandinavian construction industry.
Why is this happening? The logic of the supply structure.
Design procurement construction: The dominant model
The traditional procurement model follows a sequential process: the client engages an architect, who designs the building and prepares the tender documents. The architect brings in consulting engineers for MEP (Mechanical, Electrical, and Plumbing) design. The finished tender documents are put out to tender to a main contractor, who then sub-contracts out various trades – ventilation, electrical, plumbing, and BMS (Building Management System).
Herein lies the structural problem: the trade contracts are specified based on the individual functionality of each system. The CTS contract comes in at the very end and has to integrate what has already been specified and contracted.
“BACS” as a marketing term
Virtually all suppliers of technical building services market their product today as “a BACS system” or “full BMS.” The client is left with four “BACS systems” and no integration. The correct technical term is defined in EN ISO 52120 and in the EU’s EPBD directive, which sets specific functional requirements: continuous monitoring, analysis and adjustment of energy consumption, interoperability across systems, and documentation of indoor climate conditions. An HVAC controller that starts and stops a ventilation unit according to a schedule does not meet these requirements.
The consequences: a lose-lose setup
Energy waste
Incorrectly configured or fragmented building management systems are estimated to account for 20 percent of a building's total energy consumption — energy that is consumed without providing any comfort or productivity gain. A building without a coherent BMS typically uses 10 to 30 percent more energy than a comparable building with a well-integrated system.
The problem of responsibility
Operating and maintenance costs
A building engineering installation typically has a lifespan of 15 to 25 years. With a fragmented system of three to four separate control systems, this means four separate service agreements, troubleshooting across systems that do not share data, vendor-specific software, and access rights for each system — and at the time of technological change, the risk of one system's update breaking the integration with the others.
The solution: BACS as the first tender
The solution is not technologically complex. It is organisationally and procedurally simple — but requires a break from established practice.
BACS must be specified and tendered as the first and overarching technical system — not as the last. The overarching BACS system defines the technical architecture, communication protocols, and integration requirements that all subsequent trade contractors must comply with.
The ventilation contract is not specified as “deliver a ventilation unit with a DDC controller” – but as “deliver a ventilation unit with BACnet integration to the overarching BACS.” The lighting contract supplies DALI-compatible luminaires and infrastructure – but the control resides in the BACS. The solar shading supplies motors and mechanics – but not the intelligence.
The role of the advisor: A necessary shift
For the new model to be realised, it is necessary that the consulting engineers who draft the tender documents possess the BACS technical competence required to specify it correctly. This is rarely the case today. The result is tender documents that specify mechanical and electrical deliverables precisely – but are vague or lacking with regard to BACS architecture, communication protocols, and integration requirements.
The solution is for BACS consulting to be established as an independent, early phase in project planning — a BACS consultant who specifies the technical architecture and integration requirements before the architect and other consultants draw up the discipline-specific tender documents.
Business case for the client
| Lower life cycle costs | An integrated system with a single operations and maintenance interface costs significantly less to operate over the building's lifetime. |
| Energy savings | Up to a 30% reduction in energy consumption over 20 years |
| EPBD compliance from day one | No subsequent adaptation required — the building meets the requirements from the outset |
| Increased property value | Documented low energy consumption and integrated control are more attractive to tenants and investors. |
| Dispute avoidance | Clear areas of responsibility reduce the risk of the inevitable responsibility gaps that exist today. |
Frequently asked questions
What is the problem with the traditional procurement model and BACS?
In the traditional Design-Bid-Build model, CTS contracting comes in at the very end and has to integrate systems that are already specified and contracted separately. The result is typically three to four separate control systems that do not communicate, no unified energy documentation, and unclear lines of responsibility when something doesn't work.
What does it mean to specify BACS “first”?
This means that the BACS system is specified and tendered as the overarching technical system before the other specialist contracts. BACS defines the technical architecture, communication protocols, and integration requirements. All subsequent specialist contracts—ventilation, lighting, solar shading—are specified to integrate with BACS, not to have their own control systems.
Does an HVAC controller system meet the EPBD’s requirements for BACS?
No. The EPBD and EN ISO 52120 set specific functional requirements for a BACS: continuous monitoring, logging, analysis and adjustment of energy consumption; benchmarking and identification of energy losses; interoperability across building systems; and monitoring of indoor climate conditions. An HVAC controller that starts and stops a ventilation unit according to a schedule does not meet these requirements – whatever the supplier calls it.
Hvad er en BACS-rådgivers rolle i et byggeprojekt?
A BACS consultant specifies the technical architecture, communication protocols, and integration requirements before the first specialist contract goes out to tender. The consultant ensures that all subsequent contracts are specified to integrate with the overall BACS— and that the client ends up with an integrated system rather than a collection of independent systems. Arinn offers this consultancy as a service to assist in the early stages of project design.
Sources
- European Commission Energy Performance of Buildings Directive (2024/1275), Article 13. EUR-Lex: CELEX:32024L1275
- EN ISO 52120: Standardised building automation and control systems — definition of BACS and classification of automation levels
- Wattsense Challenges in Building Management Systems (2024). blog.wattsense.com
- Wikipedia/ASHRAE Building Automation Systems — documentation for energy waste from incorrectly configured BMS systems
