Why Your BMS Commissioning Was Probably Done Wrong

If you manage a commercial building in the UK, there is a better than even chance the BMS was never properly commissioned. Controllers were installed, software loaded, graphics built, points checked, and a commissioning certificate was signed saying the system was complete. But the building was never proven to work under real conditions.

The gap exists because BMS commissioning happens at the worst possible time in a construction project. The programme has slipped, the client wants to move in, the main contractor needs practical completion, and the BMS is one of the last systems to be commissioned because it depends on everything else being finished first. The mechanical plant needs to be running, the electrical systems need to be live, the ductwork pressure-tested, and the pipework flushed and balanced. By the time the BMS engineer gets access, there are usually two weeks left, half the plant is not ready, and the client is already moving furniture in.

The result is commissioning that proves the system can turn things on and off, but does not prove the building will be comfortable, efficient, or operable. And because nobody comes back once the building is occupied — the defects period is focused on snagging, not performance — the building starts its operational life with controls that have never been fully tested under real-world conditions.

What is BMS commissioning supposed to be?

BMS commissioning is not the same as BMS installation, and it is not the same as BMS testing. Installation is putting the hardware in place and making the electrical connections. Testing is verifying that each point is wired correctly, each sensor reads accurately, and each output drives the correct device. Commissioning is the process of proving that the complete system — controllers, software, plant, and control strategy — works together to deliver the design intent under all operating conditions.

That last phrase is critical: under all operating conditions. A BMS that works in mild autumn weather when the building is lightly occupied has not been commissioned. It has been witnessed in the one condition that happened to exist on the day the commissioning engineer visited. Genuine commissioning means testing the heating strategy in cold weather, the cooling strategy in warm weather, the night setback and optimum start logic across different seasons, the frost protection in freezing conditions, the fresh air economy cycle when outdoor conditions are suitable, and the alarm and failsafe behaviour when things go wrong.

CIBSE Commissioning Code M, the definitive UK guidance on commissioning management, defines commissioning as "the advancement of an installation from static completion to full working order to specified requirements." It explicitly includes seasonal commissioning, performance testing under representative load conditions, and handover of a system that has been demonstrated to meet the design intent — not just a system that has been switched on and checked for obvious faults.

Why does poor BMS commissioning matter in a real building?

Poor BMS commissioning has consequences that persist for the entire life of the building, or at least until someone pays to fix it. The most immediate is energy waste. A BMS that has not been properly commissioned will have incorrect setpoints, timing schedules that do not match occupancy, control loops that are poorly tuned (causing hunting, overshoot, or sluggish response), and energy-saving features like optimum start, weather compensation, and night purge that are either disabled or configured incorrectly. CIBSE TM54, which provides a methodology for evaluating operational energy performance, consistently shows that the gap between design-stage energy predictions and actual operational energy consumption is 150 to 300 percent in UK commercial buildings — and poor commissioning is one of the primary causes.

The second consequence is comfort complaints. If control loops are not tuned, temperature setpoints will not be maintained reliably. If the AHU fresh air strategy is not commissioned, some zones will be stuffy while others are draughty. If the heating and cooling changeover is not properly configured, the system will fight itself — heating and cooling the same zone simultaneously — which is both wasteful and uncomfortable.

The third consequence is maintenance burden. A poorly commissioned BMS generates nuisance alarms, requires frequent manual intervention to maintain conditions, and creates a maintenance overhead that would not exist if the system had been properly set up in the first place. The FM team spends their time compensating for poor commissioning rather than managing the building proactively.

What usually goes wrong with BMS commissioning?

The most common commissioning failure is insufficient time allocation. BMS commissioning typically appears as a single line item on a construction programme, sandwiched between mechanical and electrical completion and practical completion. In reality, BMS commissioning cannot start until all other systems are complete, balanced, and operational — which usually happens weeks or months later than planned. The commissioning period gets compressed from the specification requirement of four to six weeks down to one or two weeks, and the commissioning engineer has to prioritise getting the building to a state where it can be occupied rather than optimising performance.

The second common failure is the absence of seasonal commissioning. A building commissioned in September has not been tested in heating mode. A building commissioned in February has not been tested in cooling mode. The control strategies for the season that was not tested will contain errors that are not discovered until six months later — by which time the commissioning engineer is on another project, the defects period may have expired, and the FM team is left to figure it out themselves. BSRIA BG 11/2010, the Soft Landings framework, addresses this by extending the aftercare period to three years and requiring the design team to return for seasonal performance checks. In practice, Soft Landings is specified on many projects but fully implemented on very few.

The third failure is inadequate documentation. A proper commissioning record should include every control sequence tested, the conditions under which it was tested, the results, and any deviations from the design intent. In practice, commissioning records are often generic checklists with ticks in boxes, containing no evidence that the specific control sequences in the building were actually tested. The handover pack contains the O&M manuals from the equipment manufacturers, the as-built drawings, and a commissioning certificate — but not the information the FM team needs to understand how the controls are supposed to work, what the setpoints should be, or how to troubleshoot common problems.

The fourth failure is commissioning by the installing contractor rather than an independent party. The contractor who installed the system has a commercial interest in achieving practical completion as quickly as possible. They are not incentivised to spend additional time fine-tuning control loops, testing edge cases, or documenting the system to a standard that helps the FM team. Independent commissioning, where a separate specialist verifies performance against the specification, produces significantly better outcomes — but it is rarely specified because it adds cost and programme time.

Which standards and guidance govern BMS commissioning in the UK?

CIBSE Commissioning Code M defines the commissioning management process, including the roles and responsibilities of the commissioning manager, the commissioning programme, the witnessing and recording requirements, and the criteria for demonstrating that the system meets the specification. It requires that commissioning is planned from the design stage, not treated as an afterthought during construction.

CIBSE Commissioning Code A covers the commissioning of air distribution systems and is directly relevant to BMS commissioning because the BMS controls the AHU, the fan speeds, the damper positions, and the zone temperature control. Code A specifies the measurements required (supply air temperature, return air temperature, fresh air percentage, duct static pressure) and the tolerances within which the system must perform.

BSRIA BG 11/2010, the Soft Landings framework, is the most important guidance document for addressing the commissioning gap. Soft Landings extends the project team's involvement beyond practical completion through three years of aftercare, during which the building's performance is monitored, the control strategies are adjusted based on actual use, and seasonal commissioning is completed. The framework includes five stages: inception and briefing, design development, pre-handover, initial aftercare (first twelve months), and extended aftercare (years two and three). When properly implemented, Soft Landings closes the gap between design intent and operational reality — but implementation requires contractual commitment from the outset, not a retrospective bolt-on.

BSRIA BG 29/2012 provides specific guidance on commissioning variable flow pipework systems, which are increasingly common in modern HVAC installations with variable speed pumps and two-port control valves. The BMS strategy for variable flow systems — including differential pressure control, minimum flow management, and valve authority — needs to be commissioned under multiple load conditions to verify stable operation, which is rarely achieved in the compressed commissioning periods typical of UK construction projects.

What does a real BMS re-commissioning job look like?

We were brought in to investigate comfort complaints and high energy consumption in a four-year-old commercial office in London. The building had a reputable BMS system installed by a reputable contractor, and the commissioning certificate stated that all systems were tested and operational. The reality was rather different.

The optimum start algorithm was configured but had never been tuned for the building's thermal mass, so the heating was starting two hours earlier than necessary every morning — wasting gas and electricity for no benefit. The weather compensation curve on the heating circuit was set to the manufacturer's default, not calibrated to the building's actual heat loss characteristics, so the flow temperature was consistently too high in mild weather. The cooling changeover was set at a fixed outdoor temperature rather than being based on actual cooling demand, which meant the chillers were running on mild spring days when opening the economy cycle dampers would have provided free cooling. The AHU fresh air control was in manual override — someone had set it during commissioning "temporarily" and never returned it to automatic. And the BMS graphics showed green status across the board, because the alarm setpoints had been widened to the point where nothing triggered.

We spent three weeks re-commissioning the system: tuning control loops, calibrating compensation curves, testing seasonal strategies, resetting alarm thresholds, and documenting the correct operational parameters. The building's gas consumption dropped 28 percent in the first heating season after re-commissioning, and the comfort complaints dropped to near zero. The total cost was a fraction of the capital works that had been proposed by another contractor who wanted to add additional plant to solve what was fundamentally a controls problem.

What does good BMS commissioning look like?

Good BMS commissioning starts in the design stage with a commissioning specification that defines what will be tested, how it will be tested, under what conditions, and what the acceptance criteria are. The specification should be written by the controls engineer and agreed with the commissioning manager before the contract is let.

The commissioning programme should allocate sufficient time — typically four to six weeks for a medium-sized commercial building — and should not start until the mechanical and electrical systems are complete and ready. Attempting to commission the BMS while the pipework is still being balanced or the ductwork is still being sealed produces unreliable results and wastes everyone's time.

Seasonal commissioning should be contractually required, with the BMS contractor returning to the building at least twice — once in heating season and once in cooling season — to test and tune the strategies that could not be proven during the initial visit. This should be included in the contract price, not treated as an additional cost.

The handover should include building-specific documentation: an operational narrative that explains how the controls work in plain English, a setpoint schedule that documents every setpoint and why it is set to that value, a fault-finding guide that covers the most common issues the FM team will encounter, and training for the people who will actually operate the system day to day.

When should you re-commission a BMS?

If your building is less than three years old and has never had a post-occupancy performance review, it almost certainly has commissioning deficiencies that are costing you energy, generating complaints, and creating maintenance work. A re-commissioning exercise — sometimes called retro-commissioning — is the most cost-effective way to improve building performance because it works with the existing plant and controls rather than adding new equipment.

If your building is being handed over and the BMS commissioning is being compressed into the final week of the programme, push back. The cost of an extra two weeks of commissioning at construction stage is a tiny fraction of the cost of re-commissioning a building that was handed over in a half-finished state.

If you are writing a specification for a new BMS installation, include a Soft Landings requirement with contractual teeth — not a vague aspiration, but a defined aftercare programme with seasonal commissioning visits, performance KPIs, and a retention that is not released until the aftercare is complete.

How do you get BMS commissioning right?

BMS commissioning is where the value is won or lost. The most expensive controllers, the best sensors, the most sophisticated supervisory platform — none of it matters if the system is not properly commissioned, tuned, and handed over. The gap between a system that has been switched on and a system that has been commissioned is the difference between a building that wastes 30 percent of its energy budget fighting itself and a building that runs efficiently, comfortably, and reliably.

If your building's BMS was commissioned in a rush and has never been revisited, a retro-commissioning exercise is the single best investment you can make in building performance. Alpha Controls carries out BMS commissioning and re-commissioning for all major platforms, and we work with the FM team to ensure the system is not just functional but optimised.

Contact us or request a quote to discuss BMS commissioning for your building.