When a building relies on 24-hour cooling for critical rooms and equipment, even a small oversight can lead to a major failure.
On a recent commercial office project commissioned by our team, a design error created exactly that scenario. The cooling towers – essential to the building’s heat-rejection system – were designed with automatic water-level control but no independent level alarms.
Although the BMS provided various system alarms, without a standalone level sensor with high and low thresholds, the operator had no visibility of a critical risk. The omission led directly to an avoidable operational event during initial occupancy.
Identifying the critical omission
At the early design stage, we identified that the open-circuit cooling towers — supporting 24-hour cooling for critical rooms — weren’t equipped with high or low-level alarms to alert operators to abnormal conditions.
Potential failure scenarios were numerous: inadvertent valve closure, pump failure, low rainwater levels, a failed-open blowdown valve or a basin drain valve left open. Each would have the same outcome – a declining water level and reduced cooling capacity.
The issue was raised early through our services and maintainability review and later entered into the commissioning issues log. But with many competing priorities during construction and commissioning, it remained open and low priority, until it became a real operational problem during early occupancy.
When the system failed during commissioning, the cooling tower basin ran low on water without warning. With no low-level alarm in place, the operations team had no indication that water levels had fallen below the threshold. The first sign of a problem was a drop in cooling performance – a critical risk for a building reliant on uninterrupted cooling for essential services.
The operations team had to respond immediately once the issue was noticed. Emergency top-up was carried out manually using the nearest fire hose reel to restore operation – a workaround that, while effective in the moment, is far from ideal and not a sustainable solution for ongoing risk management.
This event confirmed, beyond doubt, that independent level alarms on cooling towers are not optional.
Cooling towers 101
For wet cooling towers, basin water level is one of the most critical operating parameters. Along with chemical and microbiological control, maintaining the correct level ensures effective heat rejection. If the level is too high, the tower overflows, wasting treated water and increasing operating costs. If it’s too low, the system can no longer reject heat effectively and quickly fails to meet its design intent.
In this building, each tower’s basin level was controlled by a solenoid on/off valve responding to a level probe, maintaining make-up water to account for normal losses such as evaporation, blowdown and drift. The towers were located on the uppermost plant level with make-up water supplied from a rainwater recycling system via a duplex booster pump set. The pump set also had a potable water backup when insufficient rainwater was available.
Because the make-up water system was several floors below the towers, any loss of pressure, valve fault or pump failure could interrupt supply, without any direct feedback to operators via the building management system (BMS).
A holistic commissioning approach
A commissioning process needs to apply process engineering principles to building services, anticipating how systems behave under both normal and fault conditions.
By taking a holistic view across hydraulics, controls and operations, the team should ensure that even simple systems include the checks and alarms needed to protect performance. In this scenario, our team recommended a single level sensor with high and low alarm thresholds as a low-cost, high-impact safeguard that gives operators the visibility they need to act before failure occurs.
Taking action after commissioning
Following the event, independent level sensors and associated alarms were installed, commissioned and verified. These provide early warning to the operations team if water levels deviate beyond safe limits, allowing prompt corrective action.
The client now has confidence that under any failure scenario – from a blocked valve to a pump fault – the system will alert their team before service is interrupted. It’s a simple enhancement that prevents costly disruption and protects the building’s operational integrity.
Cooling towers are essential to the reliability of many high-performance buildings. They’re also deceptively simple which is why small oversights can have big impacts.
Designing for reliability means thinking beyond system performance to consider maintainability, risk visibility and operational continuity. In this case, a single missing alarm turned into a building-wide issue that impacted tenants.
Embedding proactive risk visibility and management into design and commissioning, we can prevent these issues from ever reaching the operations phase.
