Indoor Air Quality Complaints Versus an 8% Energy Target
A 400-person open-plan office across three floors is recording return-air CO2 peaks of 1,300–1,500 ppm between 14:00 and 16:00 on two floors. Occupants report afternoon headaches and drowsiness; the pattern tracks the CO2 curve. A recent fit-out added 60 workstations in a former storage area without new diffusers or an updated ventilation calculation. The energy manager, facing an 8% reduction target, proposes cutting air handling unit hours by two hours a day and reducing the minimum outside-air damper position from 30% to 20%. The economiser dampers were last verified four years ago. The building has no documented ventilation rate against a current standard.
1. How do you respond to the energy manager's proposal?
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Distinguish between the two measures, because they are not equivalent.
- Reducing outside air below the ventilation requirement is not available as a saving. The minimum outside-air rate exists to protect occupant health and performance; if the current design minimum no longer serves the actual population (60 new workstations), the system may already be non-compliant. Cutting it further converts an energy project into a liability with a documented complaint trail behind it.
- Reducing operating hours is only defensible where the building is genuinely unoccupied. Two hours a day across the board would be cutting into occupied afternoon time - precisely the period when CO2 is already peaking. If there is a real unoccupied window (early morning, evening), that is a legitimate saving and should be quantified separately.
- There are better savings available. The economiser has not been verified in four years; a stuck damper means free cooling is being missed and mechanical cooling is running instead. Simultaneous low airflow with reheat, or over-ventilation in sparsely occupied zones, is common and is what demand-controlled ventilation exists to fix.
Offer a counter-proposal: hold outside air at or above the required rate, verify and repair the economiser, implement demand-controlled ventilation tied to measured occupancy, and re-cut the schedules against actual use. Those measures can plausibly deliver the 8% without touching a health-based minimum.
2. Lay out the investigation and the metrics you will track, and say what you would fix first.
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Investigation, in order:
- Establish the requirement. Calculate the required outdoor-air rate for the current layout, including the 60 new workstations, against the applicable ventilation standard. Without this number, no proposal can be judged.
- Measure actual airflow. Balometer readings at air terminals and outside-air intake; compare with design and with the calculation. CO2 is a screening tool, not a compliance measure - it tells you something is wrong, not how much air is moving.
- Check distribution, not just quantity. The storage-area conversion is the prime suspect: correct total air with no diffusers in that zone still leaves occupants in stale air. Measure local air speed, temperature stratification and CO2 zone by zone.
- Check the economiser and dampers for stuck linkages, and verify CO2 sensor calibration - a drifting sensor can drive either over- or under-ventilation.
- Review the fit-out for return-air short-circuiting and blocked returns.
Metrics: zone-level CO2 (occupied hours, 95th percentile rather than average), measured outside-air l/min per person against requirement, complaint count and location, afternoon temperature and humidity, and kWh - tracked on the same chart so energy and air quality are never reported separately.
Fix first: restore distribution and verify the economiser, because both improve air quality and energy simultaneously. Then tune ventilation to occupancy.
3. How do you handle communication with occupants and with the energy manager while the investigation runs?
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Both audiences need different things, and silence will be read as inaction.
Occupants: acknowledge the complaint with the specific pattern observed (afternoons, two floors), state what is being measured and when they will hear back, and give an interim measure if one is safe - for example, adjusting local airflow or reducing dense seating in the converted area. Do not speculate about causes. Follow up with results even if the fix is incomplete; an unresolved complaint with no feedback escalates to formal grievance or a regulator.
Energy manager: do not frame this as sustainability blocking savings. Reframe it as redirecting effort to savings that are real and defensible: economiser repair, demand-controlled ventilation, schedule alignment. Offer to co-present the joint business case, and commit to delivering the 8% through those measures with M&V.
Senior management: a short note setting out the risk - a documented complaint pattern, a possible ventilation shortfall following an unassessed fit-out, and a proposed remedy - protects the organisation if the issue escalates and gives the FM team the authority to fund the diagnostic work.
Reasoning: the conflict is only a conflict if air quality is treated as a cost. Managed properly, the ventilation fix and the energy target share most of the same actions.