Retro-commissioning: optimising existing buildings without major works

Retro-commissioning (RCx) applies the commissioning process to an existing building, often several years after handover. The goal: identify operational drift and restore systems to their optimal performance level, without major investment.

Why performance drifts

• • Undocumented changes: new partitions, changes of room use, furniture placed in front of air terminals.
• • Gradual maladjustment: control setpoints are changed over time in response to one-off complaints.
• • Sensor ageing: temperature and humidity sensors drift and distort control.
• • Fouling: filters, heat exchangers and coils gradually lose efficiency.
• • Change of occupants: needs are no longer the same as at the original design stage.

Retro-commissioning methodology

• 1. Initial audit: collect the drawings, the original design calculations and consumption data (last 3 years).
• 2. Site inspection: technical walk-round of all HVAC systems, visual identification of faults.
• 3. Measurement campaign: temporary instrumentation (temperature loggers, energy meters) for 2 to 4 weeks.
• 4. Data analysis: comparison of actual and intended operation. Identification of deviations.
• 5. Action plan: list of corrective measures ranked by cost/benefit ratio (quick wins first).
• 6. Implementation: adjustments, sensor recalibration, cleaning, re-balancing.
• 7. Post-works verification: measurement of the savings achieved over 3 to 6 months.

Typical results

• • Energy savings: 10 to 30% reduction in consumption, often without any equipment investment.
• • Payback: 1 to 3 years, sometimes under a year for quick wins.
• • Improved comfort: occupant complaints reduced by 50 to 70%.
• • Longer equipment life: equipment operates within its rated conditions.

"The greenest building is the one that consumes the least. Retro-commissioning is the first step to take before any major investment." — ADEME