Commissioning: proving a new system before handover
Commissioning runs alongside construction. It starts with the owner's project requirements, follows the design through submittals and installation checks, and finishes with functional performance testing of every system and interlock. The deliverable is documented proof that what was specified is what was built and what now operates.
Retro-commissioning: recovering performance in an existing building
Retro-commissioning applies the same discipline to a building already in service. It begins by measuring current performance, then finds the gap between how the building runs and how it should run. Typical findings are simultaneous heating and cooling, schedules overridden years ago and never restored, economisers stuck closed, and setpoints drifted far from design.
How to choose
If the building is under construction or major refurbishment, commissioning is the right process and should be written into the contract early. If the building is occupied and energy bills, comfort complaints or equipment failures are rising, retro-commissioning usually returns more per pound spent than replacing plant.
A note on continuous commissioning
Neither process is permanent. Buildings drift as tenants change, controls are overridden and equipment ages. Periodic re-verification keeps the gains from eroding.
