A ventilation design is a set of promises — so many litres per second to this room, so many air changes to that one. Commissioning is where the promises get kept. Gemini AMPM measures, balances and documents ventilation systems to CIBSE Commissioning Code A and BSRIA BG 49, so that handover actually means something.
Commissioning is measurement with consequences. We balance ventilation systems proportionally — the method in CIBSE Commissioning Code A and BSRIA BG 49 — finding the index terminal, then adjusting dampers so every grille takes its designed share of the air before the fan is trimmed to suit. Done properly, the whole system lands on its design figures together; done badly, one room roars while another suffocates. No guesswork survives contact with an anemometer.
Alongside airflow and air change rates we measure what the building type demands: room pressure differentials and cascades for healthcare and laboratories, filtration integrity, fan speeds and smoke visualisation where a design needs its airflow patterns proven. Hospitals get HTM 03-01 methodology; cleanrooms get ISO 14644-1. The instruments are calibrated, and every reading is traceable to them.
The deliverable is documentation that stands up: measured-versus-design air volumes for every terminal, fan and pressure readings, damper positions recorded so the balance can be restored after maintenance, and commissioning certificates signed by the engineer who took the readings. Approved Document F expects ventilation to be commissioned and evidenced — our packs are written to satisfy building control the first time.
Call us at the obvious moment — a new installation, ours or another contractor’s — but also at the less obvious ones: after refurbishment changes the room layout, after duct cleaning disturbs damper settings, or when a building simply never felt right and nobody can prove why. Independent commissioning finds the answer in numbers. It sits naturally alongside our wider ventilation services, from hygiene to pressure testing.
It is the method that makes every part of a ventilation system take its fair share. The engineer finds the index terminal — the grille the system finds hardest to serve — then adjusts dampers so all terminals deliver the same proportion of their design airflow, before trimming the fan so the whole system arrives at design duty together. Balance one branch in isolation and you unbalance another; proportional balancing avoids that trap, which is why CIBSE Code A specifies it.
Yes — a large share of our commissioning work is exactly that, and independence has value. We work from the design figures, not the installer’s assumptions, and report what the system actually delivers. Where it cannot achieve design — undersized ducts, leaking joints, a mis-selected fan — you get the evidence stated plainly, which is precisely what you need for the conversation with whoever built it. The numbers are neutral; that is their power.
A commissioning pack: schedules showing measured against design airflow for every terminal, air change rates per room where specified, fan speeds, pressure readings and final damper positions, plus certificates signed by the commissioning engineer. Approved Document F requires ventilation systems to be commissioned and the results made available to building control — the pack is written to meet that duty directly, and to let a future engineer restore the balance after any works.
A named engineer, not a call centre, comes back within 24 hours. Tell us the building and what you’re dealing with, and we’ll scope it properly.