Air changes per hour (ACH)

Air changes per hour (ACH) is how many times, in one hour, a space's entire volume of air is replaced — a room that gets its full air volume of *fresh* air swapped out six times an hour is at 6 ACH. It matters because it's the difference between air that's genuinely ventilated and air that's merely being recirculated and cooled. A common Dubai misunderstanding: your split or ducted AC mostly recirculates the same indoor air over a cold coil — it dehumidifies and cools, but brings in little or no outside air, so it doesn't raise fresh-air ACH much on its own. That's why a sealed, well-cooled apartment can still feel stuffy, hold cooking or paint smells, or stay humid: low fresh-air turnover. Different spaces need different rates — bedrooms and living areas modest, but kitchens and bathrooms need strong extraction (what the extraction hood and bathroom fan are for), and offices and shops have minimum fresh-air targets set by ventilation standards such as those from ASHRAE. If rooms feel stale despite good cooling, the fix is usually ventilation and extraction, not more AC — worth checking the fresh-air and extract setup alongside AC coil and filter cleaning and a wider airflow review.