The most found air conditioning system, often referred to as a 'split system' consists of an indoor ceiling or wall mounted unit, linked to an exterior condenser by black insulted pipes that contain refrigerant. The condenser, whether linked to one or more interior units, is often a large white box mounted on a wall or flat roof that dispenses around 4 kilowatts (kw) of cooling. The regulations stipulate that where the cooling capacity of a building exceeds 12 kW, then an assessment is required. That is not where one unit has greater capacity than 12 kW itself but where the total of whatever units are installed exceeds that amount.
Larger systems can often be air handling units (AHU). This is a large exterior unit which will cool air and then distribute it around a building through ducting and louvred ceiling vents. As a rule, the cooling capacity of an AHU tends to be greater than a split system and where one or more exceeds the 12 kW threshold, then they too need to be assessed. Others can contain chillers to cool water and then distribute that to cool air in a zone.