20.—(1) This Part applies to air-conditioning systems with an effective rated output of more than 12kW.
(2) Where the relevant person has the power to control the temperature of more than one individual air-conditioning unit in a building, each unit shall be considered to be a component of a single air-conditioning system for the purposes of paragraph (1).
(3) In this Part “effective rated output” means the maximum calorific output specified and guaranteed by the manufacturer of the system as being deliverable during continuous operation while complying with the useful efficiency indicated by the manufacturer.