reg 24 Methodology of calculation and expression of energy performance
(1) The Secretary of State shall approve— (a) a methodology of calculation of the energy performance of buildings, including methods for calculating asset ratings and operational ratings of buildings; and (b) ways in which the energy performance of buildings, as calculated in accordance with the methodology, shall be expressed. (2) In this regulation— “ asset rating ” means an energy performance indicator determined from the amount of energy estimated to meet the different needs associated with a standardised use of the building; and “operational rating” means an energy performance indicator determined from the amount of energy consumed during the occupation of a building over a period of time and the energy demand associated with a typical use of the building over that period.