How ALF was developed
ALF was developed using the building energy simulation tool SUNCODE. SUNCODE is an old, well validated program that provides a detailed understanding of the heat flows into and out of a building.
In order to simplify the process, multiple runs of SUNCODE were undertaken for a number of building designs, for various locations around New Zealand, with various levels of insulation, thermal mass and glazing.
From the multiple simulation runs, annualized factors were calculated to account for the seasonal heat loss of various building elements (the Annual Loss Factors or ALFs) as well as the seasonal solar gains through the windows (the Annual Gain Factors of AGFs). The usefulness of solar gains through the windows was assessed and was related back to the thermal mass of the building. Version 3 of ALF allowed for heating to be used at different times of the day which required the inclusion of a factor to account for the thermal mass within the building being cold at the start of the heating period (the Warm-Up Load).
The methods used to determine these factors are discussed in chapter 6 of the ALF manual (ALF3 The 'Annual Loss Factor' Method: A design tool for energy-efficient houses, 3rd Edition). This manual is no longer in publication but is available from the BRANZ Library.