We are preparing an experiment that will run during the coming winter, where we assess certain energy performance indicators on a set of single-family houses in Europe.
We are interested in finding out which factors have the greatest impact on these indicators. These factors will include the age of the building, its insulation level, its inertia, etc. I'm minded to treat these factors as, well, factors taking on a set of discrete values. For example, the age of the building will be coded as the decade in which it was built; the insulation level will be factored as poor, medium, good; etc.
I know more or less how to design an (fractional) factorial design when the factors can take on 2 values. But how should I design an experiment where, for the sake of the example, one factor can have 5 levels, another 3, and another 3?