Accumulators should

Accumulators should be possible to include in the model.
 A model must contain clear system boundaries for what is to be included in the calculations and how measurements are performed. As a basis, the system boundaries presented in the SEPEMO project [12] is recommended.
 The model must be transparent so it is possible to follow and understand the calculations. The studied models all contain parts that are more or less transparent. For example how the estimation of the number of equivalent heating hours is performed is not shown in any method.