If we assume that the return temperature recorded is the annual average return temperature, we can utilise the customer type above in the same way as the factors for cooling. We assume that the customer type, viewed from this angle, will not be registered previously in the customer database. Therefore, every customer must be assigned customer type 1 on import. This customer typ 1 is a linear curve with the factor value set to 1.0 and is predefined in the table.