Key energy driving factors need to be identified and recorded for the baseline and reporting periods. These may include local heating degree days (See Appendix 4 Degree Days Calculated Accurately for Locations Worldwide) and cooling degree days (where cooling demand is significant). A good source is degree days net which provides degree days freely for the last 3 years from a wide range of locations. The quality and coverage of the data should be considered; in general airport weather stations have good quality data over a long period, but other sources may be considered if there are no airport weather stations close to the facility. On site weather monitoring equipment may be used where it is regularly and properly calibrated and situated properly at or near the facility.
Other factors which influence energy use but are not expected to change routinely should also be recorded such as building operating hours, occupancy levels, set points, outages etc. Where energy changes due to these changes are deemed significant this data may be used to make what is termed a non-routine baseline adjustment. This allows the savings calculation to take account of the change without over or under reporting the savings.