1. Calculate Daily Average Temperature
"Daily average temperature can be calculated using various increments (e.g., half-hourly, hourly), as long as the daily temperature represents the average temperature for the day across a full 24-hour period. For example, the temperature may be measured every hour on the hour, summed for the day, and then divided by 24.
Temperature data collected from a weather monitoring station located at the plant, or data from a nearby weather reporting station, must be used to compute daily average temperature. Missing daily average temperature readings may be linearly interpolated for the purposes of computing HDD and CDD data."
2. Calculate HDD and CDD via the Daily Average Temperature Approach
"EPI users are required to calculate HDDs/CDDs based on the deviation of the daily average temperature from the base temperature (65°F for the EPI calculation). This approach is used by EPA across all forms of facility benchmarking offered by ENERGY STAR.
When the daily average temperature is lower than the base temperature (65°F), HDDs will be calculated as:"