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Degree Day Normalization
The Degree Day normalization option provides an answer to the question “What would be the value of consumption, if temperature during the report period would be equal to some base temperature?” The base temperature is usually set to 65˚F, which is the balance temperature (at balance temperature no cooling or heating is required to maintain required indoor air temperature).
The degree-day normalization is a three step process:
- First, the degree-day values are calculated for each day of the report period except days that were excluded from report via the 'days of week' widget. This calculation is done by averaging the high and low Outside Air Temperature (OAT) for a site for every day and subtracting from it 65˚F.
Note: OAT data can be linked from one site to another so that you do not have to log that data for every site in order to calculate degree-day.
The difference in temperature is the number of Cooling or Heating degree days. So if today’s average temperature is 67˚F, then today we would have two Cooling Degree Days.
- Second, we determine the slope of the linear regression line (the 'A' parameter in regression formula Y=A*X+B). This calculation is explained under Scatter Plot above. The only difference is that we substitute the degree days that were calculated in place of the actual temperature in the graph.
- Third, Based on the slope we can calculate the average amount of energy that is needed at 65˚F. Since we assume no heating or cooling is required at 65˚F, all energy consumption must be independent of Outside Air Temperature. The slope (calculated in the previous step) shows us the calculated consumption as it is directly related to Outside Air Temperature. Deviations of plotted consumption away from the slope indicate energy consumption that is not attributable to a change in Outside Air Temperature. As we normalize the consumption values to the established base temperature (zero degree day), we will see the amount of consumption accounting for non-temperature related load. Subtracting temperature normalized consumption from observed consumption, we can get the amount of energy consumed by heating/cooling equipment (if they are not metered separately).
This allows us to compare sites located in different weather regions or compare data collected during different weather conditions.
Note: Degree-day normalization only applies to temperature dependent points. Do not attempt to perform degree-day normalization for points (such as lighting) that do not normally have any relationship to temperature.
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