Old Timer: It was a cold winter!
Newcomer: How cold was that?
Old Timer: Let’s just say I wasn’t blue then.
Measures the impact of weather on energy consumption. Because weather patterns vary widely day-to-day and year-to-year, weather for a given season may be colder or warmer. Energy used in keeping warm is directly dependent on how cold it is. Comparing the weather or energy consumption from one year to the next would provide only the change between those years. However, when energy consumption is “Weather Normalized” you are comparing your energy consumption over a normal weather period. Weather normalization adjusts energy usage so it can be compared to energy usage in other years over a longer period.
Once your energy usage has been weather normalized, you will know what amount of energy will be used, for a given normal year. Any usage profile can be weather normalized as long as it covers a full year. With a weather normalized energy usage profile, you can evaluate your energy needs based upon the projections for the coming year. A forecast for a warmer than normal year would result in your energy consumption being less, likewise a colder forecast would require more energy. Weather forecasts are almost universally provided based upon a normal weather period.
Therefore, using weather normalized energy usage you could expect to use that amount of energy, on average, for each of the next thirty years. Comparing changes between weather normalized usage profiles can detect deteriorations in heating plant efficiencies, uncover energy losses, or indicate increased process demand.
This is based on a 30-year average consisting of three consecutive decades. Currently the years 1981 through 2010 are used for calculating normal. Normal weather takes into account the degree days or specifically the Heating Degree Days for 30 years. Using a 30-year normal for comparison allows for meaningful analysis instead of just year-to-year fluctuations.
Heating Degree Days
Weather’s effect on energy consumption is measured in degree days. The higher the number of degree days will result, in colder than normal weather. Heating degree days is a value reflecting the amount of energy needed to heat a building. It is computed by subtracting the Average Temperature (usually rounded to the nearest degree) for the day from a base temperature. For North America the base temperature is typically considered 65 degrees Fahrenheit.
For summary-of-the-day observations, the average of the maximum and minimum temperatures recorded from that day is calculated. In some displays, the value is rounded off to the nearest degree.
When rounding is performed, it is done away from zero. That is, a value of 2.5 becomes 3 and -2.5 becomes -3.