How are we doing with heating degree days this year?
A heating degree day is a weather index designed to make weather data easier to use in planning.
The index estimates fuel consumption needs, and fuel distributors use it to schedule home deliveries. Electric and natural gas utilities predict power demands by adding up this index over time.
The following mathematical formula defines this index.
Each degree that the daily mean temperature is below 65 degrees is one heating degree day. So, if today’s average temperature is -5F, that is 70 heating degree days, or HDDs. The higher the HDD, the colder it is.
This baseline of 65 degrees was determined by engineers who found that when the mean outdoor temperature drops below 65, most buildings require heating to maintain an indoor temperature of 70.
The amount of heat required to maintain a building’s temperature is proportional to the accumulated heating degree days. So, heating degree day totals are usually reported each day, as well as the total sum for the season. This allows us to quickly judge whether the season is above, below or near normal in terms of heating bills.
Over a year, northern Wisconsin has about 9,000 HDDs, while southern Wisconsin has about 7,000 HDDs. It will be no surprise that as of Jan. 28, Madison was above normal for this time of year, at 4,418 HDDs compared with 4,173 HDDs, though significantly below the very cold 1976-77 winter record of 5,347 HDDs for Jan. 28.
So, Madison was frigid last month, but we have experienced colder winters.