Degree Days Can Mean Unexpected Electricity Consumption

A little math goes a long way to understanding how much a heating or cooling system has to run


65degreetemp

Understanding the gap between outdoor temperatures and a targeted indoor temperature can help consumers manage energy consumption and spending.

Heating Degree Days and Cooling Degree Days are concepts and calculations that propel some engineers, facility managers and electricity generators straight to their whiteboards. They’re also significant factors in the amount of electricity every home and business uses, so a little math can go a long way in managing electricity use and spending.

At their hearts, heating degree days (HDDs) and cooling degree days (CDDs) measure the gap between hourly outdoor temperatures and a targeted indoor temperature.

For example, if the average temperature between midnight and 1 a.m. is 35 degrees and the targeted indoor temperature is 65, there is a 30-degree difference. The people who measure these kinds of things divide those 30 degrees by 24 to get 1.25 HDDs for that hour. They do the same thing for each hour of the day and then add them all up for the day’s total HDDs or CDDs. (Weather.gov uses 65 as a base for its report, though 68 also is a common base and 68 is the winter thermostat setting that energy.gov recommends.)

The more HDDs or CDDs for the day, the more a heating or cooling system has to run. Longer run-times mean more electricity consumption and sometimes larger-than-anticipated invoices. They also mean more maintenance and potentially shorter equipment lifespans, which are additional reasons engineers and facility managers follow degree days so closely.

“Consumers often compare the bottom line of their invoices from month-to-month or year-to-year,” said Scott Harrison, director of engineering and innovation for TXU Energy. “Weather is one of the biggest factors in electricity consumption and we know it changes all of the time.

“Take January for example,” Scott added. “Many of us in North Texas forgot how cold it was at the beginning of January because we were wearing shorts and T-shirts at the unseasonably warm start of February. The recent wintry spell in late February also generated a significant number of HDDs, which affected how much electricity homes and businesses were using.”

In addition to comparing details of the weather using degree days, Scott said consumers can:

  • Compare the number of days included in the meter read cycle for each invoice they are reviewing.
  • Log in to their TXU Energy MyAccount or TXU Energy MyEnergy DashboardSM to see estimated spending for the current month and review when they are using electricity.
  • Set up alerts so they know when their usage appears headed toward an invoice that’s more than any level they want.

“Knowing the various factors that affect electricity consumption is the first step in managing consumption and spending,” he said.

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