Degree days, measure of stress on air conditioners, up slightly in 2012

  • Dyana DeSantis of Baltimore reads a book at Fort McHenry on an unusually hot day in April.
Dyana DeSantis of Baltimore reads a book at Fort McHenry on an… (Barbara Haddock Taylor…)
September 17, 2012|By Scott Dance, The Baltimore Sun

Summer 2012 may have been the coolest in three years, but you nevertheless have likely paid slightly more to cool your house than you did a year earlier.

The number of cooling degree days tallied so far this year is slightly ahead of where they were a year ago, at 1,505 versus 1,491 last year. Degree days are a measure of heating or cooling; in the summer months, they count up the amount by which average temperatures rise above 65 degrees.

So, for example, it would take 75 days with an average temperature of 85 degrees to accumulate 1,500 degree days (20 degrees, for the difference between 65 and 85, times 75 days equals 1,500).

The average temperature was 77.4 degrees for the meterological summer, which includes June, July and August. That was down slightly from 77.8 degrees last summer and 79.3 degrees in summer 2010, the warmest on record.

The degree days tally includes all of the year so far, so warmth in May helped push this year's total ahead of last year's. May's average temperature of 69 degrees was seventh-warmest on record, about two degrees warmer than May 2011.

With highs in the 70s for most of the past week and a half, many have likely shut off the air conditioning by now, so the tally has slowed. Once average temperatures get down into the 50s, the year's count of heating degree days will resume.

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