TABLE OF CONTENTS Experience has shown that, for buildings requiring an inside air temperature of approximately 70 F, the amount of fuel or heat used per day is proportional to the number of degrees the average outside temperature falls below about 65 F. The degree day is based upon this principle. Thus the number of degree days (65 F base) per day is the difference between 65 F and the daily mean temperature when the latter is less than 65 F.
The number of degree days for a given day is thus: (65 F daily mean temperature for that day) 1 (day), and the number of degree-days for any longer period is the sum of all such products for as many days as the period covers.
No attention is given to those days when the outside temperature averages above 65 F.
The highest temperature recorded in Baltimore on December 12, 1931, was 70 F and the minimum was 52 F. The daily mean temperature was therefore (70 + 52) 2 or 61 F. The number of degree days for that day in Baltimore was thus (65 61) 1 = 4. Carrying through this operation for each of the 31 days for December 1931, it is found that the number of degree-days in Baltimore for that month was 601.
The degree-day thus defined is now so widely used that when the unit is mentioned in the United States it is understood that the 65 F base is referred to unless some other base or some...
