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Heating and Cooling Degree Days Degree days are based on the assumption that when the outside temperature is 65°F, we don't need heating or cooling to be comfortable. Degree days are the difference between the daily temperature mean, (high temperature plus low temperature divided by two) and 65°F. If the temperature mean is above 65°F, we subtract 65 from the mean and the result is . If the temperature mean is below 65°F, we subtract the mean from 65 and the result is Cooling Degree Days.Heating Degree Days-------------------------------------------------------------------------- Example 1: The high temperature for a particular day was 90°F and the low temperature was 66°F. The temperature mean for that day was:( 90°F + 66°F ) / 2 = 78°F Because the result is 78°F - 65°F = 13
Cooling Degree Days The high temperature for a particular day was 33°F and the low temperature was 25°F. The temperature mean for that day was:Example 2: ( 33°F + 25°F ) / 2 = 29°F Because the result is
below 65°F:65°F - 29°F = 36 .Heating Degree DaysThe calculations shown in the two examples above are performed for each day of the year and the daily degree days are accumulated so that we can compare months and seasons. When comparing energy use, you should also consider other energy uses that are not impacted by weather such as lights, appliances, etc. You can estimate the energy used for these purposes by examining the energy used during temperate months such as May and October when little heating or cooling energy is used. The energy used during these periods reflect your base monthly consumption. Subtracting the base use from the total consumption during a winter month will yield an estimate of the energy used just for heating. It is also important to consider the usage period reflected in your energy bill. Your meter is probably not read on the first day of each month and therefore will not be for the same time period as the degree day totals. You can allow for this by comparing over a longer period, such as an entire heating season or several months.OTHER FACTORS : To order offical climate data, contact the National Climatic Data Center (NCDC) at http://www.ncdc.noaa.gov |

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- Page last modified: September 21st 2010 7:58 PM