Course: GFM 102 Technical Aspects of Energy, Resources & Conservation

Reading

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Knowing Heating and Cooling Degree Days (and Their Influences)

Graphing energy data can yield a wealth of information on how building energy loads perform. The above are a series of charts that show the relation between outside temperature and energy use. Data elements are composed of cooling degree days )CDD), heating degree days (HDD) electrical energy consumption (kWH), and natural gas (therm) consumption.

In the above chart you will notice that although the number of cooling degree days (CDDs) are less than heating degree days (HDD), they represent a higher energy load. This is because, for cooling, energy is needed to run fans and high energy consuming compressors. Whereas, heating is provided primarily by natural gas and on the fans are running to distribute the warm air.

The lower chart shows the correlation of natural gas consumption to heating degree days (HDD) is much closer because natural gas is primarily used for heating, whereas electricity also runs lights and other non-temperature related loads.

DEGREE DAYS  –  This unit is used to show the relationship between days when virtually no energy is needed to run air-conditioning and heating system. Theoretically the outside temperature (or balance point) where neither indoor heating nor cooling is needed is 65 degrees F. Actually the balance point for each building an vary. There is often a difference balance point for cooling and for heating. This difference between the daily average temperature for a given day and the balance point (65 degrees F in the above chart) is called a degree day. The number  of degrees above the balance point is cooling degree days (CDD). The number above the balance point is cooling degree days (CDD). The number of degrees below are heating degree days (HDD).

Click here to access the Wikipedia page explaining Heating Degree Days (HDD).
Click here to access the Frederick Community College (MD) Sustainability Program guide (depicting HDD and CDD relationships with electricity and natural gas consumption).