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PROGRAM RESOURCES |
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INFORMATION RESOURCES |
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EDUCATIONAL RESOURCES |
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Charts & Graphs |
Graphing energy data can yield a wealth of information on how building energy loads perform. Below 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 (thm) consumption. See below for explanation of units.
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In the above chart you will notice that although the number of cooling degree days (CDDs) are less than heating degree days (HDDs), 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 only the fans are running to distribute the warm air. |
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The correlation of natural gas consumption to heating degree days 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 a relationship between days when virtually no energy is needed to run air-conditioning and heating systems. 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 can vary. There is often a different balance point for cooling and for heating. The 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 (CCD). The number of degrees below are heating degree days (HDD).
Therm
A therm is just over 97 cubic feet of natural gas (100,000 Btu's) and is what Gas Companies use to measure consumption. |
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