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What Causes Changes in Energy Use?

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  rev. 22/12/2010        

Excerpted from ENERGY ACCOUNTING:  A Key Tool in Managing Energy Costs; California Energy Commission; 2000

Before considering what methods and means of energy accounting will best serve your organization, it is important to look at what causes building energy use to vary.  These are some of the major factors:


Energy used for heating and cooling varies as a result of changing temperatures.

Only a portion of a building's total energy is weather dependent.  While energy use for cooling or heating (chillers, boilers, heat pumps, and use of some fans) is weather dependent, for example, lighting, office equipment, and ventilation energy use is not.  Advanced energy accounting systems will automatically determine how much of your usage is weather dependent, and how much is not.  For ongoing monitoring and tracking, look for software providers who will keep your weather data current for all of your buildings, so you don't have to do it manually.

Building area changes

Changes in building size will also strongly influence energy consumption. If square footage is added to a facility, energy use can be expected to increase.  Most energy accounting software can correct for changes in building area by assuming that energy use will increase (or decrease) proportionately to square footage.  Some software programs can account for non-proportional changes by adding or subtracting a fixed amount or percentage to the baseline consumption for each month.

Operations and schedule changes

Changes in building occupancy or schedules for building and equipment operation will affect energy use.  If a building is open longer, more energy will be used for heating, cooling, and lighting.  If a school cafeteria brings in pre-cooked meals in disposable containers instead of doing local cooking and dishwashing, kitchen energy use will be reduced.

Changes in building equipment

When new equipment is added or existing heating, cooling, ventilation, hot water, lighting, or other energy using equipment is replaced, modified, or abandoned, energy consumption will change. Energy accounting can document savings due to energy efficiency retrofits, or other changes in equipment.

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