Alternating current. Mode of transmission of energy, predominant in public supply, in which the voltage varies (usually sinusoidally) between positive and negative limits, typically at 50 cycles per second.

Activity-based targets
The process of estimating expected consumption volumes by reference to production throughput, prevailing weather and other “driving factors”. Comparison between expected and actual consumption reveals randomly-occurring accidental avoidable waste. More detail...

Air handling unit - a device used to condition and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system.

Air compressors
Read article...

Air conditioning
Use of energy in chillers to provide comfortable temperatures (and sometimes humidities) during hot weather. Read this article on how to minimise demand for comfort cooling.

Instrument for measuring the flow of electric current. Where automatically read and results are stored in a database, can be used as a proxy for energy consumption meters.

Automatic meter reading Read article...

Ill-defined term usually denoting automatic meter reading coupled to an analysis and reporting scheme. More..

Air source heat pump. Refrigeration device employed typically for providing heat by cooling the outside air; sometimes reversible so as to provide air cooling.

Aspects, energy
The concept of "energy aspect" first appeared in national energy-management-system standards like IS393 and later EN16001. It was dropped in their successor, ISO50001. See this article from 2010 discussing the value of the idea.

Audit, energy
Systematic inspection of a building, facility, process or transport fleet undertaken with the aim of identifying significant opportunities for improvement in energy efficiency. Requirements are given in the EN16247 European Standard.

Automatic controls
See Controls, automatic.

Avoidable waste
Excess energy consumption, often occurring at random, which can be cured quickly at little or no cost and without disruption Examples...