Active Power

The power, in Watts, used by a device to produce serviceable work. Also referred to as input power.

Active Solar Energy System

see Active Solar Heating System

Active Solar Heating System

A solar water or space-heating system that uses pumps or fans to circulate fluid from the solar collectors to a storage tank system. There are two types of solar heating systems: solar air heating and solar liquid heating. Solar air heating is an air-based system that heats air in an air collector, whereas solar liquid heating is a fluid-based system that heats water or an antifreeze solution in a hydronic collector. Also referred to as active solar energy system.


Adiabatic means impassable, and the adiabatic process refers to a thermodynamic process where a change in temperature of parcel of air can occur without gain or loss of heat from outside the air parcel.

Advanced Meter

A utility meter, new or appropriately retrofitted, that provides real-time information about energy or water consumption and enables two-way communication between a utility and a consumer. Since advanced meters record usage on an hourly basis, or at an interval set by regulatory authorities, consumers are able to voluntarily participate in price-based demand response programs. These programs can potentially help shift consumer usage from peak to off-peak hours, reducing consumer costs and the need for utilities to purchase additional power to meet demand at critical peak times. Also referred to as the smart meter.

Advanced Metering Infrastructure (AMI)

AMI includes the advanced meter, Advanced Metering Communication Device (AMCD), Local Area Network (LAN), Advanced Metering Regional Collector (AMRC), Advanced Metering Control Computer (AMCC), Wide Area Network (WAN), and related hardware, software, and connectivity required for a fully functioning data collection system.

Air Change Rate

A measure of how fast the air in an interior space is replaced by outside (or conditioned) air by ventilation and infiltration. The air change rate is measured in appropriate units, such as cubic meters per hour divided by the volume of air in the room, cubic feet per hour divided by the volume of air in the room, or by the number of times the home's air changes over with outside air.

Air Collector

Device used to heat air using solar energy (part of a solar air heating system). Air collectors are usually installed on a roof or exterior south facing wall.

Air Conditioner

A device for removing heat and moisture from the air by passing it over a cold surface. The end result is cooler and drier air, which is more comfortable. There are a variety of air conditioners available on the market, such as a room air conditioner, a unitary air conditioner, or a central air conditioner.

Air Conditioning

The regulation of the quality, quantity, circulation, temperature, and humidity of an interior space, such as a room, building, or vehicle.

Air Diffuser

An air distribution outlet, usually located in the ceiling, which is designed to mix conditioned air with existing air in the room.

Air Pollution

Refers to the contamination of the atmosphere or air in a building caused by harmful gases, vapors, aerosols, and dust particles. Contamination levels primarily result from human activities, but natural processes also contribute on a much smaller scale. Examples of human-caused pollutants: carbon monoxide from vehicles, smoke from burning wood, coal, and oil, and crop-spraying. Examples of natural pollutants: pollen particles, debris from volcanic eruptions, and salt-water spray.

Alternative Energy

A term that refers to cleaner, alternate energy sources, such as wind, solar, hydro, and geothermal energy. This term excludes reference to traditional, non-renewable resources with high carbon dioxide emissions, such as fossil fuels and nuclear energy.

Automated Meter Read (AMR)

A meter reading that is obtained by the utility through wireless technology. Also referred to as a Network Meter Read, NMR.

Average Daily Usage (ADU)

A value that represents the daily amount of electricity that a customer uses over one billing period. Usually calculated by dividing the total amount of electricity used during the billing period by the number of days in the billing period. Can also apply to water or gas usage.

Average Monthly Usage (AMU)

A value that represents the monthly amount of electricity or water that a customer uses over one year. Usually calculated by dividing the total amount of electricity used during the year by 12. Can also apply to water or gas usage.

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