Glossary of Terms

Term	Definition
ABSORPTANCE	The ratio of the radiation absorbed by a surface to the total energy falling on that surface described as a percentage. The ratio of the radiation absorbed by a surface to the total energy falling on that surface described as a percentage.
ACCESS CHARGE	A charge paid by all market participants withdrawing energy from the ISO controlled grid. The access charge will recover the portion of a utility's transmission revenue requirement not recovered through the variable usage charge.
ACOP (Adjusted Coefficient of Performance)	A standard rating term that was used to rate the efficiency of heat pumps in California. ACOP was replaced by Heating Seasonal Performance Factor (HSPF) in 1988.
ACTIVE SOLAR ENERGY	Solar radiation used by special equipment to provide space heating, hot water or electricity.
ACTIVE SOLAR ENERGY SYSTEM	A system designed to convert solar radiation into usable energy for space, water heating, or other uses. It requires a mechanical device, usually a pump or fan, to collect the sun's energy.
ADDITION	An alteration to an existing building that increases conditioned space.
ADJUSTMENT BID	A bid that is used by the ISO to adjust supply or demand when congestion is anticipated.
ADVERSE HYDRO	Water conditions limiting the production of hydroelectric power. In years having belownormal levels of rain and snow, and in seasons having less than usual runoff from mountain snowpack, there is then less water available for hydro energy production.
AFTER-MARKET	broad term that applies to any change after the original purchase, such as adding equipment not a part of the original purchase. As applied to alternative fuel vehicles, it refers to conversion devices or kits for conventional fuel vehicles.
AFUE (Annual Fuel Utilization Efficiency)	A measure of heating efficiency, in consistent units, determined by applying the federal test method for furnaces. This value is intended to represent the ratio of heat transferred to the conditioned space by the fuel energy supplied over one year.
AGGREGATOR	An entity responsible for planning, scheduling, accounting, billing, and settlement for energy deliveries from the aggregator's portfolio of sellers and/or buyers. Aggregators seek to bring together customers or generators so they can buy or sell power in bulk, making a profit on the transaction.
AIR CHANGE	The replacement of a quantity of air in a space within a given period of time, typically expressed as air changes per hour. If a building has one air change per hour, this is equivalent to all of the air in the building being replaced in a onehour period.
AIR CONDITIONER	An assembly of equipment for air treatment consisting of a means for ventilation, air circulation, air cleaning, and heat transfer (either heating or cooling). The unit usually consists of an evaporator or cooling coil, and an electricallydriven compressor and condenser combination.
AIR FILM	A layer of still air adjacent to a surface which provides some thermal resistance.
AIR FILM COEFFICIENT	A measure of the heat transfer through an air film. [See ASHRAE Table 1, ASHRAE Handbook, 1985 Fundamentals]
AIR POLLUTION	Unwanted particles, mist or gases put into the atmosphere as a result of motor vehicle exhaust, the operation of industrial facilities or other human activity./
AIR-TO-AIR HEAT EXCHANGER	A device with separate air chambers that transfers heat between the conditioned air being exhausted and the outside air being supplied to a building.
ALCOHOL FUELS	A class of liquid chemicals that have certain combinations of hydrogen, carbon and oxygen, and that are capable of being used as fuel.
ALTERATION	Any change or modification to a building's construction. [See Addition].
ALTERNATING CURRENT	(AC) Flow of electricity that constantly changes direction between positive and negative sides. Almost all power produced by electric utilities in the United States moves in current that shifts direction at a rate of 60 times per second.