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Air Change Efficiency A measure of how quickly the air in the room is replaced. It represents, the ratio between the nominal time constant, and the air change time, for the room. Air Change Rates The volumetric rate at which air enters (or leaves) a building or zone expressed in units of building or zone volume. Air Change Time This is the time for all of the air in a room to be changed, and is equal to twice the room mean age. (see air change efficiency; coefficient of air change performance; local air change index; nominal time constant; room mean age; specific flow). Air Cleaner Any device that removes undesirable particles from moving air. Air Conditioner A mechanical refrigeration device used to control temperature, humidity, cleanliness, and movement of air in a confined space. Engineers define the process as one in which a system of mechanical components-usually including a compressor, a fan, condenser coil, evaporator coil and a chemical refrigerant - extracts heat from indoor air and transfers it outside, leaving the cooled indoor air to be recirculated. Any device that can change the temperature, humidity or general quality of the air. Air Curtain A stream of high velocity, temperature controlled air, which is directed downward across an opening. It is designed to exclude exterior draughts, and pollutants blown in from outside. It also prevents the transfer of heat across the boundary, and permits the air-conditioning of a space with an open entrance. Air Distribution The delivery of outdoor or conditioned air to various spaces in a building, usually by mechanical means. Air Duct Pipes that carry warm air and cold air to rooms and back to furnace or air conditioning system. See also duct work and duct systems. Air Exchange Rate Used in two ways 1 ) the number of times that the outdoor air replaces the volume of air in a building per unit time, typically expressed as air changes per hour 2) the number of times that the ventilation system replaces the air within a room or area within the building. Air Exfiltration The uncontrolled outward leakage of indoor air through cracks, interstices, and other unintentional openings of a building, caused by the pressure effects of the wind and/or stack effect. Air Handler The portion of a central air conditioning or heat pump system that moves heated or cooled air throughout a home's ductwork. In some systems, a furnace handles this function. Indoor unit of an air conditioning system which contains heat exchange coil, filters, and fan. Provides conditioned air into the space. Air Infiltration The uncontrolled inward leakage of outdoor air through cracks, interstices, and other unintentional openings of a building, caused by the pressure effects of the wind and/or the stack effect. Air Infiltration The amount of air leaking in and out of a building through cracks in walls, windows and doors. Air Inlet A deliberate opening in a room or a duct wall for the provision of outdoor or conditioned air into the room. Air Leakage The leakage of air in or out of a building or space usually driven by artificially induced pressures. Air Leakage Rate The rate of air leakage in or out of a building or space. Air Outlet A deliberate opening in a building envelope or a duct through which air is expelled to the outside. Air Pollutant Any unwanted substance in air. Air Pressure The force per unit area that air exerts on any surface in contact with it.(si units, pascal (pa), 1 pa is equivalent to 1 n/m2). Air Quality (See acceptable air quality). Air Speed The speed of the air relative to its surroundings. Air Tightness A general descriptive term for the leakage characteristics of a building. The smaller the air leakage rate at a given pressure difference across a building envelope, the greater the air tightness. Air Tightness Standard A standard value of building or component air leakage corresponding to a reference pressure difference across the building envelope or component. Standard values may be expressed in terms of air change rate, flow rate per unit area of opening, flow rate per unit length of crack, or equivalent leakage area. Air To Air Heat Pump A packaged piece of equipment that contains one fan to be connected to ductwork to cool or heat the indoor atmosphere, and one fan to reject (or reclaim) heat to the external atmosphere. These units may be positioned externally or they may be manufactured to be positioned internally (less usual). Air To Water Chillers See air cooled chillers. Air To Water Heat Pump As air to air heat pump but provided with a reversing valve and hot water as well as chilled water. Air Vapor Barrier A moisture impervious layer applied to the surfaces enclosing a space to limit moisture migration. Air Velocity The rate and direction of air movement. (important when considering cooling effects and comfort criteria). Air Vent A purpose provided air inlet or outlet. Air-Conditioning (Also Known As Environmental Control) Technically this is the treatment or control of the air in buildings so as to render it more comfortable or healthful. More commonly associated with the cooling process of indoor air Airflow The mass/volume of air moved between two points. Airflow Rate The mass/volume of air moved per unit of time through a space opening or duct. (si units mass flow rate - kg/s volume flow rate - m3/s). |