ASHRAE Terminology

controlled release of a tracer gas by a pressurized system or pump. (Term is used in ventilation rates measurement.)

a measure of the amount of air moving into and out of a space because of leakage or mechanical ventilation. One air change is a volumetric flow of air equal to the cubic content of the space. For example, if a space has a cubical content of 10,000 cubic feet and the ventilation rate is 1000 cfm, 0.1 (1000/10,000) air change is occurring every minute, or 6 (60 × 0.1) air changes occur per hour.

ventilation airflow divided by room volume. It indicates how many times, during one hour, the air volume from a space is replaced with outdoor air.

exchange of outdoor air with the air already in a building can be divided into two broad classifications: ventilation and infiltration.

an assembly that hangs above the stove or cooktop in the kitchen and contains a skirt or capture panel to contain the rising gases or effluent plume, one or more grease filters, and a fan or tangential blower for forced ventilation used to remove airborne grease, combustion products, smoke, odors, heat, and steam from the air by a combination of filtration and evacuation of the air outside of the building. Air extraction cooker hoods may be ducted (or vented) application, or ductless (or recirculating) application. Ductless or recirculating hoods use particulate and gaseous filtration (activated charcoal) to clean the air to an acceptable quality for returning to the room. Hoods may include lighting. See also cooker hood, Hood, Type I Hood, Type II Hood.

see ventilation air.

natural ventilation by window opening.

introduction of cool, outdoor air into an attic by exhausting its warm air to the outdoors.

fluid flows where the design supply flow volumetric rate equals the design return/exhaust volumetric rate. Also called balanced ventilation or balanced system.

model based on first-principles engineering methods that provides information on the energy-using systems in a building (heating, ventilation, and air conditioning; lighting; occupancy; plug loads; building envelope). The model, along with weather data, serves as the input data for a specific computer building energy simulation program. When run, the computer simulation program will estimate the energy use and demand in the described building for a time interval specified in the building energy model. Depending on the kind of simulation program and how it is set up to run, various kinds of output may be produced.

chilled ceiling systems have a very low profile (often flush with the ceiling) and work by means of convection heat transfer and induced air movement in the room in which they are placed. Chilled ceilings lack the ability to control the humidity or provide ventilation and must be paired with a ventilation system in order to maintain latent heat gains.

single, functional element forming a part of a ventilation or an air-conditioning installation.

the sum of all site energy in kilowatt-hours required to provide cooling via vapor compression, ventilation, dehumidification, humidification, evaporation, absorption, adsorption, or other means.

air terminal device intended to be installed above a natural ventilation exhaust duct with the aim (by creating negative pressure and depending on wind speed) of avoiding reverse flow and increasing flow rate. It may or may not have moving parts.

(1) natural ventilation in which the airflow mainly results from wind pressure effects on the building facades and where stack effects in the building are of less importance. (2) type of ventilating with air supply and exhaust points at opposite sides of ventilated space.

a ventilation system that delivers 100% outdoor air to each individual space in a building.

1. A dedicated outdoor air system (DOAS) uses separate equipment to condition all of the outdoor air brought into a building for ventilation and delivers it to each occupied space, either directly or in conjunction with local or central HVAC units serving those same spaces. The local or central HVAC units are used to maintain space temperature. 2. Primary Air System

Outdoor air unit that provides ventilation directly to a space or sensible heating/cooling units. If equipped with an exhaust fan it can control building pressure. Can have an air-to-air recovery device to save energy . Other options include custom air cleaning, enhanced dehumidification devices, compressors, condensors. 2. Make up air unit.

a type of air-distribution system, used only for cooling purposes, in which air at a temperature below room temperature is supplied to the floor level at a low discharge velocity [<100 fpm (0.5m/s)] and is returned near ceiling level. Thermal plumes, which develop over heat sources in the room, drive the overall floor to ceiling air motion, producing a stratified environment with cooler and fresher air near the floor and warmer and less fresh air near the ceiling.

(1) leakage of indoor air out of a building through similar types of openings. Like natural ventilation, it is driven by natural and/or artificial pressure differences. (2) uncontrolled outward air leakage from conditioned spaces through unintentional openings in ceilings, floors, and walls to unconditioned spaces or the outdoors caused by pressure differences across these openings due to wind, inside-outside temperature differences (stack effect), and imbalances between supply and exhaust airflow rates.

a system consisting of one or more fans that remove air from the building, causing outdoor air to enter by ventilation inlets or normal leakage paths through the building envelope.

(1) a machine used to create flow within a fluid, typically a gas, such as air. (2) any device with two or more blades or vanes attached to a rotating shaft used to produce an airflow for the purpose of comfort, ventilation, exhaust, heating, cooling, or any other gaseous transport. The opening(s) may or may not have an element or elements for connection to ductwork. (3) fan consists of a rotating arrangement of vanes or blades that act on the air (impeller). Usually it is contained within some form of housing or case. This housing or case may direct the airflow or increase safety by preventing objects from contacting the fan blades. Most fans are powered by electric motors, but other sources of power may be used, including hydraulic motors and internal combustion engines. Fans produce airflows with high volume and low pressure, as opposed to compressors, which produce high pressures at a comparatively low volume. A fan blade will often rotate when exposed to an air stream, and devices that take advantage of this, such as anemometers and wind turbines, often have designs similar to that of a fan. (4) see also impeller.

a containment system for the transportation of air and grease vapor. The system is designed and installed to reduce the possibility of the accumulation of combustible condensation, thus reducing the possibility of damage if a fire occurs within the ventilation system.

the entire air volume of a space or building in which the ventilation air is distributed, including ductwork and plenums. The volume of indoor furnishings, equipment, and occupants must be subtracted from the gross indoor volume that is based on interior dimensions of the space or building.

an installation in which a furnace or boiler is installed indoors and all combustion and ventilation air is admitted through grilles or ducts from outdoors and (all such air) does not communicate with air in the conditioned space.

air terminal device that is designed for thermally controlled ventilation (e.g., displacement flow applications). Also see air terminal device.

(1) dedicated replacement air. (2) air brought into a building from the outdoors to replace air that is exhausted. Makeup air may or may not be conditioned. (3) any combination of outdoor and transfer air intended to replace exhaust air and exfiltration. (4) in a cleanroom, air introduced to the secondary air system for ventilation, pressurization, and replacement of exhaust air. (5) in a laboratory or kitchen, outdoor air deliberately brought into the building from the outside and supplied to the vicinity of an exhaust hood to replace air, vapor, and contaminants being exhausted. Makeup air is generally filtered and fan forced, and it may be heated or cooled depending on the requirements of the application. Makeup air may be delivered through outlets integral to the exhaust hood or through outlets in the same room.

a modulating damper or set of dampers used to control the outdoor airflow to the system in excess of minimum ventilation outdoor air for free cooling (airside economizer). Also called economizer outdoor air damper. May also serve to provide the minimum outside airflow control.

(1) the active process of supplying or removing air to or from an indoor space by powered equipment such as motor-driven fans and blowers but not by devices such as wind-driven turbine ventilators and mechanically operated windows. (2) ventilation provided by mechanically powered equipment, such as motor-driven fans and blowers, but not by devices such as wind-driven turbine ventilators and mechanically operated windows.

a damper in parallel with the maximum outdoor air damper to provide the minimum outdoor air required for ventilation.

movement of air into and out of a space primarily through intentionally provided openings (such as windows and doors), through nonpowered ventilators, or by infiltration.

(1) air outside a building or taken from the external atmosphere and, therefore, not previously circulated through the system. (2) ambient air that enters a building through a mechanical ventilation system, through intentional openings for natural ventilation, or by infiltration. (3) compare to outside air.

uses a pipe surrounded by a coil in order to form a radiator system. Passive chilled beams have no method for maintaining the humidity of a room and must be paired with a ventilation system in order to maintain latent heat gains.

a series of numbers and letters consisting of the letters AM, AI, or AU and a two or three digit number. AM identifies an \"as manufactured\" test, that is, the laboratory hood is built and assembled by the manufacturer and testing is performed at the factory. The typical equipment remains in the hood and other activities in the laboratory continue. AI identifies an \"as installed\" test, that is, the laboratory hood is installed at the location of the customer. The hood is tested empty, but with the ventilation system in the installation balanced and the hood in its final location. AU identifies an \"as used\" test, that is, the tests are conducted after the hood has been installed and used by the chemist. An example of the series of numbers and letters is AM yyy where AM identifies an \"as manufactured\" test and yyy is the control level of tracer gas established by the test in ppm. A test rating of AU 0.5, for example, would indicate that the hood controls leakage into the laboratory to 0.5 ppm at the mannequin's sensing point with a tracer gas release rate of 4.0 Lpm (70 mL/s).

natural ventilation by means of a duct mounted vertically or near vertically.

the term may apply to a combination of ailments (a syndrome) associated with a place of work, residence, or assembly. Sick building syndrome can be related to a lack of adequate outdoor air ventilation, improper exhaust, ventilation of odors, chemicals or fumes, or poor indoor-air quality. Other sources of sick buildings may be linked to contaminants produced by outgassing of some types of building materials, VOC, bacteria molds, etc. This syndrome does not conform to a particular illness and is difficult to trace to a specific source. See indoor air quality, volatile organic compounds (VOC).

(1) movement of air into and out of buildings, chimneys, flue gas stacks, or other containers and is driven by buoyancy. Buoyancy occurs due to a difference in indoor to outdoor air density resulting from temperature and moisture differences. The result is either a positive or negative buoyancy force. The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect is also referred to as the chimney effect, and it helps drive natural ventilation and infiltration. (2) movement of air or other gas in a vertical enclosure (e.g., duct, chimney, building), induced by the density difference between the air or other gas in the enclosure and the ambient atmosphere. Note: stack effect is a significant concern in heating-system design for tall buildings in cold climates. Sometimes referred to as chimney effect. (3) pressure difference caused by the difference in density between indoor and outdoor air due to an indoor/outdoor temperature difference. (4) the vertical airflow within buildings caused by temperature differences between the building's interior and exterior.

(1) air delivered by mechanical or natural ventilation to a space, composed of any combination of outdoor air, recirculated air, or transfer air. (2) air entering a space from an air-conditioning, heating, or ventilating apparatus for the purpose of comfort conditioning. Supply air is generally filtered, fan forced, and either heated, cooled, humidified, or dehumidified as necessary to maintain specified conditions. Only the quantity of outdoor air within the supply airflow may be used as replacement air.

fan coil unit package devised for applications in which the use of outdoor and return air mixing is intended to satisfy tempering requirements and ventilation needs.

(1) the process of supplying air to or removing air from a space for the purpose of controlling air contaminant levels, humidity, or temperature within the space. (2) the process of supplying or removing air by natural or mechanical means to or from any space. Such air may or may not have been conditioned.

the minimum amount of outdoor air required for the purpose of controlling air contaminant levels in buildings.

value indicating how effectively specified contaminants in a defined volume are removed or diluted based on the relationship of the concentrations of those contaminants in the air supplied to, removed from, and remaining within the defined volume.

measure of the relationship between the pollutant concentration in the exhaust air and the pollutant concentration in the specified zone.

measure of the relationship between the pollutant concentration in the exhaust air and the pollutant concentration in the specified zone.

rate of airflow to or from a space, expressed in terms of volume per unit of time, either through the ventilation system or infiltration through building envelope. These are commonly expressed as cubic feet per minute (CFM) in USCS units or liters per second (l/s) in SI units.

the sum of the motor nameplate horsepower of all fans that are required to operate as part of the system.

ventilation rated to sustain life and safety.