Our glossary provides you with alphabetized entries for the most common industry terms/words. Periodically, we update this glossary, adding more terms/words and their definitions. If you don't find the definition(s) you seek, please check again later, or contact us and we'll gladly add it to our glossary.
The weight of water divided by the weight of air containing the water vapor. This corresponds directly to the dewpoint temperature and does not change with air temperature. (source: ASHRAE F97)
A mechanical refrigeration device used to control temperature, humidity, cleanliness, and movement of air in a confined space.
Indoor unit of an air conditioning system which contains heat exchange coil, filters, and fan. Provides conditioned air into the space.
(AAERVE) Energy recovery components and packaged energy recovery ventilation which employ Air-to-Air Heat Exchangers to recover energy from exhaust air for the purpose of pre-conditioning outdoor air prior to supplying the conditioned air to the space, either directly or as part of an air-conditioning (to include air heating, air cooling, air circulating, air cleaning, humidifying and dehumidifying) system.
Air containing various gaseous components plus water vapor and miscellaneous components (smoke, pollen, other gaseous and biological pollutants not normally contained in free air away from pollution sources). (source: ASHRAE F97)
A ventilation strategy using both an exhaust air blower and a supply or makeup air blower that have equal air flow at equal pressure that will not pressurize or depressurize a building. (source: ASHRAE F97)
British Thermal Unit. Used to measure cooling or heating capacity.
Refrigerating rating system usually measured in BTU ’s per hour (or Btu/h).
A colorless, odorless, incombustible gas, CO 2, formed during respiration, combustion, and organic decomposition.
A colorless, odorless, extremely poisonous gas, CO, formed by incomplete combustion of carbon or a carbonaceous material.
An IP measure of airflow and volume, “Cubic Feet per Minute” also can be expressed in “Cubic Meters per Hour” - M3/H in SI. 1 CFM=0.58 x M3/H.
A pump found in a refrigerating or air conditioning system which pumps refrigerant through pipes between an outdoor condensing unit and an indoor evaporating unit, using pressure. Sometimes referred to as the heart of the refrigeration or a/c system.
Outdoor unit of an air conditioning system which contains compressor, propeller fan, circuit board, and heat exchange coil. Pumps refrigerant to evaporator.
A system for supplying outdoor ventilation air to a building independent of the HVAC air distribution or conditioning system.
Ventilation strategy where ventilation rates are based upon actual occupancy (CO2 DCV is the most common usage and is clearly defined in ASHRAE 62-1989 as “employing CO2 concentration as a surrogate for the concentration of occupancy-related contaminants such as bioeffluents, thus allowing the rate of outdoor air supplied to spaces to be modulated during periods of low occupancy.)
To decrease or maintain lower than normal air pressure in a building environment. To prevent exfiltration or escape of indoor air from a conditioned space.
The saturation temperature at which condensation of water vapor to liquid water takes place. (source: ASHRAE F97)
Air, where all water vapor and contaminants have been removed from atmospheric air.
The measure of energy recovery effectiveness not adjusted to account for that portion of the psychrometric change in the leaving supply air that is the result of leakage of entering exhaust air rather than the exchange of heat or moisture between the airstreams. (source: ARI-1060)
A ventilator combining a full enthalpic air-to-air heat exchanger which transfers both sensible heat and humidity (latent heat) between air streams with some combination of fans or blowers to provide fresh air into a building and exhaust air out of a building at minimized cost.
The exchange of both sensible and latent heat energies.
A thermodynamic function of a system, equivalent to the internal energy plus the product of the pressure and the volume.
stale indoor air leaving a building
The tracer gas concentration difference between the leaving supply air and the entering supply (outdoor) air stream divided by the tracer gas concentration in the entering exhaust (return) air at the 100% rated air flow, expressed as a percentage. (source: ARI-1060)
Airflow leaving the conditioned space.
Outside ventilation air entering a building.
An air conditioning system that is capable of reversing the direction of refrigerant flow to provide either cooling or heating to the indoor space.
A ventilator combining an air-to-air heat exchanger which transfers sensible heat between air streams with some combination of fans or blowers to provide fresh air into a building and exhaust air out of a building.
Heating Season Performance Factor. A rating of the average efficiency of a heat pump unit when operating in the heating mode.
The weight of water divided by the weight of air containing the water vapor. This corresponds directly to the dewpoint temperature and does not change with air temperature.
General term and abbreviation for the industry of Heating, Ventilation, and Air Conditioning.
Mitsubishi Electric’s MSZ and MXZ outdoor units use inverter compressor technology (Variable Frequency Drive) to provide exceptional indoor, high-speed cooling and heating. By responding to indoor temperature changes, these systems reduce power consumption by varying the compressor speed for extra energy savings. The system operates only at the levels needed to maintain a constant and comfortable indoor environment.
Potential heat energy as water vapor / Humidity.
Electrical component consisting of integrated circuits which may accept, store, control, and output information.
A binary (two component) mixture of dry air and water vapor. (source: ASHRAE F97)
The measure of energy recovery effectiveness adjusted to account for that portion of the psychrometric change in the leaving supply air that is the result of leakage of entering exhaust air rather than the exchange of heat or moisture between the airstreams. (source: ARI-1060)
That portion of the Leaving Supply Airflow that originated as Entering Supply Airflow. The Net Supply Airflow Is determined by subtracting air transferred from the exhaust side of the heat exchanger from the gross airflow measured at the Supply Airflow leaving the heat exchanger.
The entering supply (outdoor) airflow divided by the measured (gross) leaving supply airflow. (source: ARI-1060)
Air outside a building in its natural state – Atmospheric Air.
The difference in pressure between two specific points in two separate airstreams (i.e. supply airflow static pressure verses exhaust airflow static pressure).
Pressure drop through the heat exchanger shall be expressed as the difference in static pressure between the Entering Supply Airflow and the Leaving Supply Airflow.
To increase or maintain greater than normal air pressure in a building environment. To prevent infiltration in a building by increasing the internal air pressure above the ambient outside air pressure.
Copper tubing through which refrigerant flows between condenser and evaporator coils. These lines are typically insulated when installed.
The ratio of the amount of water vapor in a volume of air to the greatest amount of water vapor that could be in the same volume of air at the same temperature and pressure expressed as a percent. (source: ASHRAE F97)
Air inside a building returning to an HVAC system or ventilation system.
Seasonal Energy Efficiency Ratio. A rating of the average efficiency of an air conditioning unit in cooling mode.
Comprised of a remote outdoor condensing unit connected by refrigerant pipes to a matching, non-ducted indoor air handler. Special cases for introducing fresh air may call for limited ducting to air handler from outside.
Air weighing 0.075 lb/ft3 [1.2 kg/m3] which approximates dry air at 70º F [21º C] and at a barometric pressure of 29.92 inches of Hg [101.3 kPa]
Pressure classified as having a small or undetectable change with time. (source: ASHRAE F97)
To cause (a solid or gas) to change state without becoming a liquid.
A resistor having semiconductor properties where resistance varies rapidly and predictably with changes in temperature.
A ventilation condition having either a greater supply rate than exhaust rate (pressurization) or a greater exhaust rate than supply rate (depressurization) in a building or other structure.
The pressure exerted by a vapor – at equilibrium with liquid at atmospheric pressure. (source: ASHRAE F97)
The controlled introduction of outside air into a structure, complete with an equal amount of exhaust air.