Glossary

Absolute Humidity

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)

Air Conditioner

A mechanical refrigeration device used to control temperature, humidity, cleanliness, and movement of air in a confined space.

Air Handler

Indoor unit of an air conditioning system which contains heat exchange coil, filters, and a fan. Provides conditioned air into the space.

Air-to-Air energy recovery ventilation equipment

(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.

Atmospheric Air

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)

Balanced Ventilation

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)

BTU

British Thermal Unit. Used to measure cooling or heating capacity.

Capacity

Refrigerating rating system usually measured in BTU ‘s per hour (or Btu/h).

Carbon Dioxide

A colorless, odorless, incombustible gas, CO 2, formed during respiration, combustion, and organic decomposition.

Carbon Monoxide

A colorless, odorless, extremely poisonous gas, CO, formed by incomplete combustion of carbon or a carbonaceous material.

CFM

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.

Compressor

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.

Condensing Unit

Outdoor unit of an air conditioning system which contains compressor, propeller fan, circuit board, and heat exchange coil. Pumps refrigerant to evaporator.

Dedicated Outdoor Air System (DOAS)

A system for supplying outdoor ventilation air to a building independent of the HVAC air distribution or conditioning system.

Demand Control Ventilation (DCV)

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.)

Depressurization

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.

Dewpoint

The saturation temperature at which condensation of water vapor to liquid water takes place. (source: ASHRAE F97)

Dry Air

Air, where all water vapor and contaminants have been removed from atmospheric air.

Effectiveness

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)

Energy Recovery Ventilator (ERV)

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.

Enthalpy

A thermodynamic function of a system, equivalent to the internal energy plus the product of the pressure and the volume.

Enthalpy Exchange

The exchange of both sensible and latent heat energies.

Exhaust Air (EA)

Stale indoor air leaving a building

Exhaust Air Transfer Ratio (EATR)

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)

Exhaust Airflow

Airflow leaving the conditioned space.

Fresh Air (FA)

Outside ventilation air entering a building.

Heat Pump

An air conditioning system that is capable of reversing the direction of refrigerant flow to provide either cooling or heating to the indoor space.

Heat Recovery Ventilator (HRV)

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.

HSPF

Heating Season Performance Factor. A rating of the average efficiency of a heat pump unit when operating in the heating mode.

Humidity Ratio

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.

HVAC

General term and abbreviation for the industry of Heating, Ventilation, and Air Conditioning.

Inverter

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.

Latent Energy

Potential heat energy as water vapor / Humidity.

Microprocessor

Electrical component consisting of integrated circuits which may accept, store, control, and output information.

Moist Air

A binary (two component) mixture of dry air and water vapor. (source: ASHRAE F97)

Net Effectiveness

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)

Net Supply Airflow

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.

Outdoor Air Correction Factor (OACF)

The entering supply (outdoor) airflow divided by the measured (gross) leaving supply airflow. (source: ARI-1060)

Outside Air (OA)

Air outside a building in its natural state – Atmospheric Air.

Pressure Differential

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

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.

Pressurization

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.

Refrigerant Lines

Copper tubing through which refrigerant flows between condenser and evaporator coils. These lines are typically insulated when installed.

Relative Humidity

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)

Return Air (RA)

Air inside a building returning to an HVAC system or ventilation system.

SEER

Seasonal Energy Efficiency Ratio. A rating of the average efficiency of an air conditioning unit in cooling mode.

Sensible Heat

Temperature

Split Ductless System

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.

Standard Air

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]

Static Pressure

Pressure classified as having a small or undetectable change with time. (source: ASHRAE F97)

Sublimation

To cause (a solid or gas) to change state without becoming a liquid.

Thermistor

A resistor having semiconductor properties where resistance varies rapidly and predictably with changes in temperature.

Unbalanced Ventilation

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.

Vapor Pressure

The pressure exerted by a vapor – at equilibrium with liquid at atmospheric pressure. (source: ASHRAE F97)

Ventilation

The controlled introduction of outside air into a structure, complete with an equal amount of exhaust air.