Glossary of Terms
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.
Air Conditioner:
Assembly of equipment for the simultaneous control of air temperature, relative humidity, purity, and motion.
Air Cooled:
Uses a fan to discharge heat from the condenser coil to the outdoors.
Air-Source: Air is being used as the heat source or heat sink for a heat pump.
Air Handler:
Indoor unit of an air conditioning system which contains heat exchange coil, filters, and 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).
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.
BTU:
British Thermal Unit. The amount of energy needed to change the temperature of one pound of water by one degree Fahrenheit. In practical terms, it represents a unit of measure of heat extracted from your home for cooling.
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.
Central Air Conditioner System:
System in which air is treated at a central location and carried to and from the rooms by one or more fans and a system of ducts.
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:
The pump that moves the refrigerant from the indoor evaporator to the outdoor condenser and back to the evaporator again. The compressor is often called “the heart of the system” because it circulates the refrigerant through the loop.
Condenser Coil:
A series or network of tubes filled with refrigerant, normally located outside the home, that removes heat from the hot, gaseous refrigerant so that the refrigerant becomes liquid again.
Condensing Unit:
Outdoor unit of an air conditioning system which contains compressor, propeller fan, circuit board, and heat exchange coil. Pumps refrigerant to evaporator.
Cooling Capacity:
A measure of the ability of a unit to remove heat from an enclosed space.
COP:
Coefficient of Performance of a heat pump means the ratio of the rate of useful heat output delivered by the complete heat pump unit (exclusive of supplementary heating) to the corresponding rate of energy input, in consistent units and under operating conditions.
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.
Dry Air:
Air, where all water vapor and contaminants have been removed from atmospheric air.
EER:
Energy Efficiency Ratio means the ratio of the cooling capacity of the air conditioner in British Thermal Units per hour, to the total electrical input in watts under ARI-specified test conditions.
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.
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 Exchange:
The exchange of both sensible and latent heat energies.
Enthalpy:
A thermodynamic function of a system, equivalent to the internal energy plus the product of the pressure and the volume.
Evaporator Coil:
A series or network of tubes filled with refrigerant located inside the home that take heat and moisture out of indoor air as liquid refrigerant evaporates.
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.
Exhaust Airflow:
Airflow leaving the conditioned space.
Free Delivery:
There are no ducts and the unit may be installed in the field without ducts if needed.
Fresh Air (FA):
Outside ventilation air entering a building.
Ground-Source:
The ground or soil below the frost line is being used as the heat source or heat sink for a heat pump.
Ground Water-Source:
Water from an underground well is being used as the heat source or heat sink for a heat pump.
Heat Pump:
An air conditioner capable of heating by refrigeration. It may or may not include a capability for cooling. Outside air or water is used as a heat source or heat sink, depending upon whether the system is heating or cooling.
Heating Capacity:
A measure of the ability of a unit to add heat to an enclosed space.
HSPF:
Heating Seasonal Performance Factor means the total heating output of a heat pump in British Thermal Units during its normal usage period for heating divided by the total electrical energy input in watt-hours during the same period.
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.
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.
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.
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.
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.
Return Air (RA):
Air inside a building returning to an HVAC system or ventilation system.
SEER:
Seasonal Energy Efficiency Ratio means the total cooling output of a central
air conditioner in British thermal units during its normal usage period for
cooling divided by the total electrical energy input in watt-hours during the
same period as determined using the ARI-specified test procedure. This rating
is only for units with cooling capacity less than 65,000 Btu/hr. The higher
the SEER, the more efficient the unit. The more efficient the unit, the lower
the operating cost.
Single Package: A central air conditioner which combines both condenser and
air handling capabilities in a single packaged unit.
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.
Split System:
A central air conditioner consisting of two or more major components. The system usually consists of a compressor-containing unit and condenser, installed outside the building and a non-compressor -containing air handling unit installed within the building. This is the most common type of system installed in a home.
Standard Air:
Air weighing 0.075 lb/ft3 [1.2 kg/m3] which approximates dry air at 70° F [21° 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.
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.
Ton:
The unit of measurement for air conditioning system capacity. One ton of air conditioning removes 12,000 Btu’s of heat energy per hour from a home. Central air conditioners are sized in tons. Residential units usually range from 1 to 5 tons.
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.
Ventilation:
The controlled introduction of outside air into a structure, complete with an equal amount of exhaust air.
Water-Source:
Water is being used as the heat source or heat sink for a heat pump. Sources of underground water are wells and sources of surface water are lakes, large ponds, and rivers.
Year-Round:
Air Conditioner which uses gas or oil for heating.
