Absolute Pressure
Gauge pressure plus atmospheric pressure.
Absolute Temperature
Temperature measured from absolute zero.
Absolute Zero Temperature
Temperature at which all molecular motion ceases( -273 C.)
Absorbent
Substance with the ability to take up or absorb another substance.
Absorption Refrigerator
Refrigerator which creates low temperature by using the cooling effect formed when a refrigerant is absorbed by chemical substance.
Accumulator
Storage tank which receives liquid refrigerant from evaporator and prevents it from flowing into suction line before vaporizing.
ACH- Air Changes Per Hour
The number of times that air in a house is completely replaced with outdoor air in one hour.
Actuator
That portion of a regulating valve which converts mechanical fluid, thermal energy or electrical energy into mechanical motion to open or close the valve seats.
Adiabatic Compression
Compressing refrigerant gas without removing or adding heat.
Adsorbent
Substance with the property to hold molecules of fluids without causing a chemical or physical damage.
Aeration
Act of combining substance with air.
Agitator
Device used to cause motion in confined fluid.
AHU (Air Handler Unit)
The inside part of the A/C system that contains the blower, cooling (evaporator) coil, and heater.
Air Change
The amount of air required to completely replace the air in a room or building; not to be confused with recirculated air.
Air Cleaner
Device used for removal of airborne impurities.
Air Conditioner
Device used to control temperature, humidity, cleanliness and movement of air in a confined space.
Air Conditioning
Control of the temperature, humidity, air movement and cleaning of air in a confined space.
Air Cooler
Mechanism designed to lower temperature of air passing through it.
Air Diffuser
Air distribution outlet or grille designed to direct airflow into desired patterns.
Air Diffusion
Distribution of the air in a space, called the treated space, by means of devices, called air terminal devices, in a manner so as to meet certain specified conditions, such as air change rate, pressure, cleanliness, temperature, humidity, air velocity and noise level.
Air Distribution
The transportation of a specified air flow to or from the treated space or spaces, generally by means of duct work.
Air Gap
The space between magnetic poles or between rotating and stationary assemblies in a motor or generator.
Air Handler
Fan-blower, filter and housing parts of a system.
Air-Cooled Condenser
Heat of compression, plus the heat of absorption, is transferred from refrigerant within coil to surrounding air, either by convection or fan or blower.
Airflow
The distribution or movement of air
ASHRAE
A leading HVAC/R Association - American Society of Heating, Refrigerating and Air Conditioning Engineers
ASTM
American Society for Testing and Materials.
Blower (Fan)
An air handling device for moving air in a distribution system.
BTU (British Thermal Unit)
Quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit.
CFC (Chlorofluorocarbon)
A class of refrigerants. Generally refers to the Chlorofluorocarbon family of refrigerants. Sometimes called Freon
CFM (Cubic Feet per Minute)
A standard measurement of airflow that indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being forced through the system. A typical system produces 400
Comfort Zone
The range of temperatures, humidities and air velocities at which the greatest percentage of people feel comfortable.
Compressor
Pump of a refrigerating mechanism which draws a low pressure on cooling side of refrigerant cycle and squeezes or compresses the gas into the high pressure or condensing side of the cycle.
Condenser Coil
Part of the outdoor portion of a split-system air conditioner or heat pump. By converting refrigerant that is in a gas form back to a liquid, the coil sends heat carried by the refrigerant to the outside.
Condensing Unit
Part of a refrigerating mechanism which pumps vaporized refrigerant from the evaporator, compresses it, liquefies it in the condenser and returns it to the refrigerant control
Conduction
The transfer of heat through a solid material.
Convection
The movement of heat by air flow.
COP (Coefficient Of Performance)
COP compares the heating capacity of a heat pump to the amount of electricity required to operate the heat pump in the heating mode.
DAMPER
A device that is located in duct work to adjust air flow.
DB
Dry Bulb Temperature
db (Decibel)
A decibel describes the relative loudness of a sound
De humidification
The reduction of water vapor in air by cooling the air below the dew point; removal of water vapor from air by chemical means, refrigeration, etc.
Duct
A pipe or closed conduit made of sheet metal, fiberglass board, or other suitable material used for conducting air to and from an air handling unit.
EER (Energy Efficiency Ratio)
A ratio calculated by dividing the cooling capacity in Btu's per hour (Btu h) by the power input in watts at any given set of rating conditions, expressed in Btu h per watt (Btu h/watt).
Evaporator Coil
Part of a split-system air conditioner or heat pump located indoors. The evaporator coil cools and dehumidifies the air by converting liquid refrigerant into a gas, which absorbs the heat from the air. The warmed refrigerant is then carried through a tube to the outdoor unit (condenser coil).
Exhaust
The air flow leaving the treated space.
Filter
A device for removing dust particles from air or unwanted elements from liquids.
HCFC (Hydro chloro fluoro carbon)
A class of refrigerants. Generally refers to Halogenated Chlorofluorocarbon family of refrigerants.
Heat Gain
The amount of heat gained, measured in BTU's, from a space to be conditioned, at the local summer outdoor design temperature and a specified indoor design condition.
Heat Loss
The amount of heat lost, measured in BTU's or Kcal from a space to be conditioned, at the local winter outdoor design temperature and a specified indoor design condition.
Heat Pump
Compression cycle system used to supply heat to a temperature controlled space. Same system can also remove heat from the same space.
HFC (Hydro fluoro carbon)
A class of refrigerants. Generally refers to Hydro fluoro carbon family of refrigerants
Humidifier
A device that adds moisture to warm air being circulated or directed into a space.
Humidistat
A device designed to regulate humidity input by reacting to changes in the moisture content of the air.
Humidity
The amount of moisture in the air. Air conditioners remove moisture for added comfort.
HVAC
Heating, Ventilating and Air Conditioning
Infiltration
Air flow inward into a space through walls, leaks around doors and windows or through the building materials used in the structure.
ISO 9000
A family of international standards for quality management and assurance by the ISO (International Standards Organization).
kW
kilowatt, equals 1,000 watts.
kWh
kilowatt hour is the amount of kilowatts of electricity used in one hour of operation of any equipment.
Latent Heat
Heat, that when added or removed, causes a change in state - but no change in temperature.
Manometer
An instrument that measures air pressure differences between locations. Tubes are usually attached to a manometer and run to the spaces where pressures are measured.
Pascals (Pa)
A small unit of air pressure.
Plenum
Air flow passage made of duct board, metal, drywall, or wood. Joins supply and return ducts with HVAC equipment.
Radiation
The transfer of heat directly from one surface to another (without heating the intermediate air acting as a transfer mechanism).
Reciprocating Compressor
A type of compressor used in air conditioners that compresses refrigerant by using a type of "piston" action.
Refrigerant
Substance used in refrigerating mechanism. It absorbs heat in evaporator by change of state from a liquid to a gas,and releases its heat in a condenser as the substance returns from the gaseous state back to a liquid state.
RH
Relative Humidity
ppm
Parts per million
Saturation Temperature
Also referred to as the boiling point or the condensing temperature. This is the temperature at which a refrigerant will change state from a liquid to a vapor or visa versa.
SEER (Seasonal Energy Efficiency Ratio)
The total cooling of a central unitary air conditioner or unitary heat pump in Btu's during its normal annual usage period for cooling divided by the total electric energy input in watt-hours during the same period.
Sensible Cooling Load
The heat gain of the home due to conduction, solar radiation, infiltration, appliances, people, and pets. Burning a light bulb, for example, adds only sensible load to the house. This sensible load raises the dry-bulb temperature.
Sensible Heat
Heat, that when added or removed, causes a change in temperature but not in state.
Set point. The temperature to which a thermostat is set to result in a desired heated space temperature.
Split System
Refrigeration or air conditioning installation, which places condensing unit outside or away from evaporator. These unit are connected together by a supply and return refrigerant lines.
Sub cooled Liquid
Liquid refrigerant which is cooled below its saturation temperature.
Super heated Vapor
Refrigerant vapor which is heated above its saturation temperature. If a refrigerant is superheated, there is no liquid present.
Thermostat
A temperature sensitive switch for controlling the operation of a heater or furnace.
Ventilator
Captures heating or cooling energy from stale indoor air and transfers it to fresh incoming air.
VFD
Variable Frequency Drive, Electronic speed control for motors.
W-Watt, a unit of electricity.
WB
Wet Bulb
WC (Water Column)
Common measure of air pressure used in HVAC systems.
Wet-bulb Temperature
When a wet wick is placed over a standard thermometer and air is blown across the surface, the water evaporates and cools the thermometer below the dry-bulb temperature. This cooler temperature (called the wet-bulb temperature) depends on how much moisture is in the air.
Zone
1) Conditioned space in a house under the control of a thermostat. 2) A space within a house with a distinct pressure compared to other pressure zones.
Zoning
A system in which living areas or groups of rooms are divided into separate spaces and each space's heating/air conditioning is controlled independently.