Helpful Event Information - Climate Control / HVAC Glossary

The next time you need to rent a HVAC climate control equipment, you'll know your stuff! Below is a comprehensive Climate Control / HVAC Glossary of Terms that will give you the information you need to know.

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Climate Control / HVAC Glossary of Terms

A
Absolute Zero: Complete absence of heat; believed to be -459.67°(-273.15°C).

AFUE (Annual Fuel Utilization Efficiency): A measure of a gas furnace’s efficiency in converting fuel to energy. The higher the rating, the more efficient the unit.

Air Change: The amount of air required to completely replace the air in a room or building.

Air Conditioning: A process that maintains comfort conditions in a defined area.

Air Diffuser: Air distribution outlet or grille designed to direct airflow into desired patterns.

Airflow: The distribution or movement of air.

Air Vent: A fitting used to vent air manually or automatically from a system.

Ambient Temperature: Temperature of surrounding air. In air conditioning, it refers to outside air temperature.

Atmospheric Pressure: Weight of air and liquid at various altitudes.

B
Balance Point: The lowest outdoor temperature at which the refrigeration cycle of a heat pump will supply the heating requirements without the aid of a supplementary heat source.

Blower (Fan): An air handling device for moving air in a distribution system

Boiling Point: Temperature at which a liquid changes to a vapor.

BTU: Abbreviation for British Thermal Unit. Quantity of heat required to raise temperature of one pound of water 1°F. All substances are rated in relation to water as standard of measurement.

Burner: A device used to prepare and burn fuel.

C

Capacity: The output or producing ability of a piece of cooling or heating equipment. Cooling and heating capacities are measured in BTUs.

Carbon Monoxide: A poisonous, colorless, odorless, tasteless gas generated by incomplete combustion.

Celsius: Thermometer scale based on O°C as freezing point of water and 100°C as the boiling point.

CFM (Cubic Feet per Minute): A standard measurement of airflow commonly used to measure the rate of air flow in an air conditioning system.

Charge: Specific amount of refrigerant by weight or volume in a refrigerating unit.

Code: The local, state, or national rules that govern safe installation and service of systems and equipment for the purpose of safety of the public and trade personnel.

Compression: Reduction in volume and increase of pressure of a gas or vapor.

Compressor: Component used to change low pressure refrigerant to high pressure refrigerant.

Compressor Shaft Seal: A seal surrounding the compressor shaft that permits the shaft to turn without loss of refrigerant or oil.

Condensate: The moisture collected on an evaporator coil.

Condensate Pump: A small pump used to pump condensate to a higher level.

Condensation: Process of changing a gas to a liquid.

Condenser: The condenser's function is to radiate heat. Radiator-type component where refrigerator gives off heat by being changed from a gas to a liquid.

Condensing Pressure: Head pressure read from gauge at high side service valve; pressure from discharge side of compressor into condenser.

Condensing Temperature: Temperature at which compressed gas in condenser changes from gas to a liquid.

Conduction of Heat: Ability of substance to conduct heat (metal and glass conduct heat more readily than insulating material such as spun glass).

Cycle: A complete sequence of events (from start to finish) in a system.

D

Damper: Found in ductwork, the damper is a movable plate that opens and closes to control airflow. Dampers can be used to balance airflow in a duct system. They are also used in zoning to regulate airflow to certain rooms.

Defrost Cycle: The process of removing ice or frost buildup from the outdoor coil during the heating season.

Dehumidification: 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.

Density: Weight or mass of a gas liquid or solid.

Desiccant: A drying agent used inside air conditioning systems to absorb and hold moisture.

Dew Point: The exact temperature at which moisture begins to form.

Discharge Line: Line connecting compress outlet to the condenser inlet.

Downflow: Refers to a type of precision air conditioning system that discharges air downward, directly beneath a raised floor, commonly found in computer rooms and modern office spaces.

Ductwork: Pipes or channels that carry air throughout your home. In a home comfort system, ductwork is critical to performance — as critical as the equipment itself, in fact.

E

Emergency Heat (Supplementary Electric Heat): The back up electric heat built into a heat pump system. The same as an auxiliary heater, except it is used exclusively as the heat source when the heat pump needs repair.

Energy Efficiency Ratio (EER): An equipment efficiency rating that is determined by dividing the output in Btu by input in watts.

Evacuate: To create a vacuum to remove air and moisture in the system. The purpose of the vacuum is to extract any moisture from the system as well as provide assurance against possible leaks.

Evaporation: Process of changing a liquid to a gas.

Evaporator: The evaporator serves as the heat absorption component. Component where liquid refrigerant is changed to a gas as it absorbs heat from inside air.

Expansion: Reduced pressure on liquid refrigerant lowers boiling point and refrigerant changes to a gas and absorbs heat.

Expansion Valve: Device which restricts flow of high pressure refrigerant thus lowering refrigerant pressure.

F

Fahrenheit: Thermometer scale based on 32°F as freezing point of water and 212°F as the boiling point of water.

Fahrenheit Scale: The temperature scale that places the boiling point of water at 212'F and the freezing point at 32'F.

Fan: A device that produces a pressure difference in air to move it.

Filter: A device for removing dust particles from air or unwanted elements from liquids.

Fittings – Hoses: Air conditioning hoses are designed to control liquid and gas at high pressures and temperatures.

Flooded Evaporator Coil: Too much liquid refrigerant in evaporator coil resulting in poor cooling.

Flush: During installation or repair of air conditioning systems, the system should be flushed with clean special purpose fluids prior to the evacuation and charge with new R12 or R134a. Flushing removes contamination such as particles of rubber or metal that could be harmful to the system.

Free Cooling System: Typically a water cooled or glycol cooled system with an additional coil that provides chilled water cooling when the outdoor ambient is cold thereby reducing or eliminating compressor operation.

Freeze Up: Excess ice or frost accumulation on an evaporator to the point that airflow may be affected.

Freon: A general term used to identify, any of a group of partially or completely halogenated simple hydrocarbons containing fluorine, chlorine or bromine, which are used as refrigerants.

Furnace: That part of an environmental system which converts gas, oil, electricity or other fuel into heat for distribution within a structure.

G

Gas: A vapor having no particles or droplets of liquid.

Gas Furnace Heat Exchanger: Located in the furnace, the heat exchanger transfers heat to the surrounding air, which is then pumped throughout your home.

Gauge Set: A set of gauges attached to the compressor service valves for testing or measuring pressure or vacuum.

H

Head Pressure: Pressure of refrigerant from discharge reed valve through lines and condenser to expansion valve orifice.

Heat: Energy that causes molecules to be in motion and to raise the temperature of a substance.

Heat Exchanger: A device that transfers heat from one substance to another.

Heat Pump: Compression cycle system used to supply heat to a temperature controlled space. Same system can also remove heat from the same space.

Hg: Chemical symbol for mercury. Inches of mercury is a measure of pressure or vacuum.

Hot Gas Bypass Line: Line connecting compressor outlet to evaporator inlet.

HSPF (Heating Seasonal Performance Factor): This rating is used in measuring the heating efficiency of a heat pump. The higher the number, the more efficient the unit.

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.

HVAC (Heating, Ventilation and Air Conditioning): The general industry term encompassing a variety of home comfort equipment, including air conditioners, furnaces, thermostats, filters, ductwork and filters.

J

Joule: In air conditioning it is the metric unit of energy or heat (1J = 1055 Btu).

Junction Box: A metal or plastic box within which electrical connections are made.

L

Latent Cooling Capacity: An A/C system's capability to remove moisture from the air.

Latent Heat: Amount of heat energy required to change a substance from one state of matter to another without changing its temperature.

Liquid Line: Pipe or hose connecting condenser to expansion valve.

Low Side: That portion of system from orifice in expansion valve through evaporator line or lines through compressor service valve to compressor reed valve. Also called suction side.

M

Modulator Valve: A device that limits and maintains minimum pressure in the evaporator.

N

Natural Gas: A fossil fuel formed over millions of years from dead vegetation and animals that were deposited or washed deep into the earth.

P

Pilot Light: The flame that ignites the main burner on a gas furnace.

Precision Air Conditioning: Precision A/C systems are primarily designed for cooling electronic equipment, rather than people. 

Pressure: Force upon a body, as force upon a liquid, increases the liquid's boiling point.

Pressure Drop: Difference in pressure between any two points caused by friction, restriction, etc.

Pressure Switch: The pressure switch senses internal pressures and can cycle the compressor off and back on based on minimum and maximum pressure limits. Pressure switches also turn on or off your condenser fan or radiator fan.

Pressure Relief Valve: The pressure relief valve relieves pressure from the system to protect components when internal pressures become too high.

Propane: An LP gas used for heat.

PSI: Abbreviation for pounds per square inch above atmospheric pressure.

Pump: A device that forces fluids through a system.

Purge: To remove or release fluid from a system.

R

Radiation: Heat flow through space, traveling and acting much like light rays.

Ram Air: Air that is forced around the condenser coils as the vehicle travels in a forward direction.

Refrigerant: Liquid used in refrigeration system producing cold by removing heat.

Register: Combination grille and damper assembly covering an air opening or end of an air duct.

Relay: A small electromagnetic device to control a switch, motor, or valve.

Return Air: Air drawn into a heating unit after having been circulated from the heater's output supply to a room.

Rollout Switch: A heat-sensitive protective device that opens the circuit if flame migrates away from the burner box.

Room Temperature: This is an often quoted figure of around 20°C.

S

Seasonal Energy Efficiency Ratio (SEER): An equipment efficiency rating that takes into account the startup and shutdown for each cycle.

Sensible Heat: Heat which causes a change in temperature of a substance but not a change in state.

Sensor: A component for detection that changes shape, form, or resistance when a condition changes.

Set Point: The temperature to which a thermostat is set to result in a desired heated space temperature.

Sight Glass: Window in receiver-drier or in liquid line to observe refrigerant flow.

Specific Heat: Quantity of heat required to change the temperature of some amount of a substance.

Split System: The combination of an outdoor unit (air conditioner or heat pump) with an indoor unit (furnace or air handler). Split systems must be matched for optimum efficiency.

Substance: Any form of matter that can be weighed or measured; may be solid, liquid, or gas.

Suction Line: Line connecting evaporator outlet to compressor inlet.

Superheat: Added heat intensity to a gas after complete evaporation of a liquid; controlled by increasing pressure in air conditioning systems.

T

Temperature: A word used to describe the level of heat of molecular activity.

Thermostat: A thermostat consists of a series of sensors and relays that monitor and automatically control the functions of a heating and cooling system.

Ton: A unit of measurement used for determining cooling capacity. One ton is the equivalent of 12,000 BTUs per hour.

Tonnage: The unit of measure used in air conditioning to describe the cooling capacity of a system.

U

Upflow: A type of air conditioning system that discharges air into the conditioned space via a top-mounted discharge structure or through an overhead duct system.

V

Vacuum: Referred to as less than atmospheric pressure and expressed as inches of mercury in Hg or kilopascals kPa.

Vapor: The gaseous state of a substance.

Viscosity: The measure of resistance of a fluid to flow.

W

Watt: In air conditioning, capacity is shown in Btu or Watts (1 Btu/hr = 0.293 W/hr).

Water Cooled System: A type of air conditioning system that uses freon as a refrigerant and water as a condensing medium. 

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