Understanding HVAC terminology can be challenging, especially if you're new to the field or trying to troubleshoot your system. This glossary covers common HVAC terms and concepts to help you better understand the systems that keep your indoor environment comfortable and efficient. Whether you're a homeowner, a technician, or someone interested in the industry, this guide serves as a quick reference to key terms used in heating, ventilation, air conditioning, and refrigeration systems.
Below is an alphabetized list of common HVAC-related terms to provide clarity on phrases used by professionals in the HVAC industry.
Absolute Pressure (Pabs): The total pressure measured, including both gauge pressure and atmospheric pressure.
AC (Alternating Current): Electric current that reverses its direction periodically. In the US, the current alternates 60 times per second (60 Hz), while in Europe, it alternates 50 times per second (50 Hz).
AFUE (Annual Fuel Utilization Efficiency): A measure of furnace efficiency, representing the percentage of fuel converted into usable heat over the heating season.
Air compressor oil: A lubricant used in air compressors to reduce friction, cool components, and prevent wear.
Air conditioning: The process of removing heat and moisture from an enclosed space to improve indoor comfort.
Air filter: A device that removes dust, pollen, and other particles from the air passing through HVAC systems.
Air handler: A unit used to circulate air as part of heating, cooling, or ventilation systems, often housing components like blowers, filters, and heating/cooling elements.
Ambient Temperature (Tamb): The temperature of the surrounding environment or fluid (usually air) in which a piece of equipment operates.
Ammonia refrigeration: A type of industrial refrigeration system that uses ammonia (NH₃) as a refrigerant due to its high efficiency and environmental benefits.
Ampere (A): The unit of electric current. One ampere represents a flow of one coulomb of charge per second.
Automatic purgers: Devices used in refrigeration systems to remove non-condensable gases that can reduce system efficiency.
B
Boiler: A closed vessel that heats water or produces steam for heating or industrial processes.
Brazed Plate Heat Exchangers (BPHE): Compact heat exchangers that use thin metal plates brazed together to transfer heat between two fluids.
BTU (British Thermal Unit): A unit of heat energy. One BTU is the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit.
C
Calibration Gas: A reference gas used to calibrate gas detectors to ensure accurate readings.
Capacitor (Run and Start): Electrical devices used to store energy. Run capacitors help maintain motor efficiency, while start capacitors provide a short burst of energy to start a motor.
Capillary Tubing: A refrigerant metering device that controls refrigerant flow by restricting its passage through a small-diameter tube.
Check Valve: A valve that allows fluid to flow in only one direction, preventing backflow.
Coefficient of Performance (COP): A measure of efficiency in heating and cooling systems. It is the ratio of heat output to energy input.
Cold storage: Facilities used to store perishable goods at low temperatures, often relying on industrial refrigeration systems.
Commercial refrigeration: Large-scale refrigeration systems used in businesses, such as supermarkets and restaurants, to preserve food and other perishable items.
Compressor: A mechanical device in refrigeration systems that compresses refrigerant gas, increasing its pressure and temperature.
Condenser: A heat exchanger in refrigeration and air conditioning systems where refrigerant releases heat and changes from a gas to a liquid.
Condensing Pressure (Pcond): The pressure of the refrigerant as it changes from a gas to a liquid in the condenser.
Condensing Temperature (Tcond): The temperature at which refrigerant vapor releases heat and becomes liquid in the condenser.
Conduction: The transfer of heat through a material by direct contact of molecules.
Convection: The transfer of heat through the movement of fluids (air or liquid).
Controls (Refrigeration): Devices and systems that regulate the operation of refrigeration equipment, such as thermostats, pressure controls, and timers.
D
DC (Direct Current): Electrical current that flows in one direction only, used in some HVAC systems and controls.
Defrost Controllers: Devices that manage the defrost cycle in refrigeration systems, which is necessary to prevent frost buildup on the evaporator.
Dehumidification: The process of removing moisture from the air to improve indoor air quality and prevent mold growth.
Dew Point: The temperature at which air becomes saturated with moisture, causing condensation.
Dry Bulb Temperature (DBT): The temperature of air measured by a regular thermometer, without considering humidity.
Ductless mini-splits: A type of HVAC system that allows for individual room control without the need for ductwork.
Ductwork: A system of ducts used to distribute heated or cooled air throughout a building.
E
EER (Energy Efficiency Ratio): A ratio that measures the cooling output of an air conditioning system relative to its energy consumption.
Energy Star: A government-backed program that certifies energy-efficient products, including HVAC systems, to reduce energy use and environmental impact.
Enthalpy: The total heat content of a substance, including both its internal energy and the energy required for any phase changes (e.g., liquid to gas).
EPA guidelines: Regulations set by the Environmental Protection Agency to ensure HVAC systems comply with environmental and safety standards.
Evaporative coolers: Devices that cool air by evaporating water, commonly used in dry climates.
Evaporator: The part of a refrigeration system where refrigerant absorbs heat and changes from liquid to gas.
Expansion valves: Components that regulate the flow of refrigerant into the evaporator.
F
Fixed gas detection: Systems that monitor the presence of hazardous gases, such as refrigerants, in industrial environments.
Float switches: Devices used to detect the level of liquid in a tank or system and control pumps or alarms accordingly.
Floodback: The return of liquid refrigerant to the compressor, which can cause damage.
Furnace: A heating unit that produces heat through combustion or electric resistance, typically used in homes or buildings.
G
Gas detector: A device that monitors the presence of gases, including refrigerants, to ensure safety in HVAC and refrigeration systems.
Gas-powered valves: Valves controlled by gas pressure, often used in industrial refrigeration systems.
Gauge pressure: The pressure measured relative to atmospheric pressure.
Gauges & Thermometers: Instruments used to measure pressure, temperature, and other system parameters in HVAC and refrigeration systems.
Geothermal systems: HVAC systems that use the earth’s stable underground temperature to heat and cool buildings efficiently.
H
Heat pump: A system that transfers heat from one location to another, providing both heating and cooling functions.
Heat recovery systems: Systems that capture and reuse waste heat, improving overall energy efficiency.
Heating: The process of raising the temperature of an indoor space for comfort or industrial purposes.
Horsepower (HP): A unit of power used to measure the output of engines and motors in HVAC systems.
HSPF (Heating Seasonal Performance Factor): A rating system for heat pumps that measures heating efficiency over a season.
Humidity: The amount of moisture present in the air, affecting comfort levels and system performance.
HVAC (Heating, Ventilation, and Air Conditioning): A system that provides indoor environmental comfort through heating, cooling, and ventilation.
I
Industrial refrigeration: Large-scale refrigeration systems used in industries like food processing, pharmaceuticals, and chemical manufacturing.
Inverter technology: A technology used in HVAC systems to control compressor speed and adjust output based on demand, improving energy efficiency.
L
Latent heat: The heat absorbed or released during a phase change (e.g., from liquid to gas) without a change in temperature.
Level controls: Devices used to monitor and regulate fluid levels in HVAC and refrigeration systems.
M
Microprocessor boards: Control boards used in HVAC systems to manage various operations such as temperature regulation and fan speed.
Motorized valves: Valves operated by electric motors to control the flow of fluids in HVAC and refrigeration systems.
Motor types (PSC, Shaded Pole, Split Phase): Different types of motors used in HVAC systems. PSC (Permanent Split Capacitor) motors are efficient and commonly used in fans. Shaded Pole motors are simple and inexpensive but less efficient. Split Phase motors are used in higher-torque applications like compressors.
N
Non-condensable gases: Gases that do not liquefy under normal refrigeration system pressures, often reducing system efficiency.
O
Oil filters: Devices used to remove contaminants from the oil in compressors, extending their lifespan.
Oil separator: A device used to separate oil from refrigerant gas to ensure the compressor operates efficiently.
Oil temperature valves: Valves that regulate oil temperature in refrigeration systems to prevent compressor damage.
Overload protector: A safety device that shuts down an HVAC or refrigeration system if it overheats or experiences excessive current draw.
P
Portable gas detectors: Handheld devices used to detect hazardous gases in confined spaces.
Pressure controls: Devices that regulate system pressure to maintain safe and efficient operation in HVAC and refrigeration systems.
Pressure regulators: Components that ensure system pressure stays within safe operating limits.
Pressure relief valve: A safety valve that releases pressure when it exceeds a preset level to prevent system damage.
Probes: Instruments used to measure temperature, pressure, or humidity in HVAC systems.
Psychrometrics: The study of the physical and thermodynamic properties of air-water vapor mixtures.
Pump down procedure: A method used to remove refrigerant from the evaporator to prevent liquid from entering the compressor.
Purgers: Devices used to remove non-condensable gases from refrigeration systems to improve efficiency.
R
Radiant heating: A heating method that uses infrared radiation to transfer heat directly to objects and people in a space.
Receiver: A storage tank that holds liquid refrigerant in a refrigeration system.
Reciprocating compressors: Compressors that use a piston to compress refrigerant gas, commonly used in HVAC systems.
Refrigerants (HFCs, HCFCs, natural): Chemicals used in HVAC and refrigeration systems to transfer heat. HFCs (hydrofluorocarbons) and HCFCs (hydrochlorofluorocarbons) are synthetic refrigerants, while natural refrigerants include ammonia, COâ‚‚, and hydrocarbons.
Refrigeration: The process of removing heat from a space or substance to lower its temperature.
Refrigeration oil: Specialized oil used in compressors to lubricate moving parts and improve system efficiency.
Relief valves: Safety devices that release excess pressure from HVAC and refrigeration systems.
Relays and contactors: Electrical components used to control high-power devices in HVAC systems.
Resistance: The opposition to the flow of electric current, measured in ohms.
Retrofitting: The process of upgrading or modifying existing HVAC systems to improve efficiency or meet new regulations.
S
Saturated refrigerant: A refrigerant at its boiling point, ready to change from liquid to gas or vice versa.
Screw compressors: Compressors that use rotating screws to compress refrigerant gas, known for their reliability in industrial applications.
SEER (Seasonal Energy Efficiency Ratio): A rating system that measures the efficiency of air conditioning systems over a typical cooling season.
SEPR (Seasonal Energy Performance Ratio): Measures the seasonal energy efficiency of process chillers by comparing annual cooling demand to energy input.
Sensors & Transmitters: Devices used to monitor and transmit data on system conditions such as temperature, pressure, and humidity.
Sensible heat: The heat that causes a change in temperature but not in the state of a substance.
Service valves: Valves used to isolate sections of an HVAC or refrigeration system for maintenance or repair.
Short cycling: A condition where an HVAC system turns on and off rapidly, reducing efficiency and potentially causing damage.
Shut-off valves: Valves used to stop the flow of refrigerant or fluid in a system for maintenance or emergency purposes.
Sight glass: A window that allows technicians to visually inspect refrigerant flow and check for contaminants or bubbles.
Single-phase power: A type of alternating current electricity used in residential and small commercial HVAC systems.
Slugging: A condition where liquid refrigerant enters the compressor, potentially causing severe damage.
Smart thermostats: Thermostats that can be programmed or controlled remotely to optimize HVAC system performance and energy efficiency.
Solenoid valves: Electrically controlled valves used to regulate the flow of refrigerant or fluid in HVAC systems.
Specific heat: The amount of heat required to raise the temperature of a unit mass of a substance by one degree Celsius.
Subcooling: The process of cooling a liquid refrigerant below its condensation temperature to improve system efficiency.
Superheating: The process of heating refrigerant gas above its boiling point to ensure only gas enters the compressor.
T
Thermostat: A device used to control the temperature in an indoor space by regulating heating or cooling equipment.
Three-phase power: A type of alternating current electricity used in larger commercial and industrial HVAC systems.
Three-way valves: Valves that allow fluid to flow in one of three directions, often used in complex HVAC systems for temperature control.
Ton of Refrigeration: A unit of cooling capacity equal to the amount of heat needed to melt one ton of ice in 24 hours (12,000 BTU per hour).
Transducers: Devices that convert physical measurements (such as pressure or temperature) into electrical signals.
TXV (Thermostatic Expansion Valve): A component that controls the flow of refrigerant into the evaporator based on temperature and pressure readings.
V
Valve actuators: Devices that operate valves automatically in HVAC systems.
Valve parts: Components of valves, including seals, springs, and diaphragms, which ensure proper operation.
Valve stations: Centralized locations in refrigeration systems where multiple valves are installed for fluid control.
Valve strainers: Filters used to remove debris from fluid before it enters the valve, preventing clogging and wear.
Variable refrigerant flow (VRF): An HVAC technology that allows multiple indoor units to be connected to one outdoor unit, providing independent temperature control for different zones.
Ventilation: The process of circulating fresh air into a space and removing stale air, crucial for indoor air quality and comfort.
Voltage: The electrical potential difference that drives current through a circuit, measured in volts.
Volumetric efficiency: The ratio of the actual amount of refrigerant gas a compressor moves compared to its theoretical capacity.
W
Wet Bulb Temperature (WBT): The lowest temperature that air can reach through evaporation, often used in cooling calculations.
More Common HVAC Terms & Resources
Below, we’ve also compiled a list of essential HVAC acronyms, unit conversions, and formulas to provide you with a quick guide for understanding the technical side of HVAC systems.
HVAC Acronyms and Abbreviations
These acronyms represent commonly used terms in HVAC systems and measurements. Familiarity with them can help you interpret product specifications, system ratings, and energy efficiency standards:
AC (Alternating Current): The type of electric current that reverses its direction periodically, used in most electrical systems worldwide.
AFUE (Annual Fuel Utilization Efficiency): Indicates how efficiently a furnace converts fuel into heat over a typical heating season, expressed as a percentage.
BTU (British Thermal Unit): A unit of heat energy. One BTU is the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit.
COP (Coefficient of Performance): A measure of efficiency in heating and cooling systems, showing the ratio of heat output to energy input.
DBT (Dry Bulb Temperature): The temperature of air measured by a thermometer without considering humidity.
EER (Energy Efficiency Ratio): Evaluates the efficiency of an air conditioning unit by comparing its cooling output to the energy it consumes.
HFC (Hydrofluorocarbon): A type of refrigerant with low ozone depletion potential, commonly used in modern HVAC systems.
HP (Horsepower): A unit of power, often used to describe the capacity of motors and compressors.
HSPF (Heating Seasonal Performance Factor): Rates the efficiency of heat pumps in heating mode over an entire heating season.
HVAC (Heating, Ventilation, and Air Conditioning): Refers to the systems responsible for maintaining indoor comfort through temperature control, ventilation, and air quality.
PSC (Permanent Split Capacitor): A type of motor commonly used in HVAC systems, known for its efficiency and durability.
SEER (Seasonal Energy Efficiency Ratio): Measures the efficiency of air conditioning systems over a typical cooling season.
SEPR (Seasonal Energy Performance Ratio): Used to evaluate the efficiency of process chillers in industrial applications.
TXV (Thermostatic Expansion Valve): A device that regulates the flow of refrigerant into the evaporator, ensuring optimal system performance.
VRF (Variable Refrigerant Flow): A technology that allows for precise temperature control across multiple zones by varying the flow of refrigerant.
WBT (Wet Bulb Temperature): The lowest temperature air can reach through evaporation, used in cooling calculations.
HVAC Unit Conversions
Accurate unit conversions are crucial for understanding system capacities and power requirements. Below are key conversions relevant to HVAC systems:
1 Ton of Refrigeration = 12,000 BTU/hr: Indicates the cooling capacity of air conditioning systems, commonly used in residential and commercial units.
1 Horsepower = 746 Watts: Defines the electrical power equivalent of one horsepower, useful for sizing motors and compressors.
1 kW = 3,412 BTU/hr: Converts kilowatts (a common power measurement) into BTUs for understanding energy use in HVAC systems.
HVAC Formulas
Understanding the fundamental calculations in HVAC can help with system design, troubleshooting, and performance analysis. Here are two commonly used formulas:
Heat Load Calculation (Q): Q = U * A * ΔT
Q: Heat transfer rate (BTU/hr)
U: Overall heat transfer coefficient (BTU/hr·ft²·°F)
A: Surface area of the material (ft²)
ΔT: Temperature difference across the material (°F) This formula calculates the amount of heat that needs to be added or removed to maintain a specific indoor temperature.
EER Calculation (Energy Efficiency Ratio): EER = Cooling Capacity (BTU/hr) / Power Input (W) This formula measures the efficiency of an air conditioning system, helping consumers compare energy performance among models.
These acronyms, conversions, and formulas provide a foundational understanding of HVAC systems, empowering you to make informed decisions whether you’re purchasing equipment, performing maintenance, or troubleshooting issues.
Your HVAC Cheat Sheet for Success
Mastering HVAC terminology, conversions, and formulas is key to understanding the systems that keep buildings comfortable and efficient. Whether you’re troubleshooting a system, comparing products, or designing new installations, having this knowledge at your fingertips makes the process easier and more effective. With this comprehensive guide, you’ll be better equipped to communicate with industry professionals, evaluate system performance, and make informed decisions. Use this as your go-to reference to simplify the complex world of HVAC and ensure every system runs at its peak performance.
For those looking to deepen their understanding of the HVAC and industrial refrigeration industry, check out our article on Industrial Refrigeration Books for expert recommendations and next steps in your learning journey.
