Glossary of HVAC Terms
Here are some common words and their translations used around the HVAC world:
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- Access Port: Usually a small valve opening designed to check pressure. It does not have a service valve so it cannot control the flow of refrigerant.
- AFUE: Annual Fuel Utilization Efficiency is a measurement used to rate furnace efficiencies by dividing the ratio of heat output by heat input.
- AGA: American Gas Association, Inc.
- AHRI: The Air-Conditioning, Heating, and Refrigeration Institute (AHRI) is the trade association representing manufacturers of HVACR and water heating.
- Air Conditioner: A device that changes humidity levels, temperature or quality of air.
- Airflow Volume: Measured in cubic feet per minute (cfm), this is the amount of air circulated in a space.
- Air Handler: Indoor part of the air conditioning system including the circulating fan and evaporator (summer) / condenser (winter) coil.
- Air Cooled Condensers: Typical type. Air is drawn over the metal fins/grates.
- BTU: A British Thermal Unit is a measurement of the amount of heat required to raise or lower the temperature of one pound of water one degree Fahrenheit.
- BTU/h: British Thermal Units per hour
- Burner: The device that facilitates the combustion of air and gas.
- Burner Orifice: The opening in the burner through which the gas or fuel passes prior to combustion.
- Capacity: HVAC capacity is the output produced by the heating or cooling unit and is measured in BTUs per hour.
- Capillary Tube: Seen in smaller appliances like window units, refrigerators. This has a fixed orifice. The phase change of the refrigerant is smaller due to the smaller amount of refrigerant making it’s way through the orifice. This makes more super heat.
- Compressor: “Vapor compressor” This is designed to increase pressure of refrigerant in order to increase temperature. Outdoor Unit.
- Celsius: A temperature scale that registers the freezing point of water as 0° and the boiling point as 100° under normal atmospheric pressure.
- CFM: Cubic Feet per Minute – A measurement of airflow volume.
- Charging a System: Adding coolant, or refrigerant, to an HVAC system.
- Condensate: As warm air is pulled or pushed across the cool evaporator coil the coil perspires, creating liquid, or condensate which is mechanically drained away from the equipment.
- Condenser Fan: A fan that accelerates the movement of air over the condenser coil, facilitating the removal of heat from the refrigerant.
- Compressor Inlet: This controls the capacity of a rotary screw compressor. By opening and closing the air intake, the capacity of a rotary screw compressor can change.
- Discharge Line: Line between compressor & condenser.
- Condenser Coil: “Heat rejector” Outdoor unit that exhausts hot air absorbed from the refrigerant allowing the refrigerant to be converted from vapor to liquid and complete the refrigeration process.
- DC:Direct Current. A type of electrical current that only flows in one direction.
- Damper: Found at the junction points of ductwork, these sheet metal plates can be opened or closed to control the flow of air into a zone.
- Dehumidifier: A device that removes humidity, or moisture, from the air.
- Diffuser: A grille over an air supply duct with vanes that distribute the discharging air in a specific pattern or direction.
- DOE: Department of Energy.
- Downflow Furnace: A furnace with an intake on the top and an air discharge at the bottom.
- Drain Pan: Also know as a condensate pan. As the refrigerant vapor is liquefied, the drain pan collects the condensate and funnels it to the drain line.
- Dry Bulb Temperature: The temperature as measured without the consideration of humidity.
- Duct work: A network of metal, fiberboard or flexible material flowing throughout a space which delivers air from an HVAC unit to the respective zones of a home or office.
- Electronic Expansion Valve (EEV or EXV): Just like the TXV except it using electronics to monitor it.
- Expansion Line: (not always there). Sometimes found on ductless systems, not as common.
- Evaporator: “Heat Absorber” – Indoor coil. Connected to the airflow outlet of the furnace. Conditioned refrigerant is circulated through the coil to cool the structure in the summer and heat in the winter. As warm indoor air passes through the indoor or evaporator coil, temperature and humidity are removed creating cooler indoor air. Installing a correctly sized and rated evaporator coil is essential for getting both optimal performance & comfort from your air conditioning or heat pump system.
- EER: The Energy Efficiency Ratio of a particular cooling device. The ratio of output cooling energy (in BTU) to input electrical energy at a given operating point.
- Energy Star®: ENERGY STAR is a U.S. Environmental Protection Agency (EPA) voluntary program that helps businesses and individuals save money and protect our climate through superior energy efficiency.
- EPA: The United States Environmental Protection Agency is an agency of the US federal government which was created for the purpose of protecting human health and the environment by writing and enforcing regulations based on laws passed by Congress.
- Expansion Valve: A valve that meters the levels of refrigerant through a temperature or pressure control.
- Fahrenheit: A temperature scale in which water freezes at 32 degrees and boils at 212 degrees at normal atmospheric pressure.
- Filter: The air filter is crucial to the system, preventing contaminants from entering the equipment and must be maintained or replaced at regularly. There is also a filter in the refrigeration system, also referred to as a drier, which acts like a strainer to remove dirt and undesired particles from the system. Can be multiple filters on one unit.
- Flue: A vent that removes the byproducts of combustion from a furnace/fireplace/etc.
- Furnace: A device that creates heat and then circulates it through the home by means of a fan.
- Fuse: A delicate metal strip connecting two parts of an electrical circuit. This strip works as a safety, or circuit protector, and breaks, or melts, in the event of excess electrical charge, breaking the electrical circuit.
- Filter Drier: Absorb water vapor in the system so that the water vapor isn’t mixed with the refrigerant. Saves the compressor which is an electrical motor system & wires that is hermetically sealed. Has limited capacity.
- Heat Exchangers: Unit that transfers heat between two (or more) fluids. These are energy efficient.
- Shell & Tube: A bunch of tubes that contain cooler liquid are looped in a cylindrical container (pressurized shell) that hot liquid circulates through. It is the most common type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications. Exchanges heat between the fluid in the tubes.
- Plate Heat Exchangers: Company & efficient. Fluid moving between the plates, plates touch and exchange heat off each other. Can increase or decrease depth. Pattern on plates create turbulent flow which increases the heat transfer. Gaskets separate the plates creating a thin channel between them for the fluid to flow. The thermal energy flows through the sheets.
- HSPF: Heating Seasonal Performance Factor.
- Heat Gain: The amount of heat added or created in a designated area.
- Heating Coil: A coil that acts as a heat source for a heating system.
- Heat Loss: The amount of heat lost or subtracted from a designated area.
- Heat Pump: A device used for either the heating or cooling of a space by transferring heat between two reservoirs.
- Heat Transfer: The flow of heat from one area to another by conduction, convection, and/or radiation. Heat flows naturally from a warmer to a cooler material or space.
- HSPF: The Heating Seasonal Performance Factor (HSPF) is a term specifically used to define the measurement of efficiency of a residential heat pump system.
- Humidifier: A device that adds humidity, or moisture, to the air.
- Humidistat: The device that measures humidity and turns the humidifier on and off.
- Humidity: Dampness in the air caused by water vapor.
- Ignition: Elevating the temperature of a substance to the point of causing a combustive reaction.
- Ideal Gas Law: Pv = nRT (pressure + volume = mass + temperature). If you change any of these units, you change them all. Mass tends to remain more constant. Increasing pressure of refrigerant = increasing temperature. Decreasing pressure of refrigerant = decreasing temperature
- Indoor Blower Motor: the fan on the HVAC which causes the outgoing air to circulate out of the system and into the rooms of your home. The blower motor is the part of your HVAC system that gets your home to the temperature set on your thermostat.
- Liquid Line: Line between condenser and metering device.
- Piston Device: Found more on 0lder/low efficiency systems. This has a fixed orifice. The phase change of the refrigerant is smaller due to the smaller amount of refrigerant making it’s way through the orifice. This makes more super heat.
- Metering Device: “Pressure Dropper” Lower temperature of refrigerant in order to decrease temperature
- Package Unit: A heating and cooling system contained in one outdoor unit.
- Particulates: Fine liquid or solid particles. The quantity and size of particulates emitted by cars, power and industrial plants, wood stoves, etc are regulated by the U.S. Environmental Protection Agency.
- Programmable Thermostat: A type of thermostat that allows the user to program into the devices’ memory a pre-set schedule of times and temperatures enabling or disabling the HVAC equipment.
- PSI: A pound per square inch is a unit of pressure resulting from the force of one pound-force applied to an area of one square inch.
- Radiant floor: A type of radiant heating system where the building floor contains channels or tubes through which hot fluids such as air or water are circulated.
- Radiation: The transfer of heat through matter or space by means of electromagnetic waves.
- Refrigerant Charge: The amount of refrigerant in a system.
- Refrigerant: The fluid used in air conditioners, heat pumps, and refrigerators to transfer heat into or out of an interior space. This fluid boils at a very low temperature enabling it to exude and absorb heat. Something that we’re continuously pressurizing & depressurizing in order to manipulated the temperature. Also cools down the compressor motor. Boiling refrigerant effectively removes heat from the air that’s passing over it.
- Rotary Compressors: Round with two cylinders. These are hermetically sealed. A rotary compressor compresses refrigerant inside its compression chamber with the help of the rotary motion of the roller and vertical movement of the vane
- Reciprocating/Piston Compressors: Oval (looking down) in ACs. Most common and long standing. Uses pistons driven by crankshaft to compress refrigerant & move it with high pressure.
- Self-contained System: A package unit.
- Service Valve: A manually operated valve used for checking the pressures, normally found on the compressor.
- SEER: Seasonal energy efficiency ratio. Higher SEER rating means high efficiency within the system. The more efficient the system, the more money saved. Calculated by dividing the total amount of heat removed from the house BY the total energy consumed by the cooling system.
- Scroll Compressors: Round & tall, generally 1 cylinder. Compression of the refrigerant takes place inside the scroll wrap with the help of scrolls. Works in circular motion vs up and down. Used in both lower and higher efficiency air conditioners, scroll compressors are common because they feature fewer moving parts than reciprocating compressors. This means for a more efficient operation, higher tolerance to liquid refrigerant, less mechanical failure and smoother, plus a quieter operation.
- Single-Speed: A single-speed motor runs at top speed until it satisfies your temperature setting and then shuts off. They’re generally louder at start-up, consume more energy than alternative motor types and can cause more stress on mechanical parts.
- Split System: An outdoor unit combined with an indoor unit (as opposed to a package unit), generally providing more efficiency and configuration options.
- Suction Line: line that goes back from the evaporator to the compressor. The suction line is to return gas to the compressor. It is between the evaporator and compressor on a standard cooling system and between the reversing valve and the compressor on a heat pump.
- Temperature: Average molecular velocity. The average speed that the molecules are moving within a substance.
- Thermostat: A wall mounted device that monitor and controls the output of an HVAC system.
- Two-Speed: The base required for a high-efficiency air conditioner, two-speed motors cycle on in low gear and attempts to satisfy the cooling load for the home, shifting to high gear if necessary. Once it reaches the desired temperature, it cycles back down to low before shutting off. With just two speeds, it reduces start-up noise, operates with greater energy efficiency and causes less stress on mechanical parts compared to single-speed motors.
- Thermostatic Expansion Valve (TXV): A lot better at controlling the super heat across the evaporator coil in order to reduce the humidity & heat load in the building really quickly. Much faster than a piston or fixed orifice metering device would be able to do. Got a bad reputation for leaking, but new ones are stainless steal vs older metal.
- Upflow Furnace: A furnace that pulls in air from the bottom and releases it through the top.
- Variable-Speed: Ideal for high-efficiency air conditioners, a variable-speed motor functions much like a two speed, only with several speeds of operation. When compared with single- or two-speed motors, it facilitates smoother cycling and more precise performance control, as well as the most quiet operation, highest energy efficiency and least stress on mechanical parts.
- Ventilation: The process of air exchange & moving air into and out of an interior space mechanically.
- Volt: Unit for electrical potential and electromotive force.
- Voltage: The force pushing electrical current along wires and cables.
- Watt:Used to express the rate of energy transformation with respect to time. Can be defined as joule per second.
- Wet Bulb Thermometer: A thermometer that measures the relative humidity in the air.
- Zoning: A system that divides a home or space into different regions in order to better control the temperature and effectiveness of a heating and cooling system.
- Vapor Line: On a split system heat pump, the connecting lines are the vapor line and the liquid line. The vapor line can be cool suction vapor or hot gas depending on the mode of operation (heat/cool).