Glossary of HVAC HVACR Refrigeration Terms - Advanced Services Advanced Heating & Cooling

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Glossary of Terms

Let's start at the beginning: HVAC stands for Heating, Ventilating and Air Conditioning and are the initials often used to describe the industry that produces the equipment that brings comfort to your home. Your may also see HVACR, which is the same industry that includes refrigeration as well.

The following terms are commonly used in the HVACR industry. It is good to know and be familiar with these terms, when discussing HVACR system options with a technician. If you do not understand what a technician is talking about, just ask.

Efficiencies

AFUE

This is a percentage measurement of a furnace's heating efficiency. The U.S. Government's minimum efficiency level is 78%. The higher the AFUE, the more efficient the furnace. The initials stand for Annual Fuel Utilization Efficiency.

ENERGY STAR

Products/Homes/Buildings that earn the ENERGY STAR prevent greenhouse gas emissions by meeting strict energy efficiency guidelines set by the U.S. Environmental Protection Agency and the U.S. Department of Energy. To learn more, please visit www.energystar.gov.

EER

The EER is the efficiency rating for the equipment at a particular pair of external and internal temperatures. SEER rating more accurately reflects overall system efficiency on a seasonal basis and EER reflects the system’s energy efficiency at peak day operations.

SEER

This is a measurement of the efficiency of cooling products. The U.S. Government's minimum efficiency level is 13 SEER for split systems and packaged units. The higher the SEER, the more efficient the cooling product. SEER stands for Seasonal Energy Efficiency Rating.

HSPF

This is a measurement of a heat pump's heating efficiency. There is no governmental minimum rating. The higher the HSPF, the more efficient the heat pump's heating performance. HSPF stands for Heating Seasonal Performance Factor.

COP

Coefficient Of Performance. A ratio that compares a heat pump system's heating efficiency to that of electric resistance heat. For example, a heat pump system with a COP of 3.0 provides heat at 3 times the efficiency of electric resistance heat. A heat pump's system COP will decrease as outdoor temperatures drop, eventually providing little or no efficiency advantage over electric resistance heat - and that's when your auxiliary heat strips start to heat your home.

A Note About Efficiencies: When you're getting ready to replace an older heating or cooling system, it's very important for you to get a Load Calculation done by your dealer/contractor. The greater the difference between the efficiency of your old system to the new system, the more likelihood that the dealer will recommend a smaller sized unit. This should not cause alarm, as the dealer, by running a Load Calculation, will be able to accurately size the system to the load in your home. It can be quite detrimental to equipment if the units are too large for the load in your home - they can start to "short cycle" (they run often but for very short periods of time, because they are pumping out too much heat/cooling and reach the thermostat's setting too quickly), which can shorten the life of the unit dramatically.

Capacities & Ratings

BTU

British Thermal Unit. This is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. You'll see this measurement when you look at heating and cooling capacities - for example, your dealer may recommend a 75,000 Btu furnace and a 24,000 Btu air conditioner for your home.

GPH

Gallons Per Hour. You might see this rating if you are looking at an oil furnace. In addition to input and output, an oil furnace also has a rating of gallons per hour, the volume of oil a furnace is capable of burning in 60 minutes.

Ton

You'll often see this as a measurement of the capacity of an air conditioning system. Don't panic, it doesn't measure weight! Just like gas and oil furnaces, air conditioners and heat pumps are rated in Btus. One ton of air conditioning is 12,000 Btus per hour. This means that a "one ton" air conditioning system has the capability of removing 12,000 Btus of heat per hour from your home.

     A Note About Capacities: Gas furnaces are generally rated by "input" in Btus per hour (Btuh). A furnace rated at 100,000 Btuh that is 80% efficient (80% AFUE) will have an output of 80,000 Btuh. In other words, 80% of the total heat produced by burning the gas will be in the form of usable heat to warm your home. The other 20% is exhausted from your house along with the flue products.
     By the same token, a 100,000 Btuh furnace that is 90% efficient only sends 10% of the total heat out the chimney - thus burning less gas to get the same results and reducing your gas heating costs.
     A Note About Oil Furnaces: Many oil furnaces are dual rated. That is, they are listed with two different heating capacities.
     A Note About Air Conditioning: You've heard the saying "It's not the heat, it's the humidity." Air conditioning systems do more that just cool your home - they remove moisture. The more humid it is outside, the harder an air conditioner has to work. But does that mean that if you get a bigger unit, it will work better? NO. An air conditioning system that is too large will neither cool nor dehumidify properly, and the result will be an uncomfortable, clammy home.

Equipment Shorthand

Split System

This describes an air conditioning or heat pump system that is split into two sections - an outdoor section and an indoor section. It won't work without the outdoor section plus an indoor section to move the air.

Packaged System

Packaged units provide both heating and cooling from one unit that is placed outside the home - on the ground, on the roof, or sometimes mounted through the walls of the building. Packaged units come in several combinations of fuel sources - gas heat/electric cooling; heat pump; electric heat/electric cooling; oil heat/electric cooling.

Condensing Unit

This is the outdoor section of a split system air conditioning system. You'll know it best as the air conditioner that sits outside your home.

Air Handler

This is the indoor section of a split system. It can be a dedicated air handler, or could be your furnace. Also known as a fan-coil.

Indoor/Evaporator Coil

If your furnace is the air handler section of your split system, then you'll need an indoor coil added to your furnace to complete the system. The coil transfers heat to give you cool air and also aids in dehumidification. If you do not have a furnace and you have a split system air conditioning system - The Indoor Coil or Evaporator is located in the inside unit.

Outdoor/Condenser Coil

Heat Pump

A unit that both cools and heats your home. A heat pump system can be either a split system or a packaged system. A heat pump can be used in conjunction with a gas/oil/LP furnace (using the furnace instead of electric resistance heat when temperatures fall below about 35° F with the addition of a fossil fuel kit) These type of heat pumps are known as dual-fuel heat pumps.

Gas-Pack

Short hand for a packaged system that uses gas fuels such as LP or Natural Gas for the heating process.

Dual Fuel System/Unit

A unit that both cools and heats your home. A dual fuel system can be either a split system or a packaged system. A dual fuel system is designed to use two types of fuels or energy sources to heat your home. The system determines the most economical fuel to use depending on the outside temperature to heat your home. The systems usually utilize a heat pump and gas heat exchanger as the fuel or energy options.

Mini-split System/Unit

A HVAC system that has no ductwork, so they avoid the energy losses associated with the ductwork of central forced air systems. Duct losses can account for more than 30% of energy consumption for space conditioning, especially if the ducts are in an unconditioned space such as an attic. They are relatively small in size and a great option for room additions.

PTAC (Packaged Terminal/Type Air-Conditioner

A unit that is packaged together in one unit, which is usually mounted in a wall in hotels or motels.

Inverter System/Unit

A unit that contains a modulating compressor. This compressor can run at a variation of capacity ratings to save on energy usage.

Geothermal System/Unit

A Geothermal system uses the earth's ground for a heat or cooling source. Thermal conducting lines are installed in the ground to heat or cool a home. Geothermal Systems can save a homeowner anywhere from 30 to 40% on their energy bill. Geothermal Systems can also use ponds or wells for a heating or cooling source.

A Note About Capacities: Gas furnaces are generally rated by "input" in Btus per hour (Btuh). A furnace rated at 100,000 Btuh that is 80% efficient (80% AFUE) will have an output of 80,000 Btuh. In other words, 80% of the total heat produced by burning the gas will be in the form of usable heat to warm your home. The other 20% is exhausted from your house along with the flue products.
By the same token, a 100,000 Btuh furnace that is 90% efficient only sends 10% of the total heat out the chimney - thus burning less gas to get the same results and reducing your gas heating costs.

Component Shorthand

Metering Device

A Component in air conditioning and refrigeration systems that meters the amount of refrigerant flow into the evaporator.

Thermal Expansion Valve (TXV/TEV)

A valve designed to regulate the rate at which liquid refrigerant flows into the evaporator. This controlled flow maximizes the efficiency of the evaporator.

Electronic Expansion Valve (EEV)

A valve designed to regulate the flow of refrigerant entering a direct expansion evaporator. They do this in response to signals sent to them by an electronic controller. A small motor is used to open and close the valve port. The motor is called a step or stepper motor. Step motors do not rotate continuously. They are controlled by an electronic controller and rotate a fraction of a revolution for each signal sent to them by the electronic controller.

Evaporator

The evaporator is a heat exchanger that allows the refrigerant circulating through it to absorb the heat and change the state of refrigerant to a vapor.

Condenser

The condenser is a heat exchanger that allows the refrigerant circulating through it to release the heat it contains and change the state of refrigerant to a liquid.

Reversing Valve

A component in a heat pumps refrigerant circuit, that changes the direction of refrigerant flow. By reversing the flow of refrigerant, the heat pump refrigeration cycle is changed from cooling to heating or vice versa.

Lineset

Usually copper piping that allows refrigerant to flow from the outside condenser to the inside air handler that contains the evaporator.

Compressor

The compressor is the heart of of your refrigeration circuit, which is responsible for circulating and compressing refrigerant. Compressors can be hermetic (sealed) or semi-hermetic (non-sealed, where basic repairs can be made).

Crankcase Heater (CCH)

A electric resistance heater that keeps the crankcase of a compressor warm, which prevents liquid migration to the compressor.

Contactor

An electrical switch, which opens or closes the circuit to a compressor and fan usually.

Capacitor

An electrical component that shifts a phase of voltage to help start an electric motor. Larger capacitors can be used as start capacitors.

Defrost Board

A control board that initiates the defrost of the outdoor coil when certain conditions are met.

Electronically Commutated Motor (ECM)

An electric motor, which function using a built-in inverter and a magnet rotor, and as a result are able to achieve greater efficiency in air-flow systems than some kinds of AC motors. (Although AC current is used for ECM, the ECM’s internal rectifier converts the current to DC voltage).

Variable Speed Motor

An electric motor, which compensates for any added pressure drop introduced to the system. For example, if a duct system layout has an increased static pressure due to a dirty filter, the presence of a media filter or simply because of poor design, the motor will automatically ramp up to ensure that the programmed amount of airflow is delivered. This is accomplished without the use of any additional components.

Ignition Control Module

A control board which integrates the operation of all the components required to operate a gas fired furnace or gaspack. This module controls components, such as the: gas valve, pilot valve, ignitor, draft motor or flame sensor.

Combination Gas Valve

A valve that controls the flow of gas in a HVAC system. This valve contains: a manual shutoff, control solenoid, pressure regulator, pilot gas solenoid and optionally a thermocouple sensor.

Thermocouple

A device that converts thermal energy into electrical energy. This device is used to sense a flame or temperature.

Thermopile

A device that converts thermal energy into electrical energy. This device is used to sense a flame.

Ignitor

A device that utilizes direct spark or hot surface to ignite gases entering the gas heat exchanger.

Accumulator

A refrigerant vessel that meters refrigerant in the refrigerant circuit to prevent excess refrigerant liquid or oil entering the compressor.

Receiver

A refrigerant storage vessel that stores excess refrigerant when not in circulation or needed.

Orifice

A restricted flow regulator that restricts the flow of a medium such as refrigerant or gas. When used to restrict the flow of refrigerant, it then also becomes a metering device for the refrigerant circuit.

Sequencer

An electrical switch that closes a circuit when control voltage is applied.

Heat Strips / Elements

A set of electric resistance heating coils that heat up when voltage is applied to them. A fan motor circulates air across them to result in warm supply air.

Heat Exchanger

A device used to transfer heat from one medium to another. This is usually the device contained in a gas furnace or gaspack that heats up, while air moves across it to be heated up. There are other types of heat exchangers in the HVAC & refrigeration field, also.

Inducer Draft Motor

An electric motor that induces or pulls air through a heat exchanger.

Forced Draft Motor

An electric motor that forces air through a heat exchanger.

High-Limit Safety

A temperature safety switch that switches a circuit off due to high temperatures.

Pressure Transducer

A refrigerant pressure switch that sends proper voltage signals to an Electronic Control Unit, to determine refrigerant pressures.

Electronic Control Unit (ECU)

An electronic unit that processes signals from electronic transducers to control system components to maintain proper functionality of the system.

Thermostat

A control device that switches the HVAC or Refrigeration systems or devices on and off.

Low-Ambient Kit

An optional kit for HVAC & Refrigeration systems that allows a unit to run normally in cooling mode, when the outside temperatures are colder than the unit is designed for.

Low Pressure Safety Switch

A refrigerant pressure switch that prevents the unit from running when the refrigerant suction pressure is low.

High Pressure Safety Switch

A refrigerant pressure switch that prevents the unit from running when the refrigerant head pressure is high.

Fan Cycling Switch

A refrigerant pressure switch that cycles the fan motor(s) on or off, depending on the refrigerant pressures.

Cut In / Cut Out Switch

A refrigerant pressure switch that cycles the unit on and off, based on the refrigerant pressures.

Draft Hood

A device used on older gas furnaces to bring ambient air into the vent gasses to cool the vent gasses and provide a way for downdrafts to exit without affecting the burner flame.

Duct / Ductwork

This is the metal, fibrous, fabric, pvc or flex that circulates supply and return air throughout the structure.

Flame Rod

A small diameter stainless steel rod on a gas furnace used to sense flame rectification by being placed in the flame.

Hot Surface Ignitor (HSI)

A device that when electricity is passed through, warms to a high temperature to ignite gas burners.

Integrated Furnace Control (IFC)

Integrated furnace control Electronic control used to control most operations for newer gas furnaces including flame safety control, circulating fan control, inducer control and safety sensors.

Flame Rod

A small diameter stainless steel rod on a gas furnace used to sense flame rectification by being placed in the flame.

Technician Shorthand

Ambient Temperature

This is the air temperature (usually the outdoor air temperature) surrounding the equipment.

Dry-Bulb Temperature

The temperature of air measured by a thermometer freely exposed to the air but shielded from radiation and moisture.

Wet-Bulb Temperature

The temperature a parcel of air would have if it were cooled to saturation (100% relative humidity) by the evaporation of water into it, with the latent heat being supplied by the parcel.

Humidity

The amount of water vapor in the air. Water vapor is the gaseous state of water and is invisible.

Delta T

This describes a temperature difference between two reference points.

Superheat

Any temperature of a gas above the boiling point for that liquid.

Subcooling

The condition where the liquid refrigerant is colder than the minimum temperature (saturation temperature) required to keep it from boiling and, hence, change from the liquid to a gas phase.

Approach Temperature

The the difference between the saturated refrigerant temperature and the leaving air or water temperature.

Static Pressure

The air pressure that is created by the fan blowing air into the ductwork system. The level of static pressure is dependent ability of the fan to increase the pressure and amount of air the outlets are able to remove from the system.

External Static Pressure (ESP)

The measurement of all the resistance in the duct system that the fan has to work against. Examples are filters, grills, A/C coils and the ductwork. It is the sum of the suction pressure (negative) and discharge pressure (positive) created by the equipment blower.

Total External Static Pressure (ESP)

Generally, when measuring total external static pressure, measure the pressure at the point where airflow enters the equipment and where the airflow exits the equipment. The pressure entering the equipment is a suction or negative pressure. The pressure exiting the equipment is a discharge or positive pressure.

Flooded Evaporator

When the evaporator is receiving more refrigerant than needed, which usually results in liquid refrigerant flooding the evaporator.

Starved Evaporator

When the evaporator is not receiving enough refrigerant to perform properly.

Short-Cycle

The term used when an HVAC or Refrigeration unit starts and shuts off quickly.

Suction Pressure

The refrigerant pressure in the vapor line exiting the evaporator and entering the accumulator or compressor.

Head Pressure

The refrigerant pressure in the liquid line exiting the condenser and entering the metering device or evaporator.

Combustion Air

Air used to supply the burners with enough oxygen to allow complete combustion.

Continuity

An electrical term indicating that the wire or component tested is broken or more accurately has an open circuit.

Shorted

An electrical term indicating that the circuit has bypassed the load and passed through to the other side of the circuit with little or no resistance causing excessive current and consequent opening of circuit protection (fuse or breaker).

Intermittent Pilot

A pilot burner that only operates when there is a call for heat.

Latent Heat

The heat released or absorbed by a change of state, usually liquid to gas or gas to liquid.

Media

A type of filter that uses a type of paper or fiberglass to catch particles moving thru the ductwork.

Natural Draft

A gas furnace that uses the heat of the burning gasses to move the products of combustion.

Normally Open (NO)

The position of contacts of a switch when power is not applied. Open means no power can pass through.

Normally Closed (NC)

The position of contacts of a switch when power is not applied. Closed means power can pass through.

Original Equipment Manufacturer (OEM)

A part designed for a specific appliance model as opposed to general replacement part.

Open

The position of an electric switch that will not allow electricity to pass through.

Closed

The position of an electric switch that will allow electricity to pass through.

Gas Prepurge

Operation of inducer prior to flame initiation to clear any gasses from the heat exchanger.

Return Air

Ductwork designed to bring air that is circulated through the structure back to the HVAC system.

Run Load Amps (RLA)

Running load amps. This is the maximum amperage that the air circulating fan motor can draw. The RLA is listed on the model plate of the motor. A much lower reading may indicate blockages in the ductwork. A high reading may indicate failing bearings or a motor that is too small for the application.

Locked Rotor Amps (LRA)

Refers to the maximum amperage the motor will draw when the rotor is locked into position and will not turn.

Roll Out Switch

A high temperature limit switch that must be manually reset placed near the burners to detect flames that have "rolled out" from the front of the furnace.

Stack Temperature

Temperature of exhaust gasses as they leave the heat exchanger.

Return Air

Ductwork designed to bring air that is circulated through the structure back to the HVAC system.

Sensible Heat

Heat that can be measured by a thermometer.

Standing Pilot

A gas ignition system that uses a standing pilot to ignite the main gas burners.

Conditioned Space

This is the space of a structure that needs to be heated or cooled.

Unconditioned Space

This is the space of a structure that does not need to be heated or cooled - such as an attic space or crawl space.

Refrigerants

R-12

Dichlorodifluoromethane (R-12), usually sold under the Freon-12, is a halomethane (CFC), used as a refrigerant and aerosol spray propellant. Complying with the Montreal Protocol, its manufacture was banned in the United States along with many other countries in 1994 due to concerns about damage to the ozone layer. It is soluble in many organic solvents.

R-134A

Also called simply tetrafluoroethane, R-134a, Genetron 134a, Suva 134a or HFC-134a, is a haloalkane refrigerant with thermodynamic properties similar to R-12 (dichlorodifluoromethane), but without its ozone depletion potential.

R-22

(HCFC) It is better known under its code names of HCFC-22, R-22, Genetron 22 or Freon 22, and is commonly used in air conditioning applications, such as residential split systems in the US, rooftop units and window air conditioners. It will soon be phased out due to ozone depletion potential and status as a potent greenhouse gas. All air-conditioning and heating equipment that uses R-22 will cease production of such by January 1, 2010. The refrigerant supply and production of R-22 will then be slowly cut back and banned by January 1, 2020.

R-404A

A blend of HFC refrigerants commonly used for medium and low temperature refrigeration applications. It’s composition comprises: HFC-125 (44%), HFC-143a (52%), HFC-134a (4%). It is non toxic and non flammable meeting the highest A1/A1 classification.

R-407C

A mixture of hydrofluorocarbons used as a refrigerant. It is a zeotropic blend of difluoromethane, pentafluoroethane, and 1,1,1,2-tetrafluoroethane

R-407F

A blend of HFC refrigerants designed to replace R22, R404A and R507 in low temperature refrigeration applications. Major compressor manufacturers including Bitzer and Copeland have endorsed its use in their equipment. It's composition comprises of HFC-32, HFC-125 and HFC-134a. It is non toxic and non flammable meeting the highest A1/A1 classification.

R-408A

A blend of HCFC refrigerants introduced to retrofit R502 in medium and low temperature refrigeration applications.It’s compositon is made up of HFC-125 (7%), HFC-143a (46%), HCFC-22 (47%)

R-409A

A blend of HCFC refrigerants introduced to retrofit R12 in air conditioning and refrigeration applications. It’s compositon is made up of HCFC-22 (60%), HCFC-124 (25%), HCFC-142b (15%).

R-410A

Sold under the trademarked names Puron, Genetron R410A, and AZ-20, is a near-azeotropic mixture of difluoromethane (CH2F2, called R-32) and pentafluoroethane (C2HF5, called R-125) which is used as a refrigerant in air conditioning applications. Unlike many haloalkane refrigerants it does not contribute to ozone depletion, and is therefore becoming more widely used as ozone-depleting refrigerants like R-22 are phased out. However, it has a high global warming potential of 1725 (1725 times the effect of carbon dioxide), similar to that of R-22.

R-427A

A blend of HFC refrigerants designed to retrofit R22 installations. R22 is a HCFC and therefore being phased out in Australia. R427A offers similar performance to R22 usually without any need for modification to the existing R22 installation. It can be used to retrofit low temperature refrigeration equipment and air conditioning installations. It is non toxic and non flammable meeting the highest A1/A1 classification. R427A, as a blend of HFCs, requires polyolester (POE) lubricants but is tolerant of high levels of alkylbenzene or mineral oils of up to 10%.

R-438A

(MO99) A versatile R22 replacement refrigerant. It combines R22 pressure-enthalpy characteristics with mineral oil compatibility in a unique HFC refrigerant that can be used in R22 replacement over a wide range of evaporator temperatures. As an R22 replacement, R438A may be used in a wide range of applications and has advantages over other R22 replacements. R438A has been designed to closely match the pressure, temperature, enthalpy, and mass flow properties of R22, for a seamless R-22 replacement. R438A has a 42% lower global warming potential (GWP) than R404A. R438A matches R22 in terms of capacity and efficiency in most systems, but with a significantly lower discharge temperature which may prolong life of the compressor. It’s compatible with traditional and new lubricants, providing quick, cost-effective R22 replacements and can be topped off during service without removing the entire refrigerant charges. For most R22 systems, when retrofitting to R438A all you need to do is recover the R22, replace critical seals, charge refrigerant, restart and monitor for leaks, label the system, and you’re done. R22 replacement can’t get any easier.

R-507

Sometimes referred as AZ50, is a blend of HFC refrigerants commonly used for medium and low temperature refrigeration applications. It’s composition comprises: HFC-125 (50%), HFC-143a (50%). It is non toxic and non flammable meeting the highest A1/A1 classification.