Week 5 - Trade Terms

Compressor: In a refrigeration system, the mechanical device that converts low-pressure, low-temperature refrigerant gas into high-temperature, high-pressure refrigerant gas.

Condenser: A heat exchanger that transfers heat from the refrigerant flowing inside it to the air or water flowing over it.

Evaporator: A heat exchanger that transfers heat from the air flowing over it to the cooler refrigerant flowing through it.

Expansion device: Also known as the liquid metering device or metering device. Provides a pressure drop that converts the high-temperature, high-pressure liquid refrigerant from the condenser into the low-temperature, low-pressure liquid refrigerant entering the evaporator.

Heat pump: A comfort air conditioner that is able to produce heat by reversing the mechanical refrigeration cycle.

Heat transfer: The transfer of heat from a warmer substance to a cooler substance.

Hydronic: A heating or air conditioning system that uses water as a heat transfer medium.

Mechanical refrigeration: The use of machinery to provide cooling.

Mechanical refrigeration cycle: The process by which a circulating refrigerant absorbs heat from one location and transfers it to another location.

Noxious: Harmful to health.

Toxic: Poisonous.

Bond: Short for surety bond. It is a funded guarantee that a contractor will perform as agreed.

Carbon monoxide (CO): A common byproduct of combustion processes, CO is a colorless, taste-less, and odorless gas that is lighter than air and quite toxic. CO reacts with blood hemoglobin to form a substance that significantly reduces the flow of oxygen to all parts of the body. In some countries, CO is responsible for the majority of fatal air poisoning events.

Chlorofluorocarbon (CFC) refrigerant: A class of refrigerants that contains chlorine, fluorine, and carbon. CFC refrigerants have a very adverse effect on the environment.

Easement: A portion of a property that is set aside for public utilities or municipalities.

Hydrochlorofluorocarbon (HCFC) refrigerant: A class of refrigerants that contains hydrogen, chlorine, fluorine, and carbon.

International Building Code (IBC): A series of model construction codes. These codes set standards that apply across the country. This is an ongoing process led by the International Code Council (ICC).

Reclaimed: Used refrigerant that has been re-manufactured to bring it up to the standards required of new refrigerant.

Recovery: The removal and temporary storage of refrigerant in containers approved for that purpose.

Recycling: Circulating recovered refrigerant through filtering devices that remove moisture, acid, and other contaminants.

Sustainable construction: Construction that involves minimum impact on land, natural resources, raw materials, and energy over the building’s life cycle. It uses material in a way that preserves natural resources and minimizes pollution.

Chiller: A high-volume hydronic cooling unit.

On the job learning (OJL): Learning obtained while working under the supervision of a journeyman.

Absolute pressure: The total pressure that ex-ists in a system. Absolute pressure is expressed in pounds per square inch absolute (psia). Absolute pressure = gauge pressure + atmospheric pres-sure.

Area: The amount of surface in a given plane or two-dimensional shape.

Atmospheric pressure: The standard pressure exerted on Earth’s surface. Atmospheric pressure is normally expressed as 14.7 pounds per square inch (psi) or 29.92 inches of mercury.

Barometric pressure: The actual atmospheric pressure at a given place and time.

Coefficient: A multiplier (e.g., the numeral 2 as in the expression 2b).

Force: A push or pull on a surface. In this mod-ule, force is considered to be the weight of an ob-ject or fluid. This is a common approximation.

Mass: The quantity of matter present.

Newton (N): The amount of force required to ac-celerate one kilogram at a rate of one meter per second.

Unit: A definite standard of measure.

Vacuum: Any pressure that is less than the pre-vailing atmospheric pressure.

Volume: The amount of space contained in a giv-en three-dimensional shape.

Coefficient: A multiplier (e.g., the numeral 2 as in the expression 2b).

Constant: An element in an equation with a fixed value.

Exponent: A small figure or symbol placed above and to the right of another figure or symbol to show how many times the latter is to be multi-plied by itself (e.g., b3 = b × b × b).

Variable: An element of an equation that may change in value.

Polygon: A shape formed when three or more straight lines are joined in a regular pattern.

Alternating current (AC): An electrical current that changes direction on a cyclical basis.

Ampere (A): The basic unit of measurement for electrical current, represented by the letter A.

Conductor: A material through which it is rela-tively easy to maintain an electrical current.

Current: The rate or volume at which electrons flow in a circuit. Current (I) is measured in amperes.

Direct current (DC): An electric current that flows in one direction. A battery is a common source of DC voltage.

Electromagnet: A coil of wire wrapped around a soft iron core. When current flows through the coil, magnetism is created.

Loads: Devices that convert electrical energy into another form of energy (heat, mechanical motion, light, etc.). Motors are the most common significant loads in HVACR systems.

Power: The rate of doing work, or the rate at which energy is dissipated. Electrical power is measured in watts.

Rectifier: A device that converts AC voltage to DC voltage.

Resistance: An electrical property that opposes the flow of current through a circuit. Resistance (R) is measured in ohms.

Transformer: Two or more coils of wire wrapped around a common core. Used to raise and lower voltages.

Volts (V): The unit of measurement for voltage, represented by the letter V. One volt is equiva-lent to the force required to produce a current of one ampere through a resistance of one ohm.

Arc: A visible flash of light and the release of heat that occurs when an electrical current crosses an air gap.

Continuity: A continuous current path. The ab-sence of continuity indicates an open circuit.

Inductive: Of a load, able to become electrically charged from being near another electrically charged body, or to become magnetized by being within an existing magnetic field. The process itself is called induction.

Insulator: A device or substance that inhibits the flow of current; the opposite of conductor.

Ohms (Ω): The basic unit of measurement for electrical resistance, represented by the symbol Ω.

Relay: A magnetically operated device consist-ing of a coil and one or more sets of contacts.

Thermistor: A semiconductor device that changes resistance with a change in temperature.

Watts (W): The unit of measure for power con-sumed by a load.

Ammeter: A test instrument for measuring elec-trical current.

Analog meter: A meter that uses a needle to in-dicate a value on a scale.

Clamp-on ammeter: An ammeter with operable jaws that are placed around a conductor to sense the magnitude of the current flow.

Digital meter: A meter that provides a direct nu-merical reading of the value measured.

In-line ammeter: A current-reading meter that is connected in series with the circuit under test.

Multimeter: A test instrument capable of read-ing voltage, current, and resistance. Also known as a volt-ohm-milliammeter (VOM).

Contactors: Control devices consisting of a coil and one or more sets of contacts used as switch-ing devices in high-voltage circuits.

Ground fault: An unintentional, electrically conducting connection between an energized conductor of an electrical circuit and another conductor, such as metal objects, earth, or an equipment frame. The fault current passes through the grounding system, as well as a per-son or other conductive surface in the path.

Inrush current: A significant rise in electrical current associated with energizing inductive loads such as motors.

Ladder diagram: A simplified schematic dia-gram in which the load lines are arranged like the rungs of a ladder between vertical lines rep-resenting the voltage source.

Line duty: A protective device connected in se-ries with the supply voltage.

Motor starters: Magnetic switching devices used to control heavy-duty motors.

Pilot duty: A protective device that opens the motor control circuit, which then shuts off the motor.

Short circuit: The bypassing of a load by a conductor, causing a very high current flow.

Annual Fuel Orifices: Precisely drilled holes that control the flow of gas to the burners.

Radiation: In the context of heat transfer, the direct transmission of heat through electro-magnetic waves through space or another medium. No contact between the two substances is required.

Annual Fuel Utilization Efficiency (AFUE): HVAC industry standard for defining furnace efficiency, expressed as a percentage of the total heat available from a fuel. The AFUE goes beyond the specific thermal efficiency of a unit in that it accounts for both the peak measurement of fuel-to-heat conversion efficiency and the losses of efficiency that occur during startup, shutdown, etc.

Atomized: Broken into tiny pieces or fragments, such as a liquid being broken into tiny droplets to create a fine spray.

Combustion: The process by which a fuel is ignited in the presence of oxygen.

Condensing furnace: A furnace that contains a secondary heat exchanger that extracts latent heat by condensing exhaust (flue) gases.

Conduction: In the context of heat transfer, the process through which heat is directly transmitted from one substance to another when there is a difference of temperature between regions in contact.

Convection: The movement caused within a fluid (air or water, for example) by the tendency of hotter fluid to rise and colder, denser material to fall, resulting in heat being transferred.

Heat exchanger: A device that is used to transfer heat from a warm surface or substance to a cooler surface or substance.

Hot surface igniter (HSI): A ceramic device that glows when electric current flows through it; used to ignite the fuel/air mixture in a gas furnace.

Induced-draft furnace: A furnace in which a motor-driven fan draws air from the surrounding area or from outdoors to support combustion and create a draft in the heat exchanger.

Natural-draft furnace: A furnace in which the natural flow of air from around the furnace provides the air to support combustion and venting of combustion byproducts.

Electronically commutated motor (ECM): A DC-powered motor able to operate at variable speeds based on the programming of its electronic control module, which is AC-powered and converts AC to three-phase DC. ECMs also operate more efficiently than standard motors.

Flame rectification: A method of proving the existence of a pilot flame by applying an AC current to a flame rod, which is then rectified to a DC current as it flows back to a ground source. Monitoring the DC current flow provides the means of proving a pilot flame has been established.

Infiltration: Air that unintentionally and naturally enters a building through doors, windows, and cracks in the structure.

Manometer: An instrument that measures air or gas pressure by the displacement of a column of liquid.

Multipoise furnace: A furnace that can be configured for upflow, counterflow, or horizontal installation.

Redundant gas valve: A gas control containing two gas valves in series. If one fails, the other is available to shut off the gas when needed.

Spud: A threaded metal device that screws into the gas manifold. It contains the orifice that meters gas to the burners.

Standing pilot: A gas pilot that remains lit continuously.

Thermocouple: A device comprised of two different metals that generates electricity when there is a difference in temperature from one end to the other.

Balance point: An outdoor temperature value that represents an exact match of a structure’s heat loss with the capacity of a heat pump to produce heat. At the heating balance point, a heat pump would need to run continuously to maintain the indoor setpoint, without falling below or rising above it.

Dual-fuel system: A heating system typically comprised of a heat pump and a fossil-fuel furnace. Heat pumps supplemented by electric heat are not considered dual-fuel.

Fusible link: An electrical safety device that melts to open a circuit but does not respond to current like a common fuse.

Geothermal heat pump: A heat pump that transfers heat to or from the ground using the earth as a source of heat in the winter and a heat sink in the summer. The system makes use of water as the heat-transfer medium between the earth and the refrigerant circuit.

Sectional boiler: A boiler consisting of two or more similar sections that contain water, with each section usually having an equal internal volume and surface area. Sectional boilers are often shipped in pieces and assembled at the installation site.

Absolute pressure: Positive pressure measurements that start at zero (no atmospheric pressure). Gauge pressure plus the pressure of the atmosphere (14.7 psi at sea level at 70°F) equals absolute pressure. Absolute pressure is expressed in pounds per square inch absolute (psia). Absolute pressure = gauge pressure + atmospheric pressure.

Atmospheric pressure: The pressure exerted on all things on Earth’s surface due to the weight of the atmosphere. It is roughly 14.7 psi at sea level at 70°F; the standard pressure exerted on Earth’s surface. Atmospheric pressure may also be expressed as 29.92 inches of mercury.

Barometer: An instrument used to measure atmospheric pressure, typically in units of inches of mercury (in. Hg).

British thermal unit (Btu): The amount of heat needed to raise the temperature of one pound of water one degree Fahrenheit.

Comfort cooling: Cooling related to the comfort of humans in buildings and residences. The temperature range for comfort cooling is typically considered to be 60°F (15.5°C) to 80°F (26.6°C).

Condensation: The process related to the change of state of a substance, such as water, from the vapor or gaseous state to a liquid state.

Conduction: In the context of heat transfer, the process through which heat is directly transmitted from one substance to another when there is a difference of temperature between regions in contact.

Conductors: Relevant to heat transfer, materials that readily transfer heat by conduction.

Convection: The movement caused within a fluid (air or water, for example) by the tendency of hotter fluid to rise and colder, denser material to fall, resulting in heat being transferred.

Enthalpy: The total heat content (sensible and latent) of a refrigerant or other substance.

Gauge pressure: The pressure measured on a gauge, expressed as pounds per square inch gauge (psig) or inches of mercury vacuum (in. Hg vac.). Pressure measurements that are made without including atmospheric pressure.

Insulators: Materials that resist heat transfer by conduction.

Latent heat: The heat energy absorbed or rejected when a substance is in the process of changing state (solid to liquid, liquid to gas, or the reverse of either change).

Latent heat of condensation: The heat given up or removed from a gas in changing back to a liquid state (steam to water).

Latent heat of fusion: The heat gained or lost in changing to or from a solid (ice to water or water to ice).

Latent heat of vaporization: The heat gained in changing from a liquid to a gas (water to steam).

Pressure: The force exerted by a substance against its area of containment; mathematically defined as force per unit of area.

Radiation: The movement of heat in the form of invisible rays or waves, similar to light.

Saturation temperature: The boiling temperature of a substance at a given pressure. In the saturated condition, both liquid and vapor is likely present in the same space.

Sensible heat: Heat energy that can be measured by a thermometer or sensed by touch.

Specific heat: The amount of heat required to raise the temperature of one pound of a substance one degree Fahrenheit. Expressed as Btu/ lb/°F. The specific heat of water (H2O) is 1.0, thus providing the basis for defining one Btu.

Subcooling: The reduction in temperature of a refrigerant liquid after it has completed the change in state from a vapor. Only after the phase change is complete can the liquid begin to decrease in temperature as heat is removed.

Superheat: The additional, increase in temperature of a refrigerant vapor after it has completed the change of state from a liquid to a vapor. Only after the phase change is complete can the vapor begin to increase in temperature as additional heat is applied.

Thermistor: A semiconductor device that changes resistance with a change in temperature.

Thermocouple: A device made up of two different metals that generates electricity when there is a difference in temperature from one end to the other.

Ton of refrigeration: Large unit for measuring the rate of heat transfer. One ton is defined as 12,000 Btus per hour, or 12,000 Btuh.

Total heat: Sensible heat plus latent heat.

Compound: As related to refrigerants, a substance formed by a union of two or more elements in definite proportions by weight; only one molecule is present.

Fluorocarbon: A compound formed by replacing one or more hydrogen atoms in a hydrocarbon with fluorine atoms.

Halocarbon: Hydrocarbons, like methane and ethane, that have most or all their hydrogen atoms replaced with the elements fluorine, chlorine, bromine, astatine, or iodine.

Halogens: Substances containing chlorine, fluorine, bromine, astatine, or iodine.

Hydrocarbons: Compounds containing only hydrogen and carbon atoms in various combinations.

Mixture: As related to refrigerants, a blend of two or more components that do not have a fixed proportion to one another and that, however thoroughly blended, are conceived of as retaining a separate existence; more than one type of molecule remains present.

Rupture disk: A pressure-relief device that protects a vessel or other container from damage if pressures exceed a safe level. A rupture disk typically consists of a specific material at a precise thickness that will break or fracture when the pressure limit is reached, creating a controlled weakness, thereby protecting the rest of the container from damage.

Brine: Water that is saturated with (contains) large amounts of salt. In the HVACR industry, the term typically describes any water-based mixture that contains substances such as salt or glycols that lower its freezing point.

Desiccant: A material or substance, such as silica gel or calcium chloride, that seeks to absorb and hold water from any adjacent source, including the atmosphere.

Pump-down control: A control scheme that includes a liquid refrigerant solenoid valve that closes to initiate the system off cycle. Once the valve closes, the compressor continues to operate, pumping most or all of the remaining refrigerant out of the evaporator coil. Pump-down control eliminates the possibility of excessive liquid refrigerant forming in the evaporator coil during the off cycle, and is primarily used in refrigeration applications. A thermostat typically controls the liquid solenoid valve, while a low-side pressure switch and/or a timer controls the compressor.

Refrigerant floodback: A significant amount of liquid refrigerant that returns to the compressor through the suction line during operation. Refrigerant floodback can have several causes, such as a metering device that overfeeds refrigerant or a failed evaporator fan motor.

Slug: Traditionally refers to a significant volume of oil returning to the compressor at once, primarily at startup. For example, a trap in a suction line may fill with oil during the off cycle, and then leave the trap as a slug at start-up. However, slugging is also a term incorrectly used by some to describe refrigerant floodback.

Surge chamber: A vessel or container designed to hold both liquid and vapor refrigerant. The liquid is generally fed out of the bottom into an evaporator, while vapor is drawn from the top of the container by the compressor to maintain refrigerant temperature through pressure.

Hygroscopic: Describes a material that readily, and sometimes aggressively, absorbs water from the atmosphere or other adjacent material.

Blower door: An assembly containing a fan used to depressurize a building by drawing air out, to support duct leak testing. It is usually installed temporarily in place of an outside door.

Cubic feet per minute (cfm): A unit for the volume of air flowing past a point in one minute. Cubic feet per minute can be calculated by multiplying the velocity of air, in feet per minute (fpm), times the area it is moving through, in square feet (cfm = fpm × area). The metric value is cubic meters per hour (m3/h).

Dew point: The temperature at which air becomes saturated with water vapor, and the water starts to condense into droplets; a state of 100 percent relative humidity.

Dry-bulb temperature: The temperature measured using a standard thermometer. It represents the measure of sensible heat present.

External static pressure (ESP): The total resistance of all objects and ductwork in the air distribution system beyond the blower assembly itself.

Pitot tube: A tool used to capture pressure measurements in a moving air stream.

Psychrometric chart: A graphic method of showing the relationship of various air properties.

Relative humidity (RH): The ratio of the amount of moisture present in a given sample of air to the amount it can hold at saturation. Relative humidity is expressed as a percentage.

Revolutions per minute (rpm): The number of rotations made by a spinning object over the course of one minute.

Static pressure (s.p.): The pressure exerted uniformly in all directions within a duct system, usually measured in inches of water column (in. w.c.) or centimeters of water column (cm H2O).

Total pressure: The sum of the static pressure and the velocity pressure in an air duct.

Velocity: The speed at which air is moving. The rate of airflow usually measured in feet per minute.

Velocity pressure: The pressure in a duct due to the linear movement of the air. It is the difference between the total pressure and the static pressure.

Wet-bulb temperature: Temperature taken with a thermometer that has a wick wrapped around its sensing bulb, saturated with distilled water before taking a reading. The reading from a wet-bulb thermometer, through evaporation of the water, takes into account the moisture content of the air. It reflects the total heat content (sensible and latent) of the air.

Ak factor: The area factor of registers, grilles, and diffusers that reflects the free area for airflow relative to a square foot.

Boots: Sheet metal fittings designed to transition from the branch duct to the receptacle for the grille, register, or diffuser to be installed.

Free air delivery: The condition that exists when there are no effective restrictions to airflow (no external static pressure) at the inlet or outlet of an air-moving device.

Plenum: A chamber at the inlet or outlet of an air handler. The air distribution system attaches to the plenum.

Stratify: To form or arrange into layers. In air distribution, layers of air at different temperatures will tend to stratify unless an outside influence forces them to move and mix. Warmer air will stratify on top of cooler air.

Takeoffs: Connection points installed on a trunk duct that allow the connection of a branch duct.

Vapor barrier: A barrier placed over insulation to stop water vapor from passing through the insulation and condensing on a cold surface.

Venturi: A ring or panel surrounding the blades on a propeller fan to improve fan performance.

R-value: A number, such as R-19, that is used to indicate the ability of insulation to resist the flow of heat. The higher the R-value, the better the insulating ability.

Transfer grille: A grille usually installed in walls or doors, with a grille of the same size mounted on each side, that allows air to pass freely in or out of an enclosed space.