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A
A-Coil
A heat exchanger consisting of two diagonal coils that are joined together in a manner that looks like the letter "A".
AC
Abbreviation for alternating current, a type of electric current in which the polarity is constantly reversing causing the electron flow to reverse.
ACCA
Air Conditioning Contractors of America
AFUE
Annual Fuel Utilization Efficiency, a rating that reflects the efficiency of a gas furnace in converting fuel to energy. A rating of 80 means that approximately 80 percent of the fuel is utilized to provide warmth to your home, while the remaining 10 percent escapes as exhaust.
AGA
Abbreviation for American Gas Association, Inc.
AHU
Air Handling Unit. The inside part of the A/C system that contains the blower, cooling evaporator coil, and heater.
ARIThe Air Conditioning and Refrigeration Institute.
ASHRAE
American Society of Heating, Refrigeration and Air Conditioning Engineers.
Acoustical
Of or pertaining to sound. AC or DC - Abbreviation for equipment capable of operating on alternating or direct current.
Add On Heat Pump
Installing a heat pump in conjunction with an existing fossil fuel furnace. The result is a dual fuel system.
Adiabatic Compression
Compressing refrigerant gas without removing or adding heat.
Adjustable Grille
A grille with linear blades which can be adjusted to vary the direction of the discharged air. The linear blades are normally vertical, horizontal, or both vertical and horizontal.
Air Balance Test
A test used to measure airflow across a tower or air handler system.
Air Balancing Hood
Measures airflow from grilles and diffusers.
Air Change
The amount of air required to completely replace the air in a room or building; not to be confused with recirculated air.
Air Changes Per Hour
is the number of times that air in a building is completely replaced with outdoor air in one hour.
Air Cleaner
Any device that removes undesirable particles from moving air.
Air Coil
Coil on some types of heat pumps used either as an evaporator or condenser.
Air Conditioner
Any device that can change the temperature, humidity or general quality of the air.
Air Diffuser
Air distribution outlet or grille designed to direct airflow into desired patterns.
Air Distribution
The transportation of a specified air flow, generally by means of ductwork.
Air Flow Volume
The amount of air the system circulates through your home, expressed in cubic feet per minute (cfm). Proper air flow depends on the outdoor unit, the indoor unit, the ductwork and even whether the filters are clean.
Air Handler
An air moving and/or mixing unit. Residential air handlers include a blower, a coil, an expansion device, a heater rack and filter. Heaters for air handlers are sold as accessories. In some models heaters are factory installed.
Air Terminal Device
Grille or air distribution outlet designed to direct airflow into desired patterns.
Amp (Ampere)
The practical meter-kilogram-second unit of electric current that is equivalent to a flow of one coulomb per second or to the steady current produced by one volt applied across a resistance of one ohm.
Amp/Ohm/Volt Meter
Measures motor amperage and voltage test controls.
Apparent Thermal Conductivity
A value assigned to a material that exhibits thermal transmission by several modes of heat transfer resulting in property variation with specimen thickness or surface emittance.
Automatic Changeover Thermostat
A thermostat that automatically selects either heating or cooling based on the temperature and set-points.
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B
BTU (British Thermal Unit)
British Thermal Unit. In scientific terms, it represents the amount of energy required to raise one pound of water one degree Fahrenheit. One BTU is the equivalent of the heat given off by a single wooden kitchen match. For your home, it represents the measure of heat given off when fuel is burned for heating or the measure of heat extracted from your home for cooling.
BTUhBritish thermal units per hour. 12,000 BTUh equals one ton of cooling. This number indicates the amount of heat it takes to raise one pound of water one degree Fahrenheit. The higher the BTU rating, the larger the heating capacity of the furnace or air conditioner. Homes are measured to determine the number of BTUs required from a heating or cooling system.
Baffles
Device to maintain a ventilation space between the insulation and roof deck, assuring air flow from the eave/soffit vents to ridge vent or other roof vents provided in attics and cathedral ceilings (Owens Corning product is Raft-R-Mate).
Balancing
The process of adjusting the flow of air in duct systems, or water flow in hot-water heating systems. Proper balancing is performed using accurate instrumentation to deliver the right amount of heating or cooling to each area or room of the building.
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.
Band Joist
Vertical member that forms the perimeter of a floor system in which the floor joists tie in. Also known as the rim joist.
Baseline Data
Baseline (or historical) data is compiling for review.
Basin
Cold water reservoir in the cooling tower system.
Basin Temperature
The actual temperature of the cold water basin in the cooling tower system.
Bearing
A support or guide by means of which a moving part such as a shaft or axle is positioned with respect to the other parts of a mechanism.
Bearing Oil Reservoir
Excess oil used in the lubrication of the bearing system located in the compressor system.
Biocide
A substance (as DDT) that is destructive to many different organisms.
Blockage
Blockage is obstruction of flow, i.e., valve, debris, etc.
Blower
Fan or air handling device for moving air in a distribution system.
Blower Door
A large powerful variable-speed fan mounted in a doorway that blows air into (pressurizes) or sucks air out of (depressurizes) a building. It’s used to test for air leakage.
Boot
A piece of duct used to connect ducts with registers.
BoroscopeA fiber-optic camera or lens, used to inspect tube bundles or piping.
Bottom Plate (Sole Plate)
The lowest horizontal member of a wall which rests on the sub-floor, to which the studding is nailed.
British Thermal Unit (Btu)
The heat required to raise the temperature of a pound of water 1°F.
Burner
A device that uses fuel to support combustion.
Burner (sealed combustion)
A burner that obtains all air for combustion from outside the heated space.
Burner Orifice
The opening through which gas flows to the air/gas mixing chamber of the burner.
Bypass Valve
A valve used to detour flow, i.e., to detour water from the hot deck to the tower basin to control tower basin temperature.
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C
CFM
Abbreviation for cubic feet per minute, a standard measurement of airflow. A typical system requires 400 cfm per ton of air conditioning. A measurement of airflow that indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being forced through the system.
COP
The Coefficient of Performance rates a heat pump's ability to efficiently use electricity in its operation.
CSA
Canadian Standards Association.
Capacity
The output or producing ability of cooling or heating systems. Cooling and heating capacities are referred to in British thermal units (BTUs) per hour.
Carryover
The movement of a fluid from one area to another. Carryover of this liquid may contaminate another liquid, causing undesired results.
Celsius
The metric temperature scale in which water freezes at zero degrees and boils at 100 degrees, designated by the symbol "C". To convert to Fahrenheit, multiply a Celsius temperature by 9, divide by 5 and add 32 (25 x 9 equals 225, divided by 5 equals 45, plus 32 equals 77 degrees Fahrenheit).
Charge
To add refrigerant to a system. This is refrigerant contained in a sealed system or in the sensing bulb to a thermostatic expansion valve.
Charging a System
Adding coolant, or refrigerant, to an HVAC system.
Chiller (Centrifugal Chiller)
A heat exchanger using air, refrigerant, water and evaporation to transfer heat (BTUs) to produce air conditioning (measured in tons). A chiller is comprised of an evaporator, condenser and compressor system.
Chill Water
Chill water is the water in the closed loop (closed to the atmosphere) or evaporator system of the chiller.
Chiller Barrel
Passes Many chillers are designed with more than one pass to maximize heat transfer. Baffels and gaskets are used to separate each pass to ensure design flow through the chiller barrel.
Chiller Design Tonnage
The design capacity of the chiller measured in tons produced in an hour.
Chiller Efficiency
Chiller efficiency is measured in Kilowatts per ton (Kw/Ton) of cooling produced. The higher the Kw/Ton, the lower the heat transfer efficiency and the higher the cost to produce a ton of cooling.
Chiller Log Sheet
A sheet on which specific chiller readings are documented.
Chiller Manufacturer
The company that built the chiller, i.e., York, Trane, Carrier, McQuay, etc. The manufacturer name is typically prominently displayed on the chiller control panel or technical documentation.
Chiller Stall
A chiller stalls when the refrigerant is no longer moving through the compressor and there is no cooling effect. All shaft work is being converted into heat in the compressor that may lead to permanent damage.
Chiller Startup
The chiller manufacturer’s recommendation on startup including pre-heating the compressor oil temperature prior to chiller startup.
Chiller Surge
When the refrigerant flows backwards through the compressor wheel every few seconds until the pressure builds up and the refrigerant moves forward again. This is even more dangerous than a stall because it reverses loads of thrust bearings in the compressor shaft.
Chiller Vein (Inlet Guide Veins)
Chiller veins are used to control the capacity of the compressor. As the inlet guide veins start to close, they change the gas entry angle to the impeller and reduce gas flow and compressor capacity. As the vanes near the closed position, they throttle the refrigerant flow.
Climatuff® Compressor
The Trane Climatuff® Compressor was the world's first successful heat pump compressor. To this day it's the only compressor Trane uses in its residential systems. It's well known for its superior durability, its low noise levels, and high efficiency.
Closed Loop
The evaporator side of the chiller system, closed to the atmosphere.
Collar Beam
A horizontal board connecting two opposite rafters at a level considerably above the wall plate. Also known as collar tie.
Cooling Tower/Condenser System
The cooling tower system includes tower fans, plenum, drift eliminators, fill, levelers, hot deck and cold basin combined with the condenser barrel and piping making up the open loop or open recirculating system.
Comfort Zone
The range of temperatures, humidities and air velocities at which the greatest percentage of people feel comfortable.
Comfort-R ™ Coil or Evaporator Coil
A Trane Comfort Coil is the other, less visible half of your air conditioning system, and is located inside your home in the indoor unit. It's a tubing coil in which a volatile liquid evaporates and absorbs heat. This is where the refrigerant evaporates as it absorbs heat from the indoor air that passes over the coil. It serves as a "heat exchanger," moving heat into your home in the winter and away from your home in the summer.
Comfort-R ™ Airflow System
An exclusive feature of a high efficiency home comfort system from Trane. This method of ramping airflow gives you greater humidity control when cooling and provides warmer air during heating start up.
Compressor
Pump of a refrigerating mechanism which draws a low pressure on cooling side of refrigerant cycle and squeezes or compresses the gas into the high pressure or condensing side of the cycle. This is the heart of an air conditioning or heat pump system. It is part of the outdoor unit and pumps refrigerant in order to meet the cooling requirements of the system.
A mechanical device where the refrigerant is compressed from a lower pressure and lower temperature to a higher pressure and higher temperature. The compressor maintains a low pressure in the evaporator by continually removing refrigerant vapors. This low pressure, low temperature vapor is then compressed into a higher pressurize, hot refrigerant vapor which leaves the compressor and travels to the condenser. The motor in the compressor is the main consumer of energy in the chiller system. The energy used by the compressor is dependent on the pressure increase. The head pressure divided by the suction pressure or the condenser pressure divided by the evaporator pressure expresses this. If the compressor operates out of its original design, it will effect the energy consumption
Compressor Erosion/Corrosion
Damage to the bearings and impeller caused by poor lubrication, low oil levels or operating conditions such as liquid refrigerant carryover into the compressor system.
Compressor Motor Amps
The energy used to power the refrigerant cycle in a chiller system. The input energy is dependent upon the pressure increase in the compressor. The head pressure divided by the suction pressure or the condenser pressure divided by the evaporator pressure determines it.
Compressor Oil Temperature
Compressor oil temperature is the temperature of the oil in the compressor bearing lubrication system. This temperature is predetermined by manufacturers specifications.
Condenser Water GPM (Gallons Per Minute)
The velocity of the condenser water measured in gallons per minute. All chiller condensers have a manufacturers design GPM flow rate.
CondensateVapor that liquefies due to the lowering of its temperature to the saturation point.
Condensation
Changing a substance from a vapor to a liquid state by removing the heat. The condensate shows up on surfaces as a film or drops of water. The process a vapor goes through to change phase from vapor to a liquid.
Condenser
Heat exchanger where the system heat is rejected and the refrigerant condenses into a liquid. The condenser is where hot pressurized refrigerant vapors in the compressor are cooled and liquefied by cooling tower water circulating through the tubes of the condenser. The condenser side is commonly referred to as the open recirculation system or open loop.
Condenser coil (or outdoor coil)
In an air conditioner, the coil dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid. In a heat pump system, the coil absorbs heat from the outdoors.
Condenser fanThe fan that circulates air over the air-cooled condenser.
Condenser Pressure
The head pressure produced in the condenser dependent on the entering condenser water temperature and the saturated refrigerant temperature. The condenser pressure can affect the refrigerant cycle and heat transfer. The pressure correlates to saturated refrigerant temperature on a pressure/temperature chart for each refrigerant type.
Condensing Unit
Part of a refrigerating mechanism which pumps vaporized refrigerant from the evaporator, compresses it, liquefies it in the condenser and returns it to the refrigerant control. The outdoor portion of a split system air conditioner contains the compressor and outdoor coil ignoring the reverse cycle operation, also the outdoor in a heat pump system.
Conditioned Fluid
The fluid being acted upon by the working fluid. Example: in an air conditioning system the air is conditioned by the refrigerant (refrigerant is the working fluid).
Conductance, Thermal (C)
The time rate of steady state heat flow through a unit area of a material or construction induced by a unit temperature difference between the body surfaces. C = Btu/hr·ft2·°F (W/m2·°C)
Conductivity, Thermal
The time rate of steady state heat flow through a unit area of homogeneous material induced by a unit temperature gradient perpendicular to that unit area. k = Btu·in/hr·ft2·°F (l = W/mS°C)
Contactor
A switch that can repeatedly cycle, making and breaking an electrical circuit. When sufficient current flows through the A-coil built into the contactor, the resulting magnetic field causes the contacts to be pulled in or closed.
Contamination
Any foreign object or substance not normally found in a specific location.
Cooling Degree Day (hour)
A unit, based on temperature difference and time, used in estimating fuel consumption and specifying nominal cooling load of a building in summer.
Corrosion
The decay and loss of a metal due to a chemical reaction between the metal and its environment. It is a transformation process in which the metal passes from its elemental form to a combined (or compound) form.
Cost of Blowdown
The total cost of water sent to drain/sewer, typically determined on a per 1,000 gallon basis. This value can be found on the water and sewer utility bill or from the utility company.
Cost of Kw
The cost of electricity charged by the electric and is typically $0.04 to $0.15 per kilowatt depending on geographic location.
Crankcase Heater
This is the electric resistance heater installed on compressor crankcases to boil off liquid refrigerant that may have combined with compressor oil. Many newer cooling systems do not require crankcase heaters, however heat pumps do require crankcase heaters.
Crawlspace Vents
An opening to allow the passage of air through the unfinished area under a first floor. Ideally there should be at least two vents per crawlspace.
Cross Bridging
Small wood pieces placed at angles so that they extend from the bottom of one floor joist to the top of the adjacent joist to add stability to the structural members.
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D
DC
Direct current electricity. This type of electricity (as opposed to Alternating Current, or AC) flows in one direction only, without reversing polarity.
DOE
Department of Energy
DX
Direct expansion; a system in which heat is transferred by the direct expansion of refrigerant.
Damper
Found in ductwork, this movable plate 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
To melt frost; as in from an air conditioner or heat pump coil.
Defrost Cycle
The process of removing ice or frost buildup from the outdoor coil during the heating season.
Degree-day
A degree-day is a computation that gauges the amount of heating or cooling needed for a building. A degree-day is equal to 65 degrees Fahrenheit minus the mean outdoor temperature.
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.
Dehumidifier
An air cooler that removes moisture from the air.
DiffuserA grille over an air supply duct having vanes to distribute the discharging air in a specific pattern or direction.
Direct Gas-Fired Heater
The burner fires directly in the air stream being heated, rather than through a heat exchanger. 100% of available BTUs are delivered to the heated space because no flue or heat exchanger is required. This results in no wasted energy.
Downflow furnace
A furnace that intakes air at its top and discharges air at its bottom.
Drain Pan
This also referred to as a condensate pan. This is a pan used to catch and collect condensate (in residential systems vapor is liquefied on the indoor coil, collected in the drain pan and removed through a drain line).
Dry Bulb
The ambient outside temperature.
Dry Bulb Temperature
Heat intensity, measured by a dry bulb thermometer.
Dry Bulb Thermometer
An instrument that measures air temperature independently of humidity.
Duct
A pipe or closed conduit made of sheet metal, fiberglass board, or other suitable material used for conducting air to and from an air handling unit.
Ductwork
A pipe or conduit through which air is delivered. Ducts are typically made of metal, fiberboard or a flexible material. In a home comfort system, the size and application of ductwork is critical to performance and is as important as the equipment.
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E
ECWTEntering Condenser Water Temperature
EER
Energy Efficiency Ratio (steady state)
EPA
Environmental Protection Agency
ERV
Energy Recovery Ventilator is a device that preheats incoming outside air during the winter and pre-cools incoming air during the summer to reduce the impact of heating and or cooling the indoor air.
Eave Vents
Vent openings located in the soffit under the eaves of a house to allow the passage of air through the attic and out the roof vents.
Economic Thickness (of insulation)
That thickness which provides the lowest possible annual cost of energy, insulation and energy producing equipment.
Efficiency
The rating on heating & cooling equipment, similar to the miles per gallon rating on your car. The higher the rating number, the more efficient the system and the lower your fuel consumption will be.
Electronic Air Cleaner
An electronic device that filters out particles and contaminants in indoor air.
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. Filter: A device for removing dust particles from air or unwanted elements from liquids. Furnace: That part of an environmental system which converts gas, oil, electricity or other fuel into heat for distribution within a structure.
Emittance
The ratio of the radiant flux emitted by an ideal, perfect emitter and absorber of thermal radiation at the same temperature and under the same conditions.
Emulsification
The entrainment of one substance into another, i.e., oil in water or oil in refrigerant.
Energy Balance
Energy cannot be created or destroyed during heat transfer; therefore the amount of energy leaving the source must equal the amount reaching the sink.
ENERGY STAR®
Trane high efficiency systems carry the ENERGY STAR label. The result of Trane's partnership with the U.S. Department of Energy, Environmental Protection Agency (EPA), ENERGY STAR products are more energy efficient and help reduce our whole earth's pollution problems. Choosing a Trane ENERGY STAR Comfort System assures homeowners of lower energy bills and improved indoor air quality for their home.
Entering Condenser
Water Temperature Entering condenser water temperature is the temperature of water entering the condenser.
Enthalpy
The quantity of internal energy of a body plus the product of its volume and pressure.
Equivalent Thickness (of insulation)
When r1 = the inner radius of a single layer of cylindrical insulation and r2 = the outer radius, equivalent thickness = r2 1n r2/r1.
Evaporator Coil (or indoor coil)
The other half of your air conditioning system located inside your home in the indoor unit. This is a tubing coil in which a volatile liquid evaporates and absorbs heat. This is where the refrigerant evaporates as it absorbs heat from the indoor air that passes over the coil.
Exfiltration
Uncontrolled air leakage out of a building.
Exhaust
The air flow leaving the treated space by one of the following methods:
Extraction: air is discharged into the atmosphere
Relief: air is allowed to escape from the treated space if the pressure in that space rises above a specified level
Recirculation: air is returned to the air treatment system
Transfer: air passes from the treated space to another treated space
Exhaust Air Terminal Device
Air terminal device through which air leaves the treated space.
Expansion Valve
A refrigerant-metering valve with a pressure or temperature controlled orifice.
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F
FRK
A vapor retarder laminate of foil/ scrim (reinforcement) kraft construction. Also known as FSK.
Face Staple
Stapling facing flange to the front side of a stud or rafter, along the 1½" dimension.
Faced Insulation
Insulation with a facing already attached. Kraft paper or foil-backed paper are common facings.
Fahrenheit
The temperature scale on which water freezes at 32 degrees and boils at 212 degrees; designated by the letter F. To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit number, multiply by 5 and divide by 9 (77 -32 equals 45, times 5 equals 225, divided by 9 equals 25 degrees Celsius).
Fan
Any device that creates air currents.
Fan Coil
An indoor component of a heat pump system used in place of a furnace, to provide additional heating on cold days when the heat pump does not provide adequate heating.
Filter
Any device that removes impurities through a straining process.
Fire Dampers
Components that are installed in an air distribution system between two fire separating compartments and are designed to prevent propagation of fire and or smoke.
Flow Hood
A diagnostic tool used to measure air flow through ducts, supply registers and return grilles.
Flue
Any vent or passageway that carries the products of combustion from a furnace.
Flute
Allows the transfer of liquid refrigerant from the condenser back to the evaporator.
Flute Frosting
A problem associated with rapid movement of liquid refrigerant at low temperatures from the condenser to the evaporator, causing frost to form on the flute.
Forced Air
A type of heating system that uses a blower motor to move air through the furnace and into the ductwork.
Fouled Tubes
Debris or substance which impedes flow or heat transfer. Fouling can be caused by trash, chip scale “flash corrosion”, microbio, etc.
Free Oil
“Free” or floating oil on top of a liquid with a higher specific gravity.
Frequency (Hz)
The number of cycles per second measured in units of Hertz.
Furnace
That part of the heating system in which the combustion of fossil fuel and transfer of heat occurs.
Furring Strips
Flat pieces of lumber used to build out framing to an even surface, either the leveling of a part of a wall or ceiling. In block or concrete construction, they may be used as a means of attaching the interior or exterior finish.
Fuse
A metal strip in an electrical circuit that melts and breaks the circuit when excessive current flows through it. The fuse is designed to break in order to save more expensive electrical components.
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G
GAMAGas Appliance Manufacturers Association
GPM
Gallons Per Minute
Gable End Walls
The triangular end of an exterior wall above the eaves.
Gable Vents
A louver vent mounted in the top of the gable to allow the passage of air through the attic.
Gas Furnace Heat Exchanger
Located in the furnace, the heat exchanger transfers heat to the surrounding air, which is then pumped throughout your home.
Gasket
Any of a wide variety of seals or packings used between matched machine parts or around pipe joints to prevent the escape of a gas or fluid.
Gauge
An instrument or device for measuring, indicating or comparing a physical characteristic, i.e., temperature or pressure.
Glass Fibers
Glass in a strand form. The ingredients are essentially the same that go into any glass product such as a window pane or drinking glass.
Grille
An air terminal device with multiple passages for the air.
Grille
Coverings for the ducts where they open to the conditioned space. Also referred to as Registers.
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H
HERS
HOME ENERGY RATING SYSTEM PROGRAM.
HRV (Heat Recovery Ventilator)
A device that brings fresh, outside air into a building while simultaneously exhausting stale indoor air outside. In the process of doing this, an HRV removes heat from the exhaust air and transfers it to the incoming air, pre-heating it.
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 heat pump system.
HVAC
Abbreviation for Heating, Ventilating and Air Conditioning
HVAC/R
Heating, Ventilation, Air Conditioning, & Refrigeration.
Heat Exchanger
An area, box or coil where heat flows from the warmer to the colder fluid or surface.
Heat Gain
Heat added to the conditioned space by infiltration, solar radiation, occupant respiration and lighting.
Heat Loss
The rate of heat transfer from a heated space to the outdoors.
Heat Pump
A mechanical-compression cycle refrigeration system that can be reversed to either heat or cool the controlled space.
Heat Source
A body of air or liquid from which heat is collected.
Heat Transfer
The movement of heat energy from one point to another. The means for such movement are conduction, convection, and radiation.
Heating CoilAny coil that serves as a heat source.
Hertz
In alternating current (AC electricity), the number of cycles per second.
High Efficiency Air Cleaner
An air filter installed in your central system that collects up to 99% of particles 5 microns or larger. In comparison your standard air filter only picks up about 8% of these same particles.
Horizontal Flow
A type of furnace, installed on its "side," that draws in air from one side, heats it and sends the warm air out the other side. Most often used for installations in attics or crawl spaces.
Hot Deck
The top deck of the cooling tower where the condenser water returns to the tower prior to be cooled by evaporation, also referred to as the hot basin.
Hot Deck Distribution
Holes Holes in the hot deck that distribute the flow of returning condenser water evenly across the tower fill.
Hot Gas Piping (Piping) A means of recirculating hot discharge refrigerant back into the evaporator. The refrigerant must pass through a pressure-reducing device (hot gas bypass valve). The purpose of hot gas bypass is to maintain a minimum gas volume flow rate through the compressor to avoid surging or stalling during low load conditions. A disadvantage is that the work of compression on the recirculated refrigerant does not generate any refrigeration effect.
Hot Wire Anemometer
Measures air velocity in grilles, filters, coils and ducts.
Humidifier
A machine that adds water vapor to the air to increase humidity.
Humidistat
A humidity-sensing control that cycles the humidifier on and off.
Humidity
The presence of water vapor in the air.
Humidity, absolute
Weight of water vapor per cubic foot of dry air, expressed as grains of moisture per cubic foot.
Humidity, relative
The amount of moisture in the air expressed as a percentage of the maximum amount that the air is capable of holding at a specific temperature.
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I
IAQ
Indoor Air Quality.
IPLV – Integrated Part Load Value
A single number, part-load efficiency indicator calculated using the ARI method at standard rating conditions. Introduced in ARI Standard 550-1986, the definition of IPLV was changed in ARI Standard 550/590-1998 to more closely reflect actual operating experience found in the field for a single chiller.
IWC
Inches of water column, commonly used in the USA.
Ignition
The lighting of a fuel to make it burn.
Indoor Coil
The refrigerant containing portion of a fan coil unit, typically made of several rows of copper tubing with aluminum fins.
Indoor Unit
This is usually located inside the building and contains the indoor coil, fan, motor, and filtering device, sometimes called the air handler.
Induction
Process by which the primary air sets into motion an air volume, called secondary air, in the room.
Induction ratio
Ratio of the total air flow rate to the primary air flow rate.
Infiltration
Air flow inward to a space through walls, leaks around doors and windows, or through the building materials in the building.
Inset Staple
Stapling to the inside portion of the stud or rafter.
Insulation Density
Denser insulation products have more fibers per square inch and, therefore, give you greater insulating power through higher R-values.
Insulation Supports
16" or 24" wire rods, nylon banding, or crisscrossed wire to hold floor insulation in place.
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J
Joist
Horizontal framing member set from wall to wall to support the floor or ceiling.
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K
Kilowatt (kW)
A kilowatt equals 1,000 Watts. A kilowatt hour (kWh) is the amount of kilowatts of electricity used in one hour of operation of any equipment.
Kilowatt Hour (kWh)
A kilowatt hour (kWh) is the amount of kilowatts of electricity used in one hour of operation of any equipment.
Knee Walls
Walls of varying length. Used to provide additional support to roof rafters with a wide span or to finish off an attic.
Kraft-Faced Vapor Retarder
Created by coating kraft paper with a thin layer of asphalt adhesive. The coated side of the kraft paper is then applied to the unfaced insulation material. The asphalt adhesive bonds the kraft paper and the insulation together.
Kw/ton
A kilowatt (Kw) is a measure of electrical energy. A ton is a measure of cooling and is defined as 12,000 BTU of cooling per hour.
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L
Latent Cooling Load
The net amount of moisture added to the inside air by plants, people, cooking, infiltration, and any other moisture source.
Latent Heat
A type of heat, which when added to or taken from a substance, does not change the temperature of the substance. Instead, the heat energy enables the substance to change its state.
Lay-up
The process of winterizing a tower or condenser system when not in use.
Legionella
A bacterium of the genus legionella, especially pneumophila, that can cause Legionnaires’ disease - an acute, sometimes fatal respiratory disease caused by and characterized by severe pneumonia, headache, and a dry cough.
Liquid Piping
Refrigerant piping from the condenser outlet to the evaporator inlet.
Liquid Refrigerant
The compressor coolant used in the refrigerant cycle of a chiller for heat transfer.
Liquid Refrigerant Stacking
This condition occurs can be caused by mechanical failure or low head pressure in the condenser and evaporator caused by low condenser water temperature.
Load
Amp load is compared to full load and the percentage value equals the load of the chiller. Actual amps divided by full load amps is the percentage of full load design.
Load Calculation
The process of mathematically calculating the necessary cooling or heating your home or business will need to properly cool each area.
Load Estimate
Also heat load. A series of studies performed to determine the heating or cooling requirements of your home. An energy load analysis uses information such as the square footage, window and door areas, insulation quality and local climate to determine the heating and cooling capacity needed by your furnace, or air conditioner. When referring to heating, this is also called Heat Loss Analysis, since a home’s heating requirements are determined by the amount of heat lost through the roof, entry ways and walls.
Load Swing
A large or radical change in cooling load requirements, i.e., weather or building operations requirements.
Log Mean
Temperature Difference A specialized average temperature difference used to determine the heat transfer rate.
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M
Matched System
A heating and cooling system comprised of products that have been certified to perform at promised comfort and efficiency levels when used together, and used according to design and engineering specifications.
Mean Temperature
The arithmetic mean between hot and cold surface temperatures of an insulated pipe, duct or vessel. tm = (t1 + t2)/2.
Media
The material in a filter that traps and holds the impurities.
Metal Flue
A metal channel through which hot air, gas, steam or smoke may pass.
Microbe
An organism of microscopic or ultramicroscopic size.
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N
NEC
National Energy Council / National Electric Code
NEMA
National Electrical Manufacturing Association
NPS
Nominal Pipe Size, inches. Metric equivalent of DN (Diameter, Nominal, millimeters).
Noise Reduction Coefficient (NRC)A single number rating, the arithmetic average of the individual sound absorption coefficients of a material at 250, 500, 1000 and 2000 Hz to the nearest .05.
Noncombustible
The material will not burn. The glass fibers in fiber glass insulation have a natural fire resistance, and are considered non-combustible when tested in accordance to ASTM E136.
Nozzle
An air terminal device designed to generate a low energy loss.
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O
OEM
Original equipment manufacturer.
Operating Cost
The day-to-day cost to run your home comfort system, based on the energy required to run it.
Orifice
An opening or hole; an inlet or outlet.
Outdoor Coil
Refrigerant containing portion of a fan coil unit similar to a car radiator, typically made of several rows of copper tubing with aluminum fins. Also referred to as the condenser coil.
Outdoor Unit
Air conditioner or heat pump.
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P
PSI
Pounds per square inch.
PSIA
Pounds per square inch, absolute.
PSIG
Pounds per square inch gauge.
PVC
Polyvinyl chloride; a type of plastic.
Package Unit
A heating and cooling system contained in one outdoor unit. A package unit is typically installed beside, on the roof, or sometimes in the attic of a home.
Packaged System
A piece of air conditioning and heating equipment in which all components are located in one cabinet. Used occasionally in residential applications, the packaged unit is installed either beside or on top of the home.
Payback Analysis
Overall measure of the efficiency and value of your home comfort system. By combining your purchase price and ongoing operating costs, a payback analysis determines the number of years required before monthly energy savings offset the purchase price.
Perm
The mass rate of water vapor flow through one square foot of a material or construction of one grain per hour induced by a vapor pressure gradient between two surfaces of one inch of mercury or in units that equal that flow rate.
Plate Exchanger
A heat exchanger used to create free cooling (not using a compressor or refrigerant to transfer heat) by running colder tower water over stainless steel plates which transfers heat between the closed loop to the open loop.
Plenum
Air flow passage made of duct board, metal, drywall or wood. Joins supply and return ducts with HVAC equipment.
Polyethylene Vapor Barrier
Plastic film used to prevent moisture from passing through unfaced insulation. Both 4- and 6-mil polyethylene are preferred because they are less likely to be damaged during construction.
Power Factor
The ratio of actual power (Kw) to apparent power (kVA). Most centrifugal motors have a power factor between 0.87 and 0.91. Additional capacitors can be added to raise the power factor to a practical limit of 0.95. In the table below, the closer the length of the kVA line is the the kW line the more efficient the user of the energy.
Pressure Balancing
The process of neutralizing pressure differences within a building.
Primary Air Flow Rate
Volume of air entering a supply air terminal device within a time unit.
Programmable Thermostat
An electronic thermostat with a built in memory that can be programmed for the different temperature settings at different times of day.
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R
Rafters
A slope framing member that supports a pitched roof.
Reciprocating Compressor
A type of compressor used in cooling systems to compress refrigerant by using a piston action. A compressor whose piston or pistons move back and forth in the cylinders.
Reclaiming
Processing or returning used refrigerant to the manufacturer or processor for disposal or reuse.
Refrigerant
A chemical that produces a refrigerating effect while expanding and vaporizing. Most residential air conditioning systems contain R-22 refrigerant. R-22 is regulated under the Montreal Protocol and in the United States by the Environmental Protection Agency. R-22 is scheduled to be in production until the year 2020. It's used in approximately 95 percent of air conditioning equipment manufactured in the U.S. today.
Refrigerant Charge
The required amount of refrigerant in a system.
Refrigerant Lines
Two copper lines that connect the Condenser or Outdoor Coil to the Evaporator or Indoor Coil.
Refrigerants
The working fluid in a two-phase refrigeration cycle is called a refrigerant. A useful way to classify refrigerants is to divide them into primary and secondary. Primary refrigerants are those fluids (pure substances, azeotropic mixtures which behave physically as a single pure compound, and zeotropes which have temperature glides in the condenser and evaporator) used to directly achieve the cooling effect in cycles where they alternately absorb and reject heat. Secondary refrigerants are heat transfer or heat carrier fluids.
Refrigeration
The cooling of a space or substance below the environmental temperature. Mechanical refrigeration is primarily an application of thermodynamics wherein the cooling medium, or refrigerant, goes through a cycle so that it can be recovered for reuse. The commonly used basic cycles, in order of importance, are vapor-compression, absorption, steam-jet or steam-ejector, and air. Each cycle operates between two pressure levels, and all except the air cycle use a two-phase working medium which alternates cyclically between the liquid and vapor phases.
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S
SEER
Seasonal Energy Efficiency Ratio; a measure of cooling efficiency for air conditioners and heat pumps. The higher the SEER, the more energy efficient the unit. The U.S. Government's minimum SEER rating is 10.
Self-Contained System
A refrigerating system that can be moved without disconnecting any refrigerant lines; also know as a package unit.
Sensible Cooling Load
The heat gain of the building due to conduction, solar radiation, infiltration, appliances, people, and pets.
Sensible Heat
That heat which, when added to or taken away from a substance, causes a rise or fall in temperature.
Sensor
Any device that reacts to a change in the conditions being measured, permitting the condition to be controlled.
Setback Thermostat
An electronic thermostat with a built-in memory that can be programmed for different temperature settings at different times of the day.
Setpoint
The temperature or pressure at which a controller is set with the expectation that this will be a nominal value depending on the range of the controller.
Single Package
A year ‘round heating and air conditioning system that has all the components completely encased in one unit.
Sorption
Refers to the taking up and holding of water by various processes such as absorption and adsorption.
Sound Absorption
The process of dissipating or removing sound energy; the property possessed by materials, objects and structures (such as rooms) of absorbing sound energy; the measure of the magnitude of the absorptive property of a material, object or structure.
Sound Absorption Coefficient
The percentage of sound energy incident on the surface of a material that is absorbed by the material.
Sound AttenuatorsComponents which are inserted into the air distribution system and designed to reduce airborne noise which is propagated along the ducts.
Spine Fin™
Coil All-aluminum outdoor coil that features the patented Spine Fin™ design. It provides greater heat exchanging capabilities (meaning higher efficiencies) and is more resistant to corrosion than traditional copper/aluminum
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.
Stapling Flange
A protruding edge on faced insulation used to staple the insulation to the framing.
Static Pressure
The normal force per unit area at a small hole in the wall of a duct through which a fluid is flowing.
Stud
A vertical framing member used in both exterior and interior walls.
Subcooled Liquid
Liquid refrigerant which is cooled below its saturation temperature.
Subfloor
The structural material that spans across floor joists. It serves as a working platform during construction and provides a base for the finish floor.
Superheat Test
A superheat test is the excess of the gas suction temperature above the gas saturation temperature. The purpose of the superheat is to ensure that liquid refrigerant does not enter the compressor. Typically the standard is between 10 and 20°F. A high superheat value is an indication of low refrigerant levels and low superheat value is an indication of high refrigerant levels especially when the compressor is operating at full load.
Superheated Vapor
Refrigerant vapor which is heated above its saturation temperature. If a refrigerant is superheated, there is no liquid present.
Supply
The ductwork that carries air from the air handler to the rooms in the building.
Supply Air
The air flow entering the treated space.
Switchover Valve
A device in a heat pump that reverses the flow of refrigerant as the system is switched from cooling to heating. Also called a reversing valve or four-way valve.
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T
Therm
Another measurement of heat. One therm equals 100,000 BTUH.
ThermostatA thermostat consists of a series of sensors and relays that monitor and control the functions of a heating and cooling system.
Thermostatic Expansion Valve
A refrigerant metering device that maintains a constant evaporator temperature by monitoring suction vapor superheat; also called a thermal expansion valve.
Ton
A unit of measurement used for determining cooling capacity. One ton is the equivalent of 12,000 BTUs per hour.
Top Plate
The horizontal member nailed to the top of the studding of a wall.
Two-stage heating / Two-stage cooling
Two-stage heating and cooling is considered to be more efficient, because it operates at low speed most of the time. However, on days when more heating or air conditioning is required, it switches to the next stage for maximum comfort.
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U
U-Factor
The factor representing resistance to heat flow of various building materials.
UL
Underwriters Laboratories
Unfaced Insulation
Insulation with no attached facing.
Upflow Furnace
A furnace in which air is drawn in through the sides or bottom and discharged out the top.
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V
VAV
Variable Air Volume.
VAV Box
A device connected inline to a system duct containing a damper to control the volume of airflow. A thermostat controls the action of the box.
VFD
Variable Frequency Drive. Electronic speed control for motors.
Vacuum
A pressure below atmospheric pressure. A perfect vacuum is 30 inches Mercury (periodic symbol "Hg").
Valves
Components inserted into air ducts or devices which permit modification of the air resistance of the system and consequently a complete shut-off of the air flow.
Vapor Retarder
Helps control the amount of moisture passing through the insulation and collecting inside exterior walls, ceilings and floors.
Variable-speed motor(s)
The fan motor inside Trane's variable-speed air handlers is designed to vary its speed based on your home's heating and air conditioning requirements. Working in conjunction with your thermostat, it keeps the appropriate-temperature air (e.g. warm air on cold days) circulating throughout your home, reducing temperature variances in your home. It also provides greater air circulation and filtration, better temperature distribution, humidity control, higher efficiency, and quiet performance.
Ventilator
A ventilator captures heating or cooling energy from stale indoor air and transfers it to fresh incoming air.
Voltage
The force that pushes electrical current along wires and cables.
Volts
The practical meter-kilogram-second unit of electrical potential difference and electromotive force equal to the difference of potential between two points in a conducting wire carrying a constant current of one ampere when the power dissipated between these two points is equal to one watt and equivalent to the potential difference across a resistance of one ohm when one ampere is flowing through it ; abbreviated by the symbol "v".
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W
WCWater Column. Common measure of air pressure used in HVAC systems.
Wall Plates
In wood-frame construction, the wall is composed of both vertical and horizontal wood members. The vertical members are usually called studs, while the horizontal members are usually called plates. A bottom plate is at the bottom of the wall frame assembly, while two plates are usually used at the top (double top plate).
Warm-In-Winter Side
In heating climates, it is the interior side of an exterior wall assembly.
Water Vapor Permeance
Time rate of water vapor transmission through unit area of flat material or construction, induced by vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions.
Water Vapor Retarder
A material or system that adequately impedes the transmission of water vapor under specified conditions.
Watt
The unit of electrical power equal to the flow of one amp at a potential difference of one volt.
Wet Bulb Thermometer
A thermometer whose bulb is covered with a piece of water-soaked cloth. The lowering of temperature that results from the evaporation of water around the bulb indicates the air's relative humidity.
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Z
Zoning System
A method of dividing a home into different comfort zones so each zone can be independently controlled depending on use and need; an air conditioning system capable of maintaining varying conditions for various rooms or zones.
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HVAC Glossary