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http://www.engineeringtoolbox.com/hvac-terms-d_246.html
http://www.bergquistcompany.com/fans-blowers/glossary.php
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ABSOLUTE HUMIDITY - The weight of water vapor in a given amount of air.
ABSOLUTE PRESSURE - Pressure measured with the base of zero.
ABSOLUTE TEMPERATURE - A temperature scale expressed in degrees oF or oC
using absolute zero as a base. Referred to as the Rankin or Kelvin scale.
ABSOLUTE ZERO - The temperature at which molecular activity theoretically ceases. 456.69 oF or -273.16 oC.
AIR CONDITIONING - The process of controlling the temperature, humidity, cleanliness
and distribution of the air.
AIR, Standard Conditions - Conditions at which capacity ratings for air conditioning
equipment is rated.
AMBIENT - Refers to the temperature surrounding a body or unit under test.
ATMOSPHERIC PRESSURE - The weight of a 1 unit column of the earth's atmosphere.
BIMETAL - Two metals with different rates of expansion fastened together. When heated
or cooled they will warp and can be made to open or close a switch or valve.
BOILING POINT - The temperature at which the addition of any heat will begin a change
of state from a liquid to a vapor.
BRITISH THERMAL UNIT (BTU) - The amount of heat necessary to change the
temperature of 1 pound of pure water 1 degree Fahrenheit (oF).
CAPILLARY TUBE - A refrigerant control consisting of a small diameter tube which
controls flow by restriction. They are carefully sized by inside diameter and length for
each particular application.
CENTIGRADE - A temperature scale with the freezing point of water 0 oC and the boiling
point 100 oC at sea level.
CHECK VALVE - A valve designed to permit flow in one direction only.
COMPRESSION - The reduction of volume of a vapor or gas by mechanical means.
COMPRESSION RATIO - The ratio determined by dividing the discharge pressure, in
PSI (Pa), by the suction pressure in PSI (Pa).
COMPRESSOR - A mechanical device used to compress gases. Three main types reciprocating, centrifugal and rotary.
CONDENSATION POINT - The temperature at which the removal of any heat will begin
a change of state from a vapor to a liquid.
CONDENSING MEDIUM - The substance, usually air or water, to which the heat in a
condenser is transferred.
CONDENSING UNIT - The portion of a refrigeration system where the compression and
condensation of refrigerant is accomplished. Sometimes referred to as the 'high side'.
CONDUCTION - The transfer of heat from molecule to molecule within a substance.
CONTACTOR - An electromagnetic actuated relay. Usually used to refer to the relay
which closes the circuit to a compressor.
CONVECTION - The transfer of heat by a moving fluid.
COOLING ANTICIPATOR - A resistance heater (usually not adjustable) in parallel with
the cooling circuit. It is 'on' when the current is 'off", adding heat to shorten the off cycle.
COP - Ratio of work performed or accomplished as compared to the energy used.
CUBIC FEET PER MINUTE - A common means of assigning quantitative values to
volumes of air in transit, usually abbreviated CFM.
CYCLE - The complete course of operation of a refrigerant back to a selected starting
point in a system.
DENSITY - Mass or weight per unit of volume.
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DISCHARGE LINE - A tube used to convey the compressed refrigerant vapor from the
compressor to the condenser inlet.
DISCHARGE PRESSURE - The pressure read at the compressor outlet. Also called
head pressure or high side pressure.
DRY AIR - Air which contains no moisture vapor.
DRY BULB TEMPERATURE - Temperature read with an ordinary thermometer.
EFFECTIVE TEMPERATURE - An arbitrary concept which combines into a single value
the effect of temperature, humidity, and air movement as sensed by the human body.
ENTHALPY - Total amount of heat in one pound (kg) of a substance calculated from
accepted temperature base, expressed in BTU's per pound mass (J/kg).
EQUIVALENT LENGTH - That length of straight tubing which has the same pressure
drop as the fitting, valve or accessory (of the same nominal size) being considered.
EVAPORATIVE COOLING - The cooling effect of vaporization of a liquid in a moving air
stream.
EVAPORATOR - A device in which a liquid refrigerant is vaporized. Some superheating
usually takes place.
EVAPORATOR SUPERHEAT - The actual temperature of the refrigerant vapor at the
evaporator exit as compared to the saturated vapor temperature indicated by the suction
pressure.
EXTERNAL STATIC PRESSURE - The sum of the static and velocity pressures of a
moving air system at the point of measurement.
FAHRENHEIT - A temperature scale with the freezing point of water 32 oF and the
boiling point 212 oF at sea level.
FEET PER MINUTE - A term assigned to a velocity of a moving air stream, usually
express FPM.
FILTER-DRIER - A device that removes moisture, acid and foreign matter from the
refrigerant.
FLASH GAS - Instantaneous evaporation of some liquid refrigerant at the metering
device due to pressure drop which cools the remaining liquid refrigerant to desired
evaporation temperature.
FREEZING POINT - The temperature at which the removal of any heat will begin a
change of state from a liquid to a solid.
GAUGE PRESSURE - Pressure measured with atmospheric pressure as a base.
HEAT - A form of energy causing the agitation of molecules within a substance.
HEAT EXCHANGER - A device for the transfer of heat energy from the source to the
conveying medium.
HEAT FLOW - Heat flows from a warmer to a cooler substance. The rate depends upon
the temperature difference, the area exposed and the type of material.
HEAT OF COMPRESSION - The heat added to a vapor by the work done on it during
compression.
HEAT OF THE LIQUID - The increase in total heat (Enthalpy) per pound of a saturated
liquid as its temperature is increased above a chosen base temperature. (Usually - 40 oF
for refrigerants).
HEAT TRANSFER - The three methods of heat transfer are conduction, convection and
radiation.
INCHES OF MERCURY - Atmospheric pressure is equal to 29.92 inches of mercury.
LATENT HEAT - Heat that produces a change of state without a change in temperature;
i.e., ice to water at 32 oF or water to steam at 212 oF.
LATENT HEAT OF CONDENSATION - The amount of heat energy in BTU's that must
be removed to change the state of one pound of a vapor to one pound of liquid at the
same temperature.
LATENT HEAT OF FUSION - The amount of heat energy, in BTU's required to change
the state of one pound of a liquid to one pound of solid at the same temperature.
LATENT HEAT OF MELTING - The amount of heat energy, in BTU'S, that must be
removed to change the state of one pound of solid to one pound of liquid at the same
temperature.
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LATENT HEAT OF VAPORIZATION - The amount of heat energy in BTU's required to
change the state of one pound of a liquid to one pound of vapor at the same
temperature.
LIFT - To elevate a fluid from one level to a higher level.
LIQUID LINE - A tube used to convey the liquid refrigerant from the condenser outlet to
the refrigerant control device of the evaporator.
MANOMETER - A tube filled with a liquid used to measure pressures.
MBH - One MBH is equivalent to 1,000 BTU's per hour.
MEAN TEMPERATURE DIFFERENCES - The mean of difference between the
temperature of a fluid receiving and a fluid yielding heat.
MELTING POINT - The temperature at which the addition of any heat will begin a
change of state from a solid to a liquid.
MERCURY MANOMETER - Used to measure vacuum in inches of mercury.
MICRON - A unit used to measure high vacuums. One micron equals 1/25,400 of one
inch mercury.
MOLLIER CHART - A psychrometric chart. How-to convert between Mollier and
Psyhrometric charts?
MUFFLER - Device installed in hot gas line to silence discharge surges.
OIL SEPARATOR - A device for separating out oil entrained in the discharge gas from
the compressor and returning it to the crankcase.
PARTIAL PRESSURE - The pressure exerted by any individual gas in a mixture.
PITCH - The slope of a pipe line for the purpose of improving drainage.
PITOT TUBE - A device comprising a small diameter orifice projecting directly into an air
stream measuring total pressure and surrounded by an annular section with small
diameter entrances normal to the flow, measuring static pressure; both sections are
usually connected to a manometer to indicate velocity pressure.
PRECHARGED LINES - Refrigerant line's which are filled with refrigerant and are
sealed at both ends. The seals are broken when the lines are installed and the line
charge becomes part of the total system charge.
PRESSURE DROP - The decrease in pressure due to friction of a fluid or vapor as it
passes through a tube or duct or/and lift.
PRESSURE - TEMPERATURE RELATIONSHIP - The change effected in temperature
when pressure is changed or vice versa. Only used at saturated conditions. An increase
in pressure results in a temperature increase. A decrease in temperature results in a
pressure decrease.
PUMPDOWN - Process of pumping refrigerant out of the evaporator and suction line at
the end of the on- cycle by closing a solenoid valve in the liquid line and letting the
compressor shut-off by the low pressure control.
PSYCHROMETER - A devices having both a dry and wet bulb thermometer. It is used to
determine the relative humidity in a conditioned space. Most have an indexed scale to
allow direct conversion from the temperature readings to the percentage of relative
humidity.
PSYCHROMETRIC CHART - A chart on which can be found the properties of air under
varying conditions of temperature, water vapor content, volume, etc.
QUICK CONNECT - Name given to the end connections on precharged lines which
screw on to mated fittings of the outdoor and indoor sections. Tightening the quick
connections ruptures the seals on the fittings and the line charge becomes part of the
total system charge.
RADIATION - The transfer of heat without an intervening medium. It is absorbed on
contact with a solid surface.
RECEIVER - A vessel for holding refrigerant liquefied by the condenser.
REFRIGERANT - A substance which produces a refrigerating effect while expanding or
vaporizing.
REFRIGERANT CONTROL - A device used to meter the amount of refrigerant to an
evaporator. It also serves as a dividing point between the high and low pressure sides of
the system.
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REFRIGERANT DISTRIBUTOR - A device which meters equal quantities of refrigerant
to independent circuits in the evaporator coil.
REFRIGERANT MIGRATION - The movement of refrigerant through the system to the
compressor crankcase during the off-cycle, caused by its attraction to oil.
REFRIGERANT OPERATING CHARGE - The total amount of refrigerant required by a a
system for correct operation.
REFRIGERANT VELOCITY - The rate at which refrigerant is moving at a given point in a
system, usually given in feet per minute (FPM).
REFRIGERATION - The transfer of heat from a place where it is not wanted to a place
where its presence is not undesirable.
REFRIGERATION EFFECT - The amount of heat a given quantity of refrigerant will
absorb in changing from a liquid to a vapor at a given evaporating pressure.
RELATIVE HUMIDITY - The percentage of water vapor present in a given quantity air
compared to the amount it can hold at its temperature.
RELAY - A device used to open and close an electrical circuit. The relay may may be
actuated by a bimetal electrically heated strip, a rod wrapped with a fine resistance wire
causing expansion when energized, a bellows actuated by expansion of a fluid or gas or
an electromagnetic coil.
REVERSING VALVE - A device in a heat pump that is electrically controlled to reverse
the flow of refrigerant as the system is switched from cooling to heating; also called a
four-way valve.
RISER - A vertical tube or pipe which carries refrigerant in any form from a lower to a
higher level.
SATURATED VAPOR - Vapor in contact with a liquid.
SATURATION - A condition of stable equilibrium of a vapor and a liquid.
SENSIBLE HEAT - Heat that can be measured or felt. Sensible heat always causes a
temperature rise.
SIGHT GLASS - A glass installed in the liquid line permitting visual inspection of the
liquid refrigerant for the purpose of detecting vapor in the liquid. They also generally
have a device included to monitor moisture content of the refrigerant.
SLUGGING - A condition in which a quantity of liquid enters the compressor causing
hammering and possible compressor damage.
SPECIFIC HEAT - The amount of heat necessary to change the temperature of one
pound of a substance 10 F.
SPECIFIC VOLUME - The volume of a substance per unit of mass; i.e., standard air
13.33 cubic feet per pound. The reciprocal of density.
STANDARD AIR DENSITY - 0.075 pounds per cubic foot. Equivalent to dry air at 70 oF
and at sea level pressure.
STATE CONDITION - Substances can exist in three states - solid, liquid or vapor.
STATIC PRESSURE - The normal force per unit area at a small hole in the wall of a
duct.
STATIC TAP - A means by which static pressures of a duct system may be read directly,
usually consisting of a small diameter hole in the side of the duct connected to a
manometer.
SUB COOLING - Cooling of a liquid, at a constant pressure, below the point at which it
was condensed.
SUBLIMATION - A condition where a substance changes from a solid to a gas without
becoming a liquid.
SUCTION LINE - A tube used to convey the refrigerant vapor from the evaporator outlet
to the suction inlet of compressor.
SUCTION LINE ACCUMULATOR - A device located in the suction line that intercepts
quantities of a liquid refrigerant and thereby prevents damage to the compressor.
SUPERHEAT - Heat added to a vapor after all liquid has been vaporized.
TEMPERATURE - A measurement of heat intensity.
THERMISTOR - Basically a semiconductor which has electrical resistance that varies
inversely with temperature.
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THERMOSTAT - A bimetal actuated switch to close and open a circuit to indicate or
terminate operation of a heating or air conditioning system.
THERMOSTATIC EXPANSION VALVE - Refrigerant control which monitors the flow
rate according to the superheat at the evaporator outlet.
TON OF REFRIGERATION - The amount of heat of fusion absorbed by melting 1 short
ton (0.893 long ton or 0.907 t) of pure ice at 0 °C (32 °F) in 24 hours. Equivalent to the
consumption of one ton of ice per day during the transition from stored natural ice to
mechanical refrigeration.
TOTAL HEAT (Enthalpy) - Total heat energy in a substance. The sum of sensible and
latent heat.
TOTAL PRESSURE - The sum of all partial pressures in a mixture of gases.
TRAP - A depression or dip in refrigerant piping in which oil will collect. A trap may be
placed at the base of a suction or hot gas riser to improve oil return up the riser.
VACUUM - Any pressure below atmospheric pressure.
VAPOR BARRIER - The term applied to an impervious layer of material superimposed
upon a layer of insulation. Vapor barriers are always applied on the warm side of the
insulation layer.
VAPOR PRESSURE - The pressure exerted by vapor.
VELOCITY PRESSURE - In a moving fluid, the pressure capable of causing an
equivalent velocity as applied to move the same fluid through an orifice such that all
pressure energy expanded is converted into kinetic energy.
WATER MANOMETER - Used to measure pressure in inches of water.
WET BULB TEMPERATURE - Temperature read with a thermometer whose bulb is
encased in a wetted wick.
Glossary heating and cooling systems
Glossary heating and cooling systems
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Actuator
The actuator is an active component of the so-called control circuit. It is controlled through an
adjusting command (see Control variable) from the controller (see Temperature controller) and
triggers a measure that counteracts the control deviation.
Ambient temperature range
This is the admissible temperature range in which the unit can be operated in accordance with the
regulations.
ATEX
Directive 94/9/EC, also known as ATEX 100a, has been issued by the EC in order to harmonize
fundamental safety and health requirements for devices, protection systems and components that are
provided for use in accordance with the regulations for hazardous areas. This definition includes
devices for safety, test and control which are required for use outside hazardous areas with regard to
their explosion risks. Directive 94/9/EC is applicable to electrical and non-electrical devices,
protection systems and components (electrical and non-electrical operating supplies).
Bus system
see Interface.
Cascade control
see External control.
Component tested safety facilities
As a rule all temperature control units fall within the pressure equipment directive (see DGRL 97/23
EC). Depending on the heat transfer medium and the temperature, the installations have to be
equipped with special safety devices, for example safety valves, pressure, temperature or level
switches. These devices serve as a protection for the temperature control unit when the admissible
limits of the application are exceeded.
Compressor control
see injection control.
Condenser
see coolant.
Control circuit
The control circuit is the control section (see Control section) and controller. Sensors and signals,
their processing and transmission also form part of the control circuit. For example, transformers,
clamps and electric lines.
Control deviation
is the deviation of the actual value from the preset setpoint (see control circuit and controller
caracteristic).
Control section
Control section is the part of the control circuit to be influenced according to its application.
Pipework, sensors and heat transfer areas with their walls and coatings also form part of the control
section. Through distances from the test point to the final control element and through inertia at the
heat transfer for example, a characteristic response time of a control section arises. Depending on the
response time, a control section is classified from ‘good’ to ‘difficult’.
Controller characteristic
Different controllers are distinguished according to their so-called controller characteristic:
proportional response (P-controller), integral response (I-controller) and differential response (Dcontroller). As for temperature controllers, combined characteristics have stood the test. Modern
PID-controllers can be perfectly adapted to difficult control sections through freely eligible
parameters. They are therefore widely used.
Cooling output
With medium-cooled heat exchangers the cooling output always depends on the temperature
difference between the cooling medium and heat transfer fluid. The cooling output reduces at falling
outflow temperature and tends to zero when it reaches the cooling medium temperature. With
machine-aided cooling the characteristics are similar. The cooling output thus always relates to a
definite outflow temperature. At LAUDA the performance data of refrigeration machines is based on
cooling water or air with a temperature of 20 °C.
Cooling process
see coolant.
Cooling system
see coolant.
Delivery head
The delivery head is a theoretical value which is used within the pump characteristics (see Pump
characteristic) instead of the feed pressure (see Feed pressure). The advantage is that the delivery
head is valid for any given liquid. The feed pressure is then calculated for the respective feed
medium by multiplying the density by the delivery head (see Feed pressure).
Evaporator
see refrigerant
Expansion volume/Expansion tank
When heating up the heat transfer medium to the desired operating temperature, the heat transfer
medium expands. This expansion volume results from the expansion coefficient, the temperature
change and the contents of the unit. The expansion tank installed in the temperature control unit has
to collect the expansion volume safely. The assessment of the dimensions of the expansion tank for
thermal oils depends on the medium The following applies for hot water: about 0.8 percent per ∆T =
10 K. The following applies to mineral oils: about 1 percent per ∆T = 10 K. The following applies to
silicone oils: about 2 percent per ∆T = 10 K.
External control
If the outflow temperature is not the controlled variable, but it is instead a temperature measured
outside the thermostatic unit, then the outflow temperature of the heat transfer fluid is tracked in such
a way that the setpoint is reached at the external point. In practice this is achieved via a so-called
cascade control (see Cascade control). The so-called “master controller“ produces as the control
variable (see Control variable) the setpoint for the following slave controller (see Slave controller),
which in turn controls the outflow temperature of the heat transfer medium liquid.
Feed pressure
Feed pressure is the manometric pressure measured at the outlet nozzle of a pump or a compressor.
With pumps the feed pressure is also given from the pump characteristic (see Delivery head) and the
density of the feed medium.
Filling volume
In connection with a LAUDA system, the recommended filling amount of the system (volume)
which is required in order to guarantee trouble-free operation, and to allow for expansion or
contraction of the system throughout its operating temperature range.
Film temperature
The maximum film temperature, which the manufacturer indicates with reference to organic heat
transfer media, describes the temperature at which the heat transfer media begin to decompose.
Especially when organic heat transfer media are heated up with the help of electric heaters, attention
must be paid to the heat flux values because otherwise the heat transfer medium is destroyed by a
high surface or film temperature.
Flow rate
Volume flow of a pump or a compressor. The flow rate depends on the respective operating point
and the characteristics (see Pump characteristic) of each component.
GMP/FDA
In processes in which the reaction temperature or the respective temperature control represent a
critical quantity, the temperature control unit has to be qualified and validated. Qualification takes
place according to the “Good Manufacturing Practice“ (GMP). If, for example, pharmaceutical
products are produced for the American market, the manufacturing process – and with it the process
equipment including the temperature control unit – is subject to the requirements of the American
“Food and Drug Administration“ (FDA).
Hazard evaluation (HAZOP)
As far as hazard evaluation is concerned, which has to be generated by the operating company, the
information relevant for safety from the operating manual of the manufacturer has to be considered.
This especially includes: mounting and integration of the temperature control unit into the total
system, commissioning, operation, maintenance and inspection and indications for possible improper
use, as far as such an application has not already been prevented by the rating/technical measures.
Heat transfer fluid
These are liquids which supply or dissipate energy at the consumer. The heat carrier is transported to
the consumer by the circulating pump on the thermostatic unit. The larger the circulating quantity,
the lower the temperature difference at the consumer. The less the temperature difference, the better
the control accuracy.
Heater power
With electric heating, the heater power is identical to the power consumption of the built-in electric
heaters. It is always the maximum possible heater power and, in the case of electric heating, it
remains invariable at all operating temperatures. With medium-heated heat exchangers, the heater
power always depends on the temperature difference between heating medium and heat transfer
fluid. The heater power reduces at increasing outflow temperatures, and tends to zero when it reaches
the heating medium temperature. The applied pump output is helpful but not taken into account.
Injection control
With LAUDA process cooling units, the cooling power (see Cooling power) is permanently
controlled by adjusting the injection flow (0 - 100 percent). The final control element is a
continuously working control valve that is placed in the refrigerant feed line before the evaporator. If
several compressors are operated in parallel, an automatic step switch (see Compressor control)
ensures energy-saving partial-load operation.
Interface (electrical)
Always serves to exchange data and may be set up on an analogue basis (mostly standard signal 4-20
mA or 0-10 V) or on a digital basis. In the digital area you find the simple serial interfaces (RS 232)
or the more powerful, parallel addressable systems for many users (RS 485 or the different industrial
bus systems).
Master controller
see External control.
Modular engineering
This describes the modular kit from which any conceivable thermostatic system can be planned and
assembled according to a recurring pattern. It saves costs in the planning, implementation,
commissioning, documentation and servicing, because each module is itself well-proven. By using
modular engineering, a maximum safety standard is achieved.
Monofluid (single fluid) system
This is a heat transfer system which works with only one heat transfer liquid. It is useful when
heating, cooling and freezing must be done simultaneously and heating and cooling units are working
together.
Overlay pressure/Inert gas covering
Through an inert gas covering (nitrogen) on the expansion tank, oxidation of the heat transfer
medium and seeping of water vapor from the air can be prevented. If the heat transfer medium is
operated below its evaporation point, overlay pressure should be as low as possible (about 0.1 bar),
so that when heating up through the reduction of the gas space the pressure increase is not too high.
If the heat transfer medium is operated above its evaporation point and atmospheric pressure (1.013
bar), an overlay pressure of at least the respective vapor pressure is necessary in order to safely
prevent cavitation. In both cases a safety valve has to be installed on the expansion tank.
Peripheral wheel pump
Peripheral wheel pump is a centrifugal pump with a running wheel that has a so-called ‘peripheral’
shape. The almost linear characteristics of a peripheral wheel differ fundamentally from the
characteristics of a radial running wheel. At highest feed pressure and lowest feed flow rate the
highest drive energy is required with the peripheral shape. Peripheral wheel pumps are especially
suited for small feed flow rates and high pressures.
Permanent control deviation
In the case of a purely proportional controller there is always a „remaining control deviation“. The
control variable will always be proportional to the deviation. There is no adjusting command without
a deviation.
Plug & Play modules
Temperature control units and modules arrive at the construction site with clearly defined interfaces,
ready for connection, complete with pipework and insulated. They only have to be docked (see
Modular engineering).
Pressure Equipment Directive (DGRL 97/23 EC)
Temperature control units are in the control of the pressure equipment directive considered as
modules, which are assembled from several pressure devices (expansion tank, pipelines, fittings,
safety valve, etc). The fundamental safety requirements for this are described in Annex I of the
pressure equipment directive (DGRL). The process of conformity assessment for the module to be
applied depends on the category in which the module is classified. This category is determined
through the highest category of the respective built-in pressure device. In this connection, parts of
equipment with a safety function are ignored. The category that describes the hazard potential
depends on the maximum operating pressure, heat transfer medium, content and type of the built-in
pressure device. Before the temperature control unit is commissioned, the manufacturer has –
according to the operating conditions – to classify the module into a category and to submit it to a
process of conformity assessment. The temperature control unit has to be labeled with the CE label
and, starting from category II, has to be labeled with the identification number of the named testing
laboratory.
Primary side
Denominates primary energy carriers such as vapor, cooling water, air, brine, liquid nitrogen, etc.,
that have to be connected to the temperature control unit by the customer. These primary energies
can be gaseous, vaporous or fluid.
Protection type IP
Pursuant to EN 60529 two numerals assess the electric degree of protection. The first numeral
represents the quality of the touch and foreign body protection (dust). The second numeral assesses
the protection against water. For example, IP 54 protection signifies dust protection and sealing
against splashed water on all sides.
Pump characteristic
This is a diagram that shows the function of the delivery head in relation to the flow rate.
Radial pumps
Radial pumps are centrifugal pumps with a running wheel that has a so-called ‘radial’ shape. The
non-linear characteristics of a radial wheel differ fundamentally from the characteristics of a
peripheral wheel. At lowest feed pressure and highest feed flow rate the highest drive energy is
required with the radial shape. Standard pumps for the chemica industry are radial pumps. Radial
pumps are especially suited for small feed pressures and high flow rates.
Refrigerant
Operating material of the cooling process that is located in the closed refrigeration system. The
compressor sucks it from the evaporator, where it changes to the gaseous condition under heat
absorption. On the warmer side of the evaporator the medium cools down due to heat extraction. On
the high pressure side of the compressor the cooling medium is liquefied in the condenser/ heat
exchanger under heat transfer. The condenser/heat exchanger is water or air-cooled.
Risk analysis
The risk analysis has to be generated by the manufacturer of the temperature control unit. The
analysis serves to determine the dangers in connection with the unit with reference to the provided
operating conditions. Rating and construction of the temperature control unit take place in
consideration of the risk analysis. As to the remaining dangers which cannot be covered through
technical solutions, as well as measures required from the operator, the manufacturer has to inform
the operator through indications in the operating manual, and if necessary through mounting alert
labels on the temperature control unit.
Secondary side/Heat transfer medium side
Designates the side of the temperature control unit from which the heat transfer medium flows. Heat
transfer media (thermal oil, water) are chosen according to the operating temperature range and their
respective application.
Set value
Adjusting command of the controller that acts on the so-called actuator.
Slave controller
see External control.
Sound pressure level
Quantity for the acoustic emission according to DIN EN ISO 11200. In contrast to the acoustic
power level, the pressure level is always assigned to a defined distance. In practice both quantities
are stated in dbA.
System pressure
This is the pressure which is produced by pump pressure, vapor pressure at operating temperature
and overlay pressure in the heat transfer medium system. Please pay special attention to the
maximum system pressure because all components that have the heat transfer medium flowing
through them have to be suitable for the maximum system pressure (see Pressure equipment
directive).
Temperature control
Temperature control is taken to mean the controlled supply or extraction of heating or cooling energy
to achieve a constant temperature on the consumer.
Temperature control unit (TCU)
This is a comprehensive term for differently designed heating and cooling systems which in a
defined working temperature range can control temperature of the consumer by means of a liquid.
Temperature controller
A temperature controller is an active component which compares at least one actual temperature
value with one setpoint, and depending on the deviation (see Control deviation) outputs an adjusting
command (see Control variable). This so-called “adjusting command“ acts on the so-called ‘final
control element’ which also actively triggers a measure that acts against the deviation. Temperature
controllers can be of purely mechanical design (for example the so-called ‘radiator thermostat’) or
electronic, i.e. analog or digital. Often several operating modes are combined.
Through-flow cooler
A through-flow cooler is an electrically cooled or otherwise cooled heat exchanger, where a fluid is
forced to flow through the system. The cooler mainly serves as a cooler for the fluid that is flowing
through. Usually the forced flow is generated by a pump.
Through-flow heater
A through-flow heater is an electrical or otherwise heated heat exchanger, where a fluid flow is
forced through the system. The heater mainly serves as a heater for the fluid that is flowing through.
Usually the forced flow is generated by a pump.
Two-circuit cascade refrigeration
This is a cascade connection of two refrigeration systems with cooling mediums (see refrigerant) of
different thermodynamic properties. Two-circuit cascades with compression refrigerating processes
are used at working temperatures below -50 °C. The first cascade (high-temperature stage) produces
temperatures of about -35 °C in the evaporator. On the warm side of the evaporator the cooling
medium of the second stage (low-temperature stage) condenses at about -30 °C and vaporizes at
about -90 °C, and cools the heat transfer fluid to about -80 °C.
Interactive Engineering Tools
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Get definitions of Fan, Heat Transfer, and HVAC Terms
A B C D E F G H I/J K L M/N/O P/Q R S T U-Z
A
Absolute Pressure
The total of the indicated gage pressure plus the atmospheric pressure. Abbreviated "psia" for
pounds per square inch absolute.
Absolute Temperature
Temperature measured from absolute zero using an absolute temperature scale (e.g. Kelvin).
Absolute Zero
Temperature at which all molecular motion ceases (-460 °F, -273.15 °C, and 0 K.)
ACH, Air Changes Per Hour
The number of times that air in a house is completely replaced with outdoor air in one hour.
Aeration
Act of combining substance with air.
AFUE - Annual Fuel Utilization Efficiency
The ratio of annual output of useful energy or heat to the annual energy input to the furnace.
AHU (Air Handling Unit)
The inside part of the A/C system that contains the blower, cooling (evaporator) coil, and heater.
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 Coil
Coil on some types of heat pumps used either as an evaporator or condenser.
Air conditioner
Equipment that conditions air by cleaning, cooling, heating, humidifying, or dehumidifying it. A
term often applied to comfort cooling equipment.
Air conditioning
A process that maintains comfort conditions in a defined area.
Air Cooler
Mechanism designed to lower temperature of air passing through it.
Air Diffuser
Air distribution outlet or grille designed to direct airflow into desired patterns.
Air Diffusion
Distribution of the air in a space, called the treated space, by means of devices, called air
terminal devices, in a manner so as to meet certain specified conditions, such as air change rate,
pressure, cleanliness, temperature, humidity, air velocity and noise level.
Air Distribution
The transportation of a specified air flow to or from the treated space or spaces, generally by
means of ductwork.
Air Gap
The space between magnetic poles or between rotating and stationary assemblies in a motor or
generator.
Air Handler
Fan/blower, filter and housing parts of a system.
Air Infiltration
Leakage of air into rooms through cracks, windows doors and other openings.
Air Sensor
A device that registers changes in air conditions such as pressure, velocity, temperature, or
moisture content.
Air Source Equipment
Heat pumps or air conditioners that uses the outdoor air to transfer heat to and from the
refrigerant in the unit.
Air Terminal Device
A device located in an opening provided at the boundaries of the treated space to ensure a
predetermined motion of air in this space.
Air Vent
A fitting used to vent air manually or automatically from a system.
Air-Cooled Condenser
Heat of compression, plus the heat of absorption, is transferred from refrigerant within coil to
surrounding air, either by convection or fan or blower.
Airflow
The volume of air moving through a blower or duct. Units of measure are cubic feet per minute
(CFM), liters per second (LPS) or cubic meters per hour (m3h).
Anemometer
An instrument used to measure air velocities.
ARI (Air-Conditioning and Refrigeration Institute)
Air-Conditioning and Refrigeration Institute is a nonprofit, voluntary organization comprised of
heating, air conditioning and refrigeration manufacturers. ARI publishes standards for testing
and rating heat pumps and air conditioners to provide you with a standardized measure of
comparison. So, ARI ensures a level of performance within the industry.
ASHRAE
A leading HVAC/R Association - American Society of Heating, Refrigerating and Air
Conditioning Engineers - http://www.ashrae.org/
ASTM
American Society for Testing and Materials.
Automatic Control
Controls that react to a change in conditions to cause the condition to stabilize.
Automatic Expansion Valve
A refrigerant control valve that maintains a constant pressure in an evaporator.
Atmospheric Pressure
The pressure exerted upon the earth's surface by the air because of the gravitational attraction of
the earth. Standard atmosphere pressure at sea level is 14.7 pounds per square inch (psi).
Measured with a barometer.
Axial Fan
A device that propels air in an axial direction.
B
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.
Balancing
Process of adjusting the flow of air in duct systems, or water flow in hot-water heating systems.
Barometer
An instrument for measuring atmospheric pressure.
Blower
An enclosed air-moving device which redirects the airflow by 90 degrees towards one or more
exit points.
BTU (British Thermal Unit)
Quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit.
Burner
A device used to prepare and burn fuel.
C
Carbon Dioxide
A by-product of natural gas combustion that is not harmful.
Carbon Monoxide
A colorless, odorless, highly poisonous gas produced when carbon burns without sufficient air
nearby.
Centrifugal Fan
A device that draws air in axially and discharges it radially.
CFC (Chlorofluorocarbon)
A class of refrigerants. Generally refers to the Chlorofluorocarbon family of refrigerants.
Sometimes called Freon.
CFM (Cubic Feet per Minute)
A standard 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.
Charge
Amount of refrigerant placed in a refrigerating unit.
Circuit Breaker
A device that opens an electric circuit when an overload occurs.
Combustion
A reaction called rapid oxidation or burning produced with the right combination of a fuel,
oxygen, and heat.
Comfort Zone
The range of temperatures, humidities and air velocities at which the greatest percentage of
people feel comfortable.
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.
Condensate
The moisture collected on an evaporator coil.
Condensate Pump
A small pump used to pump condensate to a higher level.
Condenser Coil
Part of the outdoor portion of a split-system air conditioner or heat pump. By converting
refrigerant that is in a gas form back to a liquid, the coil transfers heat carried by the refrigerant
to the outside air.
Condensing Temperature
The temperature at which a vapor changes to a liquid.
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.
Conduction
The transfer of heat through a solid material.
Conformal Coating
Material coating to protect fan from harsh environmental conditions.
Convection
The movement of heat by fluid flow(e.g. air, water).
COP (Coefficient Of Performance)
COP compares the heating capacity of a heat pump to the amount of electricity required to
operate the heat pump in the heating mode.
D
Damper
A device that is located in ductwork to adjust air flow.
DB
Dry Bulb Temperature
dB (Decibel)
A decibel describes the relative loudness of a sound on a logarithmic scale.
Defrost Cycle
The process of removing ice or frost buildup from the outdoor coil during the heating season.
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.
Dew point
The exact temperature at which moisture begins to form.
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.
DOE (Department of Energy)
The Department of Energy is a federal agency in charge of setting industry efficiency standards
and monitoring the consumption of energy sources.
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.
E
EER (Energy Efficiency Ratio)
A ratio calculated by dividing the cooling capacity in Btu's per hour (Btuh) by the power input in
watts at any given set of rating conditions, expressed in Btuh per watt (Btuh/watt). EER & SEER
can not be compared equally. Air source equipment is rated by SEER and geothermal equipment
is rated by EER. EER changes with the inside and outside conditions, falling as the temperature
difference between inside and outside gets larger.
Efficiency
A rating on comfort equipment is similar to the miles per gallon rating on your car.
Energy Recovery Ventilator (ERV)
This device 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.
EPA (Environmental Protection Agency)
Environmental Protection Agency - http://www.epa.gov/
Evaporation
The condition that occurs when heat is absorbed by liquid and it changes to vapor.
Evaporator Coil
Part of a split-system air conditioner or heat pump located indoors. The evaporator coil cools and
dehumidifies the air by converting liquid refrigerant into a gas, which absorbs the heat from the
air. The warmed refrigerant is then carried through a tube to the outdoor unit (condenser coil).
Exfiltration
Uncontrolled air leakage out of a building.
Exhaust
The air flow leaving the treated space.
F
Fahrenheit Scale
The temperature scale that places the boiling point of water at 212°F and the freezing point at
32°F.
Fan
A device that produces a pressure difference in air to move it.
Fan Cycling
The use of a pressure control to turn a condenser fan on and off to maintain a correct pressure
within the system.
Fan Laws
A family of mathematical relationships that allows the calculation of new operating
characteristics from known system conditions.
Filter
A device for removing dust particles from air or unwanted elements from liquids.
Flow Coefficient
A dimensionless parameter relation air velocity to fan tip velocity. It's used to determine
approximate fan width for centrifugal impellers.
G
Gage
An instrument for measuring pressure.
Geothermal Equipment
Heat pumps that uses the ground to transfer heat to and from the refrigerant in the unit. The unit
circulates water through a heat exchanger in the to a closed loop buried in the ground or by
pumping water from a well through the unit.
H
HCFC (Hydrochlorofluorocarbon)
A class of refrigerants. Generally refers to Halogenated Chlorofluorocarbon family of
refrigerants.
Heat Exchanger
This is a device that enables furnaces to transfer heat from combustion safely into breathable air.
The primary heat exchanger transfers heat from combustion gases to the air blowing through the
ductwork.
Heat Gain
The amount of heat gained, measured in BTU's, from a space to be conditioned, at the local
summer outdoor design temperature and a specified indoor design condition.
Heat Loss
The amount of heat lost, measured in BTU's from a space to be conditioned, at the local winter
outdoor design temperature and a specified indoor design condition.
Heat Pump
Compression cycle system used to supply heat to a temperature controlled space. Same system
can also remove heat from the same space.
Heat Recovery Ventilator (HRV)
This device bring fresh, outside air into a home 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.
HFC (Hydrofluorocarbon)
A class of refrigerants. Generally refers to Hydrofluorocarbon family of refrigerants
Humidifier
A device that adds moisture to warm air being circulated or directed into a space.
Humidity Sensor
A device designed to regulate humidity input by reacting to changes in the moisture content of
the air.
Humidity
The amount of moisture in the air. Air conditioners remove moisture for added comfort.
HVAC
Heating, Ventilating and Air Conditioning
I/J
Inches of Water Gage or Column (IN WG or IN WC)
A unit of air pressure measurement equal to the pressure exerted by a column of water 1 inch
high.
IAQ
Indoor Air Quality
IGBT
Insulated Gate Bipolar Transistor.
Impedance
The resistance or opposition to airflow in a system. Same as back pressure or static pressure.
Impeller
The component of a fan assembly that is composed of a number of contoured blades.
Induction
Process by which the primary air sets into motion an air volume, called secondary air, in the
room.
K
KW
Kilowatt, equals 1000 Watts.
KWh
Kilowatt hour is the amount of kilowatts of electricity used in one hour of operation of any
equipment.
L
Latent Cooling Load
The net amount of moisture added to the inside air by plants, people, cooking, infiltration, and
any other moisture source. The amount of moisture in the air can be calculated from a
combination of dry-bulb and wet-bulb temperature measurements.
Latent Heat
Heat, that when added or removed, causes a change in state - but no change in temperature.
Linear Feet per Minute (LFM)
A unit of measurement. The velocity of the air.
M/N/O
Manometer
An instrument that measures air pressure differences between locations. Tubes are usually
attached to a manometer and run to the spaces where pressures are measured. Essentially a Utube partly filled with a liquid, usually water, mercury or a light oil. The pressure exerted on the
liquid is indicated by the liquid displaced. A manometer can be used as a differential pressure
gage.
Motor
A device that converts electrical energy into mechanical energy. A motor can operate on direct
current (DC) or alternating current (AC) voltage supply, not both.
P/Q
PCB
Printed Circuit Board.
Pascals (Pa)
A small unit of air pressure.
Pitot Tube
A sensing device used to measure total pressures in a fluid stream. It was invented by a French
physicist, Henri Pitot, in the 1700's.
Plenum
An air flow passage.
Pressure Coefficient
A dimensionless parameter relating the static pressure potential of a fan to its tip velocity
pressure equivalent. It's used to determine approximate fan diameter.
R
Radiation
The transfer of heat directly from one surface to another. (No intermediate air acting as a transfer
mechanism required).
Refrigerant
Substance used in refrigerating mechanism. It absorbs heat in evaporator by change of state from
a liquid to a gas, and releases its heat in a condenser as the substance returns from the gaseous
state back to a liquid state.
RH
Relative Humidity
RPM
Revolutions per minute, the measurement of fan blade speed.
Rotor
The rotating part of the motor which includes the propeller assembly.
S
Saturation Temperature
Also referred to as the boiling point or the condensing temperature. This is the temperature at
which a refrigerant will change state from a liquid to a vapor or visa versa.
SEER (Seasonal Energy Efficiency Ratio)
The total cooling of a central unitary air conditioner or unitary heat pump in BTU's during its
normal annual usage period for cooling divided by the total electric energy input in watt-hours
during the same period.
Sensible Cooling Load
The heat gain of the home due to conduction, solar radiation, infiltration, appliances, people, and
pets. Burning a light bulb, for example, adds only sensible load to the house. This sensible load
raises the dry-bulb temperature.
Sensible Heat
Heat, that when added or removed, causes a change in temperature but not in state.
Sound Attenuators
Components which are inserted into the air distribution system and designed to reduce airborne
noise which is propagated along the ducts.
Specific Speed
A dimensionless parameter based on fan rotational speed, flow rating and pressure rating. It's a
tool used to select the type of fan for a specific application. Each Different fan type achieves
peak efficiency at a unique specific speed range.
Split System
Refrigeration or air conditioning installation, which places condensing unit outside or away from
evaporator. These unit are connected together by a supply and return refrigerant lines.
Standard Cubic Feet Per Minute (SCFM)
The volumetric rate of airflow at standard air conditions.
Static Efficiency
A measure of an air mover's efficiency based on its air horsepower in terms of flow and static
pressure vs. required shaft input power.
Static Pressure
The difference in air pressure between the suction side and pressure side of the blower. Unit of
measure is inches of water column (in. wc) or Pascals (Pa).
Stator
The part of the motor that is fixed, typically found in the hub of the fan.
Subcooled Liquid
Liquid refrigerant which is cooled below its saturation temperature.
Superheated Vapor
Refrigerant vapor which is heated above its saturation temperature. If a refrigerant is
superheated, there is no liquid present.
System Impedance
The resistance to air flow when moving air through an airflow system. Examples: air filters, air
grilles and abrupt changes in flow direction.
System Operating Point
The point of operation of the air mover on its air performance curve. It is described by an airflow
and static pressure point. The operating point is that point on the air mover performance curve
where the system resistance curve crosses the air performance curve.
T
Thermometer
An instrument used to detect differences in the level of heat.
Thermostat
A device that senses temperature change and changes some dimension or condition within to
control an operating device.
Ton
A unit of measure for cooling capacity. One ton = 12,000 BTUs per hour.
Total Efficiency
A measure of an air movers efficiency based on its air horsepower in terms of flow and total
pressure vs. required shaft input power.
U-Z
Ventilator
Captures heating or cooling energy from stale indoor air and transfers it to fresh incoming air.
Venturi
The housing or frame of the fan.
W
Watt, the SI unit of power. In electricity it is Volts x Amps.
WB
Wet Bulb
WC (Water Column)
Common measure of air pressure used in HVAC systems.
Wet-bulb Temperature
When a wet wick is placed over a standard thermometer and air is blown across the surface, the
water evaporates and cools the thermometer below the dry-bulb temperature. This cooler
temperature (called the wet-bulb temperature) depends on how much moisture is in the air
Glossary of Useful Terms
AFUE - Annual Fuel Utilization Efficiency
This is the rating that all heating systems are given by the federal government, and rates the
efficiency of each manufacturers system. It is similar to the EPA ratings for gas mileage on your car.
The higher the AFUE rating, the higher the efficiency, and therefore, the lower your heating bill. Gas
systems run as high as 96% and oil as high as 86% AFUE.
Boiler
A boiler produces hot water to heat a home using hot water baseboard, radiant floor heat, European
style panel radiators, or to circulate hot water to hydro-air air handlers.
BTU’s - British Thermal Units
A measurement of heat and cooling used in the heating and cooling business. All equipment is rated in
BTU’s. The higher the number, the more heating or cooling you have. One BTU is equal to the heat a
single wood match produces when burning.
Condensing Unit
This is the outdoor unit that contains the a/c compressor (just like your refrigerator), that produces
the cooling for your central a/c system.
Dehumidifier
This device, located in the basement, dries out a humid basement in spring, summer and fall. Ideally,
it should be installed to allow a hose to drain the moisture into a sump in the basement, precluding
daily emptying of the dehumidifier bucket.
ERV - Energy Recovery Ventilator
This device is similar to an HRV except it also recovers the moisture in winter that would ordinarily be
lost to the outside. In summer, it brings in fresh air while rejecting the excess moisture to the outside.
This allows your central a/c system to work easier by not having to dehumidify the hot humid air
being introduced by the ventilator.
Warm Air Furnace
This is a popular system that produces warm air to heat the home. Metal ductwork distributes warm
air from the furnace to floor and ceiling registers throughout the house.
Geothermal Heat Pumps
These are used for heating and cooling. They use a series of 400 foot bore holes with HDPE piping
containing a mixture of water and non toxic gycol to either reject heat to the earth in summer or
extract heat from the earth in the winter.
HEPA - High Efficiency Particulate Filter
This is similar to the air filters that hospitals use, but on a smaller scale for homes. They can be free
standing devices in a room, or whole house devices attached to a warm air heating system. This
allows all rooms to get the benefit of the filtration it produces.
HRV - Heat Recovery Ventilator
This device, located in attics and basements, brings fresh air in to the home while exhausting the
same volume of air, and recovering 75 to 80% of the heat. It is more efficient and comfortable than
opening windows in winter.
Humidifier
This is the device that is attached to the basement warm air furnace or hydro-air air handler, and
produces moisture for the home in winter. Typically, 30% to 35% relative humidity is comfortable in
the winter.
Hydro Air
This is a system whereby a hot water boiler produces hot water, and pumps it into a special air
handler with both heating and cooling coils inside (they look like car radiators inside the air handlers).
It looks like the indoor air handler of a central a/c system and produces both warm air from hot water
to heat the home in winter and cooling in summer.
Media Filters
These are used on all warm air heating and central cooling systems to filter the air to a high level.
They are ideal for families with allergies.
Registers, Grilles and Diffusers
These are the “grilles” on your floor, walls and ceilings that bring warm or cool air into each room.
SEER - Seasonal Energy Efficiency Ratio
This is the ratio of electricity consumed by the a/c or heat pump system compared to the energy it
produces. The federal government rates the equipment. The higher the SEER number, the more
energy efficient the system is. Currently the minimum for a/c systems is 13 SEER.
Glossary of HVAC terms
From Wikipedia, the free encyclopedia
Jump to: navigation, search
HVAC (heating, ventilation, and air conditioning) is a major subdiscipline of mechanical
engineering. The goal of HVAC design is to balance indoor environmental comfort with other
factors such as installation cost, ease of maintenance, and energy efficiency. The discipline of
HVAC includes a large number of specialized terms and acronyms, many of which are
summarized in this glossary.
air changes per hour
Main article: Air changes per hour
The hourly ventilation rate divided by the volume of a space. For perfectly mixed air or laminar
flow spaces, this is equal to the number of times per hour that the volume the space is
exchanged by mechanical and natural ventilation. Also called air change rate or air exchange
rate. Abbreviated ACH or ac/hr.
air conditioner
Main article: Air conditioner
An appliance, system, or mechanism designed to dehumidify and extract heat from an area.
Usually this term is reserved for smaller self contained units such as a residential system.
air handler
air handling unit
Main article: Air handler
A central unit consisting of a blower, heating and cooling elements, filter racks or chamber,
dampers, humidifier, and other central equipment in direct contact with the airflow. This does
not include the ductwork through the building. Abbreviated AH or AHU.
British thermal unit (BTU)
Main article: British thermal unit
Any of several units of energy (heat) in the HVAC industry, each slightly more than 1 kJ. One BTU
is the energy required to raise one pound of water one degree Fahrenheit, but the many
different types of BTU are based on different interpretations of this “definition”. In the United
States the power of HVAC systems (the rate of cooling and dehumidifying or heating) is
sometimes expressed in BTU/hour instead of watts. Abbreviated BTU or Btu.
chiller
Main article: Chiller
A device that removes heat from a liquid via a vapor-compression or absorption refrigeration
cycle. This cooled liquid flows through pipes in a building and passes through coils in air
handlers, fan-coil units, or other systems, cooling and usually dehumidifying the air in the
building. Chillers are of two types; air-cooled or water-cooled. Air-cooled chillers are usually
outside and consist of condenser coils cooled by fan-driven air. Water-cooled chillers are usually
inside a building, and heat from these chillers is carried by recirculating water to a heat sink such
as an outdoor cooling tower.
coil
Equipment that performs heat transfer to air when mounted inside an air handling unit or
ductwork. It is heated or cooled by electrical means or by circulating liquid or steam within it.
condenser
Main article: Condenser (heat transfer)
A component in the basic refrigeration cycle that ejects or removes heat from the system. The
condenser is the hot side of an air conditioner or heat pump. Condensers are heat exchangers,
and can transfer heat to air or to an intermediate fluid (such as water or an aqueous solution of
ethylene glycol) to carry heat to a distant sink, such as ground (earth sink), a body of water, or
air (as with cooling towers).
constant air volume
Main article: Constant air volume
A system designed to provide a constant air flow. This term is applied to HVAC systems that
have variable supply-air temperature but constant air flow rates. Most residential forced-air
systems are small CAV systems with on/off control. Abbreviated CAV.
controller
Main article: Controller (control theory)
A device that controls the operation of part or all of a system. It may simply turn a device on and
off, or it may more subtly modulate the set point of components. Most controllers are
automatic but have user input such as temperature set points, e.g. a thermostat. Controls may
be analog or digital.
damper
Main article: Damper (flow)
A plate or gate placed in a duct to control air flow by increasing friction in the duct.
deep lake water cooling
Main article: Deep lake water cooling
The heat is rejected to deep lake regions to cool homes and offices, reducing the energy costs.
ΔT
(Also delta T) a reference to a temperature difference. It is used to describe the difference in
temperature of a heating or cooling medium as it enters and as it leaves a system.
duct
Main article: Duct (HVAC)
Specialized housing for the air flow.
Dehumidifier
A dehumidifier is the equipment that extracts and removes humidity from the air. It works by
cooling air to the point where water turns to liquid from vapor form and then the liquid is
removed.
Diffuser
A diffuser is placed over ductwork, and it separates air with vanes going in differing directions. It
evenly distributes air flow in the desired directions.
Dry Bulb Temperature
Dry bulb temperature is the temperature of air measured by a thermometer which is freely
exposed to the air while it is shielded from radiation and moisture. It is usually thought of as air
temperature, and it is the true thermodynamic temperature. It is a measurement of heat
intensity independently of humidity and a dry bulb thermometer is used to measure it.
Dry Bulb Thermometer
A dry bulb thermometer is a device that measures air temperature independently of humidity. It
is freely exposed to the air it is measuring and is protected from the radiation and moisture.
economizer
Main article: Economizer
An HVAC component that uses outside air, under suitable climate conditions, to reduce required
mechanical cooling. When the outside air’s enthalpy is less than the required supply air during a
call for cooling, an economizer allows a building’s mechanical ventilation system to use up to the
maximum amount of outside air.
enthalpy
Main article: Enthalpy
For a given sample of air, a measure of the total heat content (the sum of the heat energy of the
dry air and heat energy of the water vapor within it). It is typically used to determine the
amount of fresh outside air that can be added to recirculated air for the lowest cooling cost.
evaporator
Main article: Evaporator
A component in the basic refrigeration cycle that absorbs or adds heat to the system.
Evaporators can be used to absorb heat from air or from a liquid. The evaporator is the cold side
of an air conditioner or heat pump.
fan coil unit
Main article: Fan coil unit
A small terminal unit that is often composed of only a blower and a heating and/or cooling coil,
as is often used in hotels, condominiums, or apartments. Abbreviated FCU.
flow
A transfer of fluid volume per unit time.
fresh air intake
An opening through which outside air is drawn into the building. This may be to replace air in
the building that has been exhausted by the ventilation system, or to provide fresh air for
combustion of fuel. Abbreviated FAI.
furnace
Main article: Furnace
A component of an HVAC system that adds heat to air or an intermediate fluid by burning fuel
(natural gas, oil, propane, butane, or other flammable substances) in a heat exchanger.
gas furnace heat exchanger
A gas furnace heat exchanger is responsible for the transfer of heat from inside the furnace into
the air outside the furnace. The duct system then transfers this exchanged air to different rooms
in the building or space.
grille
A facing across a duct opening, often rectangular in shape, containing multiple parallel slots
through which air may be delivered or withdrawn from a ventilated space. The grille directs the
air flow in a particular direction and prevents the passage of large items.
heating coil
A heating coil is the part of the system that conducts heat. It allows electricity to act as fire.
heat exchanger
A heat exchanger is the part of the system that transfers heat from the hot parts of the machine
or a system to the cold parts of the machine or system.
heat gain
heat load
heat loss
Terms for the amount of cooling (heat gain) or heating (heat loss) needed to maintain desired
temperatures and humidities in controlled air. Regardless of how well-insulated and sealed a
building is, buildings gain heat from sunlight, conduction through the walls, and internal heat
sources such as people and electrical equipment. Buildings lose heat through conduction during
cold weather. Engineers use heat load calculations to determine the HVAC needs of the space
being cooled or heated.
heat pump
A heat pump is a compressor that cycles hot or cold air. It is a device that is designed to move
thermal energy in the opposite direction of heat flow by absorbing heat from a cold space which
is released to a warmer space.
heat transfer
Heat transfer happens when heat moves from one area to another. It is an important and vital
step in the process of cooling a space.
hspf - (Heating Seasonal Performance Factor)
Heating Seasonal Performance Factor is the measurement of heat efficiency over the period of a
heating season.
intermediate fluid
A liquid or gas used to transfer heat between two heat exchangers. An intermediate fluid is used
when the hot and cold fluids are too bulky (such as air) or difficult to handle (such as halocarbon
refrigerant) to directly transfer the heat.
louver
1. Components made of multiple smaller blades, sometimes adjustable, placed in ducts or duct
entries to control the volume of air flow. When used inside of ducts, their function is similar to
that of a damper, but they can be manufactured to fit larger openings than a single-piece
damper.
2. Blades in a rectangular frame placed in doors or walls to permit the movement of air.
makeup air unit
An air handler that conditions 100% outside air. Typically used in industrial or commercial
settings, or in "once-through" (blower sections that only blow air one-way into the building),
"low flow" (air handling systems that blow air at a low flow rate), or "primary-secondary" (air
handling systems that have an air handler or rooftop unit connected to an add-on makeup unit
or hood) commercial HVAC systems. Abbreviated MAU.
minimum outside air
The lowest amount of fresh air flow that can be allowed into a recirculating system. This limit is
sent to ensure that the interior air remains safe and comfortable to breathe.
outside air damper
An automatic louver or damper that controls the fresh air flow into an air handler and
modulates to the most energy efficient setting.
outside air temperature
A measure of the air temperature outside a building. The temperature and humidity of air inside
and outside the building are used in enthalpy calculations to determine when outside air can be
used for free heating or cooling. Abbreviated OAT.
packaged terminal air conditioner
An air conditioner and heater combined into a single, electrically powered unit, typically
installed through a wall and often found in hotels. Abbreviated PTAC.
packaged unit
Main article: Air handler
An air-handling unit, defined as either "recirculating" or "once-through" design, made
specifically for outdoor installation. They most often include, internally, their own heating and
cooling devices. Very common in some regions, particularly in single-story commercial buildings.
Also called a rooftop unit (RTU)
plenum space
Main article: Plenum space
An enclosed space inside a building or other structure, used for airflow. Often refers to the
space between a dropped ceiling and the structural ceiling, or a raised floor and the hard floor.
Distinct from ductwork as a plenum is part of the structure itself. Cable and piping within a
plenum must be properly rated for its fire and smoke indices. See also: plenum chamber
psychrometric
Main article: Psychrometrics
The study of the behavior of air-water vapor mixtures. Water vapor plays an important role in
energy transfer and human comfort in HVAC design.
rooftop unit (RTU)
Same as Air handler.
radiant ceiling panels
Usually metal panels suspended under the ceiling, insulated from the building structure. The
primary cooling/heating agent temperature is close to the room's temperature.
radiant floor
A type of radiant heating system where the building floor contains channels or tubes through
which hot fluids such as air or water are circulated. The whole floor is evenly heated. Thus, the
room is heated from the bottom up. Radiant floor heating eliminates the draft and dust
problems associated with forced air heating systems.
radiation
The transfer of heat directly from one surface to another (without heating the intermediate air
acting as a transfer mechanism).
smoke damper
A damper or adjustable louver designed to augment the ventilation of a space during a fire.
split system
A split system is the combination of an outdoor unit and an indoor unit. This is the most
common type of system.
superheat
A The number of degrees a vapor is above its boiling point at a specific pressure.
subcooling
A The condition where liquid refrigerant is colder than the minimum temperature required to
keep it from boiling which would change it from a liquid to a gas phase. Subcooling is the
difference between its saturation temperature and the actual liquid refrigerant temperature.
system
General term used to refer to the set or a subset of components that perform a specific HVAC
function within a building.
terminal unit
A small component that contains a heating coil, cooling coil, automatic damper, or some
combination of the three. Used to control the temperature of a single room. Abbreviated TU.
thermal zone
An individual space or group of neighboring indoor spaces that the HVAC designer expects will
have similar thermal loads. Building codes may require zoning to save energy in commercial
buildings. Zones are defined in the building to reduce the number of HVAC subsystems, and thus
initial cost. For example, for perimeter offices, rather than one zone for each office, all offices
facing west can be combined into one zone. Small residences typically have only one
conditioned thermal zone, plus unconditioned spaces such as garages, attics, and crawlspaces,
and basements.
thermostat
A thermostat is a system that monitors and regulates a heating or cooling system. It can be used
to set the desired temperature at which it keeps the environment either heated or cooled.
two-stage (cooling and heating)
A two-stage air conditioner is designed to operate on high and low settings during different
weather conditions and seasons. The high setting is used during extreme weather, and the low
setting is used during moderate weather. This type of air conditioner produces a balanced
temperature and is in use for a longer period of time.
txv - Thermostatic Expansion Valve
A thermostatic expansion valve is a piece of equipment that meters the flow of liquid refrigerant
into the evaporator while measuring the vapor refrigerant leaving the evaporator. It thereby
controls the superheating at the outlet of the evaporator.
underfloor air distribution
Main article: Underfloor air distribution
A method for providing ventilation and space conditioning by using the air plenum below a
raised floor to distribute conditioned air through diffusers directly to the occupied zone.
Abbreviated UFAD.
variable air volume
Main article: Variable air volume
An HVAC system that has a stable supply-air temperature, and varies the air flow rate to meet
the temperature requirements. Compared to constant air volume systems, these systems
conserve energy through lower fan speeds during times of lower temperature control demand.
Most new commercial buildings have VAV systems. VAVs may be bypass type or pressure
dependent. Pressure dependent type VAVs save energy while both types help in maintaining
temperature of the zone that it feeds. Abbreviated VAV.
zoning system
A zoning system sections a building or a space into zones which are controlled independently of
each other. This is beneficial when different areas or rooms of a building have different
temperatures as well as when the desired temperatures in different rooms are different.
Temperature is controlled by different thermostats.
References[edit]

Modern Refrigeration and Air Conditioning (August 2003) by Althouse, Turnquist, and Bracciano,
Goodheart-Wilcox Publisher; 18th edition
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International Mechanical Code (March 6, 2006) by the International Code Council, Thomson
Delmar Learning; 1 edition
ASHRAE Handbook: Fundamentals, Atlanta, GA, 2009.
Green Building and Controls Glossary, by KMC Controls, New Paris, IN, 2013.
ASHRAE Terminology www.ashrae.org/ASHRAEterms [1]
External links[edit]
HVAC Components Infographics (Sanhua - HVAC manufacturer) HVAC industry terminology
Service Champions
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HVAC (Heating, Ventilation, and Air Conditioning)
Fundamental concepts
Technology
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Air changes per hour
Building envelope
Convection
Dilution (equation)
Domestic energy consumption
Enthalpy
Fluid dynamics
Gas compressor
Heat pump and refrigeration cycle
Heat transfer
Infiltration (HVAC)
Noise control
Psychrometrics
Stack effect
Thermal comfort
Thermal destratification
Thermodynamics
Vapor pressure of water
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Absorption refrigerator
Air barrier
Air conditioning
Antifreeze
Automobile air conditioning
Autonomous building
Building insulation materials
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Central solar heating
Chilled beam
Chilled water
Constant air volume
Coolant
Components
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Dedicated outdoor air system
Deep water source cooling
Demand-controlled ventilation
Displacement ventilation
District cooling
District heating
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Energy recovery ventilation
Forced-air
Forced-air gas
Free cooling
Heat recovery ventilation
Hydronics
HVAC
Ice storage air conditioning
Kitchen ventilation
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Microgeneration
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Radon mitigation
Refrigeration
Renewable heat
Room air distribution
Solar air heat
Solar combisystem
Solar cooling
Solar heating
Thermal insulation
Thermal mass
Underfloor air distribution
Underfloor heating
Vapor barrier
Vapor-compression refrigeration
Variable air volume
Variable refrigerant flow
Ventilation (architecture)
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Air conditioner inverter
Air filter
Air handler
Air ionizer
Air-mixing plenum
Air purifier
Air source heat pumps
Back boiler
Barrier pipe
Blast damper
Boiler
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Centrifugal fan
Chiller
Condensate pump
Condenser (heat transfer)
Condensing boiler
Convection heater
Cooling tower
Damper (flow)
Dehumidifier
Duct (flow)
Durable elbow support
Economizer
Electrostatic precipitator
Evaporative cooler
Evaporator
Exhaust hood
Expansion tank
Fan coil unit
Fan heater
Fire damper
Fireplace
Fireplace insert
Firestop
Freeze stat
Flue
Freon
Fume hood
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Furnace room
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Gas heater
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Heat exchanger
Heat pipe
Heat pump
Heating system
High efficiency glandless circulating pump
High-efficiency particulate air (HEPA)
High pressure cut off switch
Humidifier
Hybrid heat
Infrared heater
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Louver
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Mechanical room
Oil heater
Packaged terminal air conditioner
Plenum space
Pressurisation ductwork
Measurement and control
Professions, trades, and services
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Radiator (heating)
Radiator reflector
Recuperator
Refrigerant
Register
Reversing valve
Run-around coil
Scroll compressor
Solar chimney
Space heater
Smoke exhaust ductwork
Thermal expansion valve
Thermal wheel
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Windcatcher
Wood-burning stove
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Air flow meter
Aquastat
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Room temperature
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Thermostat
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Architectural acoustics
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Industry organizations
Health and safety
See also
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Duct leakage testing
Environmental engineering
Hydronic balancing
Kitchen exhaust cleaning
Mechanical engineering
Mechanical, electrical, and plumbing
Mold growth, assessment, and remediation
Refrigerant reclamation
Testing, adjusting, balancing
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ACCA
AMCA
ASHRAE
ASTM International
BRE
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CIBSE
LEED
SMACNA
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Indoor air quality
Passive smoking
Sick building syndrome
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ASHRAE Handbook
Building science
Fireproofing
Glossary of HVAC terms
Template:Home automation
Template:Solar energy
Efficiency Terms
In 1992, the Federal Government established minimum efficiency requirements for all
heating and air conditioning equipment. If your present HVAC equipment — a
furnace, heat pump, or air conditioning system — was purchased and installed before
that date, it could be highly inefficient by today’s standards.
Efficiency ratings are important to understand because installing a new unit could
achieve significant energy cost reductions. And that could save you from the higher
operating expenses of some pre-1992 equipment.
AFUE% = Furnace Efficiency
“AFUE” is a measure of a furnace’s heating efficiency. It stands for Annual
Fuel Utilization Efficiency. The higher the AFUE%, the more efficient the
product. The government’s established minimum rating for furnaces is 78%.
HSPF = Heat Pump Heating Efficiency
HSPF stands for Heating Seasonal Performance Factor. The higher the
HSPF rating, the more efficient a heat pump is at heating your home. There is
no legislated minimum rating.
SEER = Cooling Efficiency
“SEER” is a measure of cooling efficiency for air conditioning products. SEER
stands for Seasonal Energy Efficiency Ratio. The higher the SEER rating
number, the more energy efficient the unit. The government’s established
minimum rating for air conditioning is 13.
Basic Heating and Air Conditioning Definitions
Air Handler
The portion of a central air conditioning or heat pump system that moves
heated or cooled air throughout a home’s ductwork. In some systems, a furnace
handles this function.
Heat Source
A body of air or liquid from which heat is collected. In an air source heat
pump, the air outside the house is used as the heat source during the heating
cycle.
Indoor Coil
The portion of a heat pump or central air conditioning system that is located in
the house and functions as the heat transfer point for warming or cooling indoor
air.
Outdoor Coil/Condensing Unit
The portion of a heat pump or central air conditioning system that is located
outside the home and functions as a heat transfer point for collecting heat from
or dispelling heat to the outside air.
Single Package
A year ’round heating and air conditioning system that has all the components
completely encased in one unit outside the home.
Split System
A heat pump or central air conditioning system with components located both
inside and outside of a building — the most common types installed in homes.
Supplemental Heat
The auxiliary or emergency heat provided at temperatures below a heat pump’s
balance point. It is usually electrical resistance heat.
Technical Heating and Air Conditioning Definitions
Balance Point
An outdoor temperature — usually between 30°F to 45°F — at which a heat
pump’s output exactly equals the heating needs of the house. Below the balance
point, supplementary electric resistance heat is needed to maintain indoor
comfort.
British Thermal Unit (Btu)
The amount of heat required to raise the temperature of one pound of water
(about one pint) by one degree Fahrenheit.
Coefficient of Performance (COP)
A ratio calculated by dividing the total heating capacity provided by the heat
pump, including circulating fan heat but excluding supplementary resistance
heat (Btu’s per hour), by the total electrical input (watts) x 3.412. (See Heating
Seasonal Performance Factor, above.)
Energy Efficiency Ratio (EER)
A ratio calculated by dividing the cooling capacity in Btu’s per hour (Btuh) by
the power input in watts at a given set of rating conditions, expressed in Btuh
per watt (Btuh/watt). (See Seasonal Energy Efficiency Ratio, above.)
eating & Cooling Glossary
AHRI: American Heating and Refrigeration Institute (responsible for rating heating and cooling equipment).
Air Change: Unlike re-circulated air, this is the total air required to completely replace the air in a room or
building.
Air Conditioner: Equipment that simultaneously controls air temperature, relative humidity, purity, and
motion.
Air Diffuser: An air distribution outlet or grille that directs airflow into desired patterns.
Air Handler: The part of the central air conditioning or heat pump system that circulates heated or cooled air
throughout a home’s ductwork. Some furnaces perform this function.
Annual Fuel Utilization Efficiency (AFUE): A rating that measures the amount of heating your equipment
delivers for every dollar spent on fuel; the higher the better. A higher rating indicates more efficient
equipment.
Balance Point: An outdoor temperature, usually between 30 °F and 45 °F, at which a heat pump’s output
equals the exact heating needs of the home. Below the balance point, supplementary electric resistance heat
must maintain indoor comfort.
Blower: An air-handling device for moving air in a distribution system.
BTU (British Thermal Unit): The standard of measurement used for the amount of heat required to raise the
temperature of one pound of water by one degree (Fahrenheit). BTUh = the number of BTUs per hour.
Capacity: The ability of a heating or cooling system to function in a given amount of space. Heating = BTUs.
Cooling = tons.
Central Air Conditioner System: Where air is treated at a central location and carried to and from the rooms
by one or more fans and a system of ducts.
CFM (Cubic Feet per Minute): Commonly used to measure the rate of an air conditioning system’s airflow.
Compressor: In an air conditioner this is known as “the heart of the system” because it circulates the
refrigerant through the loop. The compressor is the pump that moves the refrigerant from the indoor evaporator
to the outdoor condenser then back to the evaporator.
Condenser Coil: A series or network of refrigerant tubes, typically placed outside the home, which removes
heat from hot, gaseous refrigerant and re-liquefies it.
Condensing Unit: Part of a refrigerating mechanism that pumps in vaporized refrigerant from the evaporator,
compresses it, liquefies it in the condenser, and returns it to the refrigerant control.
Coefficient of Performance: The COP, or Coefficient of Performance of a heat pump, measures the ratio of
the rate of useful heat output that the pump delivers (exclusive of supplementary heating) to the corresponding
rate of energy input. In short, it is partly a measure of the efficiency of a heat pump. For example: A heat pump
with a COP of 3.5 provides 3.5 units of heat for each unit of energy consumed as compared to electric only
heat source. The higher the number the more efficient the heat pump.
Cooling Load: Heat that flows into a space from outdoors and/or indoors.
Damper: Found in ductwork, this movable plate opens and closes to control airflow and is used in zoning to
regulate airflow to certain rooms.
Defrost Cycle: The removal of ice or frost buildup from the outdoor coil during the heating season.
Dehumidification: The reduction of water vapor by cooling the air below the dew point, as well as the
removal of water vapor from air by chemical means, refrigeration, etc.
Downflow Furnace: Draws in return air from the top and expels warm air at the bottom.
Duct: Used for conducting air to and from an air-handling unit via a pipe or closed conduit made of materials
such as sheet metal or fiberglass board.
Ductwork: Building-wide air delivery conducted through pipes or channels.
Efficiency: A comfort-equipment and fuel-efficiency rating similar to the miles-per-gallon rating for
automobiles.
Emergency Heat (Supplemental or Auxiliary Heat): The backup heat built into a heat pump system.
Energy Efficiency Ratio (EER): The ratio of an air conditioning unit’s cooling capacity in British Thermal
Units (BTUs) per hour to the total electrical input in watts.
Evaporator: Absorbs heat or liquid from the surrounding air and then moves it outside the refrigerated area by
means of a refrigerant. Also known as a cooling coil, blower coil, chilling unit, or indoor coil.
Evaporator Coil: Located inside the home, a series or network of tubes filled with refrigerant that remove
heat and moisture from indoor air as liquid refrigerant evaporates.
Filter: A device that removes dust and other air particles to comfort the respiratory system and protect the
heating and cooling equipment. The higher the MERV rating, the better the filter.
Freon: Refers to hydrocarbons containing fluorine, chlorine, or bromine, which are used as refrigerants.
Furnace: The part of an environmental system that converts natural gas, oil, electricity, or other fuel into heat
for distribution within a structure.
Heat Exchanger: Transfers heat energy from its source to the conveying medium.
Heat Gain: As measured in BTUs, the amount of heat gained from a space to be conditioned, at the local
summer outdoor design temperature and a specified indoor design condition.
Heat Loss: As measured in BTUs, the amount of heat lost from a space to be conditioned, at the local summer
outdoor design temperature and a specified indoor design condition.
Heat Pump: An air conditioner with a valve that permits alternate heating and cooling.
Heat Source: A body of air or liquid from which heat is collected. With any heat pumps, the air outside the
home is the source for the heating cycle.
Heat Transfer: The movement of heat from one place to another, between two substances, or within a
substance.
Heating Capacity: The rate at which a specific device can add substantial heat to a substance, expressed in
BTUh (British Thermal Units per hour).
Heating Seasonal Performance Factor (HSPF): The total heating output of a heat pump in BTUs during its
normal usage period for heating, as divided by the total electrical energy input in watt-hours during the same
period.
Horizontal Furnace: A sideways furnace that draws in return air from one side and expels warm air from the
other.
HVAC: Heating, ventilation, and air conditioning.
Humidification: The process of adding moisture to the air within a space.
Humidistat: Regulates humidity input by reacting to moisture content changes in the air.
Humidity: The amount of moisture in the air; air conditioners remove moisture for added comfort.
Indoor Unit: Usually located inside the house, it houses the indoor coil, fan, motor, and filtering device,
sometimes called the air-handler.
Indoor Coil: A refrigerant containing a portion of a fan coil unit similar to a car radiator, typically made of
several rows of copper tubing with aluminum fins.
Infiltration: Airflow into a space usually through walls and leaks around doors and windows.
Insulation: Any material that reduces the speed of heat transfer.
Integrally Controlled Motor (ICM): A variable-speed motor that operates at low RPM when possible for
efficiency and quiet operation. More than 90% efficiency vs. 60% for conventional motors.
Kilowatt (kW): Equal to 1,000 watts of electricity, a kilowatt-hour (kWh) is a common unit of electrical
consumption measured by the total energy that one kilowatt creates in an hour.
Latent Cooling Capacity: An air conditioning system’s capability to remove moisture from the air.
Latent Heat: The heat energy needed to change the state of a substance (e.g., from a liquid to a gas) but not its
temperature.
Load Calculation: Determines a building’s heat gain and heat loss to ensure installation of properly sized air
conditioning and heating equipment.
Matched System: A heating and cooling system consisting of products certified to perform at promised
comfort and efficiency levels when used together in accordance with design and engineering specifications.
Natural-Draft Furnace: A furnace whose natural airflow around the furnace supports combustion. It depends
on the pressure that heat creates in the flue gases to force them out through the vent system.
Operating Cost: The day-to-day cost of running your home comfort equipment, based on daily energy use.
Outdoor Coil/Condensing Unit: The portion of a heat pump or central air conditioning system located
outside the home. Functions as a heat transfer point for collecting heat from and dispelling heat to the outside
air.
Payback Analysis: A general measure of your home comfort system’s efficiency and value. By combining
your purchase price with ongoing operating costs, it determines the number of years required before monthly
energy savings offset the purchase price.
Refrigerant: A substance that produces a refrigerating effect while expanding or vaporizing.
Refrigerant Lines: Set of two copper lines connecting the outdoor unit and the indoor unit.
Register: Combination grille and damper assembly covering an air opening or end of an air duct.
Relative Humidity: The ratio of the amount of vapor contained in the air to the maximum amount the air
could hold at that temperature, usually expressed as a percentage.
Return Air: Air drawn into a heating unit after having been circulated from the heater’s output supply to a
room.
Reversing Valve: A device in a heat pump that reverses the flow of refrigerant as the system switches from
cooling to heating.
SEER (Seasonal Energy Efficiency Ratio): A rating that denotes the efficiency of air conditioning equipment
in terms of the amount of cooling your equipment delivers for every dollar spent on electricity. The higher the
SEER, the more efficient the unit and the lower the operating cost.
Sensible Cooling Capacity: An air conditioning system’s capability to reduce the temperature by removing
heat from the air.
Sensible Heat: Heat energy that raises or lowers the temperature of a gas, liquid, or solid when added to or
removed from that material.
Setpoint: The temperature at which a thermostat is set for desired comfort level.
Single Package: A year-round heating and air conditioning system with all components encased in one unit
outside the home.
Split System: The most common type of home central air conditioner, it consists of a compressor (the unit and
condenser, installed outside the building) and a non-compressor (the air-handling unit installed within the
building).
Supplementary Heat: Auxiliary or emergency heat, usually electrical resistance heat, provided at
temperatures below a heat pump’s balance point.
Thermostat: A temperature control device, typically found on an inside wall, that consists of a series of
sensors and relays for monitoring and controlling a heating and cooling system.
Tonnage: The unit of measure used in air conditioning to describe the cooling capacity of a system. One ton of
cooling is based on the amount of heat needed to melt one ton (2,000 lbs.) of ice in a 24-hour period, and
equals 12,000 BTUs per hour.
Upflow: A type of air conditioning system that discharges air into the conditioned space via a top-mounted
discharge plenum or through an overhead duct system.
Upflow Furnace: A furnace that pulls return air in from the bottom and expels warm air from the top.
Vapor Barrier: A moisture-resistant layer applied to the surfaces of humid spaces that prevents moisture from
traveling to a point where it can condense due to lower temperature.
Vapor Seal: A barrier essential to prevent moisture from infiltrating into, or migrating from, a data processing
center or other “critical space” that contains sensitive electronic instrumentation. Vapor barriers may be
created using plastic film, vapor-retardant paint, vinyl wall coverings, and vinyl floor systems, in combination
with careful sealing of all openings (doors and windows) into the room.
Ventilation: The process of supplying or removing air, by natural or mechanical means, to or from any space.
Such air may or may not have been conditioned.
Watt: A unit of power that equals one joule per second, named after the Scottish inventor and mechanical
engineer, James Watt.
Zone System: A method of dividing a home into zones that makes it possible to control the amount of comfort
provided to each.
Zoning: The practice of providing independent heating and/or cooling to different areas within a structure.