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Glossary of HVAC Terms
A
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Absolute
Pressure |
Gauge pressure plus atmospheric pressure (14.7
lb. per sq. in.) equals absolute pressure. |
Absolute
Temperature |
Temperature measured from absolute zero. |
Absolute
Zero Temperature |
Temperature at which all molecular motion
ceases(-460 F. and -273 C). |
Absorbent |
Substance with the ability to take up or absorb
another substance. |
Absorption
Refrigerator |
Refrigerator which creates low temperature by
using the cooling effect formed when a refrigerant is absorbed by chemical
substance. |
ACCA |
A leading HVAC/R Association -
http://www.acca.org/ |
Accessible
Hermetic |
Assembly of a motor and compressor inside a
single bolted housing unit. |
Accumulator |
Storage tank which receives liquid refrigerant
from evaporator and prevents it from flowing into suction line before
vaporizing. |
Acid
Condition In System |
Condition in which refrigerant or oil in system
is mixed with fluids that are acid in nature. |
ACR
Tubing |
Tubing used in air conditioning and
refrigeration. Ends are sealed to keep tubing clean and dry. |
Activated
Alumina |
Chemical which is a form of aluminum oxide. It
is used as a drier or desiccant. |
Activated
Carbon |
Specially processed carbon used as a filter
drier ; commonly used to clean air. |
Actuator |
That portion of a regulating valve which
converts mechanical fluid, thermal energy or electrical energy into
mechanical motion to open or close the valve seats. |
Add
On Heat Pump |
Installing a heat pump in conjunction with an
existing fossil fuel furnace. The result is a dual fuel system. |
Adiabatic
Compression |
Compressing refrigerant gas without removing or
adding heat. |
Adjustable
Grille |
A grille with linear blades which can be
adjusted to vary the direction of the discharged air. The linear blades
are normally either vertical or horizontal, or both horizontal and
vertical. |
Adsorbent |
Substance with the property to hold molecules
of fluids without causing a chemical or physical damage. |
Aeration |
Act of combining substance with air. |
Aero seal |
A patented sealing process; the most effective,
affordable, and viable method of sealing the central heating and cooling
ductwork in your home. |
AFLU
(Annual Fuel Utilization Efficiency) |
A rating that reflects the efficiency of a gas
furnace in converting fuel to energy. A rating of 90 means that
approximately 90% of the fuel is utilized to provide warmth to your home,
while the remaining 10% escapes as exhaust. |
AFUE
(Annual Fuel Utilization Efficiency ) |
The ratio of annual output of useful energy or
heat to the annual energy input to the furnace. The higher the AFUE, the
more efficient the furnace -- higher efficiency translates to more savings
on fuel bills. This will range from 80% to 95%. |
Agitator |
Device used to cause motion in confined fluid. |
AHU
(Air Handler 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
Cleaner |
Device used for removal of airborne impurities. |
Air
Coil |
Coil on some types of heat pumps used either as
an evaporator or condenser. |
Air
Conditioner |
Device used to control temperature, humidity,
cleanliness and movement of air in a confined space. |
Air
Conditioning |
Control of the temperature, humidity, air
movement and cleaning of air in a confined space. |
Air
Cooler |
Mechanism designed to lower temperature of air
passing through it. |
Air
Core Solenoid |
Solenoid that has a hollow core instead of a
solid core. |
Air
Diffuser |
Supply air terminal device, designed to direct
airflow into desired patterns, usually placed in the ceiling, generally of
circular, square or rectangular shape, and composed of divergent
deflecting members. |
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, heat transfer coil, and
housing parts of a system. Also known as the blower section and part of
the split system, this unit is commonly in your home or attic and blows
the air through your house. This has to be matched with the condenser
properly to assure maximum efficiency. This will contain your heating and
evaporator coil. |
Air
Infiltration |
Leakage of air into rooms through cracks,
windows doors and other openings. |
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
Terminal Device, Lighting Troffer |
An air terminal device, usually in the form of
a slot or combination of slots, designed for use with a troffer unit. |
Air
Terminal Device, Linear |
Air terminal device (grille) with an aspect
ratio of 10: 1 or more. |
Air
Terminal Device, Slot |
A device with one or several slots with an
aspect ratio of 10: 1 or more for each slot (the aspect ratio is the ratio
of the length to the width of the closed rectangular opening). A slot may
or may not have an adjustable member to vary the direction of the air
jet(s) or air flow rate. |
Air
Terminal Device, Supply |
An air terminal device through which air enters
a treated space. It usually consists of one or several deflecting members
which ensure reduction of the air velocity in the occupied zone as well as
efficient mixing of the supply air with the air in the treated space.
Moreover supply air terminal devices usually determine the direction of
the air jet(s). |
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 distribution or movement of air. |
Ak
value (of an air terminal device) |
Quotient obtained by dividing a measured air
flow rate by a measured air velocity according to a specific process and a
specific instrument. |
Algaecide |
Normally in tablet form, placed in evaporator
drain pan. Used to help slow the growth of bacteria. |
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/ |
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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 |
The process of adjusting
the flow of air in duct systems, or water flow in hot-water heating
systems. Proper balancing is performed using accurate instrumentation to
deliver the right amount of heating or cooling to each area or room of the
home. |
Blower
(Fan) |
An air handling device for
moving air in a distribution system. |
BTU
(British Thermal Unit) |
The amount of heat that
will raise or lower one pound of water 1 degree F. at 39.2 degrees F. One
BTU is the equivalent of the heat given off by a single wooden kitchen
match. The British Thermal Unit is a standard of measure for cooling and
heating capacities. This is how the capacity of air conditioning is
measured. For your home, it represents the measure of heat givens off when
fuel is burned for heating or the measure of heat extracted from your home
for cooling. |
BTUH
(British Thermal Unit Per Hour) |
Establishes a time
reference to btu input or output rates. A BTUH is how many BTUs are used
per hour. |
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Capacitor |
A device used to start a
motor or compressor (or to keep it running after start up.) |
Capacity |
The output or producing
ability of a piece of cooling or heating equipment. Cooling and heating
capacity are normally referred to in BTUs. |
Central
Forced-Air Heating System |
A piece of equipment that
produces heat in a centralized area, then distributes it throughout the
home through a duct system. |
CFC
(Chlorofluorocarbon) |
A class of refrigerants.
Generally refers to the Chlorofluorocarbon family of refrigerants.
Sometimes called Freon |
CFM (Cubic
Feet per Minute) |
A standard of airflow
measurement. A typical system produces 400 CFM per ton of air
conditioning. |
Charge |
Amount of refrigerant
placed in a refrigerating unit. |
Comfort
Zone |
The range of temperatures,
humidities and air velocities at which the greatest percentage of people
feel comfortable. |
Compressor |
The heart of an air
conditioning or heat pump system. The large (usually black) part in the
condenser (outdoor unit) that pumps refrigerant. The 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. The compressor maintains
adequate pressure to cause refrigerant to flow in sufficient quantities to
meet the cooling requirements of the system. |
Condenser |
This is the unit that will
sit outside and is part of a split system, it contains the compressor
which is the heart of your air conditioner or Heat Pump, it pumps the
refrigerant through your system. Some people call the condenser the
compressor, but the compressor is a component of the condenser along with
the fan motor and condenser coil. Coil or outdoor coil dissipates heat
from the refrigerant, changing the refrigerant from vapor to 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. The outdoor portion of a split system air conditioner
contains the compressor and outdoor coil ignoring the reverse cycle
operation, also the outdoor in a heat pump system. |
Configuration |
This describes the
direction in which a furnace outputs heat. A furnace may have an up flow, down flow
or cross flow (horizontal) configuration. |
Contactor |
In the condenser, the main
switch that turns the condenser on. |
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. COPs vary with the outside temperature:
as the temperature falls, the COP falls also, since the heat pump is less
efficient at lower temperatures. ARI standards compare equipment at two
temperatures, 47 F and 17 F, to give you an idea of the COP in both mild
and colder temperatures. Geothermal equipment is compared at 32 F enter
water temperature. COP & HSPF can not be compared equally. Air Source
Equipment is rated by HSPF or COP and Geothermal equipment is rated by
COP. |
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Damper |
A device that is located in
ductwork to adjust air flow. This movable plate opens and closes to
control airflow. Dampers are used effectively in zoning to regulate
airflow to certain rooms. There are basically two types of dampers: Manual
and motorized. A manual damper generally consists of a sheet metal (or
similar material) flap, shaped to fit the inside of a round or rectangular
duct. By rotating a handle located outside of the duct a technician can
adjust (see Balancing) air flow to match the needs of a particular area or
room. A motorized damper is generally used in a zoned system (see Zoning)
to automatically deliver conditioned air to specific rooms or zones. In
particular, the following types, can be distinguished: |
DB |
Dry Bulb |
db
(Decibel) |
A decibel describes the
relative loudness of a sound. Some common sounds are fairly close to a
typical air conditioner or heat pump's sound level: human voice, 7.0
decibels; blender, 8.8 decibels. |
DDC
(Direct Digital Control) |
Direct Digital Control |
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. |
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. |
Down flow
Furnace |
A furnace that pulls in
return air from the top and expels warm air at the bottom. |
Drier |
Sometimes called
filter/drier, it removes moisture and keeps the refrigerant clean. |
Dual Fuel
System |
A dual heating system, for
example a heat pump and a fossil fuel furnace. |
Duct |
A pipe or closed conduit
made of sheet metal, fiberglass board, or other suitable material used for
conducting air to and from an air handling unit. |
Ductwork |
Pipes or channels that
carry air throughout your home. The delivery system through which warm air
from the furnace is brought to where it's needed. Ductwork is made of
sheet metal, fiberglass, or flexible plastic, and can be round or
rectangular in shape. |
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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. |
Effective
area (of an air terminal device) |
The smallest net area of an
air terminal device used by the air stream in passing through the air
terminal device. |
Efficiency |
A rating on comfort
equipment is similar to the miles per gallon rating on your car. The
higher the rating number, the more efficient the system and the lower your
fuel consumption will be. You can save a lot of money with a high
efficiency unit. Depending on your local climate, lifestyle and
electricity rates, savings will vary. For furnaces. it is the rate at
which a furnace maximizes fuel use. This rate is numerically described as
a ratio called AFUE (see AFUE). As of January, 1991, no furnaces can be
manufactured with efficiencies lower than 78% AFUE. High efficiency
furnaces will be rated 85 to 95% AFUE. |
Electronic
Air Cleaner |
An electronic
device that filters out particles and contaminants in indoor air. |
Emergency
Heat (Supplementary Electric Heat) |
The back up electric heat
built into a heat pump system. The same as an auxiliary heater, except it
is used exclusively as the heat source when the heat pump needs repair. |
Envelope |
The geometrical surface of
the points of an air jet, corresponding to a determined value of the
measured air velocity. This velocity is generally called «terminal
velocity». |
EPA
(Environmental Protection Agency) |
Environmental Protection
Agency - http://www.epa.gov/ |
ERV
(Energy Recovery Ventilator) |
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.
This means that smaller capacity heating and cooling systems can be used
in homes, which results in lower installation costs, lower peak demand for
energy, and lower operating costs. |
Evaporator
Coil |
The evaporator coil is
located inside your house in a split system in the air handler, or above
the gas furnace. This will produce cooling in the air conditioning mode
and heating in a Heat Pump mode. This coil section in the evaporator is
where refrigerant evaporates and absorbs heat from air passed over the coil. This
is also very important in removing humidity from your home. |
Exhaust |
The air flow leaving the
treated space. Exhaust may be accomplished by one or more of the following
methods: |
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a. Extraction: exhaust in
such a manner that the air is discharged into the atmosphere. |
|
b. Relief: exhaust in such
a manner that the air is allowed to escape from the treated space if the
pressure in that space rises above a specified level. |
|
c. Recirculation: exhaust
in which the air is returned to the air treatment system. |
|
d. Transfer: exhaust in
which air passes from the treated space to another treated space. |
Exhaust
Air Flow Rate |
Volume of air leaving an
exhaust air terminal device within a time unit. |
Exhaust
Air Terminal Device |
Air terminal device through
which air leaves the treated space. |
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Filter |
A device for removing dust
particles from air or unwanted elements from liquids. |
Fire
Valves (or Fire Dampers) |
Components which are
installed in an air distribution system between two fire separating
compartments and are designed to prevent propagation of fire and/or smoke.
Generally are kept open by mechanical restraint, whose effect is canceled
under specific conditions. The valve is then closed automatically. |
Forced Air |
This describes a type of
heating system that uses a blower motor to move air through the furnace
and into the ductwork. |
Furnace |
That part of an
environmental system which converts gas, oil, electricity or other fuel
into heat for distribution within a structure. |
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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. |
Grille |
An air terminal device with
multiple passages for the air. |
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HCFC
(Hydro chlorofluorocarbon) |
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. It's vital that none of the
combustion gas itself gets into the air stream. The primary heat exchanger
handles the hottest gases. In high efficiency furnaces, secondary heat
exchangers recover heat that used to be vented up the chimney with the
exhaust gases. By recovering this heat, the furnace becomes more
efficient. Part of the heat recovered here causes the water and acid to
condense out of the exhaust gas. Because this liquid is corrosive,
secondary heat exchangers must be designed to prevent deterioration.
Usually this means they are made of stainless steel or some derivative of
it. |
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 |
A Heat Pump is a reverse
cycle air conditioner. The Heat Pump uses a compression cycle system to
supply heat or remove heat remove a temperature controlled space. When you
run your air conditioner, your outdoor unit will be blowing hot air, (in
other words, removing the heat from your home and sending it outside).
When you run your heat pump, you reverse the flow of refrigerant and
remove the heat from the atmosphere outside and blow it inside. When the
temperature dips below 40 degrees outside, the Heat Pump labors in
producing heat so they install a back up or auxiliary electric heat strip
to supplement the Heat Pump. Electric Heat strips are very expensive to
operate. In southern climates where it rarely dips below 40 degrees the
heat pump is very efficient. A 3 to 1 savings in heating compared to
electric heat strips. |
Heat Pump
Cooling Mode |
In the cooling cycle of a
Heat Pump , you are removing hot air from inside the house and sending it
outside. You can feel the hot air outside, over the condenser fan motor. |
Heat Pump
Heating Mode |
In the heating mode of a
Heat Pump the refrigerant cycle is reversed and you are now removing the
heat from the outside and sending it inside the house. You can feel the
cool air outside, over the condenser fan motor. When temperatures go below
40 degrees Heat Pumps labor in producing heat and must use back up
electric heat strips. Heat strips cost 3 times as much to operate as a
Heat Pump when producing heat. |
HFC (Hydro fluorocarbon) |
A class of refrigerants.
Generally refers to Hydro fluorocarbon family of refrigerants |
Horizontal
Furnace |
A furnace that lies on its
side, pulling in return air from one side and expelling warm air from the
other. |
HRV (Heat
Recovery Ventilator) |
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 transfer it to the incoming air, pre-heating it. This
allows for the reclamation of much of the energy that otherwise would
simply be vented outside. The end result: home comfort systems operate
more efficiently. |
HSPF
(Heating Seasonal Performance Factor) |
Heating seasonal
performance factor is similar to SEER, but it measures the efficiency of
the heating portion of your heat pump. Like SEER, industry minimums have
been raised recently, and the minimum is now 6.80 HSPF. The total heating
output of a heat pump during its normal annual usage period for heating
divided by the total electric power input in watt-hours during the same
period. COP & HSPF can not be compared equally. Air Source equipment
is rated by HSPF or COP and Geothermal equipment is rated by COP. ARI
standards compares air source equipment at two temperatures, 47 F and 17
F. Geothermal equipment is compared at 32 F enter water temperature. |
Humidifier |
A device that adds moisture
to warm air being circulated or directed into a space. |
Humidistat |
A device designed to
regulate humidity input by reacting to changes in the moisture content of
the air. Much like a thermostat but turns the system on & off by
sensing the humidity level. |
Humidity |
The amount of moisture in
the air. Air conditioners remove moisture for added comfort. |
HVAC |
Heating, Ventilating and
Air Conditioning |
HVAC/R |
Heating, Ventilating, Air
Conditioning, & Refrigeration |
I
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IAQ |
Indoor Air Quality |
ICM
(Integrally Controlled Motor) |
A specially engineered,
variable-speed motor used in top-of-the-line indoor units. ICM motors are
more than 90 percent efficient versus 60 percent efficiency for
conventional motors. Continuous comfort, quiet operation and u |
Indoor
Coil |
Refrigerant containing
portion of a fan coil unit similar to a car radiator, typically made of
several rows of copper tubing with aluminum fins. |
Indoor
Coils |
A homes comfort system
consist of two components: the outdoor unit (air conditioner or heat pump)
and the indoor unit (coil or blower coil). Combinations of various units
will result in vastly different efficiency ratings. Unreasonably high
efficiency ratings can be created by using unrealistic indoor and out door
equipment combinations. The term "most popular coil" indicates
the actual tested combinations; other ratings may be simulated and
unrealistic. Be sure that the efficiency ratings you are comparing are for
"most popular coil." You'll know the ratings are attainable and
close to reality. |
Indoor
Unit |
This is usually located
inside the house and contains the indoor coil, fan, motor, and filtering
device, sometimes called the air handler. |
Induction |
Process by which the
primary air sets into motion an air volume, called secondary air, in the
room. |
Induction
ratio (i) |
Ratio of the total air flow
rate to the primary air flow rate. |
Infiltration |
Air flow inward into a
space through walls, leaks around doors and windows or through the
building materials used in the structure. |
IWC
(Inches of water column) |
Commonly used in the USA |
J-K
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kW
(kilowatt) |
A kilowatt equals 1,000
watts. |
kWh
(kilowatt hour) |
A kilowatt hour (kWh) is
the amount of kilowatts of electricity used in one hour of operation of
any equipment. |
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Latent Heat
|
Heat, that when added or
removed, causes a change in state - but no change in temperature. |
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MHPU
|
The Mobile Home Package
Unit is an air conditioner with electric or gas heat or can be a Heat
Pump. This unit has the condenser and air handler all-in-one package.
Commonly used in mobile homes and sits outside. (Self-contained unit) |
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Nozzle
|
An air terminal device
designed to generate a low energy loss and thus produce a maximum
throw by minimum entertainment. |
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Outdoor Coil
|
Refrigerant
containing portion of a fan coil unit similar to a car radiator,
typically made of several rows of copper tubing with aluminum fins. |
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Package
Unit or Package System |
A self-contained
unit or system that has the Air Handler & Condenser in same
unit. Normally placed outside the home and connected to a duct
system by a penetration through the homes foundation. Except for
geothermal which is a self-contained indoor unit that is place in
a closet, attached garage, basement, or mechanical room. |
Primary
Air Flow Rate |
Volume of air
entering a supply air terminal device within a time unit. |
Q-R
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Refrigerant |
Substance used in
refrigerating mechanism. A substance that produces a refrigerating
effect while expanding or vaporizing. 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. |
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. |
Return
Air |
Air drawn into a
heating unit after having been circulated from the heater's output
supply to a room. |
RH |
Relative Humidity |
RSES |
A leading HVAC/R
Association - Refrigeration Service Engineers Society -
http://www.rses.org/ |
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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 amount of
cooling your equipment delivers per every dollar spent on
electricity. The higher the number the lower the operating cost
(not more cooling.) SEER applies to air conditioners and heat
pumps. In the past, a unit with a SEER of 8.00 was considered
standard efficiency, and a unit with a 10.00 SEER was considered
high efficiency. After January 1, 1992, the minimum SEER required
by the DOE is 10.00 and 15.00+ SEER is considered high efficiency.
EER & SEER can not be compared equally. Air source equipment
is rated by SEER and geothermal equipment is rated by EER. 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
Heat |
Heat, that when
added or removed, causes a change in temperature but not in state. |
Set point |
The temperature to
which a thermostat is set to result in a desired heated space
temperature. |
Single
Package |
An
outdoor unit that contains both a heating and a cooling system. |
Sizing |
Refers to the
procedure a heating contractor goes through to determine how large
a furnace (measured in BTUH) is needed to heat a house
efficiently. Too small a furnace won't deliver enough heating; too
large a furnace increases energy costs and can have an adverse
effect on comfort. Sizing depends on the square-footage of the
home, the amount of ceiling and wall insulation, the window area,
use of storm doors, storm windows, and more. |
Sound
Attenuators |
Components which
are inserted into the air distribution system and designed to
reduce airborne noise which is propagated along the ducts. |
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. Also applicable to heat
pump installations. |
Spread
(LS) (for a supply air terminal device) |
Maximum distance
between two vertical planes tangent to a specified envelope and
perpendicular to a plane through the core center. The spread are
generally referred to the envelope corresponding to 0.25 m/s for
zero supply temperature differential (i.e., under isothermal
conditions). |
SRN
(Sound Rating Number) |
Sound is measured
in bels (a bel equals 10 decibels). The SRN of a unit is based on
ARI test, performed at ARI standard rating conditions. Average
sound rating range from 7.0 to 8.0 decibels. The lower the SRN
rating, the quieter the unit. |
Straight
Cool |
This is an air
conditioner that uses different forms of heating such as Natural
Gas, LP Gas, Electric Resistance heat and oil. |
Sub cooled
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. |
Supply |
The air flow
entering the treated space. |
Switchover
Valve |
A device in a heat
pump that reverses the flow of refrigerant as the system is
switched from cooling to heating. Also called a reversing valve or
four-way valve. |
T
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Therm |
Another measurement
of heat. One therm equals 100,000 BTUH. |
Thermostat |
A temperature
sensitive switch for controlling the operation of a heater or
furnace. Typically found on a wall inside the home, that consists
of a series of sensors and relays that monitor and control the
functions of a heating and cooling system. |
Thermostat,
Air-Sensing |
Thermostat unit in
which sensing element is located in refrigerated space. |
Throw
(Lt) |
The maximum
distance between the center of the core and a plane which is
tangent to a specified envelope and perpendicular to the intended
direction of flow The throw is generally referred to as the
envelope corresponding to 0.25 m/s for zero supply temperature
differential (i.e., under isothermal conditions). |
Time
Delay |
Usually refers to a
device that will not allow the condenser to restart for an average
of 5 minutes. |
Ton |
A cooling unit of
measure. Each ton equals 12,000 BTUH. Heat pumps and air
conditioners are generally sized in tons. Typical sizes for single
family residences are between two and five tons. It is important
to note that actual capacity is not constant and will change based
on outdoor or indoor temperatures. The published capacity rating
of air conditioners and heat pumps is based on performance at the
ARI standard temperature levels of 95 F outside, 80 F inside. The
number of tons a system has is the total BTU capacity of the
system. The size of the area to be cooled will determine the
correct size of the system in tons. |
Total
air flow rate (QL) |
Sum of the primary
and secondary air flow rates which are moved in the treated space. |
U-Z
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Up flow
Furnace |
A furnace that
pulls return air in from the bottom and expels warm air from the
top. |
Valves |
Components inserted
into air ducts or devices which permit modification of the air
resistance of the system and consequently a complete shut-off of
the air flow (control valves). |
VAV
(Variable Air Volume) |
Variable Air
Volume. |
VFD
(Variable Frequency Drive) |
Electronic speed
control for motors. |
W
(Watt) |
A watt is a unit of
electricity. |
WB |
Wet Bulb |
WC
(Water Column) |
Common measure of
air pressure used in HVAC systems. |
Zoning |
A system in which
living areas or groups of rooms are divided into separate spaces
and each space's heating/air conditioning is controlled
independently. This can be accomplished by using either multiple
independent systems, or a single system using electronic controls
and motorized dampers (see Damper). |
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