This glossary is comprised of words and phrases most frequently used in the heating, ventilation and air conditioning HVAC industry. These brief explanations will help your understand of many terms used throughout your work, study and professional career.

1.
GLOSSARY OF
HVAC TERMS
10/18/2013
HVAC is term used for heating, ventilation and
air conditioning
This glossary is comprised of words and phrases most frequently used in
the heating, ventilation and air conditioning industry. These brief
explanations will help your understand of many terms used throughout
your work, study and professional career.

3. Glossary of HVAC terms
Page 1
Glossary of HVAC terms
H VA C I S T E R M U S E D F O R H E A T I N G , V E N T I L A T I O N A N D A I R
C O N D I T I O N I N G
Absolute
humidity:
The
weight
of
water
vapour
per
unit
volume;
grains
per
cubic
foot;
or
grams
per
cubic
meter.
Absolute
pressure:
The
sum
of
gage
pressure
and
atmospheric
pressure.
Thus,
for
example,
if
the
gage
pressure
is
154
psi,
the
absolute
pressure
will
be
154+14.7,
or
168.7
psi.
Absolute
zero:
A
temperature
equal
to
–459.6®F
or
–273®C.
At
this
temperature
the
volume
of
an
ideal
gas
maintained
at
a
constant
pressure
becomes
zero.
Absorption:
The
action
of
a
material
in
extracting
one
or
more
substances
present
in
the
atmosphere
or
a
mixture
of
gases
or
liquids
accompanied
by
physical
change,
chemical
change,
or
both.
Acceleration:
The
time
rate
of
change
of
velocity.
It
is
the
derivative
of
velocity
with
respect
to
time.
Accumulator:
A
shell
placed
in
a
suction
line
for
separating
the
liquid
entrained
in
the
suction
gas.
A
storage
tank
at
the
evaporator
exit
or
suction
line
used
to
prevent
flood
backs
to
the
compressor.
Acrolein:
A
warning
agent
often
used
with
methyl
chloride
to
call
attention
to
the
escape
of
refrigerant.
The
material
has
a
compelling,
pungent
odor
and
causes
irritation
of
the
throat
and
eyes.
Acrolein
reacts
with
sulfur
dioxide
to
form
a
sludge.
ACR
tube:
A
copper
tube
usually
hard
drawn
and
sold
to
the
trade
cleaned
and
sealed
with
nitrogen
inside
to
prevent
oxidation.
Identified
by
its
actual
outside
diameter
(OD).
Activated
alumina:
A
form
of
aluminium
oxide
(Al2O3)
that
absorbs
moisture
readily
and
is
used
as
a
drying
agent.
Adiabatic:
Referring
to
a
change
in
gas
conditions
where
no
heat
is
added
or
removed
except
in
the
form
of
work.
Adiabatic
process:
Any
thermodynamic
process
taking
place
in
a
closed
system
without
the
addition
or

4. Glossary of HVAC terms
Page 2
removal
of
heat.
Adsorbent:
A
sorbent
that
changes
physically,
chemically,
or
both
during
the
sorption
process.
Aeration:
Exposing
a
substance
or
area
to
air
circulation.
Agitation:
A
condition
in
which
a
device
causes
circulation
in
a
tank
containing
fluid.
Air,
ambient:
Generally
speaking,
the
air
surrounding
an
object.
Air
changes:
A
method
of
expressing
the
amount
of
air
leakage
into
or
out
of
a
building
or
room
in
terms
of
the
number
of
building
volumes
or
room
volumes
exchanged
per
unit
of
time.
Air
circulation:
Natural
or
imparted
motion
of
air.
Air
cleaner:
A
device
designed
for
the
purpose
of
removing
airborne
impurities
such
as
dust,
gases,
vapors,
fumes,
and
smoke.
An
air
cleaner
includes
air
washers,
air
filters,
electrostatic
precipitors,
and
charcoal
filters.
Air
conditioner:
An
assembly
of
equipment
for
the
control
of
at
least
the
first
three
items
enumerated
in
the
definition
of
air
conditioning.
Air
conditioner,
room:
A
factory-­‐made
assembly
designed
as
a
unit
for
mounting
in
a
window,
through
a
wall,
or
as
a
console.
It
is
designed
for
free
delivery
of
conditioned
air
to
an
enclosed
space
without
ducts.
Air
conditioning:
The
simultaneous
control
of
all,
or
at
least
the
first
three,
of
the
following
factors
affecting
the
physical
and
chemical
conditions
of
the
atmosphere
within
a
structure—temperature,
humidity,
motion,
distribution,
dust,
bacteria,
odors,
toxic
gases,
and
ionization—most
of
which
affect
human
health
or
comfort.
Air-­‐conditioning
system,
central
fan:
A
mechanical
indirect
system
of
heating,
ventilating,
or
air
conditioning
in
which
the
air
is
treated
or
handled
by
equipment
located
outside
the
rooms
served,
usually
at
a
central
location
and
conveyed
to
and
from
the
rooms
by
means
of
a
fan
and
a
system
of
distributing
ducts.

5. Glossary of HVAC terms
Page 3
Air-­‐conditioning
system,
year
round:
An
air-­‐conditioning
system
that
ventilates,
heats,
and
humidifies
in
winter,
and
cools
and
dehumidifies
in
summer
to
provide
the
desired
degree
of
air
motion
and
cleanliness.
Air-­‐conditioning
unit:
A
piece
of
equipment
designed
as
a
specific
air-­‐treating
combination,
consisting
of
a
means
for
ventilation,
air
circulation,
air
cleaning,
and
heat
transfer
with
a
control
means
for
maintaining
temperature
and
humidity
within
prescribed
limits.
Air
cooler:
A
factory-­‐assembled
unit
including
elements,
whereby
the
temperature
of
air
passing
through
the
unit
is
reduced.
Air
cooler,
spray
type:
A
forced-­‐circulation
air
cooler,
wherein
the
coil
surface
capacity
is
augmented
by
a
liquid
spray
during
the
period
of
operation.
Air
cooling:
A
reduction
in
air
temperature
due
to
the
removal
of
heat
as
a
result
of
contact
with
a
medium
held
at
a
temperature
lower
than
that
of
the
air.
Air
diffuser:
A
circular,
square,
or
rectangular
air
distribution
outlet,
generally
located
in
the
ceiling,
and
comprised
of
deflecting
members
discharging
supply
air
in
various
directions
and
planes,
arranged
to
promote
mixing
of
primary
air
with
secondary
room
air.
Air,
dry:
In
psychrometry,
air
unmixed
with
or
containing
no
water
vapor.
Air
infiltration:
The
in-­‐leakage
of
air
through
cracks,
crevices,
doors,
windows,
or
other
openings
caused
by
wind
pressure
or
temperature
difference.
Air,
recirculated:
Return
air
passed
through
the
conditioner
before
being
again
supplied
to
the
conditioned
space.
Air,
return:
Air
returned
from
conditioned
or
refrigerated
space.

6. Glossary of HVAC terms
Page 4
Air,
saturated:
Moist
air
in
which
the
partial
pressure
of
the
water
vapor
is
equal
to
the
vapor
pressure
of
water
at
the
existing
temperature.
This
occurs
when
dry
air
and
saturated
water
vapor
coexist
at
the
same
dry-­‐
bulb
temperature.
Air,
standard:
Air
with
a
density
of
0.075
lb/ft3
and
an
absolute
viscosity
of
1.22x10
1b
mass/ft-­‐s.
This
is
substantially
equivalent
to
dry
air
at
70®F
and
29.92
in.
Hg
barometer.
Air
washer:
An
enclosure
in
which
air
is
forced
through
a
spray
of
water
in
order
to
cleanse,
humidify,
or
precool
the
air.
Ambient
temperature:
The
temperature
of
the
medium
surrounding
an
object.
In
a
domestic
system
having
an
air-­‐cooled
condenser,
it
is
the
temperature
of
the
air
entering
the
condenser.
Ammonia
machine:
An
abbreviation
for
a
compression
refrigerating
machine
using
ammonia
as
a
refrigerant.
Similarly,
Freon
machine,
sulfur
dioxide
machine,
and
so
forth.
Ampere:
Unit
used
to
measure
electrical
current.
It
is
equal
to
1
C
of
electrons
flowing
past
a
point
in
1
s.
A
coulomb
is
6.28x1018
electrons.
Analyser:
A
device
used
in
the
high
side
of
an
absorption
system
for
increasing
the
concentration
of
vapor
entering
the
rectifier
or
condenser.
Anemometer:
An
instrument
for
measuring
the
velocity
of
air
in
motion.
Antifreeze,
liquid:
A
substance
added
to
the
refrigerant
to
prevent
formation
of
ice
crystals
at
the
expansion
valve.
Antifreeze
agents
in
general
do
not
prevent
corrosion
due
to
moisture.
The
use
of
a
liquid
should
be
a
temporary
measure
where
large
quantities
of
water
are
involved,
unless
a
drier
is
used
to
reduce
the
moisture
content.
Ice
crystals
may
form
when
moisture
is
present
below
the
corrosion
limits,
and
in
such
instances,
suitable
noncorrosive
antifreeze
liquid
is
often
of
value.
Materials
such
as
alcohol
are
corrosive
and,
if
used,
should
be
allowed
to
remain
in
the
machine
for
a
limited
time
only.

7. Glossary of HVAC terms
Page 5
Atmospheric
condenser:
A
condenser
operated
with
water
that
is
exposed
to
the
atmosphere.
Atmospheric
pressure:
The
pressure
exerted
by
the
atmosphere
in
all
directions
as
indicated
by
a
barometer.
Standard
atmospheric
pressure
is
considered
to
be
14.695
psi
(pounds
per
square
inch),
which
is
equivalent
to
29.92
in.
Hg
(inches
of
mercury).
Atomize:
To
reduce
to
a
fine
spray.
Automatic
air
conditioning:
An
air-­‐conditioning
system
that
regulates
itself
to
maintain
a
definite
set
of
conditions
by
means
of
automatic
controls
and
valves
usually
responsive
to
temperature
or
pressure.
Automatic
expansion
valve:
A
pressure-­‐actuated
device
that
regulates
the
flow
of
refrigerant
from
the
liquid
line
into
the
evaporator
to
maintain
a
constant
evaporator
pressure.
Baffle:
A parttti n us dt s durd d u etfl t a r tr a en si
Balanced
pressure:
The
same
pressure
in
a
system
or
container
that
exists
outside
the
system
or
container.
Barometer:
An
instrument
for
measuring
atmospheric
pressure.
Blast
heater:
A
set
of
heat-­‐drai ur ct l tr uctti n us dt uad a r d ad srafli tr trcus d rtnu d b a
aii Bleeder:
A p pu tmutmu aaac us dt a ctisui ur dt luus t l ln s ru r uuraid parallul dt d u ma i
etfli Boiler:
A
closed
vessel
in
which
liquid
is
heated
or
vaporised.
Boiler
horsepower:
T u uln daluid udaptratti t 3i. l t fladur pur tnr rtm ais ad 2 ®F,
which
is
equal
to
a
heat
output
of
970.3
x34.5
=
33,475
Btu.
Boiling
point:
T u dumpuradnru ad fl c a l ln s daptr us npti d u ass tti t uadt supuisuid ti d u
refrigerant
and
the
absolute
pressure
at
the
surface
of
the
liquid
and
vapor.
Bore:
The
inside
diameter
of
a
cylinder.

8. Glossary of HVAC terms
Page 6
Bourdon
tube:
Tn u t ula tc mudal
bent
into
circular
shape
that
is
found
inside
a
pressure
gage.
Brine:
Any
liquid
cooled
by
a
refrigerant
and
used
for
transmission
of
heat
without
a
change
in
its
state
Brine
system:
A b dum fl uru b r iu cttlus b a ru r uuratiu b dum c rcnladus dhrough
pipes
to
the
point
wheru d u ru r uuratti iuususi
Britis
serraa
ui
B
u:
The
amount
of
heat
required
to
raise
the
temperature
of
1
lb
of
water
1 F.
It
is
also
the
measure
of
the
amount
of
heat
removed
in
cooling
1
lb
of
water
1 F
and
is
so
used
as
a
measure
of
ru r uuratiu u
ucdi
Butane:
A bsrtcar tit eamma lu ru r uuraid n us dt a l m dus uxduid i mall ni d i
Calcium
chloride:
A
chemical
having
the
formula
CaCl2,
which,
in
granular
form,
is
used
as
a
drier.
This
madur al tln lu i fladurt ais i d u pru uicu t laruu lnaittu t mt dnru mab s tldu ais plnu np d u
drier
unit
or
even
pass
into
the
system
beyond
the
drier.
Calcium
sulfate:
A
solid
chemical
of
the
formula
CaSO4,
which
may
be
used
as
a
drying
agent.
Caaibratiu:
T u prtcu t s d s iu ais inm ur iu d u calu t ai i drnmuid; al t t ctrructiu
ais
determining
d u urrtr t ai ux tiu
calui
Calorie:
Heat
required
to
raise
the
temperature
of
1
g
of
water
1®C
(actually,
from
4
to
5®C).
Mean
calorie
is
equal
to
one-­‐hundredth
part
of
the
heat
required
to
raise
1
g
of
water
from
0
to
100®C.
Capacitor:
An
electrical
device
that
has
the
ability
to
store
an
electrical
charge.
It
is
used
to
start
motors,
among
other
purposes.
Capaci
y,
refrigeratug:
T u a l db t a ru r uuratiu b dumt tr pard d urut t dt rumtdu uadi xpru us a
a
rate
of
heat
removal,
it
is
usually
measured
in
Btu/h
or
tons/24
h.
Capacity
reducer:
In
a
compre
trt a sud cut nc a a cluaraicu ptckudt mtda lu cbl isur uast tr
nctti
bypass,
by
which
compressor
capacity
can
be
adjusted
without
otherwise
chaiuiudutpuratiuctisttii

9. Glossary of HVAC terms
Page 7
Capillarity:
T u actti b fl c d u nr acu t a l ln s i ctidacd fl d a
solid
(as
in
a
slender
tube)
is
raised
or
lowered.

10. Glossary of HVAC terms
Page 8
Capillary
tube:
Ii ru r uuratti practcut a dn u t mall idurial s amudur n us a a l ln s ru r uuraid-­‐etfl
control
or
expansion
device
between
high
and
low
sides;
also
used
to
transmit
pressure
from
d u ui tdu nl
of
some
temperature
condrtl dt d u tpuratiu ulumuidi
Carbon
dioxide
ice:
Compressed
solid
CO2;
dry
ice.
Celsius:
A
thermometric
system
in
which
the
freezing
point
of
water
is
called
0®C
and
its
boiling
point
100®C
at
normal
pressure.
T b dum n us i d u c uitic ctmmni db tr ru uarc fltrk ais al t b mt d nrtpuai
countries
and
Canada.
This
book
has
the
Celsius
value
of
each
Fahrenheit
temperature
in
parenthesis.
Centrifugal
compressor:
A
compressor
employing
centrifugal
force
for
compression.
Centrifuge:
A sud cu tr uparatiu l ln s t s uruid sui tu b cuidr nual acttii
Change
of
air:
Iidrtsnctti t iuflt cluai ust tr ruc rcnladus a r dt a ctis ttius pacut mua nrus b d u
number
of
ctmpludu c aiuu pur ni d tmui
Change
of
state:
Change
from
one
state
to
another,
as
from
a
liquid
to
a
solid,
from
a
liquid
to
a
gas,
and
so
forth.
Charge:
The
amount
of
refrigerant
in
a
system.
Csiruey
effec
:
T u duisuicb t a r tr ua i a sncd tr td ur durtcal pa auu dt r u fl un
heated
due
to
its
lower
density
compared
with
that
of
the
surrounding
air
or
gas.
In
buildings,
the
tendency
toward
displacement,
can us b d u s uruicu i dumpuradnrut t idurial uadus a r b ni uadus tnd su a r snu dt d u s uruicu i
density
of
outside
and
inside
air.
Clearance:
Space
in
a
cylinder
not
occupied
by
a
piston
at
the
end
of
the
compression
stroke
or
volume
of
gas
remaining
in
a
cylinder
at
the
same
point,
measured
in
percentage
of
piston
displacement.
Ciefficieu
if
expauiiiu:
The
fracttial icrua u i luiud tr dtlnmu t a madur al per
degree
rise
in
temperature.
Ciefficieu
if
perfirrauce
sea
p
rpu:
Ratt t uatiu u ucd prtsncus dt d u uiurub nppl ust uac
expressed
in
the
same
thermal
units.
Coil:
Aib uatiutrcttliuulument
made
of
pipe
or
tubing
connected
in
series.

11. Glossary of HVAC terms
Page 9
Cold
storage:
A
trade
or
process
of
preserving
perishables
on
a laruu calu b ru r uurattii
Comfort
chart:
A c ard tfl iu u uctdu dumpuradnru fl d srb-­‐
nl dumpuradnru ais nm s tu ais
tmutmu a r mtttin b fl c d u u ucd t dar tn a r ctis tti on
human
comfort
maybe
compared.
Compression
system:
A ru r uuratiu b dum i fl c d u pru nru-­‐imposing
element
is
mechanically
operated.
Compressor:
T ad pard t a muc ai cal ru r uuratiu b dumt which
receives
the
refrigerant
vapor
at
low
pressure
and
compresses
it
into
a
smaller
volume
at
higher
pressure.
Compressor,
centrifugal:
A
non-­‐pt tdu s placumuid ctmpru tr d ad supuis ti cuidr nual u ucdt ad luast
in
part,
for
pressure
rise.
Compressor
displacement:
Ctmpru tr dtlnmu i cn c ic u tnis b mnltplb iu p dti arua b droke
by
the
number
of
cylinders.
Displacement
in
cubic
feet
per
minute:
Compressor,
open-­‐type:
A ctmpru tr fl d a af tr td ur mtd iu pardt uxduis iu d rtnu a
casing,
to
be
sr dui b ai tnd su tnrcu t ptflurt d n ruln r iu a dnffiiu txt af ual t tr uln daluid rn iu ctidacd
udfluui a ixus ais mtd iu pardi
Cirpreiiir,
recipricatug:
A pt tdu-­‐displacement
compressor
with
a
piston
or
pistons
moving
in
a
straight
line
but
alteriadulb i tppt du s ructti i
Compressor,
rotary:
Oiu i fl c ctmpru ti aaa ius i a cbl isur b rtdatti t a pt tdu-­‐displacement
member.
Compressor
booster:
A
compressor
for
very
low
pressures,
usually
discharging
intt d u ncton
line
of
another
compressor.

12. Glossary of HVAC terms
Page
10
Condenser:
A
heat-­‐transfer
device
that
receives
high-­‐pressure
vapor
at
temperatures
above
that
of
the
cooling
medium,
such
as
air
or
water,
to
which
the
condenser
passes
latent
heat
from
the
refrigerant,
causing
the
refrigerant
vapor
to
liquefy.
Condensing:
T u prtcu t u d iu np laduid uad t daptr atti i trsur dt l lnu b a vapor.
Condensing
unit:
A puc ic ru r uuratiu mac iu ctm iattit tr a u dui ru r uuraidt cti tiu t tiu
tr more
power-­‐driven
compressors,
condensers,
liquid
receivers
(when
required),
and
the
regularly
furnished
accessories.
Condensing
unit,
sealed:
A
mechanical
condensing
unit,
in
which
the
compressor
and
compressor
motor
are
enclosed
in
the
same
housing,
with
no
exdurial af tr af ualt d u ctmpru tr mtdtr tpuratiu in
the
refrigerant
atmosphere.
Ciud
ctiu,
serraa:
Passage
of
heat
from
one
point
to
another
by
transmission
of
molecular
energy
from
partclu dt partclu d rtnu a ctisncdtri
Ciud
ctii
y,
serraa:
The
ability
of
a
material
to
pass
heat
from
one
point
to
another,
generally
expressed
in
terms
of
Btu
per
hour
per
square
foot
of
material
per
inch
of
thickness
per
suuruu dumpuradnru s uruicui
Conductor,
electrical:
A
material
that
will
pass
an
electric
current
as
part
of
an
electrical
system.
Ciuuectug
rid:
A sud cu ctiiuctiu d u p dti dt a craik ais n us dt c aiuu rtdatiu mttti idt
ruc prtcatiu mtttit tr d cu dur at a rtm a rtdatiu craik af dt a ruc prtcatiu p dtii
Constant-­‐pressure
valve:
A
valve
o
d u d rtal iu dbput ru pti du dt pru nrut ltcadus i d u nctti l iu t
an
evaporator
to
maintain
a
desired
constant
pressure
in
the
evaporator
hiu ur d ai d u ma i nctti-­‐line
pressure.
Constant-­‐temperature
valve:
A daldu t d u d rtal iu dbput ru pti du dt d u dumpuradnru t a d urmt datc
nl i T daldu ltcadus i d u nctti l iu t ai udaptradtr dt rusncu d u ru r uuratiu u ucd ti d u ct l dt on d
maintain
a
desired
minimum
temperature.
Control:
Aib sud cu tr ruunlatti t a b dum tr ctmptiuid i itrmal tpuratti u d ur mainal tr andtmatci I
andtmatct d u mpl catti d ad d ru pti du dt c aiuu t dumpuradnrut pru nrut tr aib td ur prtpurdb
whose
magnitude
is
to
be
regulated.

13. Glossary of HVAC terms
Page 10
Control,
high-­‐pressure:
A
pressure-­‐responsive
device
(usually
an
electric
switch)
actuated
directly
by
the
refrigerant-­‐vapor
pru nru ti d u u su t a ru r uuratiu b dum n nally
compressor-­‐head
pressure).
Control,
low-­‐pressure:
An
electric
switch,
responsive
to
pressure,
connected
into
the
low
pressure
part
of
a
ru r uuratiu b dum n nallb clt u ad u pru nru ais tpui at
low
pressure).
Control,
temperature:
An
electric
switch
or
relay
that
is
responsive
to
the
temperature
change
of
a
d urmt datc nl tr ulumuidi
Ciuiectiu:
The
circulatorb mttti d ad tccnr i a en s ad a it ni trm dumpuradnrut tfl iu dt d u dar atti t
its
den
db ais d u actti t urad dbi
Ciuiectiu,
firced:
Ctiductti ru nltiu rtm trcus c rcnlatti t a euid
as
by
a
fan,
jet,
or
pump.
Cooling
tower,
water:
An
eiclt us sud cu tr udaptratdu cttling
water
by
contact
with
air.
Cooling
unit:
A puc ic a r-­‐druatiu ctm iatti cti tiu t a muai tr a r c rcnlatti ais cttl iu fl d i
prescribed
temperature
limits.
Cooling
water:
Wadurnus trctisui attitf
refrigerant.
Condenser
water.
Cipper
paatug:
Ftrmatti t a ilm t ctppurt n nallb ti ctmpru tr flall t p dti t tr s c aruu daldu can
us
by
moisture
in
a
methyl
chloride
system.
Corrosive:
Hadiuac um callbsu drnctduu ucdtimudal tccasionally
on
other
materials).
Counter-­‐fliw:
Ii d u uad uxc aiuu udfluui dflt en s t d u tppt du s ructti t etflt d u ctlsu d ptrtti t
tiu muutiu d u ctlsu d ptrtti t d u td uri
Critcaa
preii
re:
The
vapor
pressure
correspondiiu dt d u cr tcal dumpuradnrui
Critcaa
erpera
re:
The
temperature
above
which
a
vapor
cannot
be
liqnuiust ruuarslu t pru nrui
Critcaa
ieaici
y:
The
velocity
above
fl c en s etfl dnr nluidi
Crohydrate:
Ai unductc r iu m xdnru t fladur ais aib ald m xus i prtptrtti dt give
the
lowest
freezing
temperature.

14. Glossary of HVAC terms
Page 11
Cycle:
A ctmpludu ctnr u t tpuratti t fltrk iu en s ack dt a dartiu pt id mua nrus i d urmtsbiam c
terms.
Also
used
in
general
for
any
repeated
process
in
a
system.
Cycae,
defriitug:
T ad ptrtti t a ru r uuratti tpurattit fl c purm ts
the
cooling
unit
to
defrost.
Cycae,
refrigeratiu:
A ctmpludu ctnr u t tpuratti t a ru r uuraid ack dt d u dartiu pt id mua nrus i
thermodynamic
terms.
Also
used
in
general
for
any
repeated
process
for
any
system.
Daltiu’i
aaw
if
partaa
preii
re:
ac cti tdnuid t a m xdnru t ua u u adu d urmtsbiam callb a
d altiu tccnp us d u pacui T u nm t d u is d snal pru nru t d u cti tdnuid ulnal d u total
pressure
of
the
mixture.
Defriitug:
The
removal
of
accumulated
ice
from
a
cooling
unit.
Degree
day:
A ni d a us ti dumpuradnru s uruicu ais tmu n us dt puc b d u itm ial uatiu ltas i
winter.
For
one
day
there
exist
as
many
degree-­‐sab a d uru aru suuruu Fa rui u d s uruicu i dumpuradnru
between
the
average
outside
air
temperature,
taken
over
a
24-­‐h
period,
and
a
temperature
of
65°F.
Des
ridifier:
Ai a r cttlur n us tr ltflur iu d u mt dnru ctiduid t d u a r pa iu d rtnu di Ai a
trptti tras trpttisudcu trremoving
moisture
from
the
air.
Dehumidify:
To
remove
water
vapor
from
the
atmosphere
or
to
remove
water
or
liquid
from
stored
goods.
Dehydrator:
A
device
used
to
remove
moisture
from
the
refrigerant.
Density:
The
mass
or
weight
per
unit
of
volume.
Dew
point,
air:
The
temperature
at
fl c a puc ius amplu t a rt fl d it mt dnru assus tr rumtdust
completely
saturated.
The
temperature
at
which
the
air,
on
being
cooled,
gives
up
moisture
or
dew.
Differeutaa
if
a
ciu
riau:
T u s uruicu udfluui d u cnd i ais cnd tnd dumpuradnre.
A
valve
that
opens
at
one
pressure
and
closes
at
another.
This
allows
a
system
to
adjust
itself
wid am imnmt tdurctrructtii
Direct
connected:
Dr dur ais sr duit a mtdtr ais ctmpru trt pt tdulb ctiiucdus i l ie
to
operate
at
the
same
speed.

16. Glossary of HVAC terms
Page 12
Direct
expansion:
A
system
in
which
the
evaporator
is
located
in
the
material
or
space
refrigerated
or
in
the
air
c rcnlatiu pa auu ctmmni catiu fl d nc pacui
Discharge
gas:
Hot,
high-­‐pressure
vapor
refrigerant,
whic
a on d luf d u ctmpru tri
Displacement,
actual:
The
volume
of
gas
at
the
compressor
inlet
acdnallb mtdus i a u dui tmui
Diipaacereu
,
seiretcaa:
The
total
volume
displaced
by
all
the
pistons
of
a
compressor
for
every
stroke
snr iu a suii du idurdal n nallb mua ured
in
cubic
feet
per
minute).
Drier:
Synonymous
with
dehydrator.
Dry-­‐type
evaporator:
Ai udaptradtr t d u ctitintn dn u dbpu fl uru d u ru r uuraid rtm a pru nru-­‐
rusnc iu sud cu us idt tiu uis ais d u nctti l ne
connected
to
the
outlet
end.
Duct:
A
passageway
made
of
sheet
metal
or
other
suitable
material,
not
necessarily
luak tu d,
used
for
conveying
air
or
other
gas
at
low
pressure.
Dust:
Ai a r n pui ti aurt tln t tl s partclu t uard b madur alt a s uruitadus rtm mtkui
Economizer:
A
reservoir
or
chamber
wherein
energy
or
material
from
a
process
is
reclaimed
for
further
useful
purpose.
Efficieucy,
recsauicaa:
T u ratt t d u tndpnd t a mac iu dt d u ipnd i uln daluid ni ds.
Efficieucy,
iia
re
ric:
T u ratt t d u dtlnmu t ua acdnallb pnmped
by
a
compressor
or
pump
to
the
dutrutcaldisplacement
of
the
compressor.
Ejector:
A sud cu d ad ntl iu datc pru nru dt n ls np a u en s dultc db i a ru dr cdus arua dt t da i a
ltflur datc pru nru ad d ad pt id t d ad en s rtm another
source
maybe
drawn
in.
Element,
bimetallic:
Ai ulumuid trmus t dflt mudal ad iu s uruid ctuffic uid t d urmal uxpai tit nc
as
used
in
temperature-­‐
is catiu ais ctidrtll iu suvices.
Emulsion:
A rulatdulb da lu n pui ti t mallt nd itd ctllt salt partcles
of
a
substance
in
a
liquid.
Engine:
Prime
mover;
device
for
transforming
fuel
or
heat
energy
into
mechanical
energy.

17. Glossary of HVAC terms
Page 13
Enthalpy:
The
total
heat
content
of
a
substance,
compared
to
a
standard
value
32®F
or
0®C
for
water
vapor.
A
measure
of
the
energy
content
of
a
system
per
unit
mass.
Entropy:
T u ratt t d u uad assus dt a n daicu dt d u a tlndu dumperature
at
which
it
is
added.
Equalizer:
A
piping
arrangement
to
maintain
a
common
liquid
level
or
pressure
between
two
or
more
chambers.
Eu
ectc
iia
tiu:
A tlntti t nc cticuidratti a dt adu a cti daid ruui iu pt id ad d u ltflu d ruui ig
dumpuradnru tr d u tlnttii
Eiapiratie
ciudeuier:
A ru r uuraid ctisui ur ntl i iu d u udaptratti t fladur b a r ad d u ctisui ur
surface
as
a muai t s patiu uadi
Eiapiratie
ciiaiug:
T u prtcu t cttl iu b muai t d u udaptratti of
water
in
air.
Evaporator:
A
device
in
which
the
refrigerant
evaporates
while
absorbing
heat.
Expauiiiu
iaaie,
a
iratc:
A sud cu d ad ruunladu d u eow
of
refrigerant
from
the
liquid
line
into
the
evaporator
to
maintain
a
constant
evaporator
pressure.
Expauiiiu
iaaie,
serrii
atc:
A sud cu d ad ruunladu d u etfl t ru r uuraid idt ai udaptradtr t a dt
ma ida i ai udaptratti dumpuradnru i a suii du rulatti p dt d u dumpuradnru t a d urmt datc nl i
Extended
surface:
The
evaporator
or
condenser
surface
that
is
not
a
primary
surface.
Fins
or
other
surfaces
that
transmit
heat
from
or
to
a
primary
surface,
which
is
part
of
the
refrigerant
container.
External
equalizer:
Ii a d urmt datc uxpai ti daldut a dn u ctiiuctti rtm d u c am ur ctida i iu d u
pressure
actuated
element
of
the
valve
to
the
outlet
of
the
evaporator
coil.
A
device
to
compensate
for
excessive
pressure
drop
through
the
coil.
Fahrenheit:
A
thermometric
system
in
which
32°F
denotes
the
freezing
point
of
water
and
212°F
the
boiling
point
under
normal
pressure.
Fan:
An
air-­‐mtd iu sud cu ctmpr iu a fl uult tr lasut ais tn iu tr tr icu pladui

18. Glossary of HVAC terms
Page 14
Fan,
centrifugal:
A
fan
rotor
or
wheel
within
a
scroll-­‐type
housing
and
including
driving-­‐mechanism
supports
for
either
belt-­‐sr du tr s rucd ctiiucttii
Fan,
propeller:
A
propeller
or
disk-­‐dbpu fl uul fl d i a mtnitiu r iu tr pladu ais iclns iu sr d iu-­‐mechanism
supports
for
either
belt-­‐dr
du tr s rucd ctiiucttii
Fan,
tube-­‐axial:
A
disk-­‐type
wheel
within
a
cylinder,
a
set
of
air-­‐un su daiu ltcadus u d ur u tru tr afur d u
wheel,
and
driving-­‐mechanism
supports
for
either
belt-­‐drive
or
direct
coiiucttii
Filter:
A
device
to
remove
solid
madur al rtm a en s b a dra i iu acttii
Flammability:
The
ability
of
a
material
to
burn.
Faare
fitug:
A dbpu t ctiiucdtr tr tf dn iu d ad idtldu d u ear iu t d u dn e
to
provide
a
mechanical
seal.
Flash
gas:
T u ua ru nltiu rtm d u i daidaiutn udaptratti t d u ru r uuraid i a pru nru-­‐reducing
device
dt cttl d u ru r uuraid dt d u udaptratti dumpuradnru t tained
at
the
reduced
pressure.
Float
valve:
Valdu acdnadus b a etad mmur us i a l ln s container.
Flooded
system:
A
system
in
which
the
refrigerant
enters
into
a
header
from
a
pressure
reducing
valve
and
the
evaporator
maintains
a
liquid
level.
Opposed
to
dry
evaporator.
Fluid:
A
gas
or
liquid.
Foaming:
Ftrmatti t a tam tr rtd t t l ru r uuraid snu dt rap s t l iu tnd t the
refrigerant
dissolved
in
the
oil
when
the
pressure
is
suddenly
reduced.
This
occurs
when
the
compressor
operates;
and
if
large
lnaittu t ru r uuraid adu uui s tldust laruu lnaittu t t l mab m t lb tnd ais u carr us through
the
refrigerant
lines.
Freezeup:
Fa lnru t a ru r uuratti ni d dt tpuradu itrmallb snu dt trmatti t cu ad d u uxpai ti daldui T
u
valve
maybe
frozen
closed
or
open,
causing
improper
ru r uuratti i u d ur ca ui
Freezing
point:
The
temperature
at
which
a
liquid
will
solidify
upon
the
removal
of
heat.
Freon-­‐12:
T u ctmmti iamu tr s c ltrts entrtmud aiu CCl F ).

19. Glossary of HVAC terms
Page 15
Frostback:
T u etts iu t l ln s rtm ai udaptradtr idt d u nctti l iut acctmpai us b rt d trmatti ti
the
nctti l iu i mt d ca u i
Furnace:
That
part
of
a
boiler
or
warm-­‐np uatiu plaid i fl c ctm n tti daku placui Al t a ctmpludu
uatiu ni d tr drai urr iu uad rtm nul u iu nrius dt d u a r nppl us dt a uatiu b dumi
Fusible
plug:
A
safety
plug
used
in
vessels
containing
refrigerant.
The
plug
is
designed
to
melt
at
high
temperatures
(usually
about
165°F)
to
prevent
excessive
pressure
rtm nr tiu d u du uli
Gage:
Ai i drnmuid n us tr mua nr iu dar tn pru nru tr l ln s ludul i Stmutmu pullus uanuuni
Gas:
The
vapor
state
of
a
material.
Generator:
A a c ctmptiuid t aib a trptti-­‐ru r uuratti system.
Graii
y,
ipecific:
The
density
of
a
standard
material
usually
compared
to
that
of
water
or
air.
Grille:
A
perforated
or
louvered
covering
for
an
air
passage,
usually
installed
in
a suflallt cu l iut tr ettri
Halide
torch:
A luak du dur uuiurallb n iu alct tl ais nri iu fl d a lnu eamu; fl ui d u ampl iu dn u
draws
in
halocarbon
refrigerant
vaport d u ctltnr t d u eamu c aiuu dt r u d uruuii Ga u dui t b d u
burning
halocarbon
is
phosgene,
a
deadly
gas
used
in
World
War
I
in
Europe
against
Allied
troops
(can
be
deadly
ruad us i a clt us tr ctiiius area).
Halogen:
Ai ulumuid rtm d u altuui urtnp d ad cti d t c ltr iut entr iut rtm iut ais ts iui Tflt
halogens
may
be
present
in
c
ltrtentrtcar tiru ruuraid i
Heat:
Ba c trm t uiurub d ad mab u partallb ctidurdus idt td ur trm ais idt fl c all td ur trm mab
be
uitrulb ctidurdusi
Heat
of
fusion:
Latent
heat
involved
in
changing
between
the
solid
and
the
liquid
states.

20. Glossary of HVAC terms
Page 16
Heat,
sensible:
Huad d ad a tc adus fl d a c aiuu i dumpuradnru; puc ic uad uxc aiuu t dumpuradnrut
i
contrast
to
a
heat
interchange
in
which
a
change
of
state
(latent
heat)
occurs.
Hea
,
ipecific
T u ratt t d u lnaitty
of
heat
required
to
raise
the
temperature
of
a
given
mass
of
any
substance
1®
dt d u lnaitdb ruln rus dt ra u d u dumpuradnru t ai ulnal ma t a daisars n daicu
(usually
water
at
59®)
1®.
Heat
of
iapirizatiu:
Latent
heat
involved
in
the
change
between
liquid
and
vapor
states.
Heat
pump:
A ru r uuratiu b dum umpltbus dt drai ur uad idt a pacu tr n daicui T u ctisui
ur
prtd su d u uadt fl lu d u udaptradtr arraiuus dt p ck np uad rtm a rt fladurt ais t trd i Bb f iu d
u etfltf
the
refrigerant,
a
heat-­‐pump
system
may
also
be
used
to
cool
the
space.
Heatug
iyi
er:
Aib t d u udural uatiu mud ts n nallb durmus acctrs iu dt d u mud ts n us i d
uuiurattit nc a duam uatiut warm-­‐a r uatiut ais d u l kui
Heatug
iyi
em,
electric:
Huatiu prtsncus b d u r u t dumpuradnru can us b d u pa auu t ai ulucdr c
cnrruid d rtnu a ctisncdtr ad iu a u ru daicu dt d u cnrruid etfli Ru suicu ulucdr c-­‐
uatiu b dum
generally
consist
of
one
or
several
resistance
units
i dallus i a ramu tr ca iut d u suuruu t uatiu u iu
d urmt datcallb ctidrtllusi
Heatug
iyi
er,
i
ear:
A uatiu b dum i fl c uad drai urrus rtm a t lur tr td ur tnrcu dt d
u
uatiu ni d b duam adt a tdut tr ultfl admt p ur c
pressure.
Heatug
iyi
er,
iac
r:
A
two-­‐p pu duam uatiu b dum uln ppus fl d d u iucu arb accu trb apparadn
dt purmd tpuratiu d u b tem
below
atmospheric
pressure.
Heatug
iyi
er,
warr-­‐air:
A
warm-­‐a r uatiu plaid cti tiu t a uatiu ni d nul nrning
furnace)
enclosed
in
a
casing
from
which
the
heated
air
is
distributed
to
various
rooms
of
the
building
through
ducts.
Herretcaaay
ieaaed
ui
:
A ru r uuratiu ni d ctida i iu d u mtdtr ais ctmpressor
in
a
sealed
container.
High-­‐pressure
cut
out:
A
control
device
connected
into
the
high-­‐pru nru pard t a ru r uuratiu b dum dt
dtp
the
machine
when
the
pressure
becomes
excessive.

21. Glossary of HVAC terms
Page 17
High
side:
T ad pard t d u ru r uuratiu b dum ctida i iu d u u -­‐pressure
refrigerant.
Also
the
term
used
to
refer
to
d u ctisui iu ni d cti tiu t d u mtdtrt ctmpru trt ctisui urt ais rucu der
mounted
on
a
single
base.
High-­‐iide
flia
iaaie:
A etad daldu d ad etad i u -­‐pressure
liquid.
Opens
on
an
increase
in
liquid
level.
Hold
over:
In
an
evaporator,
the
abil db dt dab ctls afur uad rumtdal rtm d u udaptradtr stops.
Horsepower:
A
unit
of
power.
Work
done
at
the
rate
of
33,000
lb-­‐ftm it tr ..5 l -­‐ft i
H
ridifier:
A
device
to
add
moisture
to
the
air.
Humidify:
To
add
water
vapor
to
the
atmosphere;
to
add
water
vapor
or
moisture
to
any
material.
Humidistat:
A ctidrtl sud cu acdnadus b c aiuu i nm s db ais n us tr andtmatc ctidrtl t rulatdu
humidity.
Humidity,
absolute:
T u suii du amtnid t fladur ctida ius i a suii du lnaitdb t a r n nallb muasured
in
grains
of
water
per
pound
or
per
cubic
foot
of
air).
H
ridi
y,
reaatie:
T u ratt t d u fladur-­‐vapor
pressure
of
air
compared
to
the
vapor
pressure
it
would
have
if
saturated
at
its
dry-­‐
nl dumpuradnrui Vurb iuar dt d u ratt t d u amtnid t mtisture
contained
in
air
ctmparus dt fl ad d ctnls tls ad d u ux tiu dumperature.
H
ridi
y,
ipecific:
The
weight
of
vapor
associated
with
1
lb
of
dry
air;
also
termed
humidity
rati.
Hydrocarbons:
A
series
of
chemicals
of
similar
chemical
nature,
ranging
rtm mud aiu d u ma i cti tdnuid t
iadnral ua n d rtnu ndaiut tcdaiut ais t trd t dt uadb ln r catiu t l i All aru mtru tr lu eamma lui
Butane
and
isobutane
have
been
used
to
a
limited
extent
as
refrigerants.
Hydrolysis:
Ruactti t a madur al,
such
as
Freon-­‐12
or
methyl
chloride,
with
water.
Acid
materials
in
general
are
formed.
Hydrii
atc
preii
re:
The
pressure
due
to
liquid
in
a
container
that
contains
no
gas
space.
Hygrometer:
An
instrument
used
to
measure
moisture
in
the
air.
Hygroscope:
See
humidistat.

22. Glossary of HVAC terms
Page 18
Ice-­‐reatug
ee
iiaaeu
:
The
amount
of
heat
(144
Btu)
absorbed
by
1
lb
of
ice
at
32®F
in
liquefying
to
water
at
32®F.
Indirect
cooling
system:
See
brine
system.
Iufia
ratiu:
The
leakage
of
air
into
a
building
or
space.
Iui
aatiu:
A
material t ltfl uad ctisnctd dbi
Irritant
refrigerant:
Aib ru r uuraid d ad a ai rr datiu u ucd ti d e
eyes,
nose,
throat,
or
lungs.
Isobutane:
A
hydrocarbon
refrigerant
used
to
a
l
m dus uxduidi Id eamma lui
Kilowatt:
Unit
of
electrical
power
equal
to
1000
W,
or
1.34
hp,
approximately.
Lag
of
temperature
control:
T u sulab i actti t a dumpuradnru-­‐ru pti du ulumuid snu dt d u tmu
required
for
the
temperature
of
the
element
to
reach
the
surrounding
temperature.
Latent
heat:
T u lnaitdb t uad d ad may
be
added
to
a
substance
during
a
change
of
state
without
causing
a
temperature
change.
La
eu
sea
if
eiapiratiu:
T u lnaitdb t uad ruln rus c aiu iu 2 l t l ln s idt a vapor
with
no
change
in
temperature.
Reversible.
Leak
detector:
A
device
used
to
detect
refrigerant
luak i a ru r uuratiu b dumi
Liquid:
T u dadu t a madur al i fl c d dtp nr acu i a du ul fl ll uctmu tr itidali D tiun us rtm
solid
or
vapor
forms.
Liquid
line:
The
tube
or
pipe
that
carries
the
refrigerant
liquis rtm d uctisui urtrrucu durt aru r
uuratiu
system
to
a
pressure-­‐reducing
device.
Liquid
receiver:
That
part
of
the
condensing
unit
that
stores
the
liquid
refrigerant.

23. Glossary of HVAC terms
Page 19
Load:
The
required
rate
of
heat
removal.
Low-­‐pressure
control:
An
electric
switc
ais pru nru ru pti du ulumuid ctiiucdus idt d u nctti su t a
ru r uuratiu ni d dt ctidrtl d u tpuratti t d u b dumi
Low
side:
T ad pard t a ru r uuratiu b dumt fl c itrmallb tpuradu nisur ltfl pru nrut a tppt us dt d u
high
side.
Also
used
to
refer
to
the
evaporator.
Low-­‐iide
flia
:
A
valve
operated
by
the
low-­‐pressure
liquid,
which
opens
at
a
low
level
and
closes
at
a
high
level.
Main:
A p pu tr sncd tr s dr ntiu dt tr ctlluctiu ctis toned
air
from
various
branches.
Manometer:
A
U-­‐shaped
liquid-­‐illus dn u tr mua nr iu pru nru s uruicu i
Mecsauicaa
efficieucy:
T u ratt t fltrk stiu b a mac iu dt d u fltrk sone
on
it
or
energy
used
by
it.
Mechanical
equivalent
of
heat:
An
energy-­‐ctidur ti ratt t 7i27 l -­‐f =
1
Btu.
Methyl
chloride:
A
refrigerant
having
the
chemical
formula
CH3Cl.
Micriu
µu:
A
unit
of
length;
the
thousandth
part
of
1
mm
or
the
millionth
part
of
a
meter.
Mollier
chart:
A urap cal rupru uidatti t d urmal prtpurtu t en s t fl d dtdal uat
and
entropy
as
coordinates.
Motor:
A
device
for
transforming
electrical
energy
into
mechanical
energy.
Motor
capacitor:
A sud cu su uius dt mprtdu d u dartiu a l db t single-­‐p a u isnctti mtdtr i
Noncondensables:
Foreign
gases
mixed
with
a
refrigerant,
which
cannot
be
condensed
into
liquid
form
at
the
temperatures
and
pressures
at
which
the
refrigerant
condenses.

24. Glossary of HVAC terms
Page 21
Oil
trap:
A
device
to
separate
oil
from
the
high-­‐pressure
vapor
from
the
compressor.
Usually
contains
a
etad daldu dt rudnri d u t l to
the
compressor
crankcase.
Output:
Nud ru r uuratti prtsncus b d u b dumi
Ozone:
T u O trm t txbuuit tmutmu n us i a r ctis tti iu tr ctls-­‐storage
rooms
to
eliminate
odors,
can
be
toxic
in
concuidratti t 5i. ppm ais tduri
Packing:
T u dnffiiu artnis a af dt pruduid en s luakauu udfluui d u af ais pard artnis d u
afi
Packless
valve:
A
valve
that
does
not
use
packing
to
prevent
leaks
around
the
valve
stem.
Flexible
material
is
n nallb n us dt ual aua i d luak ais tll purm d dalve
movement.
Performance
factor:
T u ratt t d u uad mtdus b a ru r uuratiu b dum dt uad uln daluid t d u
uiuruy
n usi Var u fl d ctis tti i
Phosphorous
pentoxide:
Ai uffic uid sr ur madur al d ad uctmu unmmb ruactiu fl d mt dnru ais uicu
not
used
alone
as
a
drying
agent.
Pour
point,
oil:
The
temperature
below,
which
the
oil
surface
will
not
change
whui d u t l ctida iur tldusi
Power:
The
rate
of
doing
work
measured
in
horsepower,
flaa t k ltflaa t ais t trd i
Power
factor,
electrical
devices:
Turattt flaa dtdtld-­‐amperes
in
aialduriatiucnrruidcrcndi
Pressure:
The
force
exerted
per
unit
of
area.
Pressure
drop:
Lt i pru nrut a rtm tiu uis t a ru r uuraid l iu dt d u td urt snu dt r cttit datc uast
and
the
like.
Pressure
gage:
See
Gage.
Pressure-­‐relief
valve:
A
valve
or
rupture
member
designed
to
relieve
excu du pru nru andtmatcallbi

25. Glossary of HVAC terms
Page 20
Psychrometric
chart:
A c ard n us dt sudurm iu d u puc ic dtlnmut uad ctiduidt sufl pt idt rulatdu
humidity,
absolute
humidity,
and
wet-­‐
and
dry-­‐bulb
temperatures,
knowing
any
two
independent
items
of
those
muittiusi
Purging:
The
act
of
blowing
out
refrigerant
gas
from
a
refrigerant
containing
vessel
usually
for
the
purpose
of
removing
non-­‐condensables.
Pyrometer:
An
instrument
for
the
measurement
of
high
temperatures.
Radiatiu:
The
passage
of
heat
from
one
object
to
another
without
warming
the
space
between.
The
heat
pa us b fladu mttti m lar dt l u di
Refrigerant:
T u mus nm t uad drai ur i a ru r uuratiu b dum d ad p ck np uad by
evaporatiu ad a ltfl
temperature
and
gives
up
heat
by
condensing
at
a
higher
temperature.
Refrigeratug
iyi
er:
A ctm iatti t pard i fl c a ru r uuraid c rcnladus tr d u pnrpt u t uxdractiu
heat.
Reaatie
s
ridi
y:
T u ratt t d u fladur-­‐vapor
pressure
of
air
compared
to
the
vapor
pressure
it
would
have
if
saturated
at
its
dry-­‐bulb
temperadnrui Vurb iuarlb d u ratt t the
amount
of
moisture
contained
in
air
compared
to
what
it
could
hols ad d u ux tiu dumpuradnrui
Relief
valve:
A
valve
designed
to
open
at
excessively
high
pressures
to
allow
the
refrigerant
to
escape.
Resistance,
electrical:
T u tppt tti dt ulucdr c-­‐cnrruid etflt mua nrus i t m i
Resistance,
thermal:
The
reciprtcal t d urmal ctisnctd dbi
Room
cooler:
A
cooling
element
ftr a rttmi Ii a r ctis tti iut a sud cu tr ctis tti iu mall
volumes
of
air
for
comfort.
Rotary
compressor:
A ctmpru tr i fl c ctmpru ti aaa ius i a cbl isur b rtdatti t a um ras al
member.
R
uuiug
tre:
Unallb iscadu purcuidt tmua
refrigerant
compressor
operates.

26. Glossary of HVAC terms
Page 22
Saturated
vapor:
Vapor
not
superheated
but
of
100
percent
quality,
that
is,
containing
no
unvaporized
liquid.
Seaa,
isaf:
A muc ai cal b dum t pard tr pruduitiu ua luakauu udfluui a rtdatiu af ais a
dattiarb
crankcase.
Sealed
unit:
Suu urmutcallb ualus i di
Shell
and
tube:
Pertaining
to
heat
exchangers
in
which
a
coil
of
tubing
or
pipe
is
contained
in
a
shell
or
ctida iuri T u p pu prtd sus fl d tpui iu dt alltfl d u pa auu t a en s d rtnu dt fl lu the
shell
is
also
provided
with
an
inlud ais tndlud tr a en s etfli
Silica
gel:
A
drier
material
having
the
formula
SiO2.
Sludge:
A suctmpt tti prtsncd trmus i a ru r uuraid snu dt mpnr tu i d u t l tr snu dt mt dnrui Slnsges
may
be
gummy
or
hard.
Soda
lime:
A
material
used
for
removing
moisture.
Not
rectmmuisus tr ru r uuratti n ui
Solenoid
valve:
A daldu tpuius b a mauiutc u ucd t ai ulucdr c cnrruid d rtnu a tluit s ct li
Solid:
T u dadu t maaur i fl c a trcu cai u uxurdus i a stfliflars s ructti tilb fl ui itd ctiiius.
As
s tiun us rtm en s i
Solubility:
T u a l db t tiu madur al dt uidur idt tlntti fl d another.
Sia
tiu:
The
homogeneous
mixture
of
two
or
more
materials.
Specific
graii
y:
The
weight
of
a
volume
of
a
material
compared
to
the
weight
of
the
same
volume
of
water.
Specific
sea
:
T u lnaitdb t uad ruln rus dt ra u d u dumpuradnru t a suii du ma t a madur al dt a
suii du amtnid ctmparus dt d ad ruln rus dt ra u d u dumpuradnru t d u amu ma t water
the
same
amount.
May
be
expressed
as
Btu/
pound/
degrees
Fahrenheit.
Specific
iia
re:
T u dtlnmu t a suii du flu u d t a madur ali U nallb uxpru us i cn c uud pur ptund.
The
reciprocal
of
density.

27. Glossary of HVAC terms
Page 23
Spray
pond:
An
arrangement
for
lowering
the
temperature
of
water
by
evaporatdu cttl iu t d u fladur i
contact
with
outside
air.
The
water
to
be
cooled
is
sprayed
by
nozzles
into
the
space
above
a
body
of
previously
cooled
water
and
allowed
to
fall
by
gravity
into
it.
Steam:
Water
in
the
vapor
phase.
Steam
trap:
A
device
for
allowing
the
passage
of
condensate,
or
air
and
condensate,
and
pruduitiu d u
passage
of
steam.
Subcooled:
Cooled
below
the
condensing
temperature
correspois iu dt d u ux tiu pru nrui
S
bairatiu:
The
change
from
a
solid
to
a
vapor
state
without
an
intermediate
liquid
state.
S
ctiu
aiue:
The
tube
or
pipe
that
carries
refrigerant
vapor
from
the
evaporator
to
the
compressor
inlet.
S
ctiu
preii
re:
Pressure
on
the
nctti su t d u ctmpru tri
Superheater:
A
heat
exchanger
used
ti ettsus udaptradtr t fl uru i td l ln s ti d flab dt uidur d u
evaporator
is
cooled
by
supplying
heat
to
dry
and
superheat
the
wet
vapor
leaving
the
evaporator.
Sweatug:
Ctisui atti t mt dnru rtm d u a r ti nr acu ultfl d u sufl-­‐point
temperature.
System:
A uatiu tr ru r uuratiu c umu tr mac iut n nallb ctiiius dt d t u pard i ctidacd fl d d u
uatiu tr ru r uuratiu mus nmi
Temperature:
Heat
level
or
pressure.
The
thermal
state
of
a
body
with
respect
to
its
ability
to
pick
up
heat
from
or
pass
heat
to
another
body.
Therraa
ciud
ctii
y:
The
ability
of
a
material
to
conduct
heat
from
one
point
to
another.
Indicated
in
terms
of
Btu/per
hour
per
square
foot
per
inches
of
thickness
per
degrees
Fahrenheit.

28. Glossary of HVAC terms
Page 24
Thermocouple:
A sud cu cti tiu t dflt ulucdr cal ctisncdtr ad iu dflt onictti —one
at
a
point
whose
temperature
is
to
be
measured,
and
the
other
at
a
known
temperature.
The
temperature
between
the
two
onictti sudurm ius b d u madur al c aracdur tc ais d u ulucdr cal ptduital etup.
Thermodynamics:
The
science
of
the
mechanics
of
heat.
Thermometer:
Asudcu tr iscatiudumpuradnrui
Thermostat:
A
temperature-­‐actuated
switch.
Tiu
if
refrigeratiu:
Ru r uuratti uln daluid dt d u multiu t 2 dti t cu pur 3 i 77t555 Bdntsab,
12,000
Btu/h,
or
200
Btu/min.
Total
heat:
T u dtdal uad assus dt a ru r uuraid a tdu ai ar drarb dartiu pt id dt r iu d dt a u dui ud t
ctis tti n nallb uxpru us i Bdntptnisni Ftr i daicut i a npur-­‐heated
gas,
the
combined
heat
added
to
t
u l ln s iucu arb dt ra u d dumpuradnru rtm ai ar drarb dartiu pt id dt d u uvaporatti dumpuradnru
dt ctmpludu udaptrattit ais dt ra u d u dumpuradnru dt d u iial dumpuradnru fl uru d u ua npur
uadusi
Total
pressure:
Ii en s etflt d u nm t datc pru nru ais dultc db pru nrui
T
rb
aeu
fliw:
Fln s etfl i fl c d u en s mtdu drai dur ulb a flull a i d u s ructti t d u dn u tr p pu
ax t a tppt us dt druaml iu tr d ctn etfli
Unit
heater:
A
direct-­‐
uatiut acdtrb-­‐made,
encased
a um lb iclns iua uatiuulumuidt aitmotor,
ais s ructtial tndludi
Unit
system:
A b dum d ad cai u rumtdus rtm d u n ur’ prum u fl d tnd s ctiiuctiu ru r uuraid-­‐
ctida i iu pard t fladur ctiiucttit tr ixus ulucdr cal ctiiuctti i
Unloader:
A
device
in
a
compressor
for
equalizing
high-­‐and
low-­‐side
pressures
when
the
compressor
stops
and
tr a r u pur ts afur d dard t a dt sucrua u d u dartiu ltas ti d u mtdtri
Vacuum:
A
pressure
below
atmospheric,
usually
measured
in
inches
of
mercury
below
atmospheric
pressure.

29. Glossary of HVAC terms
Page 25
Valve:
Ii ru r uurattit a sud cu tr ruunlatti t a l ln st a rt tr ua i
Vapor:
A ua t partcnlarlb tiu iuar dt uln l r nm fl d d u l ln s p a u t d u n daicut fl c stu itd tlltfl
the
gas
laws.
Frequently
used
instead
t ua tr a ru r uuraid aist i uuiuralt tr aib ua ultfl d u cr tcal
temperature.
Viscosity:
T u prtpurdb t a en s dt ru d etfl tr c aiuu t apui
Water
cooler:
daptradtr tr cttl iu fladur i ai is rucd ru r uuratiu b dumi
Wax:
A
material
that
may
separate
when
oil/refrigerant
mixtures
are
cooled.
Wax
may
plug
the
expansion
valve
and
reduce
heat
transfer
of
the
coil.
Wet-­‐bulb
depression:
D uruid udfluui srb-­‐
and
wet-­‐bulb
temperatures.
Wet
compression:
A b dum t ru r uurattit i fl c tmu liquid
refrigerant
is
mixed
with
vapor
entering
the
compressor
so
as
to
cause
discharge
vapors
from
the
compressor
to
tend
to
be
saturated
rather
than
superheated.
Xylene:
A eamma lu tlduidt m lar dt kurt uiut n us tr s tld iu tr ltt ui iu lnsuu t and
for
cleaning
compressors
and
lines.
Zero,
absolute,
of
pressure:
T u pru nru ux tiu i a du ul d ad uitrulb umpdbi T u ltflu d pt lu
pressure.
Perfect
vacuum.
Zero,
absolute,
of
temperature:
The
temperature
at
which
a
body
has
no
heat
in
it
(–459.6®F
or
–273.1®C).
Ziue,
cirfir
aierageu:
T u raiuu t u uctdu dumpuradnru snr iu fl c d u maotr db t asnld uul
comfortable.

30. Glossary of HVAC terms
Page 26
References:
Miller,
R
&
Miller,
M.R.
(2006)
Air
Cinditininn
RerinRratin.
London:
McGraw-­‐Hill.
Althouse,
A.
&
Turnquist,
C.H.
(2004)
MidRrn
RerinRratin
and
Ari
Cinditininnn
Illinois:
The
Goodhear-­‐Willcox
Company.
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