Hvac Terms Flashcards
Hvac term knowledge
Heat that causes a change in
temperature but not a change of state.
sensible heat
Heat energy that causes a change of
state, but no temperature change
latent heat
: The amount of heat
removed that changes a gas (or vapor) into a
liquid but does not change the substance’s
temperature
Latent heat of condensation
The amount of heat
added to change a solid to a liquid but does
not change the substance’s temperature.
Iatent heat of melting
The amount of heat
added to change a substance directly from a
solid to a vapor (without passing lthrough the
liquid phase) but does not change the substance’s
temperature.
latent heat of sublimation
: The amount of heat
removed that changes a liquid to a solid but
does not change the substance’s temperature.
latent heat of freezing
Also called latent heat of fusion.
The amount of heat
added to change a liquid to a vapor but does
not change the substance’s temperature.
latent heat of vaporization
Also
called latent heat of evaporation
: A term used to describe a gas with a
temperature above its saturation point. (11, 13)
superheat
: A condition that takes place when a
liquid has a temperature below the saturation
point.
subcooling
: A device that “squeezes” low
temperature, low-pressure refrigerant vapor
into a small volume, which will result in a
high-temperature, high-pressure gas. Considered
the “heart” of a refrigeration system.
compressor
: A heat exchanger designed to remove
heat from the superheated refrigerant vapor
causing the vapor to condense (change state)
back to a liquid, and then subcool.
condenser
In a refrigeration or air conditioning
system, the heat exchanging device located
inside the area where heat is to be removed.
Low-pressure liquid refrigerant here absorbs
heat to evaporate and often increase
temperature (superheat), (11)
evaporator
A device that
meters the flow of liquid refrigerant into the
evaporator. It divides the high side from the
low side. (11, 17)
refrigerant metering device
The amount of moisture in
the air compared to the amount of moisture
the air would hold if the air was saturated
(filled to its capacity of moisture). The ratio
of actual water vapor content to the maximum
possible water vapor content is expressed as
a percentage. (28)
relative humidity
: A compressor that uses a
rotor that interacts with rotating or stationary
blades to compress gas. These are classified as
either rotating vane or stationary blade. (20)
rotary compressor
: A type of compressor that
involves the orbiting of one scroll (spiral) that
is intertwined with another scroll to form a
series of crescent-shaped pockets that reduce
in size and increase in pressure. During
compression, one scroll remains stationary
while the other scroll orbits around the space
between it and the fixed scroll. (20)
scroll compressor
A compressor that
uses an electric motor to turn a crankshaft that
operates reciprocating pistons within cylinders
to draw in and compress refrigerant. These
operate much like an automobile engine
Reciprocating compressors are one of the
most widely used types of compressors in
HVACR. (20)
reciprocating compressor
The process of removing unwanted
heat and carrying it away to be discarded
refrigeration
: Energy cannot be
created or destroyed, but energy can be converted
from one form to another. This law applies to
heat and other forms of energy, such as electrical,
mechanical, light, chemical, and atomi
First Law of Thermodynamics
: Heat always
travels from hot to cold
Second Law of Thermodynamics
: Pounds per square inch absolute, used for
pressure measurements. Readings expressed in
___ are 147 psi higher than readings expressed
in psig (pounds per square inch gauge). See
absoiute pressure. (10)
psia
: Pressure expressed in pounds per square
inch gauge. See gauge pressure. (10)
psig
A gas law that explains the
relationship between pressure and volume. It
states: “The pressure of a gas varies inverscly
opposite) as the volume, provided the temper-
ature remains constant.” (10)
Boyle’s Law
: The basic unit used to
measure quantity of heat. One Btu is the amount
of heat required to raise the temperature of
one pound of water one degree Fahrenheit. (9)
British thermal unit (Btu)
A gas law that explains the
relationship between pressure and volume.
It states: “At a constant pressure, the volume
of a confined gas varies directly as the absolute
temperature. At a constant volume, the absolute
pressure varies directly as the absolute
temperature.” (10)
Charles’s Law
A gas law of partial pressures. It
states, “In a mixture of gases, each gas behaves
as if it occupies that space alone.” To obtain
the total pressure of a confined mixture of
gases, the pressure for each gas in a mixture
must be added together. (10)
Dalton’s Law:
: A mixture of two pure refrigerants
that behaves as a single component refrigerant
with a single boiling point at a particular
pressure and temperature. ________ doe not
separate in either the gaseous or liquid state.h
azcotrope or azcotropic
: A refrigerant blend formed by
combining two or more single-component
refrigerants. ________ do not have a specific
pressure for each degree of temperature change
and thus exhibit temperature glide. _______
are designed to replace ozone-depleting CFC
and HCFC refrigerants.
zeotrope
Also called zeotropic
refrigerant or zeotropic blend. (14
: A gas that has been heated to
a temperature that is above its boiling point. (9)
superheated vapor
: A gas that has been heated to
a temperature that is above its boiling point.
superheated vapor
