Hvac Terms

Question 1

Heat that causes a change in

temperature but not a change of state.

Answer 1

sensible heat

Question 2

Heat energy that causes a change of

state, but no temperature change

Answer 2

latent heat

Question 3

: The amount of heat
removed that changes a gas (or vapor) into a
liquid but does not change the substance’s
temperature

Answer 3

Latent heat of condensation

Question 4

The amount of heat
added to change a solid to a liquid but does
not change the substance’s temperature.

Answer 4

Iatent heat of melting

Question 5

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.

Answer 5

latent heat of sublimation

Question 6

: The amount of heat
removed that changes a liquid to a solid but
does not change the substance’s temperature.

Answer 6

latent heat of freezing

Also called latent heat of fusion.

Question 7

The amount of heat
added to change a liquid to a vapor but does
not change the substance’s temperature.

Answer 7

latent heat of vaporization

Also
called latent heat of evaporation

Question 8

: A term used to describe a gas with a

temperature above its saturation point. (11, 13)

Answer 8

superheat

Question 9

: A condition that takes place when a
liquid has a temperature below the saturation
point.

Answer 9

subcooling

Question 10

: 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.

Answer 10

compressor

Question 11

: 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.

Answer 11

condenser

Question 12

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)

Answer 12

evaporator

Question 13

A device that
meters the flow of liquid refrigerant into the
evaporator. It divides the high side from the
low side. (11, 17)

Answer 13

refrigerant metering device

Question 14

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)

Answer 14

relative humidity

Question 15

: 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)

Answer 15

rotary compressor

Question 16

: 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)

Answer 16

scroll compressor

Question 17

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)

Answer 17

reciprocating compressor

Question 18

The process of removing unwanted

heat and carrying it away to be discarded

Answer 18

refrigeration

Question 19

: 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

Answer 19

First Law of Thermodynamics

Question 20

: Heat always

travels from hot to cold

Answer 20

Second Law of Thermodynamics

Question 21

: 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)

Answer 21

psia

Question 22

: Pressure expressed in pounds per square

inch gauge. See gauge pressure. (10)

Answer 22

psig

Question 23

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)

Answer 23

Boyle’s Law

Question 24

: 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)

Answer 24

British thermal unit (Btu)

Question 25

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)

Answer 25

Charles’s Law

Question 26

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)

Answer 26

Dalton’s Law:

Question 27

: 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

Answer 27

azcotrope or azcotropic

Question 28

: 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.

Answer 28

zeotrope

Also called zeotropic
refrigerant or zeotropic blend. (14

Question 29

: A gas that has been heated to

a temperature that is above its boiling point. (9)

Answer 29

superheated vapor

Question 30

: A gas that has been heated to

a temperature that is above its boiling point.

Answer 30

superheated vapor