HVAC/R STUDY GUIDE QUESTIONS
cold - Answers- The absence of heat
sensible heat - Answers- The heat that can be measured with a thermometer. Heat
energy that changes the temperature of a substance without changing its state.
latent heat of fusion - Answers- The heat required to change a solid to a liquid or vice
versa at the same temperature, expressed in Btu per pound
latent heat of vaporization - Answers- The heat required to change a saturated liquid to
a saturated vapor or vice versa, expressed in Btu per pound.
latent heat - Answers- The amount of heat required to change the state of a substance-
e.g., changing water to ice requires the removal of 144 Btu per pound of water at sea
level. Sometimes referred to as 'hidden' heat.
enthalpy - Answers- Heat content, usually based on -40°F, expressed in Btu per pound.
entropy - Answers- The amount of energy that is unavailable for work during a natural
process- i.e., energy not practically usable for a given application. A change in entropy
is the summation of the changes in enthalpy/absolute temperature for a given process
sublimation - Answers- The process of a solid changing directly to a vapor without
passing through a liquid state- for example, dry ice.
superheat - Answers- That portion of the heat in a gas that raises its temperature above
the saturation temperature corresponding to its pressure.
British thermal unit (Btu) - Answers- The amount of heat require to change the
temperature of one pound of water one degree Fahrenheit at sea level.
calorie - Answers- The amount of heat required to change the temperature of one gram
of water one degree Celsius.
Celsius - Answers- Formerly Centigrade, a thermometric scale in which 0° is the
freezing point and 100° is the boiling point of water at sea level.
compression ratio - Answers- A number found by dividing head pressure by suction
pressure, both expressed in psia (add 14.7 to the gauge pressure of each).
compressor - Answers- A device that provides the pressure increase in a refrigeration
or air conditioning system.
, clearance volume - Answers- That portion of a cylinder between the top of the piston
and valve plate at the end of the compression stroke.
closed loop - Answers- An automatic control system that incorporate a feedback signal
to correct any errors between the actual value and the desired value.
pressure, absolute (psia) - Answers- The pressure referred to that above absolute zero.
It is the sum of the gauge pressure and the atmospheric pressure.
pressure, gauge (psig) - Answers- Pressure above atmospheric pressure, measured
with atmospheric pressure as a base.
heat - Answers- A form of energy that acts on a substance to cause a rise in its
temperature.
heat, latent - Answers- The change of enthalpy during a change of state. With pure
substances, latent heat is absorbed or rejected at constant pressure.
heat, sensible - Answers- The heat associated with a change in temperature- in
contrast to a heat interchange in which a change of state (latent heat) occurs.
heat, specific - Answers- The ratio of the quantity of heat required to raise the
temperature of a given mass of any substance one degree TO the quantity required to
raise the temperature of an equal mass of a standard substance one degree.
glide - Answers- The difference in temperature between the dew point and the bubble
point for a zeotrope or nearazeotrope refrigerant.
gauge pressure (psig) - Answers- 1) The pressure read on a gauge that has been
adjusted to read zero under atmospheric pressure at sea level. 2) The amount of
pressure above atmospheric pressure.
Charles' Law for a constant volume process - Answers- If the volume remains the
same, the absolute pressure of a gas varies as the absolute temperature varies.
absolute zero - Answers- The point at which molecular motion stops and no more heat
is available (-460°F or 0°R (Rankine)) or (-273°C or 0°K (Kelvin)).
psi at sea level - Answers- 14.696 pounds per square inch = 29.92 in. Hg
pounds per square inch (psi) - Answers- A unit of measurement for pressure. Often
used to express atmospheric pressure, or the pressure exerted by a liquid or a confined
gas on a given area.
inch of mercury - Answers- A unit of pressure equal to the pressure exerted by a
column of mercury one inch high at a temperature of 32°F
cold - Answers- The absence of heat
sensible heat - Answers- The heat that can be measured with a thermometer. Heat
energy that changes the temperature of a substance without changing its state.
latent heat of fusion - Answers- The heat required to change a solid to a liquid or vice
versa at the same temperature, expressed in Btu per pound
latent heat of vaporization - Answers- The heat required to change a saturated liquid to
a saturated vapor or vice versa, expressed in Btu per pound.
latent heat - Answers- The amount of heat required to change the state of a substance-
e.g., changing water to ice requires the removal of 144 Btu per pound of water at sea
level. Sometimes referred to as 'hidden' heat.
enthalpy - Answers- Heat content, usually based on -40°F, expressed in Btu per pound.
entropy - Answers- The amount of energy that is unavailable for work during a natural
process- i.e., energy not practically usable for a given application. A change in entropy
is the summation of the changes in enthalpy/absolute temperature for a given process
sublimation - Answers- The process of a solid changing directly to a vapor without
passing through a liquid state- for example, dry ice.
superheat - Answers- That portion of the heat in a gas that raises its temperature above
the saturation temperature corresponding to its pressure.
British thermal unit (Btu) - Answers- The amount of heat require to change the
temperature of one pound of water one degree Fahrenheit at sea level.
calorie - Answers- The amount of heat required to change the temperature of one gram
of water one degree Celsius.
Celsius - Answers- Formerly Centigrade, a thermometric scale in which 0° is the
freezing point and 100° is the boiling point of water at sea level.
compression ratio - Answers- A number found by dividing head pressure by suction
pressure, both expressed in psia (add 14.7 to the gauge pressure of each).
compressor - Answers- A device that provides the pressure increase in a refrigeration
or air conditioning system.
, clearance volume - Answers- That portion of a cylinder between the top of the piston
and valve plate at the end of the compression stroke.
closed loop - Answers- An automatic control system that incorporate a feedback signal
to correct any errors between the actual value and the desired value.
pressure, absolute (psia) - Answers- The pressure referred to that above absolute zero.
It is the sum of the gauge pressure and the atmospheric pressure.
pressure, gauge (psig) - Answers- Pressure above atmospheric pressure, measured
with atmospheric pressure as a base.
heat - Answers- A form of energy that acts on a substance to cause a rise in its
temperature.
heat, latent - Answers- The change of enthalpy during a change of state. With pure
substances, latent heat is absorbed or rejected at constant pressure.
heat, sensible - Answers- The heat associated with a change in temperature- in
contrast to a heat interchange in which a change of state (latent heat) occurs.
heat, specific - Answers- The ratio of the quantity of heat required to raise the
temperature of a given mass of any substance one degree TO the quantity required to
raise the temperature of an equal mass of a standard substance one degree.
glide - Answers- The difference in temperature between the dew point and the bubble
point for a zeotrope or nearazeotrope refrigerant.
gauge pressure (psig) - Answers- 1) The pressure read on a gauge that has been
adjusted to read zero under atmospheric pressure at sea level. 2) The amount of
pressure above atmospheric pressure.
Charles' Law for a constant volume process - Answers- If the volume remains the
same, the absolute pressure of a gas varies as the absolute temperature varies.
absolute zero - Answers- The point at which molecular motion stops and no more heat
is available (-460°F or 0°R (Rankine)) or (-273°C or 0°K (Kelvin)).
psi at sea level - Answers- 14.696 pounds per square inch = 29.92 in. Hg
pounds per square inch (psi) - Answers- A unit of measurement for pressure. Often
used to express atmospheric pressure, or the pressure exerted by a liquid or a confined
gas on a given area.
inch of mercury - Answers- A unit of pressure equal to the pressure exerted by a
column of mercury one inch high at a temperature of 32°F
