HVAC/R Q&A
cold - (correct answer)The absence of heat
sensible heat - (correct answer)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 - (correct answer)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 - (correct answer)The heat required to change a saturated
liquid to a saturated vapor or vice versa, expressed in Btu per pound.
latent heat - (correct answer)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 - (correct answer)Heat content, usually based on -40°F, expressed in Btu per
pound.
entropy - (correct answer)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 - (correct answer)The process of a solid changing directly to a vapor without
passing through a liquid state- for example, dry ice.
superheat - (correct answer)That portion of the heat in a gas that raises its temperature
above the saturation temperature corresponding to its pressure.
, British thermal unit (Btu) - (correct answer)The amount of heat require to change the
temperature of one pound of water one degree Fahrenheit at sea level.
calorie - (correct answer)The amount of heat required to change the temperature of one
gram of water one degree Celsius.
Celsius - (correct answer)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 - (correct answer)A number found by dividing head pressure by
suction pressure, both expressed in psia (add 14.7 to the gauge pressure of each).
compressor - (correct answer)A device that provides the pressure increase in a
refrigeration or air conditioning system.
clearance volume - (correct answer)That portion of a cylinder between the top of the
piston and valve plate at the end of the compression stroke.
closed loop - (correct answer)An automatic control system that incorporate a feedback
signal to correct any errors between the actual value and the desired value.
pressure, absolute (psia) - (correct answer)The pressure referred to that above absolute
zero. It is the sum of the gauge pressure and the atmospheric pressure.
pressure, gauge (psig) - (correct answer)Pressure above atmospheric pressure,
measured with atmospheric pressure as a base.
heat - (correct answer)A form of energy that acts on a substance to cause a rise in its
temperature.
cold - (correct answer)The absence of heat
sensible heat - (correct answer)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 - (correct answer)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 - (correct answer)The heat required to change a saturated
liquid to a saturated vapor or vice versa, expressed in Btu per pound.
latent heat - (correct answer)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 - (correct answer)Heat content, usually based on -40°F, expressed in Btu per
pound.
entropy - (correct answer)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 - (correct answer)The process of a solid changing directly to a vapor without
passing through a liquid state- for example, dry ice.
superheat - (correct answer)That portion of the heat in a gas that raises its temperature
above the saturation temperature corresponding to its pressure.
, British thermal unit (Btu) - (correct answer)The amount of heat require to change the
temperature of one pound of water one degree Fahrenheit at sea level.
calorie - (correct answer)The amount of heat required to change the temperature of one
gram of water one degree Celsius.
Celsius - (correct answer)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 - (correct answer)A number found by dividing head pressure by
suction pressure, both expressed in psia (add 14.7 to the gauge pressure of each).
compressor - (correct answer)A device that provides the pressure increase in a
refrigeration or air conditioning system.
clearance volume - (correct answer)That portion of a cylinder between the top of the
piston and valve plate at the end of the compression stroke.
closed loop - (correct answer)An automatic control system that incorporate a feedback
signal to correct any errors between the actual value and the desired value.
pressure, absolute (psia) - (correct answer)The pressure referred to that above absolute
zero. It is the sum of the gauge pressure and the atmospheric pressure.
pressure, gauge (psig) - (correct answer)Pressure above atmospheric pressure,
measured with atmospheric pressure as a base.
heat - (correct answer)A form of energy that acts on a substance to cause a rise in its
temperature.
