MCC HVAC Electrical Midterm Exam Questions and
Answers All Correct
/. List at least five factors that must be controlled if a comfortable indoor environment is
to be maintained. - Answer-The factors that must be controlled include temperature,
humidity, air motion, dust, bacteria, odors, toxic gases, and ionization.
((Ref: 1/1))
/.Describe in simple terms the basic process by which a refrigerant transfers heat
energy. - Answer-A refrigerant is used to transfer heat when it changes states. When
liquid refrigerant evaporates into a vapor, heat is absorbed by the vapor. When
refrigerant vapor is condensed into a liquid, heat is rejected from the refrigerant.
((Ref: 2/3))
/.In your own words, state the first law of thermodynamics. - Answer-Energy can neither
be created nor destroyed, but can be changed from one form into another.
((Ref: 3/2))
/.Define work. - Answer-A force moving an object in the direction of the force.
((Ref: 3/3))
/.One horsepower (1 hp) of mechanical energy is equivalent to ______watts of electrical
energy, and one watt (1 W) of electrical energy is equivalent to ________ Btu of heat
energy. - Answer-746 Watts, 3.413 Btu
((Ref: 3/4, 5))
/.In your own words, state the second law of thermodynamics. - Answer-A temperature
difference must exist between two materials in order for heat energy to travel.
((Ref: 3/7))
/.Heat always travels from a(n) _____ material to a(n) ______ material. - Answer-
Higher-temperature, lower-temperature.
((Ref: 37-4/1))
/.Temperature is a measurement of heat _____. British thermal units and calories are
measurements of heat _____. - Answer-Intensity, quantity
,((Ref: 5/1))
/.What is the difference between latent heat and sensible heat? - Answer-Latent heat
causes a change in the state of a substance without a change in its temperature.
Sensible heat causes a change in the temperature of substance without a change in its
state.
((Ref: 6/1))
/.The latent heat of _____ causes a change in phase from vapor to liquid. The latent
heat of _____ causes a change in phase from liquid to vapor. - Answer-Condensation,
vaporization.
((Ref: 6/1))
/.What is specific heat? - Answer-Specific heat is the energy required to raise the
temperature of 1 lb of a substance by 1 degree F.
((Ref: 6/3))
/.What is superheat? - Answer-Superheat is energy that raises the temperature of a
vapor above its saturation temperature.
((Ref: 6/4))
/.Convert 68 degrees F to an equivalent Celsius temperature. - Answer-68 degrees
minus 32, divided by 1.8 = 20 degrees Celsius
((Ref: 7/2))
/.Convert 25 degrees Celsius to an equivalent Fahrenheit temperature. - Answer-25
times 1.8, plus 32
((Ref: 7/2))
/.Absolute zero on the Fahrenheit scale is _____ ^0F - Answer--460 degrees F
((Ref: 7/2))
/.Define pressure - Answer-Force per unit of area.
((Ref: 8/2))
/.One atmosphere of pressure (atmospheric pressure at sea level) is equivalent to
_____ psia. - Answer-14.696 psia
, ((Ref: 8/2))
/.Which pressure scale has the greater resolution, one calibrated in inches of mercury or
one calibrated in inches of water column? - Answer-Inches of water column.
((Ref: 8/4-9/2))
/.What is saturated vapor pressure? - Answer-The pressure exerted by a saturated
vapor above its own liquid or solid (the pressure at which vapor and its liquid, or vapor
and its solid, can exist in equilibrium at a given temperature).
((Ref: 10/5))
/.What is the mathematical relationship between specific volume and density? - Answer-
They are reciprocals of each other.
((Ref: 11/3))
/.The indoor coil of a heat pump system serves as the _____ during the cooling season,
and as the _____ during the heating season. - Answer-Evaporator, condenser.
((Ref: 16/6))
/.In which component of a refrigeration system is heat removed? - Answer-The
Condenser.
((Ref: 17/3))
/.State at least three of the five laws of heat transfer. - Answer-Law 1: Heat exists in the
air at all
temperatures.
Law 2: Heat flows from a region of higher
temperature to a region of lower
temperature, regardless of how slight the
temperature difference might be.
Law 3: All gases become warmer when they
are compressed.
Law 4: Most matter can exist as a solid,
liquid, or gas.
Law 5: The temperature at which a material
changes from a liquid to a gas, or from a gas
to a liquid, depends on the pressure to which
it is subjected.
((Ref: 32/2))
Answers All Correct
/. List at least five factors that must be controlled if a comfortable indoor environment is
to be maintained. - Answer-The factors that must be controlled include temperature,
humidity, air motion, dust, bacteria, odors, toxic gases, and ionization.
((Ref: 1/1))
/.Describe in simple terms the basic process by which a refrigerant transfers heat
energy. - Answer-A refrigerant is used to transfer heat when it changes states. When
liquid refrigerant evaporates into a vapor, heat is absorbed by the vapor. When
refrigerant vapor is condensed into a liquid, heat is rejected from the refrigerant.
((Ref: 2/3))
/.In your own words, state the first law of thermodynamics. - Answer-Energy can neither
be created nor destroyed, but can be changed from one form into another.
((Ref: 3/2))
/.Define work. - Answer-A force moving an object in the direction of the force.
((Ref: 3/3))
/.One horsepower (1 hp) of mechanical energy is equivalent to ______watts of electrical
energy, and one watt (1 W) of electrical energy is equivalent to ________ Btu of heat
energy. - Answer-746 Watts, 3.413 Btu
((Ref: 3/4, 5))
/.In your own words, state the second law of thermodynamics. - Answer-A temperature
difference must exist between two materials in order for heat energy to travel.
((Ref: 3/7))
/.Heat always travels from a(n) _____ material to a(n) ______ material. - Answer-
Higher-temperature, lower-temperature.
((Ref: 37-4/1))
/.Temperature is a measurement of heat _____. British thermal units and calories are
measurements of heat _____. - Answer-Intensity, quantity
,((Ref: 5/1))
/.What is the difference between latent heat and sensible heat? - Answer-Latent heat
causes a change in the state of a substance without a change in its temperature.
Sensible heat causes a change in the temperature of substance without a change in its
state.
((Ref: 6/1))
/.The latent heat of _____ causes a change in phase from vapor to liquid. The latent
heat of _____ causes a change in phase from liquid to vapor. - Answer-Condensation,
vaporization.
((Ref: 6/1))
/.What is specific heat? - Answer-Specific heat is the energy required to raise the
temperature of 1 lb of a substance by 1 degree F.
((Ref: 6/3))
/.What is superheat? - Answer-Superheat is energy that raises the temperature of a
vapor above its saturation temperature.
((Ref: 6/4))
/.Convert 68 degrees F to an equivalent Celsius temperature. - Answer-68 degrees
minus 32, divided by 1.8 = 20 degrees Celsius
((Ref: 7/2))
/.Convert 25 degrees Celsius to an equivalent Fahrenheit temperature. - Answer-25
times 1.8, plus 32
((Ref: 7/2))
/.Absolute zero on the Fahrenheit scale is _____ ^0F - Answer--460 degrees F
((Ref: 7/2))
/.Define pressure - Answer-Force per unit of area.
((Ref: 8/2))
/.One atmosphere of pressure (atmospheric pressure at sea level) is equivalent to
_____ psia. - Answer-14.696 psia
, ((Ref: 8/2))
/.Which pressure scale has the greater resolution, one calibrated in inches of mercury or
one calibrated in inches of water column? - Answer-Inches of water column.
((Ref: 8/4-9/2))
/.What is saturated vapor pressure? - Answer-The pressure exerted by a saturated
vapor above its own liquid or solid (the pressure at which vapor and its liquid, or vapor
and its solid, can exist in equilibrium at a given temperature).
((Ref: 10/5))
/.What is the mathematical relationship between specific volume and density? - Answer-
They are reciprocals of each other.
((Ref: 11/3))
/.The indoor coil of a heat pump system serves as the _____ during the cooling season,
and as the _____ during the heating season. - Answer-Evaporator, condenser.
((Ref: 16/6))
/.In which component of a refrigeration system is heat removed? - Answer-The
Condenser.
((Ref: 17/3))
/.State at least three of the five laws of heat transfer. - Answer-Law 1: Heat exists in the
air at all
temperatures.
Law 2: Heat flows from a region of higher
temperature to a region of lower
temperature, regardless of how slight the
temperature difference might be.
Law 3: All gases become warmer when they
are compressed.
Law 4: Most matter can exist as a solid,
liquid, or gas.
Law 5: The temperature at which a material
changes from a liquid to a gas, or from a gas
to a liquid, depends on the pressure to which
it is subjected.
((Ref: 32/2))
