NATE Air Conditioning and Heat Pump
Which of the following factors affects a customers level of comfort? -
ANSWER All of the above
A cooling load calculation estimates the sensible heat gain of the structure. The
cooling-only system should be within _____% of this calculated value. -
ANSWER +15%
The maximum sensible cooling capacity of a heat pump should be within ______%
of the calculated sensible heat gain of a structure with a large heating load. -
ANSWER +25%
The combined output of a heatpump and its auxiliary heat should not exceed the
calculated heat loss of a home by more than ____%. - ANSWER
15%
What amount of auxiliary electronic heat is needed when the output of a heat pump
on a design day equals 18,800 Btuh and the heat loss of a home is 29,700 Btuh? -
ANSWER 3.2 kWh
The three processes that transfer heat energy are conduction, convection, and
_________. - ANSWER Radiation
,Heat transfer that occurs when substances of different temperatures are in contact
with each other is called _______. - ANSWER conduction
What effect does raising the pressure in a sealed system have on refrigerant? -
ANSWER The boiling point increases
What is the primary danger to people near an accidental refrigerant release or spill?
- ANSWER suffocation caused by the heavier refrigerant displacing
oxygen in the air
The maximum temperature at which refrigerant may be stored is ______ F when
the container is no more than ____% full of liquid by volume.; - ANSWER
125 F, 80%
Boiling of the refrigerant occurs in which system component? - ANSWER
Evaporator
Why is superheat necessary in a system that utilizes hermetic compressors -
ANSWER It ensures that dry vapor reaches the compressor so that
mechanical damage does not occur
When the heat load on an evaporator increases, what is the effect on the system? -
ANSWER Suction pressure and discharge pressure both increase
What type of energy is transferred when work is done in the condenser? -
ANSWER Both latent and sensible heat energy
, What is the primary function performed by a thermal expansion valve? -
ANSWER It maintains the correct superheat in the suction vapor leaving
the evaporator
Which component pumps refrigerant through the system and raises the vapor
temperature? - ANSWER compressor
How are hermetic compressor motors cooled? - ANSWER With
suction vapor drawn from the evaporator
Heat pump compressors sometimes run hotter than compressors used in cooling-
only units because heat pump compressors _____. - ANSWER
exhibit low refrigerant density at low suction pressures during the heating cycle
When is crankcase heat most needed? - ANSWER When the
compressor is off
Work done on the refrigerant in the condenser is transferred as ____. -
ANSWER Both sensible and latent heat
Why are more circuits needed in the outdoor coils used in heat pumps than in the
condenser coils used in cooling-only units? - ANSWER To keep the
pressure drop across the outdoor coil low
Which of the following factors affects a customers level of comfort? -
ANSWER All of the above
A cooling load calculation estimates the sensible heat gain of the structure. The
cooling-only system should be within _____% of this calculated value. -
ANSWER +15%
The maximum sensible cooling capacity of a heat pump should be within ______%
of the calculated sensible heat gain of a structure with a large heating load. -
ANSWER +25%
The combined output of a heatpump and its auxiliary heat should not exceed the
calculated heat loss of a home by more than ____%. - ANSWER
15%
What amount of auxiliary electronic heat is needed when the output of a heat pump
on a design day equals 18,800 Btuh and the heat loss of a home is 29,700 Btuh? -
ANSWER 3.2 kWh
The three processes that transfer heat energy are conduction, convection, and
_________. - ANSWER Radiation
,Heat transfer that occurs when substances of different temperatures are in contact
with each other is called _______. - ANSWER conduction
What effect does raising the pressure in a sealed system have on refrigerant? -
ANSWER The boiling point increases
What is the primary danger to people near an accidental refrigerant release or spill?
- ANSWER suffocation caused by the heavier refrigerant displacing
oxygen in the air
The maximum temperature at which refrigerant may be stored is ______ F when
the container is no more than ____% full of liquid by volume.; - ANSWER
125 F, 80%
Boiling of the refrigerant occurs in which system component? - ANSWER
Evaporator
Why is superheat necessary in a system that utilizes hermetic compressors -
ANSWER It ensures that dry vapor reaches the compressor so that
mechanical damage does not occur
When the heat load on an evaporator increases, what is the effect on the system? -
ANSWER Suction pressure and discharge pressure both increase
What type of energy is transferred when work is done in the condenser? -
ANSWER Both latent and sensible heat energy
, What is the primary function performed by a thermal expansion valve? -
ANSWER It maintains the correct superheat in the suction vapor leaving
the evaporator
Which component pumps refrigerant through the system and raises the vapor
temperature? - ANSWER compressor
How are hermetic compressor motors cooled? - ANSWER With
suction vapor drawn from the evaporator
Heat pump compressors sometimes run hotter than compressors used in cooling-
only units because heat pump compressors _____. - ANSWER
exhibit low refrigerant density at low suction pressures during the heating cycle
When is crankcase heat most needed? - ANSWER When the
compressor is off
Work done on the refrigerant in the condenser is transferred as ____. -
ANSWER Both sensible and latent heat
Why are more circuits needed in the outdoor coils used in heat pumps than in the
condenser coils used in cooling-only units? - ANSWER To keep the
pressure drop across the outdoor coil low
