NATE Exam Air Conditioning and Heat Pumps questions and answers

Which of the following factors affects a customer's level of comfort? a. Air movement b. Humidity c. Temperature d. All of the above d (All of the above: air movement, humidity, temperature) A cooling load calculation estimates the sensible heat gain of a structure. The maximum sensible capacity of a cooling-only system should be within ____% of this calculated value. a. ±10% b. +10% c. +15% d. +30% c (+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. a. ±10% b. +15% c. -25% d. +25% d (+25%) The combined output of a heat pump and its auxiliary heat should not exceed the calculated heat loss of a home by more than ____%. a. 10% b. 15% c. 20% d. 25% b (15%) What amount of auxiliary electric 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? a. 2.1 kWh b. 3.2 kWh c. 5.0 kWh d. 10.9 kWh Note: 3,413 Btu/kW b (3.2 kWh) The three processes that transfer heat energy are conduction, convection, and ____. a. concentration b. radiation c. refraction d. static pressure b (radiation) Heat transfer that occurs when substances of different temperatures are in contact with each other is called ____. a. concentration b. conduction c. convection d. radiation b (conduction) What effect does raising the pressure in a sealed system have on refrigerant? a. It becomes more difficult to subcool the liquid refrigerant b. It becomes more difficult to superheat the refrigerant vapor c. The refrigerant's boiling point decreases d. The refrigerant's boiling point increases d (The refrigerant's boiling point increases) What is the primary danger to people near an accidental refrigerant release or spill? a. Blurred vision caused by the refrigerant vapor coming in contact with the eyes b. Changes in weather patterns caused by global warming c. Damage to the food chain caused by decreased ozone levels in the stratosphere d. Suffocation caused by the heavier refrigerant displacing oxygen in the air d (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. a. 120°F, 60% b. 125°F, 60% c. 125°F, 80% d. 135°F, 80% c (125°F, 80%) Boiling of the refrigerant occurs in which system component? a. Compressor b. Condenser c. Evaporator d. Metering device c (Evaporator) Why is superheat necessary in a system that utilizes hermetic compressors? a. It ensures that dry vapor reaches the compressor so that mechanical damage does not occur b. It increases system capacity c. It prevents liquid refrigerant from gassing the metering device d. Superheat is necessary only when open compressors are being used a (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? a. Suction pressure decreases and discharge pressure increases b. Suction pressure increases and discharge pressure decreases c. Suction pressure and discharge pressure both decrease d. Suction pressure and discharge pressure both increase d (Suction pressure and discharge pressure both increase) What type of energy is transferred when work is done in the condenser? a. Latent heat energy b. Sensible heat energy c. Both latent and sensible heat energy d. Neither latent nor sensible heat energy c (Both latent and sensible heat energy) What is the primary function performed by a thermal expansion valve? a. It maintains the correct superheat in the hot vapor leaving the compressor b. It maintains the correct superheat in the suction vapor leaving the evaporator c. It maintains the proper subcooling level in the liquid refrigerant d. It prevents flash vapor bubbles from developing in refrigerant entering the evaporator b (It maintains the correct superheat in the suction vapor leaving the evaporator) Which component pumps refrigerant through the system and raises the vapor temperature? a. Accumulator b. Compressor c. Condenser d. Evaporator b (Compressor) How are hermetic compressor motors cooled? a. With air drawn around the compressor shell by the condenser fan b. With water circulated through tubing wrapped around the compressor shell c. With suction vapor drawn from the evaporator d. With a combination of air and water c (With suction vapor drawn from the evaporator) Heat pump compressors sometimes run hotter than compressors used in cooling-only units because heat pump compressors ____. a. exhibit low refrigerant density at low suction pressures during the heating cycle b. pump liquid refrigerant during the cooling cycle c. must prevent ice formation during the defrost cycle d. must heat indoor spaces in the winter a (exhibit low refrigerant density at low suction) When is a crankcase heater most needed? a. Early in the morning during the cooling cycle b. When the compressor is operating in very cold winter weather c. When the compressor is operating in very humid conditions d. When the compressor is off d (When the compressor is off) Work done on the refrigerant in the condenser is transferred as ____. a. latent heat b. sensible heat c. specific heat d. both sensible and latent heat d (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? a. To keep the pressure drop across the outdoor coil high b. To keep the pressure drop across the outdoor coil low c. To provide more subcooling during the cooling cycle d. To provide more subcooling during the heating cycle b (To keep the pressure drop across the outdoor coil low) What is the typical water flow rate per ton of cooling for water-source heat pumps operating in closed-loop systems? a. 3.0 gpm per ton b. 2.5 gpm per ton c. 2.0 gpm per ton d. 1.5 gpm per ton a (3.0 gpm per ton) What tool should be used to shorten a capillary tube? a. A pair of pliers with side-cutter edges b. A small tubing cutter c. Any tubing cutter approved for use on refrigerant tubing d. A triangular or knife-edge file d (A triangular or knife-edge file) Which pressure in a TEV is the opening pressure? a. Bulb pressure b. Evaporator pressure c. Spring pressure d. A combination of bulb and spring pressures a (Bulb pressure)