Hvac Systems MCQ Practice Test

Q1. In a typical residential HVAC system, what is the primary function of the expansion valve in a refrigeration cycle?

• A. To compress the refrigerant
• B. To expand the refrigerant to a low pressure and low temperature ✓
• C. To condense the refrigerant
• D. To evaporate the refrigerant

Q2. In a typical VAV (Variable Air Volume) HVAC system, what is the primary function of the "Minimum Flow Control" dampers?

• A. To maintain a minimum airflow rate through each zone during unoccupied periods ✓
• B. To regulate the airflow rate through each zone based on the zone's cooling load
• C. To prevent over-pressurization of the building during occupied periods
• D. To ensure that the outside air intake meets the ASHRAE 62.1 ventilation requirements

Q3. In a typical air-handling unit, what is the primary function of the economizer?

• A. To control the airflow rate
• B. To recover heat from outdoor air
• C. To cool the supply air ✓
• D. To humidify the supply air

Q4. In a typical residential HVAC system, what is the primary function of the economizer?

• A. To reduce the cooling load by allowing outside air to enter the building when the temperature is lower than the indoor temperature ✓
• B. To increase the heating load by allowing outside air to enter the building when the temperature is higher than the indoor temperature
• C. To control the humidity level by removing excess moisture from the air
• D. To improve the air quality by removing pollutants and contaminants from the air

Q5. In a chilled water HVAC system, what is the primary function of the cooling tower (or other heat rejection equipment) in the condenser water loop?

• A. To reject heat absorbed by the refrigerant in the chiller to the atmosphere. ✓
• B. To provide a constant flow temperature to the chilled water loop.
• C. To increase the condenser water temperature to prevent freezing.
• D. To reduce the condenser water pressure drop.

Q6. A refrigeration system using a transcritical CO2 cycle operates with a liquid refrigerant at 40°C entering the expansion valve. Assuming the enthalpy of the refrigerant entering the expansion valve is 270 kJ/kg, what is the enthalpy of the refrigerant leaving the expansion valve, assuming an ideal expansion process?

• A. h = 240 kJ/kg
• B. h = 270 kJ/kg ✓
• C. h = 300 kJ/kg
• D. h = 330 kJ/kg

Q7. A residential HVAC system is designed to handle a maximum air flow rate of 300 CFM per ton of cooling capacity. What is the total air flow rate for a 2-ton air-source heat pump system?

• A. 450 CFM
• B. 600 CFM
• C. 900 CFM ✓
• D. 1200 CFM

Q8. A residential HVAC system is designed to maintain a temperature of 22°C in a house with a total volume of 1000 cubic meters. The system uses a heat pump with a coefficient of performance (COP) of 3.5 for heating mode. The house experiences a heat loss of 10 kW. What is the minimum power input required from the electrical supply to maintain the desired temperature?

• A. 2.86 kW ✓
• B. 3.5 kW
• C. 10 kW
• D. 35 kW

Q9. In HVAC engineering, one ton of refrigeration is defined as the rate of heat transfer needed to melt:

• A. One ton (2,000 lb) of ice in 24 hours ✓
• B. One pound of ice in one hour
• C. One kilogram of ice in 12 hours
• D. One gallon of water per hour

Q10. In a typical residential HVAC system, what is the purpose of the “subcooling” process in the condenser coil?

• A. To increase the refrigerant temperature before it enters the compressor
• B. To decrease the condensing pressure in the condenser coil
• C. To increase the cooling capacity of the evaporator coil
• D. To ensure the refrigerant is fully liquid before entering the expansion valve ✓

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