HVAC Energy Efficiency 3 — Questions and Answers
Question 1: What does ASHRAE Standard 90.1 primarily address?
- Energy efficiency requirements for commercial buildings (Correct answer)
- Indoor air quality minimums
- Refrigerant leak detection
- Safety standards for pressure vessels
Correct answer: Energy efficiency requirements for commercial buildings
ASHRAE 90.1 sets minimum energy efficiency requirements for the design and construction of commercial buildings and their HVAC systems.
Question 2: An HVAC technician notices condenser coil fins are bent and restricting airflow. What is the most likely energy impact?
- Increased condensing pressure and reduced system efficiency (Correct answer)
- Lower suction pressure and more cooling capacity
- Reduced compressor amperage draw
- Improved latent cooling due to slower airflow
Correct answer: Increased condensing pressure and reduced system efficiency
Restricted condenser airflow raises head pressure, forcing the compressor to work harder and reducing overall system efficiency.
Question 3: Which factor primarily determines the Energy Efficiency Ratio (EER) of a cooling system?
- Cooling capacity in BTU/h divided by power input in watts at a specific test condition (Correct answer)
- Total operating hours per season
- Refrigerant charge level
- Number of compressor stages
Correct answer: Cooling capacity in BTU/h divided by power input in watts at a specific test condition
EER is calculated at a fixed ARI test condition (95°F outdoor, 80°F/67°F indoor) as BTU/h of cooling divided by watts of electrical input.
Question 4: What is the role of thermal expansion valves (TXV) in maintaining efficiency?
- They maintain consistent superheat to maximize evaporator use without liquid slugging (Correct answer)
- They control condenser fan speed
- They set the refrigerant subcooling level
- They regulate compressor discharge pressure
Correct answer: They maintain consistent superheat to maximize evaporator use without liquid slugging
TXVs modulate refrigerant flow to maintain a set superheat, ensuring the evaporator is fully used without allowing liquid refrigerant into the compressor.
Question 5: Which building envelope feature most reduces HVAC cooling loads in hot climates?
- High-reflectance roofing (cool roof) (Correct answer)
- Increased ceiling height
- Larger HVAC equipment
- Additional return air grilles
Correct answer: High-reflectance roofing (cool roof)
Cool roofs reflect solar radiation, reducing roof surface temperatures and heat transfer into the building, directly lowering cooling loads.
Question 6: What is 'demand-controlled ventilation' (DCV)?
- A strategy that adjusts outdoor air intake based on occupancy, typically using CO2 sensors (Correct answer)
- A method to reduce refrigerant flow at peak demand
- A technique for cycling compressors to match load
- A system for controlling duct static pressure
Correct answer: A strategy that adjusts outdoor air intake based on occupancy, typically using CO2 sensors
DCV uses CO2 or occupancy sensors to modulate outdoor air quantities, reducing unnecessary ventilation energy during low-occupancy periods.
Question 7: Why does a dirty air filter negatively impact HVAC energy efficiency?
- It increases static pressure drop, forcing the blower to work harder for the same airflow (Correct answer)
- It raises refrigerant temperature
- It causes the thermostat to cycle more frequently
- It reduces condenser fan efficiency
Correct answer: It increases static pressure drop, forcing the blower to work harder for the same airflow
A clogged filter increases resistance in the air distribution system, increasing blower motor energy consumption and potentially reducing airflow and capacity.
HVAC Energy Efficiency 3
What does ASHRAE Standard 90.1 primarily address?