CEA Building Systems & Energy Efficiency 2 — Questions and Answers
Question 1: What is the primary function of an economizer cycle in an HVAC system?
- Recover heat from exhaust air
- Use outdoor air for free cooling when conditions allow (Correct answer)
- Preheat supply air in winter
- Reduce refrigerant charge
Correct answer: Use outdoor air for free cooling when conditions allow
An economizer uses cool outdoor air directly for space cooling when ambient conditions are favorable, reducing mechanical refrigeration energy.
Question 2: A building's chiller plant has a COP of 4.5. How many kW of cooling are delivered per kW of electrical input?
- 1.0 kW
- 3.5 kW
- 4.5 kW (Correct answer)
- 5.5 kW
Correct answer: 4.5 kW
COP (Coefficient of Performance) directly equals the ratio of cooling output to electrical input, so COP 4.5 means 4.5 kW cooling per 1 kW electricity.
Question 3: Which metric best describes the seasonal cooling efficiency of a residential air conditioner in the US?
- EER
- SEER (Correct answer)
- COP
- kW/ton
Correct answer: SEER
SEER (Seasonal Energy Efficiency Ratio) accounts for varying temperature conditions across a cooling season, making it the standard US residential efficiency metric.
Question 4: In a variable air volume (VAV) system, energy savings over a constant volume system come primarily from:
- Higher supply air temperature
- Reduced fan power at part load via cube law (Correct answer)
- Larger duct sizing
- Elimination of reheat coils
Correct answer: Reduced fan power at part load via cube law
Fan power follows the affinity laws — reducing airflow by 50% reduces fan power by approximately 87.5% (cube law), yielding substantial energy savings at part load.
Question 5: What is the purpose of a thermal break in a window frame or curtain wall assembly?
- Increase solar heat gain
- Prevent conductive heat transfer through the frame (Correct answer)
- Improve visible light transmittance
- Reduce embodied carbon
Correct answer: Prevent conductive heat transfer through the frame
A thermal break is a low-conductivity material inserted between interior and exterior frame elements to interrupt conductive heat flow and reduce U-factor.
Question 6: A lighting system has a connected load of 3.2 W/ft². What is the lighting power density (LPD) if 20% of fixtures are on occupancy sensors that reduce load by 60% during unoccupied hours?
- 2.56 W/ft²
- 3.2 W/ft² (Correct answer)
- 1.28 W/ft²
- 0.64 W/ft²
Correct answer: 3.2 W/ft²
Lighting power density is a connected-load metric (W/ft²) and does not account for controls; LPD remains 3.2 W/ft² regardless of sensor operation.
Question 7: Which building envelope component typically has the greatest impact on heating energy in a cold climate commercial building?
- Roof insulation level
- Window-to-wall ratio and glazing U-factor (Correct answer)
- Floor slab edge insulation
- Exterior wall paint color
Correct answer: Window-to-wall ratio and glazing U-factor
Windows have far higher U-factors than opaque walls, and in commercial buildings the large glazed area combined with high heat loss makes glazing the dominant envelope heat loss driver.
CEA Building Systems & Energy Efficiency 2
What is the primary function of an economizer cycle in an HVAC system?