CEA Lighting & HVAC Energy Analysis 3 — Questions and Answers
Question 1: Which ASHRAE standard provides minimum energy efficiency requirements for commercial building HVAC and lighting systems in the US?
- ASHRAE 55
- ASHRAE 62.1
- ASHRAE 90.1 (Correct answer)
- ASHRAE 189.1
Correct answer: ASHRAE 90.1
ASHRAE 90.1 sets minimum energy efficiency standards for commercial buildings, including prescriptive LPD limits and HVAC efficiency requirements.
Question 2: An air handling unit has a supply fan with a brake horsepower (BHP) of 15 and operates 4,000 hours per year. At $0.10/kWh, what is the approximate annual fan energy cost? (1 HP ≈ 0.746 kW)
- $1,800
- $2,700
- $4,476 (Correct answer)
- $6,000
Correct answer: $4,476
15 BHP × 0.746 kW/HP × 4,000 hr/yr × $0.10/kWh = $4,476.
Question 3: What does the term 'economizer mode' mean for an HVAC air-side system?
- Reducing supply air temperature below design setpoint
- Using outdoor air for free cooling when conditions are favorable (Correct answer)
- Cycling the compressor to reduce runtime
- Operating the system at minimum outside air only
Correct answer: Using outdoor air for free cooling when conditions are favorable
Air-side economizers bring in outdoor air to cool the building without mechanical refrigeration when outdoor conditions are cool and dry enough.
Question 4: A luminaire delivers 3,500 lumens using 35 watts. What is its efficacy?
- 35 lm/W
- 70 lm/W
- 100 lm/W (Correct answer)
- 122.5 lm/W
Correct answer: 100 lm/W
Efficacy = lumens ÷ watts = 3,500 ÷ 35 = 100 lm/W.
Question 5: Which control strategy reduces HVAC fan energy by lowering airflow during periods of reduced cooling or heating demand?
- Constant air volume (CAV)
- Variable air volume (VAV) (Correct answer)
- Dual-duct mixing
- Terminal reheat
Correct answer: Variable air volume (VAV)
VAV systems modulate airflow to match zone loads, saving fan energy through the cube law relationship between fan speed and power.
Question 6: What is the primary purpose of a heat recovery ventilator (HRV) in a building?
- To preheat domestic hot water using condenser heat
- To transfer heat between exhaust and incoming outdoor air streams (Correct answer)
- To recover heat from lighting fixtures for space heating
- To recirculate warm air from upper floors to lower floors
Correct answer: To transfer heat between exhaust and incoming outdoor air streams
An HRV transfers heat between exhaust and supply air streams, reducing the energy needed to condition incoming outdoor air.
Question 7: A building replaces 100 incandescent 60W lamps with 10W LEDs, operating 2,000 hours/year at $0.12/kWh. What is the annual energy cost savings?
- $480
- $960
- $1,200 (Correct answer)
- $1,440
Correct answer: $1,200
Savings = (60−10)W × 100 lamps = 5,000W; 5,000W × 2,000 hr ÷ 1,000 = 10,000 kWh; 10,000 × $0.12 = $1,200.
CEA Lighting & HVAC Energy Analysis 3
Which ASHRAE standard provides minimum energy efficiency requirements for commercial building HVAC and lighting systems in the US?