Lighting & HVAC Energy Analysis Flashcards

Which ASHRAE standard provides minimum energy efficiency requirements for commercial building HVAC and lighting systems in the US?

Answer: ASHRAE 90.1

ASHRAE 90.1 sets minimum energy efficiency standards for commercial buildings, including prescriptive LPD limits and HVAC efficiency requirements.

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)

Answer: $4,476

15 BHP × 0.746 kW/HP × 4,000 hr/yr × $0.10/kWh = $4,476.

What does the term 'economizer mode' mean for an HVAC air-side system?

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.

A luminaire delivers 3,500 lumens using 35 watts. What is its efficacy?

Answer: 100 lm/W

Efficacy = lumens ÷ watts = 3,500 ÷ 35 = 100 lm/W.

Which control strategy reduces HVAC fan energy by lowering airflow during periods of reduced cooling or heating demand?

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.

What is the primary purpose of a heat recovery ventilator (HRV) in a building?

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.

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?

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.