Lighting & HVAC Energy Analysis Flashcards

What is the 'cube law' as applied to variable speed HVAC fans and pumps?

Answer: Energy use varies with the cube of speed

The affinity law states that fan/pump power varies as the cube of speed, so reducing speed to 80% reduces power to approximately 51% (0.8³ = 0.512).

Which lighting metric represents the ratio of lumens emitted by a luminaire to lumens produced by the bare lamp(s) inside?

Answer: Light Output Ratio (LOR)

Light Output Ratio (LOR) compares the lumens exiting the fixture to those produced by its lamps, accounting for optical losses within the housing.

A retail store has 200 track lights at 75W each. The utility charges a demand charge of $12/kW-month for the peak 15-minute interval. What is the annual demand charge from these lights alone?

Answer: $2,160

Peak demand = 200 × 75W = 15,000W = 15 kW; annual demand charge = 15 kW × $12/kW-month × 12 months = $2,160.

In HVAC energy analysis, what does 'latent load' refer to?

Answer: Energy required to change moisture content (humidity) of air

Latent load is the energy required to add or remove moisture from air without changing its temperature, critical in humid climates.

A demand-controlled ventilation (DCV) system reduces outdoor air flow based on which sensor input?

Answer: CO₂ concentration

DCV uses CO₂ sensors as a proxy for occupancy; higher CO₂ levels trigger increased outdoor air supply, reducing ventilation energy when spaces are less occupied.

What is the Energy Efficiency Ratio (EER) of a 5-ton cooling unit that draws 6 kW at full load? (1 ton = 12,000 BTU/hr)

Answer: 10.0

EER = BTU/hr ÷ Watts = (5 × 12,000) ÷ 6,000 = 60,000 ÷ 6,000 = 10.0.

Which lamp type produces light by exciting mercury vapor to emit ultraviolet radiation, which then excites a phosphor coating to produce visible light?

Answer: Fluorescent lamp

Fluorescent lamps pass electrical current through mercury vapor, producing UV that activates the phosphor coating on the tube interior to emit visible light.