Building Systems & Energy Efficiency Flashcards

What is the primary purpose of retro-commissioning (RCx) an existing building?

Answer: Identifying and correcting operational deficiencies to restore or improve original design performance

Retro-commissioning systematically investigates existing building systems to find operational and maintenance problems — such as stuck dampers, wrong setpoints, or failed sensors — and corrects them, typically yielding 5–15% energy savings.

A simple payback period of 3.2 years means:

Answer: The initial capital cost is recovered through energy savings in 3.2 years

Simple payback = initial cost ÷ annual savings; a 3.2-year payback means savings accumulate to equal the upfront investment in 3.2 years, after which the savings are net positive.

Which of the following best describes 'whole-building energy use intensity' (EUI)?

Answer: Annual energy use per square foot of conditioned floor area (kBtu/ft²/yr)

EUI normalizes total annual energy consumption by conditioned floor area, enabling meaningful comparisons across buildings of different sizes and uses.

In a building automation system (BAS), an 'optimal start' algorithm saves energy by:

Answer: Calculating the latest possible start time to reach setpoint by occupancy, minimizing pre-conditioning hours

Optimal start learns how long the building takes to reach setpoint under different conditions and delays system startup as long as possible, reducing hours of unoccupied HVAC operation.

A facility installs a variable frequency drive (VFD) on a 50 hp cooling tower fan currently running at full speed 8,760 hours/year. If the fan can operate at 80% speed for 70% of hours, what is the approximate energy reduction for those hours?

Answer: 51%

At 80% speed, power consumption ≈ (0.80)³ = 51.2% of full-load power, meaning approximately 49% savings; the question asks for approximate reduction, which is ~51% reduction in those hours.

What does 'air sealing' address in building envelope performance?

Answer: Controlling uncontrolled air leakage (infiltration/exfiltration) that bypasses insulation

Air sealing addresses infiltration — the uncontrolled movement of air through cracks and gaps — which can account for 25–40% of heating and cooling energy loss even in well-insulated buildings.

A hospital's domestic hot water system uses a recirculation loop. The main energy benefit of insulating the recirculation piping is:

Answer: Reduced standing heat losses from piping, lowering boiler runtime

Uninsulated recirculation pipes continuously lose heat to the surrounding space, forcing the water heater to fire more frequently; insulation cuts these standing losses and reduces boiler energy by 10–20%.