CCP Existing-Building Retro-Cx 3 — Questions and Answers
Question 1: During trend log analysis, you notice that the AHU supply air temperature oscillates ±6°F around setpoint every 8 minutes. This pattern most likely indicates:
- A failed supply air temperature sensor
- Hunting caused by aggressive PID control gains (Correct answer)
- Simultaneous heating and cooling due to a failed economizer
- Duct static pressure sensor drift
Correct answer: Hunting caused by aggressive PID control gains
Rapid, regular oscillation around setpoint is the classic signature of a PID loop that is over-tuned (too high gain or too low integral time).
Question 2: Retro-commissioning of lighting systems most commonly reveals savings opportunities through:
- Replacing all fluorescent lamps with LED fixtures
- Correcting daylighting control setpoints and occupancy sensor coverage gaps (Correct answer)
- Increasing lighting power density to improve occupant satisfaction
- Replacing manual switches with automated relay panels
Correct answer: Correcting daylighting control setpoints and occupancy sensor coverage gaps
Miscalibrated daylighting sensors and poorly positioned occupancy sensors are operational faults that prevent lighting controls from delivering their designed energy savings.
Question 3: Which metric is most commonly used to prioritize retro-commissioning measures for implementation?
- Net present value at a 10% discount rate
- Simple payback period (Correct answer)
- Internal rate of return over 20 years
- Modified accelerated cost recovery schedule
Correct answer: Simple payback period
Simple payback (cost divided by annual savings) is the standard metric in RCx because it communicates project value to building owners without requiring complex financial modeling.
Question 4: A steam heating system shows persistent condensate backup in multiple traps. The most likely cause identified in RCx is:
- Oversized boiler firing rate
- Failed-open steam traps allowing live steam to pass to the condensate return
- Undersized condensate return piping installed during original construction
- Failed-closed steam traps blocking condensate drainage (Correct answer)
Correct answer: Failed-closed steam traps blocking condensate drainage
Failed-closed steam traps block condensate from draining, causing backup that floods heat exchanger coils and reduces heat transfer efficiency.
Question 5: The retro-commissioning scoping phase is primarily used to:
- Implement all identified no-cost measures
- Determine the extent of the investigation and develop the project plan (Correct answer)
- Write the final Findings and Recommendations Report
- Conduct functional performance testing of all systems
Correct answer: Determine the extent of the investigation and develop the project plan
Scoping defines the systems to be investigated, the data to be collected, and the project schedule and budget before detailed field work begins.
Question 6: When verifying economizer operation during RCx, which condition should trigger economizer lockout?
- Outdoor air temperature below 40°F
- Outdoor air enthalpy above the building's high-limit cutoff setpoint (Correct answer)
- Return air CO2 concentration above 1000 ppm
- Supply fan speed above 80% of maximum
Correct answer: Outdoor air enthalpy above the building's high-limit cutoff setpoint
Economizers should lock out when outdoor air enthalpy (or dry-bulb temperature, depending on the control strategy) exceeds the high-limit setpoint to prevent introducing warm, humid air.
Question 7: A retro-commissioning team finds that a building's BAS has hundreds of unacknowledged alarms spanning six months. This primarily indicates:
- The BAS vendor has not provided adequate software updates
- Alarm fatigue and inadequate O&M procedures for alarm management (Correct answer)
- The building has been operating safely with no real issues
- The BAS communication network has excessive latency
Correct answer: Alarm fatigue and inadequate O&M procedures for alarm management
A backlog of unacknowledged alarms indicates that O&M staff are overwhelmed or untrained on alarm management, allowing real equipment faults to go unaddressed.
CCP Existing-Building Retro-Cx 3
During trend log analysis, you notice that the AHU supply air temperature oscillates ±6°F around setpoint every 8 minutes.
This pattern most likely indicates: