HVAC Assessment/Retro-Commissioning
Poudre High School; Fort Collins, Colorado
Building Profile
Poudre High School is primarily a single-story brick building with a floor area of 275,000 SF. The original building was constructed in 1963, and a major building renovation was completed in 1995. The remodel project included installation of 18 rooftop air handling units (RTUs), which provide heating and cooling to approximately 60% of the building. The existing RTUs are constant volume, single-zone systems with DX cooling and hot water heating capability. Reheat coils serve each individual room.
Retro-Commissioning Tasks
Retro-commissioning at Poudre High School included the following tasks:
- Perform cooling and heating load calculation
- Evaluate RTU capacity, operation and schedules
- Test airflow quantities to individual rooms
- Test temperature calibration of space temp. sensors
- Review RTU control sequences
- Review control component location and function
- Recommend modifications to mechanical systems
- Implement new control sequence
- Evaluate trend data of space and RTU temperatures
Deficiencies Identified
During retro-commissioning, the following mechanical problems were identified and corrected:
- Access panel was found open in mechanical chase. It is estimated that nearly 2,000 cfm was not serving ground floor classrooms.
- Branch ducts and diffusers in ground floor classrooms were undersized. Ducts were upgraded.
- Space temperature sensors were 2 to 6°F out of calibration. Sensors were replaced.
- Mixed air sensor was mounted downstream of DX cooling coil.
- Control sequence was configured for an outside air reset strategy that
promoted comfort, not energy savings.
Solutions/Savings Potential
A new controls sequence was implemented that employs discharge air temperature reset based on space load. Savings will result from:
- Improved economizer operation
- Reduced DX compressor operation
- Reduced simultaneous heating and cooling through reheat coils
- Improved space temperature calibration
- HVAC energy savings estimated at $35,000 per year
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