Evanston Hospital, a 354-bed, 1.06 million-square-foot facility, is a comprehensive acute care facility with emphases in cardiac care, cancer care, and multiple surgical specialties. It is a Level I Trauma Center and also includes a simulation facility for training medical professionals and first responders.
- The retro-commissioning effort focused on the temperature controls and mechanical operation for 31 air-handling systems and the chilled water system serving these air-handling units (AHUs).
Eight different retro-commissioning measures (RCMs) were identified through functional performance testing, plus review of the Siemens building automation system and the temperature control system trend logs.
- RCMs included equipment scheduling, simultaneous heating and cooling remediation, improved air-side economizer operation, optimized discharge air static pressure setpoints, supply air temperature reset, and chilled water pump differential pressure setpoint adjustment.
- Before retro-commissioning, all of the AHUs in the facility operated at the same supply air temperature 24 hours per day. A reset schedule was implemented to raise the supply air temperature during off hours whenever outdoor air temperature conditions are favorable. Maintaining a higher supply air temperature allows the AHUs to use more return air during heating, reducing the amount of reheat required and cutting chilled water use during cooling season. The measure is projected to save more than $27,500 annually in electric and gas costs, with a simple payback of 1.3 months.
- Retro-commissioning also identified areas that are unoccupied at night, allowing implementation of an unoccupied schedule to specific VAV boxes. When spaces are unoccupied, the VAV boxes provide less airflow, and temperature requirements are relaxed. This RCM is projected to save more than $21,000 annually in electric costs, with a simple payback of 3.5 months.