ASHRAE Journal - December 2010 - 125

commissioning

Technical Rcx For office
By Dave mcFarlane, Member ASHRAE

Grand Forks County Office Building.
2 2 corrective action is taken to make an existing building conform to to the $0.90/ft ($9.67/m ) originally

echnical retrocommissioning (RCx) is the systematic process where
anticipated. This office building houses social services, public health and safety, taxation, county auditors, property records and administration. The entire sixth floor contains meeting rooms and the county commissioners’ offices. The RCx team met with the commissioners’ building committee, design engineers, and building maintenance staff to understand their concerns. During these meetings, we learned that the maintenance staff was overriding the original temperature setpoints in response to occupant complaints. The technicians checked equipment for flows and operation. The building’s mechanical and electrical system controls were compared to scheduled building occupancy periods. The plans and specifications were reviewed to understand the systems, types of equipment used, and actual operations data provided information for modeling. Data loggers provided actual space temperature variation measurements. The blue line in Figures 1 through 3 shows the energy use before changes were made. The first two years’ energy use was determined from actual gas,
ASHRAE Journal 125

the owner’s current facility requirements. Two approaches to RCx are in common use: process and technical. These approaches parallel the process and technical approaches taken in new building commissioning.

Process Rcx
The process RCx approach relies on the testing, adjusting and balancing report (made by others), the temperature control sequences shown in the contract documents and a review of the plans and specifications to determine corrective action. Minimal time is spent obtaining site data.

Technical Rcx
The technical RCx process requires the RCx team to determine the actual flows, temperatures and pressures for the various building systems and compare the actual control sequences to known energy-efficient control sequences. The team confirms proper operation of all dampers, control valves, variable frequency drives (VFDs) and other equipment. Controls are calibrated to scheduled setpoints and proper control loop response time is verified.
December 2010

Electrical systems are checked. Thermal imaging is used to determine loose connections. Power quality analysis is used to determine low voltage, low power factor or load imbalance in electrical systems and proper grounding is confirmed. Lighting systems are evaluated for efficient ballasts, lamps, occupancy control, daylight harvesting and lighting levels. The building envelope is evaluated for air infiltration, building pressurization and glazing efficiencies.

Technical Rcx in Practice
Our firm recently used the technical RCx process to reduce the energy use in the new Grand Forks County Office Building, a six-story 140,000 ft2 (13 000 m2) building completed in 2000. The county commissioners were concerned with the building’s relatively high energy costs of $1.40/ft2 ($15/m2) as compared

ASHRAE Journal - December 2010

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