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  • Alex Mathers


Retro-Commissioning (RCx) and Re-Commissioning (ReCx) for existing facilities

As soon as a building is operational, systems begin to drift and wear. Two commissioning methods are used to address this issue. Re-Commissioning provides a reset as if the building systems were being installed new. Similarly, Retro-Commissioning is the process to improve the efficiency of an existing building's equipment and systems. Both Retro-Commissioning (RCx) and Re-Commissioning (ReCx) are for existing buildings. The difference between RCx and ReCx is RCx is performed in buildings that have not undergone commissioning before; ReCx is performed in buildings that have already been commissioned but have drifted in operation over time.

GMC Cx has completed both RCx and ReCx projects. Several of these projects have included the addition of new or un-commissioned equipment to an existing system that has been previously commissioned, but may have lost operational efficiency over time. GMC Cx has performed these services in mission-critical chilled water central plants, where added equipment significantly changed the sequence of operations. One project included the addition of a chiller, pumps and cooling tower to a 4,000-ton chilled water central plant for added capacity and redundancy. Another project included the incorporation of existing/installed waterside heat exchangers to a 3,200-ton chilled water central plant for more efficient operation during cooler weather. Both projects required mechanical, plumbing and significant electrical upgrades.

Both central plants were in full operation and under load during commissioning – supporting critical processes – and neither could afford to lose any capacity or redundancy during functional testing. Both had tight windows of testing opportunity and required significant coordination between the commissioning team, operations, vendors and contractors.

One of the main challenges of RCx and ReCx is lack of documentation from projects 10 and 20 years prior. Setpoints, sequences of operation, alarms and other design intent may have been lost over time. Significant changes to operations, firmware and software updates, sensor changeouts, balance changes and schedules may have been made over the years which did not get documented. In many cases, changeover of key personnel over the years results in lost operational knowledge and details that may be missed. Therefore, defining the new acceptance criteria is a critical step in addition to understanding how the new equipment and control sequences change existing operations. Significant effort is required to review all existing documentation, interview operational staff and ensure a deep understanding of the systems.

To be clear, not every building or system can benefit from RCx or ReCx. Many older buildings have minimal HVAC systems installed for occupant comfort and due to their simplistic design may not benefit from a comprehensive commissioning process. However, adding additional equipment to existing large central plants and even seemingly simple HVAC systems makes RCx and ReCx essential to ensure that these systems not only operate properly but that operating personnel are well trained and thoroughly understand the changes to their buildings systems. There is also a huge value to the owner to ensure past changes are updated in proper documentation for future reference.

GMC Cx used our team-integrated, hands-on, technical commissioning approach to successfully RCx/ReCx these central plant projects. By focusing on the owners’ requirements, acceptance criteria and documentation was updated to reflect all past changes. Also, through significant team coordination, we were able to complete functional and systems integration testing without compromising the ability of the live system to service their critical load.

Building Commissioning, RCx and ReCx is the systematic process of proactively verifying that building systems are designed, installed, thoroughly tested and capable of being operated and maintained to perform as intended to the owner’s expectations. Commissioning is not only reserved for new construction. RCx and ReCx can benefit buildings and facilities by providing owners with tremendous value and savings.

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