Commissioning is often an additional service incorporated on new construction projects with complex or substantial mechanical and electrical systems. This service might be provided by the design engineer or an independent consultant. Services may include design review, second party review of submittals, and additional construction inspections. Quite often, services also include enhanced system operational tests to insure equipment and systems will perform as specified and designed.
Retro-commissioning refers to providing these services to a building that is already in service. A retro-commissioning effort might be considered for a relatively new building, such as after the one-year warranty period, to confirm systems are continuing to function as originally designed. For older buildings and systems retro-commissioning may be aimed more to troubleshoot problems, improve energy efficiency, and determine if changes in-use or other considerations warrant system changes or different control strategies. Retro-commission services often involve substantial system testing.
We are often asked to re-commission existing systems in hospitals. One such project was the chiller plant and chilled water distribution system for a North Carolina hospital that had experienced numerous additions and renovations since the original construction in the early 1980s. While the system was designed to operate with a “delta T” (difference between supply and return temperature) of 10 degrees, the operators found it difficult to achieve five degrees. This caused increased pump energy costs and made it difficult to operate the chillers at full rated capacity.
We verified the actual conditions on-site to develop a more accurate as-built of the system riser that was used to develop a computer flow model of the system. An ultra-sonic flow meter was used to measure chilled water flows at numerous locations in the system. Flows readings were taken under various operating conditions control sequences and control sensor readings were checked against actual conditions to verify accuracy.
Through these efforts we were able to identify a relatively inexpensive piping modification to correct a short circuiting issue that was the major cause of the low delta T problem. This simple fix improved energy efficiency and increased plant capacity for future expansions. Retro-commissioning efforts such as these further improve system operation and building energy efficiency.
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