Case study: Successful equipment relocation and reuse with new compliant electrical
In this example, a district energy system’s chillers were updated, and engineers ensured the electrical system remained fully compliant
The North Carolina Department of Administration (NCDOA) buildings in downtown Raleigh use district energy systems for heating and cooling. The two plants servicing these buildings provide 5,100 tons of chilled water capacity, including a 2.76-million-gallon thermal energy storage tank. This equipment is key to maintaining proper temperature conditions for workers, as well as for mission critical areas such as server rooms and information technology data closets.
As the equipment in the existing chiller plant #2 reached the end of its useful service life, NCDOA retained the services of RMF Engineering to rebuild the plant in-place and increase its capacity, enhancing resilience and addressing redundancy for maintainability. Working around budget and supply chain constraints, RMF capitalized on the remaining useful life of the two existing 1,450-ton chillers by relocating them to the new plant, where a third chiller and space for a fourth in the future would support the capacity needs of the NCDOA for years to come.
Integrating the existing chillers into the new electrical distribution became a key challenge given their short-circuit current rating (SCCR) of 42 kiloamps (kA), which was insufficient for installation in a system with available fault currents of over 50 kA.
RMF and NCDOA collaborated with a UL field evaluation agent to explore the use of a current limiting fuse to increase the chillers’ SCCR, but the field evaluation exposed components that had deficiencies and lacked tested data with current limiting fuses. An isolation transformer would also not work, due to limitations in both budget and the available footprint in the new plant. Ultimately, the project team worked with the chiller manufacturer to provide a new type of starter with adequate SCCR to move forward with installation and bring the plant online.
“The consequences of inadequate SCCR protection can be devastating to our maintenance personnel and facilities,” said Robert Talley, PE, Assistant Director, State Construction Office, North Carolina Department of Administration. “Accidents, faults and short circuits are a fact of life. When a fault occurs in a piece of equipment it needs to be dealt with by the system in a safe manner. Our maintenance employees and the people who depend on our systems to function are counting on the nondestruction shutdown of the equipment. Ensuring that equipment used by the state meets the standards for compliance is a critical, high priority. This is imperative for all owners that have yet to address SCCR compliance.”
See the related feature article for more information: The importance of SCCR and UL for equipment in district energy systems
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