Case study: Patient bed tower addition

Project goals: Provide additional standby generators for a hospital building tower addition.

Existing condition: A hospital campus added a 144,000-square-foot patient tower to the existing campus. This new tower included approximately 80 patient beds and was independent from the existing campus central plant. The existing campus had three 400-kW standby diesel generator sets operating at 480 V and they were loaded to 70% capacity. The design team considered revising or upgrading the existing system but decided that a separate emergency power supply and emergency power supply system with room for future growth would provide more flexibility.

Designing around existing generators:  The same client had a pair of 600 kW diesel generators with 4,160 V output located at a different location and they were available for relocation. The same design team had recently replaced the two 4,160-V, 600-kW generators with 4,160-V, 1,000-kW generators and the team was familiar with their specifications and knew they were available. The 4,160 V output allowed for a remote location over 1,000 feet away, in a building adjacent to the existing campus generators.

This required early planning to ensure the electrical rooms in the addition could accommodate interior transformers integrated into unit substations. A dedicated room was created to house the paralleling gear separate from the generators to allow for a clean, conditioned, place to operate electrical gear. The generator room is heated and the EPSS room has heating and cooling with a dedicated fan coil unit.

The air intakes were located on the opposite wall from the unit-mounted radiators to provide ideal airflow and minimize pressure drop (see Figure 4). Acoustical louvers were used at the generator discharge with consideration given to the calculated property line noise levels. Additional considerations include providing in-floor trench for fuel oil piping and the addition of a fuel polisher to the existing long-term fuel storage system.

Figure 4: Two relocated 4,160-V, 600-kW diesel generators in a remodeled space that was planned for three 1,000-kW generators. Courtesy: IMEG Corp.

The relocated generators were temporarily stored with the manufacturer due to the schedule difference between the replacement project at their original location and the reuse project location. The manufacturer was asked to review the generators and evaluate the physical condition of consumables. When relocated, new batteries, cables and a new best-battery charging system was provided.

The new location provided new 4,160 V paralleling gear that communicated with upgraded engine controllers. The manufacturer provided new digital engine controllers initially, but they had trouble with consistent paralleling so analog engine controllers were eventually provided.