Case study: Chiller addition adds power complexity

In this case, the building owner needed to increase generator capacity to accommodate a surgery expansion and add an electric centrifugal chiller on emergency power.


Figure 3: A new discharge plenum and louver was placed on the exterior of the existing building to accommodate the larger generators. Courtesy: IMEG Corp.A 140+ bed hospital facility had two 480/277 V 3-phase 4-wire standby diesel generators at 700 and 900 kW. The existing generators, paralleling gear, and emergency distribution were located in the same room, which is allowed by NFPA 110 The existing paralleling gear was not sized for future expansion.

Design aspects

The existing 700 kW generator set was replaced with a 1,500 kW diesel generator set. Due to the additional generator size, the radiator discharge louver was located at the building exterior wall and a new discharge plenum and louver was placed on the exterior of the existing building (see Figure 3). Additional intake air was required and new intake louvers and air pathways were added to the space, as defined in NFPA 110 7.7. The existing fuel oil storage system was re-used and the project added fuel polishing equipment to maintain fuel quality.

The existing paralleling gear had bus amperage that was too small for the additional generator load. Additional bus layers were added to increase the amperage from 2,000 to 3,600 amps, which allows for a second 1,500 kW generator to be added in the future. Generator beakers were replaced with a larger frame size for sufficient future capacity. An additional distribution section was added to allow for future loads and provides a feed to an external load bank connection cabinet.


The addition of an 800-ton electric centrifugal chiller to the emergency power system meant that additional controls were needed in the event of only the 900 kW generator being available. For this control, the paralleling gear communicated with the chiller control package and provided total available kW to stay less than 80% loaded along with suitable transfer delays. The chiller controller would equate the available kW into possible chiller output and modulate the chiller load accordingly. This allowed for the chilled water system to operate at maximum possible capacity given any combination of connected generators.

Rebuilding paralleling gear requires that it be taken out of service for several months. In order for the campus to be operational, a temporary generator was required. A 2,000-kW temporary generator was supplied and tied into the existing feeds from the paralleling gear. Due to the impact on clinical operations, the design team worked with the electrical contractor to develop outage plans that identified each task by minutes of duration for submission to the state health department. Switch-overs were conducted with on fair-weather days without scheduled surgical procedures. The outages to and from the temporary generator occurred without incident.

Richard Vedvik is senior electrical engineer and acoustics engineer at IMEG Corp. He is a member of the Consulting-Specifying Engineer editorial advisory board. 

Product of the Year
Consulting-Specifying Engineer's Product of the Year (POY) contest is the premier award for new products in the HVAC, fire, electrical, and...
40 Under Forty: Get Recognized
Consulting-Specifying Engineer magazine is dedicated to encouraging and recognizing the most talented young individuals...
MEP Giants Program
The MEP Giants program lists the top mechanical, electrical, plumbing, and fire protection engineering firms in the United States.
November 2018
Emergency power requirements, salary survey results, lighting controls, fire pumps, healthcare facilities, and more
October 2018
Approaches to building engineering, 2018 Commissioning Giants, integrated project delivery, improving construction efficiency, an IPD primer, collaborative projects, NFPA 13 sprinkler systems.
September 2018
Power boiler control, Product of the Year, power generation,and integration and interoperability
Data Centers: Impacts of Climate and Cooling Technology
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
Safety First: Arc Flash 101
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
Critical Power: Hospital Electrical Systems
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
Data Center Design
Data centers, data closets, edge and cloud computing, co-location facilities, and similar topics are among the fastest-changing in the industry.
click me