Kohler KD Paralleling System: Hospital Data Center Emergency Power
A Bay Area hospital replaced aging standby generators with a paralleled Kohler KD system — two KD1250 units with Decision-Maker 6000 controllers, KCS transfer switches, and sub-3% THD power quality for sensitive imaging and life-safety equipment.
Background
When a Bay Area regional medical center needed to replace its aging emergency power system, the engineering team faced a common hospital dilemma: the existing single-unit generator was undersized for the facility's expanded critical load, and the power quality it delivered was marginal for the MRI suites and data center infrastructure added since the original installation.
The facility required a system that met three non-negotiable criteria: NFPA 110 Level 1 compliance with sub-10-second transfer, power quality clean enough for sensitive imaging equipment, and N+1 redundancy so that a single generator failure would not leave the hospital dark during an outage.
The Challenge
The hospital's critical load had grown to approximately 1,800 kW across life-safety systems, surgical suites, imaging (MRI, CT, X-ray), pharmacy refrigeration, and the on-site data center. The existing single generator — a 1,250 kW unit from a different manufacturer — had no redundancy and produced total harmonic distortion (THD) above 5%, which caused intermittent issues with the MRI cooling systems and UPS equipment in the data center.
Key requirements:
- NFPA 110 Level 1: Automatic start and full load transfer within 10 seconds of utility failure
- N+1 redundancy: Full facility coverage even with one unit offline for maintenance or failure
- Sub-3% THD: Power quality sufficient for MRI, CT, and data center UPS equipment
- Joint Commission readiness: Complete documentation trail for surveys and AHJ inspections
- BMS integration: Generator status visible in the hospital's existing building management system
Our Approach
We specified a paralleled Kohler KD system based on the facility's load profile and power quality requirements:
Generator selection: Two Kohler KD1250 industrial diesel generators, each rated at 1,250 kW standby. In normal emergency operation, both units start and share the 1,800 kW load proportionally. If one unit fails to start or trips during operation, the remaining unit carries the full critical load at approximately 72% of its rated capacity — within the continuous operating range.
Controller platform: Kohler Decision-Maker 6000 controllers on both units, configured for isochronous load sharing on an isolated bus. The DM6000 manages the full NFPA 110 sequence automatically — utility failure detection, engine start, synchronization, and load transfer — and logs every event with timestamps for compliance documentation.
Transfer switches: Kohler KCS Series automatic transfer switches with MPAC 1500 controllers at each distribution point, providing native serial communication with the Decision-Maker 6000 system and integration with the hospital's BMS via BACnet.
Power quality: The KD1250 uses Kohler's KH-series alternator with permanent-magnet pilot exciter, delivering sub-3% total harmonic distortion at all linear loads. This was the primary technical differentiator versus competing specifications — the MRI suite and data center UPS equipment require clean power to operate without faults during emergency power events.
Results
The paralleled KD system was commissioned with full load bank testing at 100% rated capacity on each unit individually, followed by paralleling verification under simulated utility failure conditions. The system met all acceptance criteria:
- Transfer time: 8.2 seconds from utility failure to full load on emergency bus (within NFPA 110 Level 1 requirement)
- THD measured: 2.4% at full load (well within the sub-3% specification)
- Load share balance: Within 2% between units during paralleled operation
- N+1 verification: Single-unit operation at 1,800 kW sustained for 4 hours during commissioning
The hospital's facilities team now has real-time generator status in their BMS dashboard, automatic exercise scheduling with compliance logging, and a preventive maintenance program with our factory-certified Kohler technicians on a quarterly cycle.
Equipment Summary
| Component | Specification | |---|---| | Generators | 2x Kohler KD1250, 1,250 kW standby each | | Controllers | Kohler Decision-Maker 6000 (paralleling, isochronous load share) | | Alternators | Kohler KH Series, sub-3% THD, Class H insulation | | Transfer Switches | Kohler KCS Series with MPAC 1500 controllers | | Fuel System | Dual sub-base tanks, 24-hour runtime at full load | | Compliance | NFPA 110 Level 1, UL 2200, Joint Commission EC.02.05.07 |
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