Back-up power takes front-end planning

By GREG RICHARDS
Coffman Engineers

St. Joseph Medical Center in downtown Tacoma is growing. With 320 beds and plans to expand many of its departments, particularly surgery and obstetrics, hospital officials feared that it would soon outstrip its current capabilities for emergency power. This could prove to be a big problem in the event of a power failure, storm or major regional disaster.

The area had experienced few power outages in recent history. Yet to patients on life support systems, an interruption or brown-out of power could mean the difference between life and death.

What will the neighbors think? Installing heavy duty emergency generators in St. Joseph Medical Center was complicated by having a tight site in a quiet neighborhood.

Hospitals don't just go out and buy new emergency electrical back-up systems. There are a lot of considerations to weigh first. Can the capacity of existing equipment be expanded or upgraded? Should generators be replaced? If new equipment has more capacity, it's also probably larger in size and every square foot in a medical facility is expensive. Also, generators are notoriously noisy. If, like St. Joseph, you're located in a residential area populated mainly by senior citizens, you've got to worry about what the neighbors will think.

St. Joseph turned to Coffman Engineers of Seattle to perform a preliminary engineering study. Coffman found that the hospital's two 500 kW diesel standby generators were 20 years old and in good condition. But as health care has become increasingly reliant on electrically powered equipment, the demand for emergency power has been going up. Using actual recorded data, Coffman confirmed that the existing generator system was maxed out. No new loads could be added.

So the next step was to review design constraints -- and there were many. For one, no land was available for expansion, and existing space in the hospital was already cramped. The facility's current footprint would have to be used to house any new equipment. Then there were the noise considerations. Plus designers would have to work within strict "essential facility" codes. Downtime had to be kept to a minimum. And, of course, budgets were tight.

Working closely with the hospital staff, the engineering team recommended a design that would consolidate all of the hospital's generators into one location, potentially freeing up square footage in the main hospital campus. The team also recommended ways to remotely locate the generators' radiators and provide sound attenuators, saving precious space in the utility building.

Before making a final decision, the hospital brought in a group of outside consultants to perform a value engineering (VE) study. The VE group reviewed the engineering recommendations, suggested other considerations, and then performed a feasibility analysis of the various options.

The final decision was to go with Coffman's plan, and replace the old diesel generator units with larger, heavy-duty 1,500 kW units. This tripled the available emergency power.

Where do we put them?

St. Joseph chose to house the new equipment in the existing utility building, where no extra space appeared to be available. Fortunately, the radiators used to cool the generators could be separated from the main units, and mounted on the roof.

The engineers also found that it was possible to take over a bathroom adjacent to the generator room, which was used by the maintenance crew. New shower, toilet and locker facilities were then installed in a newly created mezzanine in another part of the building.

The design of the generators' sound attenuation system in a unique configuration saved yet more room, achieving the same noise-dampening effects in only half the space.

The net effect of these design solutions was that the new high-capacity generators fit into the space of smaller, older equipment, with minimal construction and reconfiguration requirements. This was made possible, in part, by synergies in the consulting team's electrical, structural and mechanical abilities.

Nixing the noise

St. Joseph is located in a sedate, established neighborhood, with many elderly homeowners. There was no way the neighbors were going to put up with the din produced by big generators.

Using the help of acoustical engineers, Coffman added sound attenuation baffles on the cooling air inlet and outlet. The baffles are perforated panels with an absorbent material inside. Louvered panels on the exterior wall permit airflow to ventilate the room, but hide the baffles from view. Within the generator area, the noise is so deafening that hearing protection must be used. Take a few steps outside, and only a hushed rumble is heard.

Design elements on the rooftop helped, too, where cooling air is discharged from the units. A new concrete-block wall was added on the roof around the radiators to act as a sound barrier. Large fans direct the cooling air away from nearby residences, decreasing the likelihood of objectionable noise.

The sound attenuation measures worked amazingly well. One of the residents across the street from the hospital asked engineers when those "big noisy machines" were going to be turned on. As it happened, the generators had been in operation for nearly a week!

With something as critical as an emergency power system, there can be no gap in service while old equipment is being replaced. Any outages had to be limited to several minutes, not hours or days, leaving installation crews no windows for mistakes or delays.

The new generators were turned on with such minimal disruption that the hospital never even noticed the change. Part of the success was attributable to an team effort between hospital personnel and the electrical contractor.

Rather than choosing a band-aid approach, the hospital administration carefully considered future requirements and long-range plans -- and installed a progressive element of infrastructure that will carry it well into the next millennium.

Greg Richards is a project manager and senior electrical engineer at Coffman Engineers in Seattle, a multidisciplinary firm offering electrical, mechanical and structural engineering and project management services.

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