Engineered Systems NEWSCase in Point

Air handlers in small spaces allow big expansion for Arizona medical center

"We needed space. The Phoenix area is growing rapidly and so was the need for medical treatment facilities. In 1999 we quantified the need to expand this facility, and we needed to do it quickly." Larry Greer, director of facilities services from Desert Samaritan Medical Center in Mesa, AZ, thus describes the urgency for a facility expansion. "Every hospital in the area was filled, and there was a critical need for more space."

Plans were developed in 1999 for a 160,000-sq-ft expansion, ranging from one to four stories and encompassing six surgical suites, labor and delivery rooms, an intensive care area, patient rooms, an endoscopy lab, and a children's center. "Normally this project would take about 18 months but, because of the critical need, we had to get it done in 12."

The expansion to the existing 500,000-sq-ft facility included an air-handling system to be served by an existing chilled water plant.

The hvac system design, developed by mechanical engineer Bridgers & Paxton (Phoenix), called for eight large air handlers located in five mechanical rooms in the facility addition, seven in the surgery tower, and one in the labor and delivery area. Because of acoustic problems with air handlers elsewhere in the facility in the past, the medical center set high acoustic performance standards.

Structural strength sought

Another job requirement was the ability to ensure IAQ by means of efficient filtration and metered ventilation. The specification required the air handlers to have the capability to provide metered ventilation air and the capability to document ventilation rates. "Also, we needed the air handlers to be structurally strong. That's one of the reasons we needed double-wall construction," said Greer.

Because of the tight construction schedule, Bridgers & Paxton specified that the units needed to be built offsite and shipped to the jobsite, where they would be assembled. After their evaluation of the bids, the owners selected Trane AireSystems(tm) custom air handlers. AireSystems were specified and design work began immediately.

The physical dimensions of the air handlers range from 36 to 40 ft in length, from 8 1/2 to 13 ft in width, and from 7 1/2 to 11 ft in height. Most were shipped to the site completely assembled where it was possible to rig them into position in one piece with a mobile crane.

In a few cases, where clearances were tight, the air handlers were shipped in sections and assembled in place. Once in place, the air handlers were connected to ductwork, piping, electric, and controls lines. Phoenix contractor Thomas Heating and Air Conditioning was responsible for the installation and start-up of the system.

Tight fit is a hit

A notable feature of the job is the very tight clearances for each unit. To conserve space within the building addition, the space around each unit was kept to a minimum - just enough to allow inspection, cleaning, and service. In two cases, the units are installed as mirror-image pairs, with essentially zero clearance between the sides of the units.

The air handlers were ordered in January 2000 and shipped in July. Unit startup was in September and the addition was opened to patients in November 2000. According to Greer, the equipment started up smoothly and, after adjustments in airflow in the mixed-air plenum, the performance exceeded expectations.

Chris Gahan from Desert Samaritan is the foreman of central plant facilities services. He is impressed with the acoustical performance of the units. He chuckles, "We had people come to the mechanical room and ask when the air handlers were going to start up. I'd tell them, 'They're running now.' They couldn't believe it."

A design feature of the units that he appreciates is the ability to safely change filters without shutting down the unit. Gahan says that his staff plans to do a complete IAQ inspection of the air handlers quarterly and to do cleaning as needed. The specifications for the air handlers also included marine-type interior lights to simplify inspection and service.

"That's another nice feature I'd recommend to anyone," suggests Gahan. While specific performance/energy savings results aren't available because of numerous additions and changes taking place at the hospital, the consensus of the engineering staff at the hospital is that the new air handlers meet all of their expectations. ES

Looking for a reprint of this article?
From high-res PDFs to custom plaques, order your copy today!