METERED VENTILATION

Another job requirement was the ability to ensure indoor air quality 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,” says Greer, “we needed the air handlers to be structurally strong. That’s one of the reasons we needed double-wall construction.” Additionally the owner made it clear that cost of the project was an important issue. “We wanted the best quality for the lowest dollar.”

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 wanted to use Trane AireSystems™ custom air handlers. “We didn’t have any actual experience with those products, so we made a visit to the AireSystems plant in Fort Smith, Arkansas. Before we committed, we wanted to find out more about this product.”

The owner and engineer specifically needed to find out about the units’ design capabilities. The air handlers feature 4-in.-thick walls filled with fiberglass insulation. Each unit has an 18-ga galvanneal steel roof and a 2-ga perforated steel inner liner to assist in sound attenuation. The units have 14-ga steel floors and hinged, insulated access doors to each air handler section. The air handler design utilizes the Trane Traq™ damper to meter, monitor, and log outdoor ventilation airflow at each air handler.

Each air handler is equipped with a 2-in. 30% prefilter, a 2-in. 30% filter, and a 12-in. 90% final filter. The specification called for each unit to have plug fans (plenum fans) for both supply and return air applications. Again, because of the acoustic standards, the air handlers are equipped with silencers upstream of the return fan and downstream of the supply fan. The units range in size from 11,500 to 27,000 cfm. All units have eight-row chilled water coils located downstream of the air handlers provide humidity control to the systems that serve surgical areas.

LITTLE ASSEMBLY REQUIRED

The physical dimensions of the air handlers range from 36 to 40 feet in length, from 8½ to 13 ft in width, and from 7½ 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 startup of the system.

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. According to Don Brandt, a sales engineer from the Trane Phoenix commercial sales office, the tight space requirements were challenging. “Both for installing the units and fitting in the ductwork, the clearances were often only an inch or two. AireSystems and the mechanical contractor did a good job of working within those space limitations.”

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. 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 the central plant facilities services. He is impressed with the acoustic 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.”

FILTER CHANGING “ON THE FLY”

A design feature of the units that he appreciates is the ability to safely change filters without shutting the unit down. “This means saving a lot of time and inconvenience for my staff. It’s a big issue for us.” Gahan says that his staff plans to do a complete IAQ inspection of the air handlers quarterly and to do cleaning as needed. He comments, “We like the multiple access points for inspection and cleaning.” The specification for the air handler also included marine-type interior lights to simplify inspection and service. “That’s another nice feature I’d recommend to anyone,” says Gahan.

The consensus of the engineering staff at the hospital is that the new air handlers meet all of their expectations and are far easier to control and to service than earlier equipment. The Traq dampers operate through the existing building control system and provide precise records of ventilation rates for all of the areas served. Best of all, the units are so quiet that most hospital employees are not even aware of their presence. The hospital later selected Trane AireSystems to provide a large, custom air handler for a laboratory addition now under construction.

Publication date: 08/13/2001