By Scott Alwine, LEED AP
For its Portland, Oregon, offices, Providence Health & Services—a Catholic healthcare ministry—includes open park space on a tight urban site. However, one of its ‘greenest’ attributes may be its floors. A raised access floor system employed in five of Office Park II’s six floors, is instrumental to the open-plan design, daylighting, and expansive views for employees of owner Providence Health & Services. The facility also boasts a U.S. Green Building Council (USGBC) Leadership in Energy and Environmental Design (LEED) Gold certification, exceeding the Silver originally sought by the building owner and required by the city.
The 21,925-m2 (236,000-sf) building is home to some of the organization’s Oregon region departments, which provide healthcare, community services, and education to communities.
The six-story building includes one level of below-grade parking and a mixed-use ground level that includes café, conference center, commercial space, and employment center.
Upstairs, offices and meeting rooms surround a structural core including stairways and two elevator shafts. This core provides the entire building’s seismic and lateral bracing.
“The structural core allowed us to eliminate cross-bracing throughout the building and raised access flooring eliminated the need for overhead ductwork,” Tom Wesel, architect at Oregon-based Jon R. Jurgens & Associates Beaverton said. “As a result, when you step out of the core area, you always have access to natural light and an unobstructed view to the outside.”
The raised access floor system consists of an understructure and 609-mm (24-in.) square, welded steel floor panels filled with lightweight cement. The understructure supporting the panels provides positive positioning, lateral retention, and leveling adjustments to ensure the floor is soundly supported on all contact points.
The resulting underfloor pathway created by the raised floor panels provides housing for the building’s wiring, cabling and heating, and HVAC systems. Power-voice-data (PVD) terminations fed through the modular floor panels offer convenient, flexible access to all these services, while air diffusers supply fresh cool air from the underfloor plenum directly into the occupied space.
Along with the ability to distribute air from under the floor, comes improved comfort control in individual work areas, the result of diffusers placed in the floor that deliver conditioned air to the space.
“These diffusers enable employees to adjust the volume and the direction of air entering their work space,” Wesel noted. “Using them helped us to achieve an important goal Providence Health & Services identified early in the planning process—to provide individual control over comfort by eliminating the hot and cold syndrome employees had experienced in other facilities.”
Just as importantly, the underfloor air distribution (UFAD) system provides employees with improved indoor air quality (IAQ). This is because air is delivered directly to the occupied space, typically identified as the space from floor level up to 1.8 m (6 ft). During the process, older, warmer air is carried to the ceiling by natural convection and removed through return outlets, keeping it out of the occupied zone.
At the same time, the access floor system supports the flexible floor plan important to the building owner. Occupants are able to reconfigure or relocate work areas without having to move walls and rewire offices.
“In addition, the ability to run all the wiring and cables under the floor eliminated the need to purchase powered furniture, which can create another set of issues and challenges with respect to reconfiguring office space,” said Wesel.
Energy costs have also decreased as a result of the access floor system.
“Oregon has a pretty high mandate for energy efficiency, so saving energy was certainly top of mind as we discussed plans for this building,” said Richard Staley, regional director of construction services for the state’s Providence Health & Services.
Additional energy-efficient design elements include:
- extensive use of daylighting;
- window glazing and sunshades;
- a rubber roof that minimizes heat loss and gain; and
- motion sensors to control lighting and HVAC.
Although Providence Health & Services used UFAD in computer rooms in other facilities, Providence Office Park II represents the first time the organization considered a raised access floor for office space.
“Using the mockup, we were able to demonstrate how the air moves through the space, allowing owner representatives to see and hear it,” explained Adam Carlson, mechanical engineer with Interface Engineering, the firm responsible for the design of the mechanical, electrical, plumbing, and lighting systems in the building. “We also presented them with a smoke video that showed airflow patterns and the positive impact a raised floor system has on indoor air quality.”
Once construction began, great care was taken to maintain the integrity of the underfloor plenum. The design team agreed sequencing and maintaining a clean plenum were the two biggest challenges of installing an underfloor air distribution system. There was an extensive walk-through to ensure all the columns went down to the floor, and things were sealed before the floor’s completion. The system was also tested.
Energy savings came in a number of ways, thanks in part to the fact air for an UFAD system can be supplied at temperatures between 16.6 and 18.3 C (62 and 65 F), as opposed to 10 and 12.7 C (50 to 55 F) in an overhead system. In Portland, the outside air temperature frequently allows for use of an economizer, providing cost-effective cooling to the building. This is because the air does not have to first mix with the warmer air at the ceiling level before descending to building occupants. As a result, the underfloor air system is able to provide more economization hours.
Additionally, ventilation air, brought into the building to make the space more comfortable, contributes to the structure’s heating and cooling load.
“The calculation we use to determine how much fresh air to bring into the space takes into consideration how effectively the air is delivered to the occupants. So, in a system that delivers air from the floor directly to the occupied space, the calculation shows less ventilation air is required, resulting in additional energy savings,” explained Carlson.
Only the 1.8-m high occupied space requires cooling, and the UFAD system can supply air at low pressure, paving the way for more energy savings. The static pressure required for UFAD systems is typically 12.5 Pa (.05-inch wg), which is significantly less than the pressure needed to force air through rigid ductwork in an overhead system. As a result, the HVAC system uses less fan energy. In the case of Providence Office Park II, UFAD provides a 30 percent savings in fan energy and a 15 percent savings in system refrigeration energy.
The underfloor system definitely helps, contributing to improved comfort levels, better IAQ, and increased efficiencies.
Scott Alwine, LEED AP, is a marketing manager with Tate Inc. He has more than 10 years of experience in the building products and services industry. Alwine holds a bachelor of science in manufacturing technology and a master of science in business administration from California University of Pennsylvania. He is a member of the Commercial Real Estate Development Association (NAIOP) and the Building Owners and Managers Association International (BOMA). Alwine can be contacted at email@example.com.