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Seattle U. LEED Library Addition’s Under Floor Ventilation is Popular with Occupants

 The new concept of fabric ducted zones inside the raised floor’s under floor air distribution plenum prevents thermal decay.

 

 

 

 

 

 

 

 

 

 

 

 

 

Patrick Baldwin-McCurdy fields daily indoor air temperature requests from employees and students, however Seattle University’s (SU) lead buildings control technician rarely hears HVAC complaints from the college’s new library addition featuring under floor air distribution (UFAD).  

The $55 million project included the construction of a new three-story, 33,000-square-foot teaching, learning and research center addition and the renovation of the university’s 92,700-square-foot, 45-year-old A.A. Lemieux library. The centerpiece of a highly successful university capital campaign, the complex is now called The Lemieux Library & McGoldrick Learning Commons (LLMLC) and has since become a state-of-the-art role model in efficiency and boasts a gold Leadership in Energy & Environmental Design (LEED®) certification.  
 
While efficient technology, such as chilled beam technology helped rack up nine LEED HVAC credits, the addition’s energy efficiency and tight temperature control tolerances are achieved with the new concept of fabric ductwork inside the UFAD called UnderFloorSox™ (UFSox), manufactured by DuctSox Corp., Peosta, Iowa. “I’m the service tech who gets around 10 hot/cold calls per day on campus, but rarely is there a call about the addition’s temperature,” said McCurdy, who with Steve DeBruhl, SU’s senior project manager, handles HVAC and other mechanical responsibilities. “I don’t feel a temperature difference anywhere in that new addition, which can be attributed to the design.”
 
The design team included consulting engineering firm, CDi Engineers, Lynnwood, Wash.; construction manager, David Bonewitz, president, Bonewitz, Seattle; mechanical contractor, McKinstry, Seattle; architect firms Pfeiffer Partners Architects, Los Angeles; and Mithun, Seattle. 
 
The design team chose a raised access floor design with UFAD, because unlike the six-story original building, the addition has a huge collection of state-of-the-art media electronics. Raised floors hide the needed cabling associated with the 80 desktop and 120 laptop computers, plus a high-definition video studio, 11 multimedia editing stations and video monitors throughout the space. The anticipated reconfigurations and serviceability required with such a media-rich space are easily accomplished with the moveable raised floor’s panels.  
 
Additionally, UFAD is specified by HVAC engineers, architects and building owners for its quietness, even temperature control and ability to aesthetically hide support utilities and HVAC ventilation. Typically UFAD acts as a pressurized plenum that disperses heated or air conditioned air evenly up through floor vents into the space. “We recommended the raised floor concept because its efficiency would help with LEED credits, plus the building design featured 18-foot floor-to-floor spaces that would be difficult to heat efficiently,” said Mark Stavig, P.E., principal, CDi Engineers, who oversaw mechanical system design along with Leslie Jonsson, P.E., LEED AP, a CDi mechanical engineer.  
 
UFAD has resurged recently after engineers have found solutions to reoccurring challenges of plenum pressurization and thermal decay in perimeter and high heat or cooling load areas near windows. Pressurization and thermal decay issues were minimized at SU by CDi’s design calling for 24 fabric duct runs per floor of UFSox, which is designed specifically for UFAD. The UFSox duct runs use a combination of non-vented lengths distributing air to vented lengths that incorporate a permeability and linear orifice design factory-engineered specifically for the project. Manufacturers representative, Air Commodities Inc., Seattle, assisted in specifying the fabric duct to fit the application. “We knew thermal decay at the perimeters is a potential problem, but the fabric duct allowed us to put conditioned air anywhere we wanted in the UFAD system,” said Stavig, who had specified a half-dozen UFAD projects previously.
 
While a conventional overhead system typically supplies 55°F and cools from top to bottom, the UFAD supplies 65°F and uses air displacement to cool the bottom five feet  of addition’s 18-foot-high areas. CDi’s LEED analysis found that the UFAD’s inherent energy-saving concept would generate nine credits and save the university approximately 32-percent in operational energy costs and a total energy savings of hundreds of thousands of dollars over the UFAD lifecycle versus a conventional overhead system. 
 
With the prevalence of various room uses and sizes, such as classrooms and high-heat-load media suites, the combination of zoned UFSox ductwork supplied by VAV boxes offers the addition an unprecedented capability of zoned individual temperature control. Each zone has its own temperature sensor that’s mounted five-foot-high and monitored by the university’s building automation system. A more conventional alternative of using 100 or more fan-powered boxes throughout the UFAD plenums was considered as too maintenance intensive by SU’s facilities people.  Plus, the use of fabric duct helps projects generate LEED credits.
 

Solving Challenges

One UFAD challenge was the architect’s use of stone flooring at a feature entrance, which CDi solved with perimeter placement of slot floor diffusers that have alternating supplies of UFAD air diffusion for cooling and hot water coils for heating.
  
For CDi Engineers, the open floor plan between two of the addition’s floors and the original building created a potential challenge of the new UFAD system coexisting with a conventional overhead system. CDi used CFD modeling software to help determine the best placement of UFAD and overhead diffusers located near the two buildings’ common areas.  
 
The LLMLC UFAD system is also very flexible because of its many zones. Floor reconfigurations only need to reroute the under floor fabric duct and reposition diffusers. Heating also can be increased by adding an electric heater to any zone’s VAV box. 
 
CDi also used chilled beams that radiate cooling down into the personal computing area combined with reduced floor vent airflow to create a comfortable space. 
 
The existing building’s 100,000-cfm HVAC system uses a chiller for cooling. The chiller system’s tonnage had been incrementally increased the last few years from 200-tons to now 650-tons, the latter which was easily added through Multistack’s modular concept to accommodate the additional cooling loads for LLMLC.  
 
Two rooftop 20,000-cfm air handlers provide supply air through metal duct chases that connect with each floor’s multiple zones. 
 
The LLMLC isn’t SU’s first encounter with under floor systems and it won’t be the last, according to McCurdy. “We (SU facility managers) like UFAD for its efficiency characteristics and LEED attributes,” said McCurdy. “Combining UFAD with fabric duct to promote even air distribution and eliminate thermal decay looks to be the temperature solution we will use in future retrofit and new construction projects at SU.”
 
 

For more information, reference the UFSox product brochure in the Media Library.

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