Meeting GSA Ceiling Height Requirements

In 2012, the Hoffman Company selected the design team of Noritake Associates (Architect), Allen & Shariff Engineering (MEP Engineer) and Fernandez & Associates Structural (Structural Engineer) to meet the modern needs of a GSA tenant within a 1960’s era office building.  The 14-story 350,000-office structure (Hoffman Building 1) is situated in the heart of the Hoffman Town Center in Alexandria, VA.  To meet the needs of the tenant, plans called for a full renovation of the building that would include a radically redesigned lobby and common areas, new exterior skin and new mechanical systems.  Among the challenges, the design team needed to meet a GSA ceiling height requirement of 9’-0” with a building that has slab-to-slab height of 9’-5”; not nearly enough space for the necessary mechanical systems.  While demolition and new construction were considered, it was not a viable option given the schedule of the tenant. Given the restrictive floor heights, the design team’s only solution was to think outside of the box to move forward with the existing building shell.

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Hoffman Building 1 - Before

Hoffman Building 1 – The Challenge

The Challenge

How did the team meet a 9’-0” ceiling height with only 9’5” slab to underside of slab as required by the GSA? Hoffman Company challenged the design team to think beyond tradition solutions to save the existing building shell.

We asked ourselves what type of HVAC systems can we use that will fit with 5 inches of ceiling space?  We though about new technologies available today, chilled ceiling panels and chilled beams, both active and passive.  When we ran the space load calculations for the required cooling, we quickly found out that the chilled ceiling panels required almost the entire floor plate to cool the space, leaving no room for lights, outside air delivery, and sprinklers. The same would hold true for the passive chilled beams. Active chilled beams would provide the delivery method for outside air, however 5 inches would not allow the ductwork to be run out to the chilled beams ruling them out as well. Even with today’s innovations and technology, the limited ceiling height proved too much to pursue a traditional approach with HVAC systems.

The Solution – Thinking outside of the box, literally!

Lighting & Fire Protection

So what can we get in 5 inches of ceiling space? Traditional lights are nominally 6 inches and the typical tree sprinkler system would require and additional 6 inches. We had to find another way. The team found 1-inch light fixtures that install from below the grid. We looked at a radial designed sprinkler system with traditional pendant heads and confirmed it would fit into 5 inches of ceiling space and meet the Nation Fire Protection Association (NFPA) requirements.

Cooling, Heating, & Outside Air

With lighting and fire protection challenges resolved, what about cooling, heating and outside air? Exterior zone and the interior zones will need to be served separately and unable to cross the 5-inch ceiling space.  We thought about designing the outside air duct down the outside of the building to feed the exterior zone with neutral air.  We went back to 1970’s technology and opted for perimeter fan coil units below the windows incorporating an outside air connection. The units are water cooled from an exterior single pipe, twin tee arrangement.

The interior zone presented an even bigger challenge. We still had to find a way to deliver outside air and provide zoned cooling. The 5’ corridor provided limited opportunities even with the allowance of an 8’-4” ceiling. We decided to provide outside through Dedicated Outside Air Supply (DOAS) units located in the core mechanical rooms with shallow ductwork surrounding the core feeding through sidewall linear diffusers below the 9’-0” ceiling.  Again, we looked at alternative ways to provide the necessary zoned cooling. The interior columns of the building once hosted wet stacks and general exhaust, which was removed during demolition. The existing holes were utilized to run vertical chilled water and condensate risers allowing us to locate high-rise vertical heat pumps at the interior columns. The units will be place on multiple sides of the column as the load dictates. The units will be covered in drywall with top-side wall discharge and low sidewall return air.

Summary

Hoffman Building 1 - After

Hoffman Building 1 – After

The challenge presented, allowed us to actually use a creative process as a team to come up with a design that met the owners objectives and provide a solution to the limited ceiling space issues that so many existing building have today.

We are proud of the extraordinary and creative leadership each consultant was able to provide for this project. The complex integration of the new building systems with this existing structure was highly organized and managed.  The team is thankful for the Hoffman Companies for the trust and design freedom during this process.

 

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