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©2017 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 59, no. 6, June 2017

By Dominic Cacolici, P.E., Member ASHRAE

About the Author
Dominic Cacolici, P.E., is a principal and senior mechanical engineer with TLC Engineering for Architecture in Tampa, Fla.

Soaring summer temperatures can make flyers sweat as they wrestle their luggage down the long boarding bridge from the terminal onto the plane. To combat this misery, an airport in hot, humid Florida installed air conditioning on each boarding bridge.

Boarding bridges connecting planes to the terminals are not typically conditioned, so during the summer temperatures frequently climb above 90°F (32°C).

The Hillsborough County Aviation Authority, owner of Tampa International Airport (TPA), retrofitted 33 existing passenger boarding bridges (PBB) and added 11 new bridges with air conditioning.

The bridges use a dedicated pre-conditioned air system, which can cool them by 45°F (25°C) in seven minutes. The new systems improve passenger thermal comfort and minimize cooling demand on the terminals.

The initial mock-up of the passenger boarding bridge air-conditioning system was completed at one gate and was evaluated for aesthetics, effectiveness, and financial feasibility prior to authorization to expand the design to 58 existing gates in four other terminals.

 

Innovation

A custom fabricated ductwork system was designed to fit the telescoping bridge. The ductwork, made of heavy gage, powder coated, continuously bent steel, has an airfoil-like design to provide stiffness, negating the need for bracing. A high performance linear diffuser was placed at the end of the first tunnel to distribute conditioned air 50 ft (15 m) down the bridge. The aesthetically pleasing ductwork has small linear diffusers and nozzles to condition the staging area, where air movement would have otherwise been limited.

Computational fluid dynamics (CFD) was used (Figure 1) to determine performance characteristics needed to cool the 125 ft (38 m) long passenger boarding bridge from 120°F to 75°F (49°C to 24°C) in seven minutes, an aggressive cooling task for any HVAC equipment. By using 20°F (–6.7°C) glycol from the existing pre-conditioned air central chiller plant, the 100% outdoor air unit positively pressurizes the bridge and achieves the design goals, which consider that the boarding bridges are uninsulated, constructed of heavy gage steel, and are located on a hot tarmac, surrounded by concrete, which creates a heat island effect.

The mock-up was tested and balanced to ensure operation matched both the CFD and the design documents. Readings were taken both while the cab door was open to the staged plane and without a plane to simulate pre-cooling the bridge before aircraft arrival. In both cases the system achieved a uniform temperature within the 3°F (1.7°C) bandwidth of the temperature sensor, located at the end of the first fixed portion of the bridge (Tunnel A). Maintaining building comfort levels from the gate to the aircraft could only be made possible by using 20°F (–6.7°C) glycol to supply subfreezing air through compact ductwork.

 

Indoor Air Quality and Thermal Comfort

Using ASHRAE's Thermal Comfort Tool (which provides consistency with ASHRAE Standard 55-2010), the air distribution is proven to provide thermal comfort throughout the bridge. This was not achievable from the original pre-conditioned air (PCA) unit designs, which offered just a set of linear bar grilles at the cab, near the aircraft. Passengers in the bridge away from this outlet received no comfort, or airflow, unless positive pressure from the terminal provided it.

 

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Figure 1
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