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©2016 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 58, no. 6, June 2016

Ken A. Warren, P.E., Member ASHRAE

About the Author
Ken A. Warren, P.E., is a capital project manager for the Port of Seattle, Sea-Tac Airport

A new preconditioned air (PC Air) system at Seattle’s airport eliminates the need for aircraft to operate onboard auxiliary power units (APU) when parked at the gate. This system helps keep passengers onboard comfortable, while increasing energy efficiency.

Beginning in the late 1990s, Seattle-Tacoma International Airport’s (Sea-Tac) staff began questioning if there were a better way to condition the indoor air for planes at the gate. Staff began by identifying a breakpoint in fuel costs that allows airlines to save money in fuel, reduce emissions of aircraft, and provide a higher quality interior environment for the traveling public.

Staff calculated that jet fuel costs were rising above $2/gallon ($0.53/L) and suggested exploring alternate means of providing aircraft services at the gate. In 2004, fuel costs began to increase for the industry.

The author led an effort to complete a feasibility analysis that analyzed the following:

  • Operating the APU;
  • Use diesel-powered mobile equipment;
  • Permanent DX system; and
  • Permanent chilled water system.

The feasibility study was developed for a life of 30 years and included first cost, replacement costs, maintenance, fuel and energy costs, and additional infrastructure requirements to support the system.

The selected design included a centralized chilled water plant (PCAP), piping and air handlers to provide cooling and heating for airplanes during boarding and deplaning to reduce costs for airlines, improve air quality, reduce noise and increase energy efficiency throughout Sea-Tac.

The PCAP delivers subcooled glycol/water through 15 miles (24 km) of piping to each of the 73 airplane gates in the existing facility to serve the complete airplane HVAC needs. The PC Air system allows airplanes to shut off their jet-fueled onboard auxiliary power units (APUs), resulting in jet fuel savings and reductions in CO2 and other gas emissions. 

The PCAP uses multiple stages and sources of cooling to serve the airplanes’ unique requirements and provide system operational flexibility. The first stage of cooling can be accomplished through the use of either a 7,750 ton-hour (98 GJ) thermal ice storage bank (with 16 tanks) or Sea-Tac’s campus chilled water system (through heat exchangers).

Two 1,500 ton (5275 kW) chillers were added to the campus’ central mechanical plant (CMP) to serve the PC Air system’s chilled water requirements and maintain campus redundancy.

The second stage of cooling in the PCAP is provided by four 300 ton (1055 kW) chillers that cool the ethylene-glycol mix down to 20°F (– 6.7°C) to serve airplanes and/or recharge the thermal tank bank. To maximize system efficiency, these four chillers use the campus’s CMP return chilled water (at 56°F [13°C]) as their condenser water source. Four secondary pumps circulate the subfreezing chilled liquid through dedicated piping to the gates for cooling.

The aircraft heating system uses existing centralized steam at various locations throughout the airport, using steam-hot water heat exchangers and variable flow hot water distributed to each gate PC Air unit.

The PC Air unit mounted at each gate delivers and directs conditioned air through a double-wall telescoping air duct mounted to the passenger loading bridge, through a flexible duct that connects to the bottom of the aircraft. The cooling or heating air is then distributed through the airplane’s cabin air system.


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