Affordable fare: DTW upgrade enjoys smooth takeoff - Cover Story

A successful flight is a matter of doing a number of small tasks correctly, and that's the approach Detroit Metro Airport took in its recent retrofit. While a new terminal got the headlines, retooling HVAC systems for existing space has revved up the savings and created first-class comfort. High-profile items like BAS and new chillers led the way, but other moves like replacing three-way valves and adding stack economizers to boilers also helped overall efficiency return to its upright position.

Anyone who has traveled to or through the Detroit Metropolitan Airport within the last ten years knows that it was due for a facelift. Aging buildings, poor lighting, and outdated HVAC equipment all contributed to lowered levels of customer satisfaction.

Not only did the airport lack consistent comfort levels, but its old chillers and inefficient boilers led to sky-high utility bills. Something had to be done. The Wayne County Airport Authority (WCAA) wanted to provide improvements that would be flexible enough to deliver world-class comfort and safety in future configurations. It also wanted to cut the airport's energy bills by 20% to 25%. This had to be accomplished by updating the airport's mechanical, electrical, and lighting systems. But there was no money to fund the enormous renovation project. The fact remained, though, that much of the HVAC equipment was failing and needed to be replaced. The airport found the solution to its problem through a performance contracting arrangement with Siemens Building Technologies.

The $15 million energy conservation project, which began in September 2001, was finished approximately 18 months later: On time, on budget, and with no changeorders. To date it is estimated that the project has saved the airport $1.8 million in energy costs.

GETTING STARTED

The energy conservation project was initially developed internally, through the airport's power plant department. The power plant oversees the central heating and cooling plants for the airport, and they had been trying to get budget approval for capital expenses for quite some time.

"We didn't have the capital funds to replace aging equipment, which was getting too expensive to maintain," said Len Cranston, power plant executive. "That's when we decided to try a performance contract or self-funding approach, whereby the cost of the contract is funded by the savings generated from the improvements."

After qualifying and competing for the project, Siemens presented the lowest price with the highest energy savings and won the contract. The scope of Siemens' work included energy efficiency audits of all the facilities, HVAC equipment retrofits and replacements, enhancements to the existing Siemens BAS, and retrofits to brighten lighting. In addition, most of the electrical systems were upgraded to include power monitoring to better manage the airport's electric power usage.



One of the airport's big problems was its chilled water system. "We ended up taking out three of their existing 2,000-ton electric chillers, which were about 30 years old," said Peter Gruener, project manager for Siemens Building Technologies in Livonia, MI. "One of the chillers was completely dead." Only one original chiller was left in place: A 1,500-ton electric unit that had been part of a partial retrofit approximately ten years ago.

In addition to old chillers, the airport had problems with the distribution network. Part of the problem was due to the ten-year-old retrofit project, which, if finished, was supposed to have updated the chilled water plant.

"They only did the first phase, which was to put in primary/secondary pumping, but they didn't do anything out in the field like replacing three way valves or correcting their bridge problems," said Greg Warner, P.E., senior energy engineer (now district performance assurance manager) for Siemens Building Technologies.

With the existing chilled water system, the airport was only getting a 3[degrees] to 5[degrees] [DELTA]T instead of a 10[degrees] [DELTA]T. This led to large energy consumption, because the existing chillers could only load 50% or 60% on a peak day. Consequently, they had to run three 300-hp secondary pumps at 80% or 90% all the time just to keep up with the flow in the system. This meant the power plant had to run two or three chillers at half load just to keep the system under control.

To solve the problem, Warner and his team first identified and replaced all the three-way valves in the system. They also rebalanced some of the nonfunctioning controls in the system. "They were set up for a tertiary loop, but they weren't controlling return water temperatures, so it wasn't getting the load out in the system that we needed. So we redid the controls," noted Warner.

When it came to replacing the chillers, Warner first looked at the energy costs of operating the chiller plant. He found that the chillers alone required 1.1 or 1.2 kW/ton--that and didn't include the power or pumps or any other equipment. Then Warner went through all the chiller logs to figure out the exact amount being pumped through the chiller plant.