The district cooling system Xcel Energy built a decade ago can help building owners cut down on energy use.
But as the latest downtown construction boom takes hold, many of the new buildings aren’t tapping into the system, which overnight makes ice that is then melted and used to cool buildings during the day.
Experts say there are a variety of factors keeping developers from connecting to the system, which operates from a hulking building next to an Xcel office at 15th and Glenarm streets.
“An office building, retail center and residential building all have very different requirements,” said Marc Able, founder of ABS Consultants, a mechanical and electrical engineering firm. “It comes down to the economic and financial plan of the owner.”
Location also is a factor. If a building is too far from the system’s basic service area, it’s costly to run the pipes to connect it. Xcel will bear some of the cost if there are several buildings that are potential customers for the system, but in many instances, that’s not the case.
The new U.S. Environmental Protection Agency building at 16th and Wynkoop streets in LoDo, for example, is on Xcel’s district steam system but not the chiller because of the distance to connect to it.
“It would have taken 1,500 feet of pipe, and there are not enough big buildings around it to justify it,” said Steve Kutska, Xcel’s development manager for thermal energy.
The chiller system generally serves buildings in the area bounded by Glenarm, 17th, Lawrence and 15th streets.
Several spurs jut outside that area to connect buildings, including the Colorado Convention Center, the Denver Art Museum, Denver Public Library and the Alfred A. Arraj U.S. Courthouse.
In January, Xcel expanded the system to include the Denver Justice Center, which will be completed in 2009.
Xcel could have put a satellite chiller in the EPA building and waited until development warranted connecting it to with the rest of the system.
But the security-conscious EPA didn’t want to deal with daily site visits from an Xcel employee.
“You win some, you lose some,” Kutska said.
Some tap in later
The downtown chiller is one of 15 district cooling systems nationwide.
A tangle of gigantic pipes snakes through the building that houses the system. They pump water from two ice tanks that each hold 850,000 gallons of water.
The floors of the tanks are 18 feet deep and the walls are 34 inches thick. About 2.7 million gallons of water is in the system at any given time.
The system, which pumps 30,000 gallons a minute to downtown buildings, uses 55 million gallons of water a year.
The plant makes ice at night in an amount that can cool about 38 buildings the size of the Grand Hyatt on 17th Street for about four hours.
It melts it during the day to pump it to the 40 downtown buildings now on the system. By making the ice at night, Xcel shifts about 40 megawatts of electricity consumption – enough to power a community of 40,000 homes for one hour – away from peak daytime periods.
Another new building that won’t use the district cooling system is The Spire, a 41-story building near the convention center that will include 503 condominiums.
The issue, Kutska said, is that the district system’s 34-degree water is too cold for a residential building.
Instead, Spire will use a heat pump and cooling tower system that makes water in the 60-70 degree range.
Other residential buildings have worked around the temperature issue, however, and The Spire could later wind up hooking into the district system anyway.
That’s because the equipment that will be used to heat and cool The Spire has a roughly 20-year life span, so eventually, it will have to be removed from the roof.
That’s when Kutska expects the building to tap into the district system because removing and installing equipment for a high-rise is challenging once the building is completed.
Being on the Xcel chiller system also would have required a more expensive distribution system, which is another reason the developer avoided it.
“It was considered, but based on the price point the owner had for selling the units, we decided not to use it,” said Able, whose firm consulted on the project.
System can save money
The expense of removing and reinstalling equipment is why developer Mike Zoellner hooked into the district system when he converted 1600 Glenarm to apartments.
The original cooling towers on the building’s lower podium were loud and didn’t comply with the city’s noise ordinance. One option was to put them on the tower’s roof, said Greg Martino, president of AE Associates, a mechanical and electrical engineering firm that did an economic analysis of the building.
“To do that was going to be extremely expensive because there was no tower crane available,” Martino said.
“Flying them in by helicopter was not an option. There was no way to economically lift the cooling towers up to the roof. That made it more economical to go with the district system.”
To deal with the temperature issue, the district system mixes the outgoing cold water with warmer water that’s returning to the plant to ensure the temperature for a residential building isn’t less than 65 degrees.
Xcel still is working with developers of other projects such as the Four Seasons Hotel and Union Station.
Kutska estimates a cooling system for a 30- to 40-story building costs about $3 million, an expense a building owner does not incur when tying into the system.
As an unregulated utility, the district cooling system negotiates agreements with each building owner. Agreements typically are for 20 years.
“Our rates are competitive, but not as low as someone putting their own chiller in,” Kutska said. “What they get is reliability.”
They also can get water savings credits and points toward Leadership in Energy and Environmental Design or LEED certification like the Wellington Webb Municipal Office Building did.
Staff writer Margaret Jackson can be reached at 303-954-1473 or mjackson@denverpost.com.
