Green Roofs - Living Architecture Monitor - Fall 2011 - (Page 17)

THE GAME CHANGER THE CITY OF MINNEAPOLIS FINDS QUICK PAYBACK ON ITS TARGET CENTER GREEN ROOF INVESTMENT By Michael Krause T wo years after the opening of the Target Center Green Roof project in Minneapolis, the City is seeing significant savings on energy use, particularly during summer cooling months. According to a recent study by Kandiyo Consulting that was commissioned by the City, cooling costs have been reduced by nearly 10 percent from 2008 to 2010, the first full year of data on energy use. Completed in September 2009, the USD $5.6 million Target Center green roof installed by Stock Roofing-Tecta America totals 113,000square-feet, making it the fifth largest green roof at the time in the U.S., and the only green roof on a major sports facility in North America. The arena, home to the Minnesota Timberwolves NBA franchise and the WNBA’s Minnesota Lynx, is heated and cooled through a district energy contract with NRG District Energy. To calculate energy savings, the amount of chilled water use in 2008 was compared with chilled water use in 2010. Although the amount of chilled water use in 2010 actually went up by about 3.4 percent, the number of cooling degree days in 2010 compared to 2008 was up by 26.7 percent. Further analysis of energy use and cooling degree, day data suggested that – without installation of the green roof – chilled water use would have gone up by 9.7 percent from 2008 to 2010. The actual reduction in cooling loads saved the City, which owns the arena, about $112,000 in the first year in energy costs for chilled water and electricity for air-handling. The City will also realize savings from at least one repair and replacement cycle of the roof that will be eliminated by installation of the green roof. The Kestrel Group of Minneapolis, which was the lead design firm on the project, designed the roof to last for at least 40 years with little or no repair or replacement. This avoided capital cost in the future was accounted for as a sinking fund with an annual contribution of $211,000 at five percent interest that would otherwise be needed to fund a roof replacement project in the next 20 years. Finally, the City’s pioneering stormwater utility fee abatement program will allow the arena to avoid an annual stormwater fee of $11,465 in the first year, and more than $379,000 in fees over the next 20 years. More important than the stormwater fee itself, Kestrel estimated the green roof will manage about one million gallons of rainwater runoff in the heart of a dense downtown district that is a stone’s throw from the Mississippi River. New water quality standards in the next two-to-three years from state and federal agencies are likely to increase costs for regulatory compliance, but the City will be able to count its green roof investment toward its goals for reducing total suspended solids, phosphorus and overall stormwater volumes flowing into the river. Overall, the City will see a payback within 7.8 years on the incremental cost of its green roof project, when compared to the costs of a standard roof replacement project. Plus, over the next 20 years, the City expects to realize $6 million in savings above and beyond its costs for the incremental costs of its green roof project. In addition, the City may explore options for generating additional sponsorship and promotional dollars by packaging the Target Center green roof with other environmental improvements at the arena and nearby LEED-certified, Target Field baseball park. The goal is to create a “green professional sports and entertainment complex” with the two facilities that will be one of a kind in the nation. Such a complex would reach several million dollars a year and be a game changer for both the City and for the green roof industry. D Michael Krause, Kandiyo Consulting, is an energy and sustainability consultant in Minneapolis, a member of the GRHC Board and chair of the Green Infrastructure Foundation. Michael Krause will be presenting the Target Center Case Study at CitiesAlive in Philadelphia for members. LIVING ARCHITECTURE MONITOR FALL 2011 17

Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Fall 2011

Green Roofs - Living Architecture Monitor - Fall 2011
From the Founder
On the Roof With…
Policy: The Game Changer
Policy: Toronto’s Green Roof by-Law
Policy: Energy Code Break-Through
GRHC: Update
GRHC: Welcome New Members
On Spec

Green Roofs - Living Architecture Monitor - Fall 2011