Aims and objectives. With two aging inefficient boilers and skyrocketing fuel bills, the Crosby-Ironton Public Schools in 2010 sought improvements to save energy and reduce utility bills. It decided to replace a 72% efficient boiler that was required to maintain a minimum operating temperature of 160 degrees F due to its design, which is inherently inefficient.
Implementation. With the help of Climate Makers, Inc., Crosby-Ironton Schools developed a plan to improve the school district’s boiler system. The contractor and Crosby-Ironton Schools installed a 93% efficient condensing boiler at its 105,000 square-foot Cuyuna Range Elementary School. One of the old boilers was kept in service as a backup and for use during extreme cold. The heating system water temperature is now running at substantially lower than the 160 degrees F it had been operating at year-round with the old boiler. “We implemented an aggressive hot water reset to take advantage of the condensing boiler,” said Bill Tollefson, the school’s business manager. “Our return temperatures vary as the system also feeds air handling units. It has taken some trial and error, but the system has been functioning well.”
Key to efficient boiler operation—low return water temps . Condensing boilers require a low return water temperature to operate at their highest efficiency, according to a publication from Natural Resources Canada , the ministry of the Canadian government responsible for natural resources, energy, and more. High-efficiency boilers are especially well suited to applications such as snow melting and in-floor radiant heating, because they typically have a large temperature drop and low return water temperatures. In general, heating systems must be able to perform adequately at return water temperatures below 135 degrees F in order to obtain operating efficiencies above 90 percent (see Figure 1).
Figure 1. This graph shows the effect of inlet water temperature on boiler efficiency.
Outcomes--energy saved, operations improved. The savings over the two and one-half years since the installation in fall 2010 are shown in the Minnesota B3 Benchmarking database. The annual natural gas consumption chart below helps show a cumulative savings of $13,700 (change from baseline therms multiplied by average cost per therm for each year) since the project completion. The B3 Benchmarking ratio for the Cuyuna Range Elementary School is currently 41 percent, meaning it uses about 60 percent less energy than if it were a new building built to current energy codes. Tollefson says the majority of the gas savings is a direct result of the boiler retrofit. The building operators are able to adjust the boiler to meet the demand much easier, he adds.
Documenting results. Crosby-Ironton Schools is able to measure its savings via the Minnesota B3 Benchmarking tool. The B3 tool is available for all state, local government, and public school buildings. To add your building to this database, go to the B3 website and click on “Contact Us.”
Funding. Crosby-Ironton Public Schools received a $52,600 Energy Efficiency and Conservation Block Grant from the Minnesota Department of Commerce and U.S. Department of Energy. The grant was provided by the American Recovery and Reinvestment Act of 2009, the federal stimulus program designed to save energy and create jobs. Financing was aided by a $7,500 energy conservation rebate from Minnesota Energy Resources, the school’s natural gas supplier. The boiler upgrade total cost was $105,200.
Resources for public building projects. Public institutions seeking energy efficiency improvements are encouraged to consult with the Minnesota Department of Commerce, Division of Energy Resources (DER) and their local gas or electric utility. DER offers technical support to local government units, state agencies, school districts, and institutions of higher learning that are seeking energy efficiency and renewable energy measures. Contact DER to discuss which of its energy efficiency programs can be of help.
All utilities in the state are mandated to achieve an annual energy savings of 1.5 percent of annual retail energy sales. Utility representatives can help assess opportunities for efficiency and identify what rebates may help finance projects.
The U.S. Department of Energy’s Advanced Energy Retrofit Guide for K-12 Schools provides guidance for building retrofits (you’ll need to register with DOE to be able to download your free copy). For more on energy efficiency, including information on B3 Benchmarking, contact the DER Energy Information Center.