New high efficient boiler have helped the Sherburne County Government Center reduce its natural gas consumption by 12 percent.
Aims and objectives. Struggling to maintain and keep two 2-million Btu per hour aging and inefficient boilers supplied with natural gas, the Sherburne County Government Center in Elk River sought improvements to save energy and reduce utility bills. It decided to replace the aging hot water boilers with high efficiency units.
Implementation. The existing boilers’ efficiency was estimated at 75 percent. Sherburne County installed two 91 percent efficient condensing boilers at the 160,000 square-foot Government Center, built in 1965. Kevin Anderson, Sherburne County building facilities manager, says they are now able to run the heating system at lower temperatures so that the return temperature to the boiler is 130 degrees F or below. With the new equipment the county no longer needs to pay for expensive repairs to the old boilers; just a little preventive maintenance is needed, he says.
Key to efficient boiler operation—low return water temperatures. Condensing boilers require a low return water temperature to operate at their highest efficiency, according to several sources, including information from the Center for Energy and Environment. In general, heating systems must be able to perform adequately at return water temperatures below about 130 degrees F in order to obtain boiler efficiencies above 87 percent (see Figure 1). Thus, the more hours during the heating season that the temperature of water returning to the boiler can be kept below that value, the higher will be the average seasonal efficiency. High-efficiency boilers are especially well suited to applications such as snow melting and in-floor radiant heating, because those applications typically have a large temperature drop and low return water temperatures.
Figure 1. This graph shows the effect of inlet water temperature on boiler efficiency.
Outcomes—energy saved, operations improved. The savings since the new boiler installations in fall 2010 are shown in the B3 Benchmarking database. The chart below (figure 2) shows a savings of $10,000 in 2012 compared to the base year of 2010. The B3 Benchmarking ratio for the Government Center was 203 percent in 2010, meaning it used more than twice the energy than if it were a new building built to current energy codes. The B3 Benchmarking ratio today improved to 160 percent, indicating there still may be opportunities for energy conservation actions.
Sherburne County annual natural gas consumption
Figure 2. This Minnesota B3 Benchmarking chart shows a 12 percent natural gas savings for the Sherburne County Government Center since 2010.
Documenting results. Sherburne County is able to quantify its savings via the Minnesota B3 Benchmarking tool. The B3 tool allows users to track their buildings’ energy use, monitor the performance of energy improvements, and readily identify poor energy performance. It 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. Sherburne County received a $100,000 Energy Efficiency and Conservation Block Grant administered by the Minnesota Department of Commerce. 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 rebate of $2,800 from CenterPoint Energy, Sherburne County’s natural gas supplier. Total cost for the boiler upgrade: $301,500.
Resources for local government 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 provides 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 efficiency programs can be of help.
Utility representatives can help assess opportunities for efficiency and identify what rebates may help finance projects. Utilities in Minnesota are mandated to achieve an annual energy savings of 1.5 percent of annual retail energy sales.
An entry on the Natural Resources Canada website called Installing High-Efficiency Boilers for Heating Plants offers guidelines for purchasing and operating high efficiency boilers. For more on energy efficiency, including information on Minnesota’s B3 Benchmarking tool, contact the DER Information Center at email@example.com or 800-657-3710.