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Paynesville City Hall/Police Station, Fire Hall

Rooftop HVAC retrofits save city energy, increase productivity


Aims and objectives.
In order to save energy and enhance comfort, the City of Paynesville made much-needed upgrades to its City Hall/Police Station’s heating, air conditioning and cooling (HVAC) system. A report by Clean Energy Resource Teams details the energy-savings project.

Implementation. The City of Paynesville replaced two old rooftop HVAC units with a 3-ton unit with economizer and a 7.5-ton unit with economizer in its City Hall/Police Station (see “What do economizers do?” below). In its Fire Hall, a lighting retrofit converted 18 fluorescent fixtures to be energy efficient.

Outcomes--energy saved, CO2 reduced, occupants pleased. Comparing the baseline year of 2010, before the upgrades were finalized, to 2012, when the project was completed, the City Hall/Police Station electric use decreased 34 percent in 2011 and 16 percent in 2012. Even though this data is weather normalized, many other variables, such as additional office equipment purchases, can significantly affect electrical consumption year to year. In 2011, the first year after the upgrades, natural gas use decreased about 15 percent and CO2 emissions were reduced by 30 percent. The city reports that the new HVAC units improved the comfort and working conditions for staff in the building.

Documenting savings. The savings are shown in the B3 Benchmarking charts below. These savings represent an annual post-project average for the two years of about $2,000 (at current energy prices). The building’s Minnesota B3 Benchmarking ratio now stands at 50 percent, meaning it now uses only half as much energy than if it were a new building built to current energy codes.

Annual Electrical Consumption 

Paynesville-elec700px.png Figure 1. This Minnesota B3 Benchmarking chart shows electrical savings of 34 percent in 2011 and 16 percent in 2012.

Annual Natural Gas Consumption

Paynesville-gas700px.png Figure 2. City Hall recorded natural gas savings of 15 percent in 2011 and 16 percent in 2012.

Annual CO2 emissions

Paynesville-CO2-700px.png Figure 3. CO2 emissions were reduced by 30 percent in 2011 and 16 percent in 2012. 

Using B3 Benchmarking, Paynesville tracks energy use for two of its major buildings. The Minnesota B3 Benchmarking tool is available for all state, local government, and public school buildings. To add your building to this benchmarking database, go to the B3 website and click on “Contact Us.”

Funding. The upgrade was funded by a $45,600 Energy Efficiency and Conservation Block Grant from the Minnesota Department of Commerce and U.S. Department of Energy. The funds were provided by the American Recovery and Reinvestment Act of 2009, the federal stimulus program designed to save energy and create jobs. A rebate from Xcel Energy helped fund the upgrade. Total project cost: $52,200. 

Resources for local government projects. The Minnesota Department of Commerce, Division of Energy Resources (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 energy efficiency programs can be of help.

In addition, public institutions seeking energy efficiency improvements are encouraged to consult with their local gas or electric utility. Utilities in Minnesota 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 Building Technologies Office also provides helpful resources for building retrofits, including “The Advanced Energy Retrofit Guide for Office Buildings.” For more on energy efficiency, including information on Minnesota’s B3 Benchmarking tool, contact the DER Information Center.

What do economizers do?


An economizer saves energy in a building by using cool outside air to cool the indoor space. During the cooling season, when the temperature of the outside air is less than the temperature of the indoor air, this strategy is much more energy efficient than running the mechanical air conditioning. Building temperature controls are programmed to operate in the economizer mode when temperature conditions are right, most often during the night. In the economizer mode, the HVAC system can take advantage of this so-called free cooling, thereby avoiding the use of mechanical cooling.