The energy upgrades to Robbinsdale City Hall are paying dividends in more ways than one.
Aims and objectives. Robbinsdale City Hall had been an uncomfortable place to work and visit. Temperatures throughout the building were either too hot or too cold both in winter and summer months, and the humidity was hard to control. According to Robbinsdale Senior Engineering Tech Robin Verkinnes, in 2010, it was time for an energy overhaul of City Hall.
Implementation. Robbinsdale City Hall is a 14,400 square-foot building that was constructed in 1970 and houses 33 staff people for conducting a range of city business. Its comprehensive energy project entailed major improvements to the heating, ventilating and cooling systems, lighting system, domestic hot water system, and exhaust fan control:
Heating system. The heating equipment was upgraded to a high efficiency condensing boiler plant. It is controlled to reset the hot water set point based on space and outdoor air conditions. The boiler has a 10-1 turndown ratio, and with low enough return water temperature it can be up to 94.6 percent efficient.
Ventilating system. The system was upgraded by installing new and properly sized variable volume air handling units and variable air volume systems. All are equipped with variable frequency drives. Direct digital controls (DDC) drive the system, now upgraded to be demand controlled ventilation (DCV). The DCV sets the ventilation rate depending on the level of CO2 in the return air, which is directly related to the number of occupants in the ventilated space.
Cooling system. Each air handling unit is equipped with a high efficiency (12.1 EER) 20-ton condensing unit operating with R-410A (which does not contribute to ozone depletion).
Lighting system. Replacement of many older T12 florescent bulbs with Full Spectrum T8 5000 K bulbs in a large number of existing 4-foot light fixtures, which, combined with lens cleaning and installation of new reflectors, allowed removal of 2 lamps from each 4 lamp fixture. A large number of 60-watt incandescent bulbs were also replaced with compact florescent bulbs.
Domestic hot water. A new direct-vent sealed combustion hot water heater was installed. The recirculating domestic hot water system pump is now controlled to cycle off during unoccupied hours.
Exhaust fan control. Five exhaust fans were wired to be controlled by the building automation system that allows the fans to be cycled off during unoccupied hours.
Outcomes : Energy saved, CO2 reduced, comfort enhanced. Now the overall comfort levels have improved dramatically. The new equipment is considerably more reliable, and energy performance has improved dramatically. The bill for electricity has been cut by about 30 percent. Before the building improvements, the Minnesota B3 Benchmarking score was 151 percent, meaning it uses about half the energy that it would use if it were a new building built to current energy codes. Now the building has a B3 Benchmarking score of 78 percent, meaning it uses a little more than three fourths as much energy if it were a new building built to current energy codes.
The electric use was reduced from the 2010 quantities by 27 percent in 2011 and 26 percent in 2012. Figure 1, available on the B3 Benchmarking database, shows the year 2010 as the baseline and the post-project reductions for 2011 and 2012. A slight rise in natural gas consumption of 2 percent occurred in 2012 (see Figure 2). This is likely due in part to the new variable air volume (VAV) system, which significantly reduces electric consumption but may slightly increase gas consumption (see sidebar below on VAV systems).
City Hall annual electric consumption
Figure 1. This chart from the Minnesota B3 Benchmarking database shows the electrical savings of 27 percent in 2011 and 26 percent in 2012.
City Hall annual natural gas consumption
Figure 2. Natural gas consumption achieved a 7 percent decrease in 2011 but went up slightly in 2012.
City Hall annual CO2 emissions
Figure 3. CO2 emissions were reduced 23 percent in 2011 and 22 percent in 2012.
Documenting results. Robbinsdale is able to quantify its energy savings via the Minnesota B3 Benchmarking tool. B3 Benchmarking is a building energy management system for all state, local government, and public school buildings. It allows users to track their buildings’ energy use, monitor the performance of energy improvements, and allow building portfolio managers to readily identify poor energy performance. The B3 tool is provided by the Minnesota Department of Administration and the Minnesota Department of Commerce, with funding from all utilities in the state supporting the effort. To add your building to this benchmarking database, go to the B3 website and click on “Contact us.”
Funding. Robbinsdale City Hall energy improvements were funded in part by an $87,000 Energy Efficiency Conservation Block Grant (EECBG) from the Minnesota Department of Commerce. The grant was provided by the American Recovery and Reinvestment Act, the federal stimulus program designed to save energy and create jobs. The grant paid for half of the $174,000 project cost to replace a number of elements of the HVAC system and change out most of the lighting in the building. The other half of funding was from the city and energy efficiency rebates from both Xcel Energy and CenterPoint Energy.
With the national phase out of magnetic ballasts and T12 lamps, Minnesota utilities no longer offer rebates for converting such lighting systems. However, with rising demand and energy charges for commercial consumers, companies that still have these in place may find it cost-effective to replace them even without rebates. Most electric utilities provide rebates to support change outs of other older lighting systems and to help fund other lighting efficiency improvements.
Resources for public building projects. When seeking energy upgrades, cities are encouraged to consult with the Minnesota Department of Commerce, Division of Energy Resources (DER) and their local utilities. DER provides technical support to local government units, state agencies, school districts, and institutions of higher learning that are seeking to implement energy efficiency and renewable energy measures. Contact DER to discuss which of its efficiency programs may be of help.
In addition, 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. For more on energy efficiency, including information on Minnesota’s B3 Benchmarking tool, contact the DER Information Center (1-800-657-3710).
The variable air volume system distributes constant temperature supply air (usually about 55 degrees F). To meet varying conditioning demands of spaces, the air flow rate is varied to meet the rising and falling gains or losses within the zone served. There is also usually “reheat” needed for some spaces. This may cause an increase in heating fuel (natural gas) use, although this is usually quite small compared to the large electrical energy savings.