Des Moines Public Schools (DMPS), Iowa’s largest school district, is no stranger to high utility costs. The district is home to 5.5 million square feet spread out over 60 facilities and accommodates more than 32,000 students and nearly 5,000 employees.
DMPS faces a stiff battle against energy consumption with a high number of aging facilities (the average is over 65 years old). It also has a handful of 100-year-old schools built between 1891 and 1910. DMPS has been using Portfolio Manager since 2008 to monitor energy and water consumption across its numerous buildings.
Not only is the Portfolio Manager tool user-friendly, but the ENERGY STAR brand carries public recognition.
“People like to hear how a tax-supported entity is saving dollars,” says Bill Good, chief operations officer for the district. “We have also been able to utilize successes in the passage of bond measures.”
The district focuses on off-the-shelf technologies and preventive measures to drive efficiency in HVAC, envelope, and electrical systems. Key strategies include:
- Exchange a building’s traditional HVAC system with geothermal. Otherwise replace outdated boilers with high-efficiency units and repair or replace steam traps.
- Upgrade building controls, particularly by replacing pneumatic controls with direct digital control (DDC) technology. This allows the district to create temperature set points, set back temperatures for unoccupied periods, and stagger the startup of equipment to avoid peak demand charges.
- Tighten the envelope by replacing single-pane windows with double-pane glazed windows and exchanging old doors for ones with internal insulation and weather stripping.
- Switch T12 lighting to T8 and T5 fixtures and install LED and motion sensors where possible.
- Maximize the use of daylighting with
- Eliminate personal appliances, such as printers, fridges, and microwaves.
- Test and adjust boiler combustion on an annual basis to maintain burner efficiency.
- Install smart controls on vending machines.
- Decrease pool energy consumption with pool covers and solar water heaters.
- Rely on zone heating and cooling,
particularly during summer schedules.
- Implement energy management procedures that automatically shut down all DMPS computers at 6 p.m., which affects over 15,000 devices.
- Use data analysis to set goals and identify consumption spikes, which can indicate mechanical or operational problems.
“We meet monthly to review energy use data. Since we have many years of trend data, we are able to sort and prioritize low-performing buildings,” Good explains. “The targeting can include retrocommissioning, review of our EMS systems, walkthroughs, or establishing strategies for equipment replacement.”
For example, the district recently targeted gym lighting retrofits. Many of the 400W mercury vapor or metal halide lamps were 10-20 years old, had lost their brightness, and required frequent maintenance. Over 500 of the old lamps were replaced by six-lamp, 345W T5HO fluorescent high bays. Not only has the new lighting rejuvenated the gyms’ appearance with improved color rendering, but they use 25% less energy.
The district has also found to its surprise that it can install air conditioning in buildings at a lesser operational cost than prior to improvements, largely due to adding geothermal systems and tightening of the envelope. There are currently 33 schools relying on geothermal with more conversions in the future.
This multi-front attack on energy consumption has resulted in 53 ENERGY STAR rated buildings with an average score of 86. DMPS is currently ranked 11th in the nation for most labeled schools. Since the 2007-2008 fiscal year, DMPS has avoided $2.4 million in energy costs.
Take Away Lessons
Think these savings come with a hefty price tag? Think again. An average of $111 per DMPS student is spent on energy costs, compared to the national average of $181.53 per student. The average energy cost per square foot is $0.62, which is significantly lower than the $0.92 per square foot for schools typically seen around the country.
In 2012 alone, the district saved $629,081 in energy costs, reduced energy use by 28%, decreased emissions by 4,651 MtCO2e (million metric tons of carbon dioxide equivalent), and increased its average ENERGY STAR score by seven points.
With the help of Portfolio Manager, the district will continue to benchmark its buildings, pursue practical and affordable efficiency measures, and one day have all of its schools wearing the ENERGY STAR label.