Managing K12 Energy

The 100,000+ K-12 schools in the U.S. are the largest energy consumers in the public sector. Within schools, HVAC energy accounts for 46% of this total energy consumption. Nationwide, regulators have increased their efforts to reduce the energy intensity of commercial buildings as a way to combat carbon emissions. K-12 schools are of particular interest given their high environmental impact and the government’s influence over these buildings.

School districts set heating and cooling policies to manage energy consumption, but individual teachers, administrators, custodians, and others can override those settings manually. This drives up peak demand, which in turn increases overall energy consumption and energy costs. Managing these competing demands—the school district’s need to reduce energy consumption and occupants’ need to stay comfortable—is crucial.

A Promising Technology

Lab demonstrations have shown the promise of a technology called dynamic model predictive control, and CEL and its partners recently conducted an experimental study of that technology. This field demonstration is unique since advanced building controls for load flexibility have not been demonstrated in the K-12 market, despite the market’s size and energy consumption. The project team performed its field test at Sonora Elementary School, which is located south of Los Angeles in Newport Mesa Unified School District. CEL’s controls were installed in two buildings at the school, each consisting of three classrooms served by their own rooftop units (RTUs).

CEL's dynamic model predictive control (or, as our customers lovingly call it, “the robot”) can adjust HVAC setpoints to shift or curtail loads during high carbon-emitting or peak demand periods. The robot optimizes the operation of a school’s HVAC system within the comfort constraints set by the school district, resulting in load shifting and peak demand reduction. Importantly, it does all of this while maintaining the comfort of teachers, students, administrators, and other occupants without them needing to manually adjust thermostats.

The Robot Works Its Magic

At Sonora Elementary, CEL’s robot reduced 24% of total peak power and 30% of HVAC peak power. It also shifted 16% of the cooling load from an on-peak price period to a low price period. The graphs below demonstrate what this means, practically speaking, for both the district and the building occupants.

What normally happens on a hot day

Even when building operators have done their best to set a rational central policy for setpoints and schedules, this is what happens:

• The top graph shows the outdoor air temperature (blue line), the setpoints for cooling and heating (dotted red lines), and the actual indoor air temperature in various HVAC zones throughout the day (all other lines). For Sonora, the district wants to keep the indoor temperature between 72-76 °F; however, occupants are overriding the controls. Even without user overrides and with optimal start technology by HVAC unit, the indoor air temperature is fluctuating dramatically. Temperatures in some zones hover near 76° while temperatures in other zones dip below 72° (one even goes as low as 68°).
• The middle graph shows when each zone's HVAC unit is running (thin lines), the total unit runtime (thick blue line), and occupant override (shaded gray areas). Even though an HVAC unit might have optimized embedded controls, it is not aware of what is happening in other zones. This means various units are able to run at the same time, increasing energy consumption and peak demand.
• The bottom graph displays the peak demand for Sonora. Notice how closely peak demand follows HVAC unit run time. HVAC is driving those peaks, meaning it is driving energy consumption, peak demand, and the resulting energy bills—even with a fairly large solar array onsite.

What happens when the robot controls on a hot day 

When CEL’s system controls cooling, this is what happens:

• In the top graph, on a similarly hot day to the first example, we can see much tighter zone temperature control. Zones fall within the dotted red lines at nearly all points throughout the day. That means the robot is managing indoor air temperature in a way that is far more consistent and comfortable for occupants.
• In the middle graph, even with occupant override, the total HVAC runtime and peak are far lower. This happens despite the fact that indoor temperatures are under better control.
• In the bottom graph, the load shape and peak are more than 20% lower than they were in the first example. This means Sonora is saving a lot of money on energy and demand charges.

By making tiny adjustments all day long, CEL’s robot saves building operators time, more closely follows district indoor air temperature guidelines, and reduces runtime and coincident peak. All of this lowers demand. The robot can also pre-cool a building. For buildings on a time-of-use rate (which rewards consumers for using electricity during off-peak hours), pre-cooling would reduce both demand spikes and overall price. These results are applicable to heating periods as well as cooling periods.

COMFORT & AFFORDABILITY = BFF

In all, the robot reduces operator time, keeps occupants comfortable, and reduces energy consumption. In addition, if a user transitions to a time-of-use rate or real-time price, the system can further autonomously optimize for energy bill savings. Since the HVAC energy consumption accounts for the largest portion of the total energy use in K-12 schools, the grid-interactive operation of their HVAC systems could lead to significant financial and environmental benefits to the grid as demand response and grid decarbonization resources. In addition, because of the unique sector of education, the grid-interactive operation could be beneficial for the future generation to learn about climate change. Furthermore, thanks to the consistent HVAC system configuration in a majority of K-12 schools, there is also a potential to have a universally applicable control solution for those buildings.

Join Us!

If your local school is interested in participating in a utility or Department of Energy-funded pilot to try the HVAC robot and save on your energy bills, then we encourage you to apply to CEL's Smart & Resilient Schools pilot program. The program pays for installation (which happens in under a day) and a one-year license to use the robot.