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August 1, 2019
Concrete can make a major difference in reaching low- or net-zero goals on any K-12 project.
“Achieving zero-energy school facilities is a strategy of reducing energy use low enough that allows roof mounted solar panels or other on-site renewables can offset the buildings energy use over the course of an entire year,” said Philip Donovan, one of the project architects for the net-positive energy Discovery Elementary School in Arlington, Virginia.
“Most of the energy savings are achieved through reducing the air leakage of the building skin thereby reducing the energy needed to heat and cool the building spaces,” Donovan said. “Concrete is a modern building material with immense structural capacity and energy efficiency contributions. It also one of the most effective air barrier systems you can utilize.”
First to zero-energy
Following are several case studies highlighting the use of concrete and the role it plays in creating zero-energy school facilities.
Richardsville Elementary School, completed in 2010, is the nation’s first zero-energy school. The 77,000-square-foot building combines drastic a reduction in energy consumption with on-site photovoltaic panels that produce more energy than is required to run the building.
The reduction in energy consumption was achieved using an insulating concrete form system for the exterior walls and geothermal heat pumps along with several passive solar strategies.
“We are tremendously proud that, since its opening in 2010, we have not paid a single utility bill on Richardsville Elementary School, said Jay Wilson, director of safety and management at Warren County Public Schools in Kentucky. “The reason for this cost avoidance is that the building actually generates more electricity than it consumes. At the end of the school year, we usually get a check back from the utility company in excess of $30,000.”
Kenny Stanfield, principal at the architecture firm Sherman Carter Barnhart and architect on Richardsville Elementary School, said energy-saving schools pay off in the long run.
“The easiest way to increase a school districts budget is to reduce energy consumption,” said Stanfield. “And the most cost-effective way to save energy is not to need it.”
Stanfield, along with CMTA Engineers, lowered the energy use intensity for Richardsville Elementary School by 75%.
Because the energy use was so low and the building construction cost was below budget, the school district was able to absorb the cost of adding a 349-kilowatt photovoltaic array to provide enough energy to power the school and sell a small amount back to the electric utility.
And since energy is the highest operational expense in schools, these savings can go towards paying for additional teachers, the highest operational expense.
In late 2016, following the first full year of operation, the 98,000-square-foot Discovery Elementary School in Virginia became certified as the first zero-energy school in the mid-Atlantic and the largest zero-energy school in the country.
To meet energy goals, the design included insulating concrete form exterior walls, roof-mounted solar panels, a geothermal heating/cooling system and LED lighting.
“Insulating concrete form walls have an effective thermal mass equivalent to around R-40,” said Donovan, one of the project architects at the time with VMDO for Discovery. “With its concrete core, it is one of the best air barrier systems you can utilize on a building. One of the most significant impacts on achieving an ultra-low energy use is reducing the air leakage of the building skin so we can reduce the size of the mechanical system and the amount of energy needed to heat and cool the building.”
He added, “Code requires an air leakage maximum for the whole building to be no greater than 0.4 cubic feet per minute. The Army Corps of Engineers sets its standard at 0.25 cubic feet per minute. At Discovery, we required an air leakage of no greater than 0.15 cubic feet per minute for the whole building. We knew insulated concrete form, with its concrete core, was going to be the main building component to help us reach that metric, and it did. The building passed the air leakage test on the first try with a rate of 0.11 cubic feet per minute.”
An energy dashboard that provides real-time energy data is utilized by both teachers and students to support and enhance the academic curriculum. The building was designed for an energy use intensity of 23, however actual energy use intensity is approximately 16, which is 76% lower than the national school average.
The school is net positive energy, meaning it produces more energy than it uses over the course of 12 months. The ultra-low energy use, coupled with the energy production of the solar array, means the school saves more than $100,000 per year on energy costs and is the easiest building to maintain in the school district’s portfolio.
This is one of the main reasons why Arlington County Schools has mandated similar performance for all-new construction moving forward. The school was named a U.S. Department of Education Green Ribbon School and was an AIA COTE Top Ten Project in 2017. The project was completed under budget, returning millions of dollars to the district.
The U.S. Department of Energy selected Discovery as its case study to launch its Zero Energy Schools Accelerator Program.
First in Florida
NeoCity Academy in Kissimmee, Florida, will open in August and is on track to become the first zero-energy school building in the state of Florida.
The three-story, 45,000-square-foot STEM school will provide 500 students seats and was constructed in just nine months using concrete tilt-wall as its primary building material.
Cast flat on the first-floor slab, the 7¼-inch thick panels are tilted into place and secured to one another and the structural steel infill. Concrete tilt-wall construction is a primary building system in Florida for schools given its high thermal mass and quick construction timeframe.
The building is expected to hit a target energy use intensity of 16 and save the School District of Osceola County more than $115,000 year in energy costs.
“The key to ensuring a tight building envelope with tilt-wall construction is to provide a belt and suspenders approach to the detailing of the panel joints and wall openings.” said Donovan, who is now community studio principal with Little Diversified Architectural Consulting and project architect.
“Building redundancy into the details ensures that the weakest part of the concrete wall system, the panel joint, remains viable even if several components of the detail fail. This keeps the high-performance air barrier intact and performing as designed.”
NeoCity Academy will generate 228 kilowatts of electricity from its 694 self-ballasted and roof mounted solar panels. The project has already been recognized with an award of merit from the Florida Educational Facilities Planners Association.
According to Stanfield, the trend toward zero-energy schools, also known as net-zero energy or zero net energy, comes down to three factors: state-of-the-art design strategies and technologies to reduce energy consumption; affordable on-site solar energy, and insulating concrete forms that can provide high R-value, low air infiltration at a low cost.
Insulating concrete forms combine two well-established building products, reinforced concrete for strength and durability, and expanded polystyrene insulation for energy efficiency.
Insulating concrete form walls are made up of two layers of rigid insulation held together with plastic ties to form insulating concrete form units with a cavity in the center. The insulating concrete form units are stacked in the shape of the wall, reinforcing steel is added into the cavity and then concrete is placed into the form.
The result is a reinforced concrete wall with a layer of insulation on each side. What makes insulating concrete forms different from traditional concrete construction is that the forms remain in place after the concrete is cured to provide thermal insulation.
The combination of reinforced concrete and insulation provides an ideal load-bearing wall, thermal envelope, air barrier, fire barrier and sound barrier.
Insulating concrete forms are part of a concrete, masonry and steel building system regularly used in school construction to achieve high performance and energy efficient schools in Kentucky, Texas, Virginia and other states.
Lionel Lemay is executive vice president and division head of structures and sustainability for the National Ready Mixed Concrete Association.