By TOM O’NEIL, AIA, LEED AP Photos by FRANCISCO MURRIETA June 25, 2013
Perhaps more than any other building type, school facilities have the potential to directly enhance the user’s experience through sustainable design. This is evidenced through standards for design such as the U.S. Green Building Council’s LEED for Schools rating, which addresses factors affecting student health and achievement. Sustainable design studies also confirm that daylighting improves the occupant’s ability to learn and that a “healthy building” helps make for healthy people.
Arizona’s Paradise Valley Unified School District put these sustainable design principles to the test in setting goals for its newest school. Fireside Elementary, in Phoenix, would produce nearly as much energy and water as it consumes, saving taxpayers money and providing a teaching tool for students. The two-story, 88,664-square-foot (8,237-square-meter) school was completed at the end of July 2012. It includes daylighting, reclaimed water for irrigation, energy-efficient construction and mechanicals and systems for solar electricity and solar water heating.
As the designers on the project, my colleagues and I at DLR Group had the benefit of a team of stakeholders committed to making their aggressive energy goals a reality. We knew that we could draw on the region’s abundant sunshine to make daylighting and solar energy key components. The location’s extreme cooling requirements and arid climate meant that building orientation and high-efficiency design, optimized through energy modeling, would be just as important as generating energy on site. Ultimately, these three factors — the client’s vision and commitment, energy modeling and reduction/production strategies — helped define success in designing Fireside Elementary for near-net-zero energy usage.
Setting the Vision
Prior to any new construction or renovation, a client must determine the vision for sustainability. This requires that they have an established benchmark for existing facilities that allows them to understand energy use, cost and demand. The visioning exercise must involve all stakeholders including staff, building users and the design team. The goal of the exercise is to create a plan for “energy independence” based on energy reduction and production initiatives.
The vision-casting sessions for Fireside Elementary, conducted in March 2011, established design goals that became guiding principles for the project and the metrics for measuring success:
- Design to a near-net-zero energy usage with low system maintenance.
- Use sustainable aspects of the design, such as the rainwater harvesting system and photovoltaic system, as teaching tools.
- Communicate the district’s commitment to sustainability to the community at large. For instance, although most rainwater harvesting systems are “behind the scenes,” collection silos are front and center at this school and in the community.
- Place monitoring displays in the lobby showing energy usage and production from the photovoltaic system.
Modeling the Design Options
Energy modeling tools can accurately measure amounts of daylight and glare entering a building at certain times of the day and through every season of the year. They can measure the operational impact of setting a building in a slightly different orientation for tremendous energy savings, or find the “hot spots” in a specific room that require moving a window to a different location.
In the case of Paradise Valley Unified School District, energy modeling helped decision makers determine how best to apply their dollars to achieve near-net-zero energy at Fireside Elementary School. This modeling encompassed every decision, from the building envelope design, to insulation, to glazing options, space conditioning methods, rainwater harvesting and Energy Star equipment. Different scenarios were communicated to the client using info-graphics, as shown in “Predicted Energy Consumption Diagram,” below.
Reducing Energy Usage
Based on energy modeling, the project team identified a design projected to reduce energy usage by 55 percent compared to average elementary school buildings of the same size and in the same ZIP code. Key sustainable design elements follow.
High thermally and acoustically efficient insulated concrete form (ICF) walls improved the thermal quality to R-22, reducing the need for cooling. The second-story portion of the ICF wall system has an additional 2 inches of insulation. The overall U-value ranges from 0.043 to 0.031. Metal stud walls at the school’s media center have 1.5 inches of polystyrene over R-19 thermal batt insulation within the stud cavity. The metal stud frame system’s overall U-value is 0.077.
We selected three types of low-e glazing based on transparency factors for different orientations. North elevation, with a more diffused daylight, has the greatest transparency and used PPG’s Solarban 60 solar control low-e glass. South elevation used Solarban 100, and east/west used 70 Solarban XL. Solatube skylights in the multipurpose room nearly eliminate the need for artificial lighting in this room during school hours.
Two-story skylight openings in the corridor reduced the effect of long hallways with a splash of light on the floor.
Overhangs and fins
Overhangs on north/ south facing windows protect classrooms from heat gain during school hours. The east/west windows also use vertical fins to reduce direct heat gain.
Extensive daylighting solutions using nLight networked lighting controls reduced the lighting load, while automatically maintaining 50 footcandles. Sloped ceilings in the classrooms pull daylight deeper into the space from clerestory windows.
Smardt high-efficiency chillers, economizers and variable-drive motors in towers and pumps configure operational conditions of HVAC equipment for heating/cooling needs based on variable parameters. The system then automatically re-programs to serve energy daily.
Sensors and monitoring
In addition to occupancy sensors for cooling and lighting, the systems are monitored off site both for security and energy use.
Generating Energy On-Site
As much as reducing a building’s carbon foot-print requires commitment to energy reduction, achieving net-zero nearly always requires some production of renewable energy. A rule of thumb in net-zero design is to shoot for 75 percent reduction of energy (compared to energy use of similar type of building in the same ZIP code using the Energy Star target finder), leaving 25 percent energy use to be met through renewable energy technologies.
The above reduction strategies, although aggressive, left an energy deficit requiring a photovoltaic (PV) system to produce 340 kilowatts (kW) at full building capacity. Installed three months after the opening of the school, parking structure-mounted PV arrays were added to produce 260 kW, which accommodated the two-thirds capacity load when the school opened last fall.
On the playground, a ground-mounted PV array provides shade from the desert sun. This unit produces 80 kW, which, combined with the parking structure arrays, will cover the school’s energy needs at full capacity.
Additionally, Fireside Elementary includes 9 square meters of glazed flat-plate collectors from Integrated Solar LLC for solar water heating. Combined, these solar energy systems are projected to meet 93 percent of energy needs. That allows the district flexibility in refining operations and further reducing energy needs, without potentially over-producing energy.
Harvesting Rain Water
In addition to its near-net-zero energy usage goal, the district wanted Fireside Elementary to raise awareness of water conservation and strive for net-zero water usage for irrigation needs. The system includes four above-ground storage tanks. One tank, open to the elements, captures rainwater and roof water runoff. At 4,200 gallons (15.9 kiloliters) capacity, the open tank is the smallest of the tanks, and is placed at the front of the media center as a focal point of the building.
The rest of the storage capacity is handled by three closed tanks, each 8,900 gallons (33.7 kiloliters) in capacity. Roof drainage pipes connect to these closed tanks via a filter housing assembly that holds the “first flush diverter” to remove any debris collected from the roof. These three tanks are connected via an underground equalizing pipe, avoiding the need for a giant 26,000-gallon capacity tank with a complicated, expensive roof drainage and collection system.
Because precipitation in Phoenix is unpredictable, city reclaimed water is used as the backup source. Of the three closed tanks, one tank acts as the control tank with a minimum level float that activates a pump, which pulls in the city reclaimed water. A maximum level float signals the reclaimed water pump to stop supplying water. The volume of water stored between the minimum and maximum water level is the amount required to irrigate all landscape zones in a peak summer day.
Assessing the Benefits
Since Fireside Elementary is only two-thirds occupied (full occupancy will occur as this new community is built out), its energy bills are not yet being used to confirm net-zero energy usage. Once the facility is operating with full-capacity energy loads, the school district will communicate to students and the community the impact of designing schools to near-net-zero.
Fireside Elementary School cost $13.5 million, or about $152 per square foot. Passive solar energy-reduction strategies, which reduced the projected energy usage from 40 to 22 kBtu, were realized at $8 per square foot. Production strategies, which further brought down energy usage from 22 to 1.6 kBtu from, were realized at $17 per square foot. In other words, since the PV solution cost almost double the passive reduction strategies, the latter reduced the district’s capital cost outlay for this near net-zero design. The school also received a $106,314.78 energy efficiency rebate from the Arizona Public Service utility company.
However, the bottom line economic impact isn’t the only way to measure success. Fireside
Elementary School includes not only solar energy components, but also an efficient building envelope and extensive daylighting in classrooms. Both government and independent studies, like the Heschong Mahone Group’s renowned day-lighting study, verify that improved natural lighting can improve test scores and reduce off-task behavior in the classroom.
The school’s solar technology offers instructional value, as well as utility bill savings. According to District Superintendent Dr. James P. Lee, “Helping students understand the real-world applications of math and science is an important part of our mission to ensure they are college and career-ready at graduation.”
Other results lie in the subjective elements of district satisfaction and community education of sustainable practices. Fireside Elementary School and the Fireside community confirm that this school has successfully made the grade in efficient, comfortable, innovative solutions to meet the demands of a 21st century school.
Tom O’Neil, AIA, LEED AP is a senior principal and the southwest regional leader for the Arizona, Nevada and Colorado offices of DLR Group (dlrgroup.com), an interdisciplinary design firm providing architecture, engineering, planning and interior design. He was also the project leader for the Fireside Elementary School as well as numerous other solar-significant projects across a variety of market sectors.
With 30 years of leadership experience, his attention to “the big picture,” keeping client goals and market forces in balance, is evidenced by nationally recognized and award-winning facility designs adhering to budgets and schedules, and an extremely high percentage of repeat valued clients, such as Paradise Valley Unified School District.