7 Keys to Unlocking Energy Efficiency in Schools

School boards and school district CEOs and CFOs are demanding ever higher levels of energy efficiency in new classroom buildings. Use these seven guidelines to make your next K-12 project a paragon of sustainable design and construction.
August 11, 2010

 

Students at Pioneer Middle School in Steilacoom, Wash.,Today’s best K-12 schools are embracing the sustainability ethos in their design and construction, and that can mean a healthier, more comfortable indoor environment and improved learning. Some studies contend that ample amounts of daylighting, for example, lead to higher test scores. High-performance HVAC systems that constantly draw fresh air into a classroom seem to help both teachers and students remain more alert during the day.


These affective benefits alone are worthwhile, but school administrators are also delighted when many of these green systems also provide hard-core savings on utility bills. While first costs are a major concern to school boards, the long life spans of K-12 buildings make it worthwhile to invest in energy-saving systems and features that have a reasonable payback period—preferably five years or less, but, in some cases, even up to 10 years. Increasingly, school boards and administrators are even interested in evaluating the pros and cons of cutting-edge systems such as geothermal and photovoltaic systems.

The latest technology doesn’t always provide the highest return on investment, however. Sometimes more tried-and-true solutions provide better value. Here are some of the best ways K-12 designers and school administrators involved with LEED-rated projects say schools can be more energy efficient and foster a better learning environment.


 Envelope Energy Loss after EnhancementsEnhanced Wall Meets IBC Restrictions
 For two elementary schools in Snohomish, Wash., the design team from NAC|Architecture and Hargis Engineers developed energy-saving strategies for foundations, roofs, walls, and windows in order to be able to reduce the size and cost of the mechanical systems. The chart shows the relative energy loss for each major component after enhancements were made. Windows and doors account for 75% of loss. Axonometric representation of the enhanced wall in two Snohomish, Wash., schools. In the rainscreen cavity, one inch of polyiso rigid insulation (R-6.7) is used where the exterior cladding is masonry veneer. The International Building Code restricts the use of foam plastic, particularly in multistory noncombustible construction, so careful attention to code requirements is needed when selecting spray foam or rigid insulation products. Where the cladding is fi ber-cement panels, metal siding, or other thin material, two inches of mineral wool semi-rigid boards (R-4.2
per inch; R-8.4 total) were used. When this is added to the six inches of spray foam in the stud framing cavity, the composite insulation value of the overall wall assembly is R-25.

1. Building envelope – Wrap it tightly

Energy efficiency in schools, as in virtually all buildings, begins with a well-insulated building envelope. Combined with a properly designed and maintained ventilation system to draw in fresh outside air, creating a tight envelope is the first step in the march toward energy efficiency.

Exemplifying good building envelope design principles are the Riverside and Machias elementary schools (each at 72,000 sf). Designed by NAC|Architecture, Seattle, the schools are currently under construction and will replace two older structures that were among the least energy-efficient in the Snohomish (Wash.) School District.

“We focused on how an enhanced envelope design could reduce the size and cost of the mechanical systems by reducing energy loss through the envelope,” says Philip Riedel, associate principal with NAC|Architecture. A key component of that strategy is a six-inch layer of closed-cell polyurethane foam insulation in lieu of batt insulation in the walls.

The foam yields an R-value of 6.7 per inch, a substantially higher insulation value than batt at that thickness, although it does comes at a significant initial cost premium—about 20% more than an equal R-value of rigid insulation. “However, we are finding that a 1% overall gap between rigid insulation boards can reduce energy efficiency by 10%,” he says. “Since the spray-on insulation eliminates seams, the payback is nearly immediate.”


NAC also took measures to mitigate the effects of thermal bridges due to metal studs and the concrete slab. By increasing stud spacing from 16 inches on center to 24 inches, the design increases the effective wall R-value from R-7.1 to R-8.6, a 21% improvement, NAC says.

In conventional foundation construction with insulation adjacent to the interior of the stem wall and below the perimeter of the slab, heat travels from the warm concrete slab out through the concrete stem wall. “We ran rigid insulation up to the top of the slab, creating a full thermal break at the perimeter,” Riedel says. “These thermal breaks provide smaller contributions to envelope efficiency than the spray foam insulation and the triple-pane glass used in all windows and curtain walls, but we wanted to take every advantage we could.”

Eliminating the Thermal Bridge in the Foundation

2. HVAC – Save energy, but don’t skimp on comfort

A tight envelope helps boost HVAC efficiency by enabling you to use smaller-sized equipment to serve a given amount of space. Certain options and features on mechanical equipment can raise the bar further.

When looking for efficiency gains, however, don’t shortchange the comfort of students and staff. Studies show that a too cold, too hot or poorly ventilated classroom has a negative impact on learning, says Dennis Bane, principal and project leader for DLR Group, the firm that designed the new 464,000-sf Metea Valley High School, in Aurora, Ill.

“People are much more conscious of temperature,” says Rod Oathout, DLR’s mechanical engineering leader. “The emphasis is on maintaining perfect temperature year-round.” As a result ventilation loads are higher. “Today, 40% of air may be brought in from the outside, while in the 1960s and 1970s, you may not have had any air brought in. So, you’ve got to find efficient ways of treating it.”

One way to do that is to use exhaust air to temper incoming air by transferring thermal energy via recovery wheels or coil systems. DLR has used enthalpy wheels—plastic or aluminum disks coated with a silica gel that rotate between exhaust and incoming air vents—on several school projects. “The efficiency of these has gotten a lot better over the last five years or so,” Oathout says, adding that enthalpy wheels also help to regulate humidity.

Another efficiency strategy that boosts comfort is demand control ventilation. Metea Valley High has CO2 and CO sensors in the auditorium and gymnasium that regulate the ventilation system. “When there’s a class of 40 to 50 people, the ventilation may not have to turn on,” Bane says. “But when there are 2,000 people in the gym, the system will automatically kick in.”

Using displacement ventilation is another effective way to raise efficiency, particularly in large spaces with high ceilings. Air enters the space at low velocities to cause minimal air induction and mixing so that heating or cooling energy is focused on the occupied zone below, say, seven feet. Intakes in the ceiling recirculate some of the air back into the room. “A displacement ventilation system saves more money than bringing all the air back to the mechanical room for treatment,” Riedel says.

Displacement ventilation is also being used within a very well-insulated space (R-31 walls, R-41 roof) in Gen 7, a modular classroom developed by American Modular Systems for sale in California. At the front of each modular classroom is a 60x36-inch diffuser that supplies all ventilation and mechanical heating and cooling. This system operates much of the day, bringing in nearly 100% fresh air, but is quiet and the air stream is virtually undetectable, says Tony Sarich, Gen 7’s vice president of operations. “If you walk up to it, you don’t really feel it” except under extreme conditions, he says.

In order to ensure that the classroom does not become pressurized, barometric relief dampers in the ceiling provide exhaust relief. “When the children come back in from recess, CO2 is off the charts,” and the ventilation system goes into overdrive, says Sarich. A computer-controlled system detects the high CO2 levels and opens dampers fully until enough CO2 is vented.

Daylighting3. Building automation – Boost efficiency with smart electronics

Most new school projects are using extensive building automation systems to monitor energy usage and control lighting, HVAC, security, and other systems. Building automation helps ensure that lights and mechanical systems operate at the right level when they should and where they should.

Maintenance staff can also monitor HVAC system efficiency with real-time data for each piece of equipment. When a chiller has to run longer to do its work compared with comparable conditions in the recent past, it’s an indication that it may need maintenance or repair.

Designing and installing a state-of-the-art BAS system has become fairly routine. Maintaining it properly can be an ongoing struggle, however.

Building and grounds personnel may have to upgrade their skills to work with these sophisticated systems. “Building automation is how staff controls heating and cooling,” says Todd DePaul, project manager with Indian Prairie School District #104, the owner of Metea Valley High. “They have to have basic computer skills. This is a far different skill set than was needed with the old pneumatic systems.” To deal with this issue, the district made it a condition of the contract that the project’s engineering consultants, KJWW Engineers, provide on-the-job staff training.

No matter the skill level of building personnel, sometimes it takes time to work out the kinks of a new automation system. At Crossroads College Preparatory School in St. Louis, an unusually cold winter taxed a new automation system installed over the previous summer. “It was not powering up fast enough in the morning,” says Billy Handmaker, the school’s headmaster. It took about a month for technicians to diagnose the problem, a software coding flaw that was easily remedied after the cause was identified. The system has helped save money on utility costs, which are down from the previous year even with a new 9,500 sf addition, Handmaker says.

4. Daylighting – Let there be lots of it

Heschong Mahone Group, a consulting firm in Fair Oaks, Calif., that specializes in energy efficiency, is known for its studies of student performance as related to daylighting. In her groundbreaking study in the San Juan Capistrano, Calif., schools, the firm’s Lisa Heschong found that students whose classrooms had the most natural lighting “progressed 20% faster on math tests and 26% faster on reading tests in one year than in those with the least” amount of daylighting.

“Clients are well aware of these studies,” says Matt Slagle, design architect with AE firm TowerPinkster, based in Kalamazoo and Grand Rapids, Mich. They expect designs to enable lots of daylighting in every classroom, and increasingly in libraries, foyers, and multi-use rooms, he says.

Of course, providing maximum daylight influences the site planning and orientation of the basic structure. The new Metea Valley High School in Aurora, Ill., features two enclosed courtyards that draw in natural light to the building. A 12,680-sf media center, checkout computer labs, forum rooms, and a technology lab are all situated around the two courtyards.

Similarly, the interior of the Linden Grove Middle School in Kalamazoo, Mich., features an atrium composed of walls, staircases, and other features that form unusual angles. In order to maximize daylighting, TowerPinkster devised a “squished design” with acute angles to fit in a limited footprint, Slagle says.

With extensive use of skylights and large windows, designers have to choose glass and glazing technology carefully in order to limit heat gain and loss, based on the façade’s orientation to the sun. At Metea Valley, design consultants DLR Group used a different type of glass in the north façade to address the indirect sun exposure.

“The correct glass can affect the size and efficiency of the HVAC equipment as well as daylighting systems,” says Chris Dolan, director of commercial glass products for Guardian Industries Corp., Auburn Hills, Mich. “Minimizing solar heat gain through low-e coatings can actually reduce the size of an HVAC unit.” Windows on the market today make it easier to allow more daylight with less heat gain than was the case several years ago. “New glass coatings can compare favorably to older dark tints or reflective glass with improved energy savings and more natural light,” Dolan says.

Windows aren’t the only way to harvest natural light, however. On the Metea Valley project, DLR’s Dennis Bane says the school district was concerned about the frequent (and costly) cleaning that glass demands, especially when it would require a maintenance crew to use a cherry picker or dangerously high ladder to maintain. “We needed daylighting, but not necessarily [entirely] with glass,” says Bane. Rather than installing glass high up on the building, DLR specified translucent panels with high thermal ratings to be installed above nine feet, four inches.

One other daylighting source being used in many LEED K-12 projects: light shelves, which bounce sunlight deep into the room and provide even light distribution.

Lighting Controls5. Lighting controls – Leverage daylight to the max

Even with abundant daylight, energy savings will be diminished or negated if lights stay on full power when they are not needed. It’s unrealistic to expect staff, teachers, and students to manually adjust lighting as daylight levels change, so automated lighting controls are a must.

At Metea Valley, photo- and motion-sensitive controls automatically turn off lights as exterior lighting levels change throughout the day. This system is projected to save the school district $21,032 annually, with a payback of less than seven years, DLR says. Timers can be set to shut off lights at night, a feature that includes a manual override accessible in the building engineer’s office so that staff members can turn on lights in a wing or a hallway for after-hours events.

Gen 7, the modular classroom developed by American Modular Systems for sale in California, pushes energy efficiency in lighting to the limit. By employing large windows, multiple 2x2-foot skylights, and a Lutron automated lighting control system that constantly measures light levels and quickly adjusts lighting up or down as needed, the Gen 7 design reduces electricity costs for lighting to a pittance.

“It typically runs lights at 5%; that’s 60 watts total for the whole classroom,” says Gen 7’s Tony Sarich. If a dark cloud hovers overhead, the system compensates. “It happens so slowly that it’s not detectable by the human eye,” he says.

One negative aspect of daylight (along with heat buildup) is how to reduce glare at certain times of the day. Shades do not regulate light efficiently if they depend on human intervention to make regular adjustments. “Teachers pull down shades, and often, they never go back up,” Slagle says. That factor reduces daylighting efficiency more than any other; however, there are new light-sensitive shade controls on the market that automatically open and close shades fairly quietly, he adds.

Geothermal6. Geothermal heating and cooling – Sound solution under the right conditions

Although the technology has been around for decades, ground source heat pumps are still considered an exotic technology by the general public, including most school board members. Nonetheless, they make a lot of sense for many school projects, despite the high initial cost, and are becoming increasingly common.

“Your payback is a function of local utility rates,” says Oathout. “The payback needs to be less than 10 years to make sense for most projects.” Once the initial costs are borne, there is virtually no ongoing maintenance on the underground systems, and most have stood the test of time, he says.

The initial investment includes the cost to drill the well field and the need for more air handling units—albeit smaller ones—than in a conventional heating system. “You typically have, say, six air handling units for a 100,000-sf building,” Oathout says. “With ground source, it’s more like one unit per classroom, so you might have 80 air handling units in the same-size structure.”

In addition, the building’s design has to provide for easy access for maintenance staff to get to filters and air compressors. The units have to be located near the area that they serve, but classrooms have to be shielded from the noise they generate. “We try to keep them as far from the classroom as we can,” Oathout says. “And we put an extra layer of drywall in the mechanical closets to absorb noise.”

Site conditions can make geothermal impractical, however. At the Crossroads school, located in an urban St. Louis neighborhood, there was little available land around the structure. Even though the project—a 9,500-sf addition and partial renovation to the existing structure—ultimately achieved LEED Platinum certification, geothermal was dismissed early in the design phase. “There just wasn’t enough space for wells on the property,” says Thomas Taylor, general manager of St. Louis-based sustainability consulting firm Vertegy.Geothermal


7. Solar –A high premium, but it still has its place

Although photovoltaic panels are still more expensive than most school systems can afford, some schools are making these investments with the help of state-managed grants or power purchase agreements with utilities. The Riverview and Machias schools, in Snohomish, Wash., will each have 440 rooftop panels forming a 100-kW system for each building—“enough to generate 17% of each school’s energy use,” according to NAC|Architecture’s Riedel. “These will be the largest arrays of photovoltaics on any public building in the state.” The school district will buy and install the panels and receive rebates from the utility. A small amount of state grant money also may be used to defer some initial costs, Riedel says.

Solar panels on a modular classroom as efficient as Gen 7 have a much bigger impact, enabling the structure to reach the Holy Grail of grid neutrality. “That doesn’t mean off the grid, but at the end of the year, whatever you pulled from the grid you have put back,” Sarich says. The Gen 7 rooftop photovoltaics generate just six kilowatts, but because the classroom consumes little energy, it’s enough to reach grid-neutral status.

The sun’s energy is also being used to provide hot water at some schools. The Crossroads school uses solar collectors to heat water for bathroom and lab sinks. “It works well year-round,” says the headmaster, Billy Handmaker. “There’s no need to supplement it with another heat source.”

Insulation Effectiveness in Framed Wall Assemblies

Insulation type Depth (inches) Nominal R-value Effective R-value Improvement due to wider stud spacing
* Washington State Energy Code, page 50
** Calculated based on interpolation of WSEC tables
Source: NAC|Architecture, with Hargis Engineers
      Metal studs 16-inch o.c. Metal studs 24-inch o.c.  
Batt 4 11 5.5* 6.6* 20%
Batt 6 19 7.1* 8.6 21%
Spray foam 6 38.4 10.4** 13.5** 23%


Energy Savings Analysis Summary

Building envelope component Code baseline building Riverview baseline
*Reduction from code minimum building due to mechanical/lighting systems.
Source: NAC|Architecture, with Hargis Engineers
  Energy use (Mbtu/yr) Energy savings (%) Energy use (Mbtu/yr) Energy savings (%)
2006 WSEC Code baseline envelope 4378 - 1847 57.8*
Triple-pane glass/curtain wall upgrades 4172 4.7 1794 2.9
Increased wall insulation (R-36 + rigid) 4200 4.1 1800 2.5
Increased roof insulation (R-45) 4170 4.7 1817 1.6
Foundation insulation (F=0.45) 4361 0.4 1840 0.4
 
Total with all envelope improvements 3893 11.1 1711 7.4
100 kW PV system included - - -325 17.6
Total with PV system included - - 1386 25.0


“Saving 30% or more on energy is within the reach of any school district with the will to do so,” according to the ASHRAE 2008 Advanced Energy Design Guide for K-12 School Buildings. The organization contends that 50% savings is within reach on projects that use computerized building energy modeling to aid design development.

To achieve the most energy-efficient design, each system and feature has to be evaluated according to first cost, payback period, and interaction with other systems. With the right mix of technologies and sound design and construction principles, new school buildings can be leaps and bounds ahead of traditional K-12 schools in energy efficiency.