By Jim French, AIA, DLR Group Senior Principal
and Rod Oathout, PE, LEEP AP, DLR Group Principal
School districts perpetually are challenged to deliver quality education with increasingly limited budgets. Part of a district's success depends on creative solutions to reduce building operational costs and while providing a quality environment that promotes learning.
With the recent spikes in energy costs and increased focus on environmental stewardship, the desire to maximize energy performance has become a necessity when planning a new facility or making improvements to an existing one.
The best opportunity for impacting the sustainability and energy efficiency in a facility starts at the earliest conceptual stage with defined goals for performance. An important issue is educating the owner about integrated design and sustainability concepts so informed decisions can be made early in the design process.
Another key factor for success is having an integrated team of planners, architects and engineers that proactively consider energy performance during the development of the design features for the facility.
Once energy consumption is optimized through design of the building envelope, the next step is to select highly efficient systems and materials that further reduce the building's overall carbon footprint. Energy modeling and life cycle costing are essential in the design process to ensure the systems selected make fiscal sense.
Benchmarking tools like Energy Star and ASHRAE 90.1 are commonly used to judge the energy performance of a building. Designs should strive to obtain an Energy Star rating and exceed 30 percent energy saving over the ASHRAE 90.1 baseline.
A recent study by the U.S. Green Building Council found sustainable schools used 33.4 percent less energy than comparable conventional schools, which saves an average $47,880 annually in utility costs. Similarly, high performing Energy Star schools have been shown to cost 40 cents less per square foot to operate.
Laying the Groundwork
When analyzing the site and developing the design concept for a school, designers should consider the building's orientation and envelope. Both of these factors can have a large impact on energy consumption without adding cost to the overall project.
Thoughtful, creative site design that maximizes the potential of the natural landscape provides opportunities to reduce energy use and site development costs. Orienting the building to minimize southwest and southeast exposures reduces the cooling and heating load for building systems.
The Marv Nelson Science and Learning Center at Green River Community College in Auburn, Wash., took the old energy-intensive science lab concept and turned it on its head. The design used a vertical laboratory arrangement that serves as a sustainable teaching tool. Arranged in ascending order of complexity, the labs share a central exhaust ventilation system that doubles as a heat recovery and cooling system as conditions warrant. Energy consumption is monitored and displayed throughout the building on green kiosks. The school received a Puget Sound Energy grant for beating local energy code requirements by 30 percent
There are several issues that have a dramatic impact on the sustainability of the site. Those issues include limiting the development footprint and reducing the heat island effect. Practical examples such as maintaining existing trees to provide shading and protection from prevailing winds, and designing with the slope of the land to protect portions of the building from the elements contribute to a green site. Using highly reflective pavement and distributed walkways and parking areas are additional design features that reduce heat absorption and the heat island effect.
It's All About the Package
The building envelope functions as one system related to energy usage. The key to maximizing efficiency is an integrated team designing all of the elements together to achieve optimal energy performance.
The goal for the building envelope is to provide a lasting image that reflects the character of the school while enhancing energy efficiency. Durability, maintainability and student comfort (visual, thermal and acoustic) need to be factored into design decisions. Designers also should include performance criteria when selecting building envelope materials, including the roof, windows, walls, and floor.
While the ideal materials for energy performance vary widely based on climate, some generalizations can be made. High mass materials such as brick and concrete block are effective for exterior walls in much of the country because they store heat in colder months and temper heat transfer in warmer climates.
Rose Hill Elementary School in Kirkland, Wash., uses 25 percent of the energy of comparable schools in the district by using small, high-efficiency gas furnaces and a block exterior. The block structure acts as a thermal mass allowing the building to maintain a constant temperature, with only moderate shifts throughout the day.
Highly reflective roofing materials and light colored walls with a high R-value reflect solar energy and are the best choice in all but the coldest climates. The International Energy Conservation Code is one source that defines the minimum thermal performance for the building envelope.
Determining the appropriate amount and type of windows in the building envelope design is a balancing act. While daylighting in schools is widely attributed to improving student learning and can reduce the cost for artificial lighting, overabundant natural light can negatively impact energy efficiency.
Quality of the natural light is more important than the quantity. Inappropriate daylighting increases the heat gain of a space, requiring additional cooling and thus offsetting any energy savings from natural lighting. Excessive daylighting can cause glare and difficulty in viewing electronic media, so a shading plan should be included in the design process.
Betty Fairfax High School is oriented to enhance daylight harvesting while minimizing thermal heat gain in suburban Phoenix, Ariz. The daylighting strategy is enhanced by insulated, low-E windows and occupancy sensors for the artificial lighting. Additionally, full cutoff light fixtures in stadium use 50 percent less energy than standard fixtures.
Effective daylighting that improves energy performance is achieved through careful placement of insulated, low-Emissivity windows and walls with a high R-value, combined with appropriate shading devices and automatic artificial light level controls. Lighting systems should be designed for each particular space to avoid over lighting any area (classroom, gymnasium, auditorium, etc.) and with the approach that artificial lighting supplements the available natural light.
The HVAC system is one of the largest energy consumers in a school, but it is an important system for maintaining student comfort year-round. Even small improvements in the performance of an HVAC system can result in significant energy savings. There are many options available for consideration when selecting an HVAC system for a high-performance building. Although a few systems are often found at the top of the list, the climate, building size, utility rates, and maintenance capabilities are the primary factors for consideration in the life-cycle analysis of the HVAC system.
A geothermal heating and cooling system is widely known as the most energy efficient method of mechanically maintaining thermal comfort in a building. These systems use the relatively stable earth temperature to heat or cool a building by circulating water through a continuous loop of buried pipes. A geothermal system is a good choice for a school if the site and sub-soil conditions can accommodate the geothermal wells.
Oak Ridge (Tenn) High School, a 55-year-old facility, recently underwent a comprehensive renovation that included incorporating a hybrid geothermal mechanical system and a water-source heat pump. These systems use 34.3% less energy than a comparable conventional chiller and gas-fired boiler system. Performance of all systems in the school is optimized with a building automation system.
Obviously, HVAC systems that conserve energy but do not provide the desired indoor environment are counter-productive. The first step in this process is defining the important environmental criteria such as temperature, humidity, and microscopic consideration. Then, selecting the right system size is crucial because oversized systems add unnecessary cost to the project, and often struggle to maintain the indoor environment and energy criteria consistent with a high performance building. Displacement ventilation systems positively impact the indoor air quality and minimize the capacity of the mechanical system.
Automated controls for the HVAC system and lighting (either with infrared or ultrasonic sensors) allow the systems to work efficiently and turn off when not in use. Implementing building commissioning also is a good means to verify the equipment installed is operating under the intended parameters. Budgetary constraints and the school staff's ability to operate and maintain a system are important factors in determining which system will work best for a particular school.
Additional renewable energy options include active and passive solar systems as well as wind turbines for on-site energy generation. Once viewed as cost-prohibitive for use in schools, the ability to incorporate these systems is increasing as the technology becomes more affordable and grants become available to offset the higher initial cost. A true sustainable design can then incorporate curriculum focused on solar and wind technologies to provide students with real-world learning opportunities and increase the intrinsic value of the systems.
When modernizing existing facilities, school districts can realize the biggest impact on improving the Indoor Environment Quality and their energy usage by replacing roofs, windows, HVAC and lighting systems. The addition or modernization of the building automation system often has a positive impact on the indoor environment and an attractive life-cycle cost. There are so many unique circumstances related to this evaluation that specific trends are difficult to quantify. It is important to make improvements to the envelope at the same time as upgrades to HVAC or building automation systems so the energy does not escape to the outdoors.
Creating an energy-efficient school starts at the earliest planning stage, usually 90 percent of the sustainable strategies are implemented in the first 10 percent of the design process. The development and implementation of these strategies is best achieved by setting project specific goals and assembling an integrated team of design professionals, contractors, and school district leaders. Besides reducing operating costs, high performance facilities contribute to the learning process, are better for the environment and provide a good example for the next generation.
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Jim French is a Senior Principal and the K-12 Education Leader for DLR Group, a nationally recognized, integrated design firm with 15 offices nationwide. Rod Oathout is a Principal, Mechanical Engineer and LEED Accredited Professional with the firm.
Published in American School & University magazine, September 2008