FIGURE
1.
CO2
emissions: ASHRAE base case vs. modeled design.
Dual-fuel boilers, demand controlled ventilation, thermal storage … these are just a few tactics used in this Connecticut community’s long-term strategy to improve performance and drive savings. See how a team-wide, high-performance-design charrette got everyone pointed toward success from the start.
In the past, K-12 school designs have rarely earned adjectives like innovative, imaginative, or environmentally friendly. However, in the last decade, a new trend has been sweeping the K-12 design industry, and K-12 designers are now emphasizing sustainable buildings with multiple high-performance characteristics.
In many ways, the K-12 facility has actually been on the forefront of the national green building trend. Tightening budgets, increases in energy costs, and pressure to improve learning environments in order to exceed baseline standardized testing requirements have prompted a reassessment of efforts and priorities. Perceptions are also changing, in part due to the amount of data now available on what building a sustainable building actually costs vs. a traditional building. Studies have shown that a sustainable school facility costs only an average of 1.7% more in upfront cost, with a life-cycle payback of 10 to 20 times the additional initial cost.
The increased emphasis on sustainable school construction led the USGBC to launch the LEED® For Schools program in 2007. Based on the LEED NC program, LEED For Schools takes into account some of the unique spatial requirements of K-12 facilities with emphasis on such considerations as classroom acoustics, mold prevention, master planning, and environmental site selection. The program seeks to encourage the nurturing of students in environments that promote natural lighting, quality acoustics, and air that is safe to breathe. The LEED For Schools program went into effect immediately on its release, without the pilot period associated with some of the USGBC’s other recently created LEED certification programs.
With encouragement from the USGBC and increasing commitment from design professionals, the positive impact to our nation and the Earth from the greening of our schools has overwhelming potential. An estimated 60 million students, teachers and staff work and learn in schools in the United States each day. Approximately $6 billion is expended annually on energy to operate these schools, an expense second only to staff and faculty salaries. Studies have shown that facilities built around sustainable criteria utilize 30% percent less energy, use 30% to 50% less water, and produce 40% less CO2. From this perspective it is easy to see the tremendous impact that the adoption of sustainable design practices can have on both the environment and on operational costs in our school districts.
FIGURE 2. Projected electric demand reductionutilizing partial thermal storage design.
Reducing demand and consumption of the built environment became the priority in the program’s sixth year, 2003. The design and operation of the schools in the New Haven School Construction Program (NHSCP) provides excellent examples of some of the sustainable trends becoming common in our nation’s newest schools.
This integrated design process begins the moment a school is scheduled for design and includes a two-day Conceptual Design High Performance Design Guidelines (HPDG) charrette in which project goals are established and strategies to meet and exceed expectations are identified. There, initiatives such as energy design, material selection, IAQ, and water consumption are addressed. The participants of this meeting include the complete architectural/engineering team and their consultants, local utility representatives, the construction manager, commissioning agent, energy modeler, and various stakeholders, including energy manager and maintenance. A high-performance plan is then established. This plan is reviewed, modified and upgraded at various design milestones (schematic design, design development, and construction documentation).
Some examples include:
- Energy modeling
- Building envelope optimization
- Lighting strategies
- Solar energy
- HVAC controls and energy management strategies
- Building commissioning
- Continuous improvement
Energy Modeling
A key ingredient of the design process of a New Haven school is the energy simulation report that is produced by the energy modeling consultant at each phase of the design. This document is used throughout the design process for several purposes. Most importantly, it allows the team to quantify the life-cycle costs of various sustainable design options. This allows team members to analyze the impact of decisions based on empirical data, rather than emotion or ‘gut feel.’ The analysis of energy conservation measures typically focuses on heating systems, cooling systems, lighting, and building envelope performance.The Energy Simulation Report also allows the team to understand how the building as designed will perform relative to a minimum energy efficiency standard (ASHRAE 90.1 2001) and the NHSCP goal standard, the Energy Star Target Finder. Typically, the Energy Star standard for a New Haven School is approximately 50 kBtuh/sq ft, while the ASHRAE 90.1 standard has averaged approximately 95 kBtuh/sq ft (these values will differ depending on the specific school being modeled). The New Haven schools that have been modeled over the past two years have ranged from 45 to 60 kBtuh/sq ft expected energy usage.
Energy modeling has contributed significant value to the high-performance design process in New Haven, particularly with building envelope and HVAC system improvements. Design teams have consistently produced designs with at least 30% energy savings above ASHRAE 90.1 2001 (the current code), and recent designs have averaged closer to 40% savings.
Several additional sustainable concepts are considered for each project during the HPDG charrette. Recently considered concepts include:
- Fuel cell
- Ground source heat pump
- Displacement ventilation
- Chilled beam cooling technology
- Micro turbine
- Wind power
- Green roof system
- Recycled material
- Construction waste management
Building Envelope Optimization
The NHSCP has directed significant focus on the optimization of the building envelope components. In all cases, various upgrades over the ASHRAE 90.1 minimum standards are analyzed using an energy model, and options are selected based on life-cycle costs. Typical envelope upgrades include:Walls and glazing. For the region that New Haven is a part of, Table B-17 in ASHRAE 90.1 2001 prescribes a minimum U-value (coefficient of transmission) of 0.57 for exterior glazing. Many New Haven schools have upgraded to high-efficiency glazing which improves U-values to 0.29 and also allows higher light transmittance to promote daylighting strategies. For exterior walls, the ASHRAE 90.1 2001 baseline of R-8.3 has typically been upgraded in most facilities to R-14 walls.
Roof and slab insulation. ASHRAE 90.1 2001 baseline standards include an R-15.8 roof and slab on grade with no additional insulation. Most New Haven schools have incorporated upgraded envelope components such as R-30 roofs and R-10 insulation added to the standard slab on grade.
Lighting Strategies
Costs related to energy usage from interior lighting can exceed 20% of the energy cost in many K-12 buildings. Reduction of lighting power density (LPD) beyond established baselines is one area that NHSCP has focused on since program inception. Using building area methods (Table 9.3.1), ASHRAE 90.1 2001 recommends a goal LPD of 1.5 W/sq ft for a school facility. This goal was lowered to 1.2 W/sq ft in ASHRAE 90.1 2004. NHSCP has set a program goal of 1.0 W/sq ft for this criterion. With the assistance of specialized lighting consultants, NHSCP has succeeded in achieving levels of 0.8 to 0.9 W/sq ft in newer facilities.Daylight harvesting is also a strategy that has been consistently utilized to reduce lighting usage in New Haven schools. Simply put, daylight harvesting is the use of natural light as a source of light to support activity in a space. Put into practice, daylight harvesting systems will automatically dim or completely shut-off lights under favorable natural lighting conditions.
In addition to the energy savings advantages, daylighting has proven to have other positive effects on learning environments. Studies have documented increases in test scores and improved student attendance in facilities that take advantage of daylighting strategies. This is a major departure in school design from the 1950s and 1960s, when many schools featured few windows or utilized black glass because of concerns over security and student attentiveness.
Solar Energy
NHSCP has also explored the use of renewable energy sources. At Barnard Environmental Studies Magnet School, a solar energy system was installed that is capable of providing an estimated 16% of the school’s electrical power requirements, and more than 2.5 million kW of electricity over the life of the system. The photovoltaic array, rated at 82 kW, is the second largest in Connecticut. Including support from the Connecticut Clean Energy Fund and anticipated state rebates, the city is expected to break even on its contribution in less than one year.In addition, the system is also proving to be a valuable tool to teach students about science and the environment. Real-time solar energy and weather data is displayed in the classroom, and a link on the New Haven Public Schools internet site provides updated data from the Barnard solar array every 15 minutes.
HVAC Controls/Energy Management Strategie
Demand control ventilation (DCV). Recent trends in HVAC design have allowed a more flexible response to actual occupancy, referred to as DCV. DCV allows the amount of outside air to be varied based on actual occupant load, as measured by CO2sensors. As a result, the AHU will treat only the amount of fresh air that is required for the actual occupant load. NHSCP has utilized this approach to great success not only in variable occupancy spaces such as gymnasiums, cafeterias, auditoriums, and libraries, but has also implemented it successfully in classrooms.Energy recovery. The current NHSCP high-performance standards encourage the use of heat recovery/energy recovery in the air-handling systems, and this feature has been incorporated at nearly all New Haven schools. This concept avoids the waste of the tempered exhaust air that is discharged from the building. In order to conserve this energy, AHUs are equipped with heat exchangers (heat recovery wheels), which utilize the exhaust airstream to heat the incoming outside air in the winter (and the reverse in the summer). This allows smaller heating and cooling equipment to be used throughout the facility.
Dual-fuel boilers. Boiler design incorporates dual-fuel systems capable of operating on either gas or oil. The capability to switch between oil (stored onsite in an above-ground tank) and interruptible gas allows the city the option to mitigate gas demand charges during an extended peak heating period.
Thermal storage. The recently designed Bishop Woods School in New Haven utilizes a partial thermal energy storage system. The justification for this approach stems from the increased electrical demand charges that are levied by the electrical utility during peak demand times. By making ice at night when electrical cost is at its lowest, the building is cooled at peak demand times without paying the peak demand cost. The application at Bishop Woods is expected to decrease peak demand during the summer months by 23%. This approach also has another advantage. Since the chillers are intended to run 24 hrs a day, the capacity of the chillers can be reduced by approximately 50% compared to a conventional design. This also reduces the initial capital expenditure.
FIGURE
3.
New Haven utility cost escalation projection in millions of dollars.
Building Commissioning
Many of the sustainable/high performance concepts currently being enacted by NHSCP do add a level of complexity not seen in a more traditional facility. These systems and concepts (such as daylight harvesting and the energy management strategies) are justified if operating as designed because of the life-cycle monetary savings and resource savings that they will provide. In order to validate the correct installation and functionality of these systems, NHSCP utilizes a building commissioning program.The building commissioning program is lead and facilitated by a commissioning agent, a third-party independent advocate for the owner. Commissioning is intended to verify that the building systems are installed, calibrated, and function according to the owner’s project requirements, basis of design, and construction documents. NHSCP has adopted a comprehensive commissioning program with the commissioning agent involved at every stage of the project, including design reviews at each stage of design, supervision of the building turnover process, and warranty phase system performance reviews. The commissioning process at several NHPS facilities has documented in excess of $500,000 of life-cycle savings at each facility through cost avoidance.
Continuous Improvement
Despite the documented successes of the NHSCP, the program has committed to further improvement. A series of no-cost and low-cost upgrades has recently been completed on 16 of the schools that were completed early in the program (prior to the refinement of the NHSCP high performance design standards). In each case, where life-cycle costing dictated that improvements be made, they were implemented. These improvements are estimated to save the city an additional $650,000 per year. Examples of these upgrades include:- The installation of mechanically deployed pool covers at those schools with swimming pools;
- The conversion of gymnasium luminaries from HID-type to more efficient T-5 fluorescent luminaries controlled by occupancy sensors;
- The de-lamping of luminaries in areas where installed light levels were well in excess of code required light levels;
- The conversion of AHUs from single zone constant volume systems to VAV systems in order to capitalize on reduced fan speeds at part-load conditions;
- The addition of VFDs to pool water recirculation pumps to allow pump motor speed to be reduced during unoccupied hours;
- The refurbishment and retrocommissioning of HVAC controls systems at schools that were constructed prior to the implementation of the building commissioning program;
- Installation of photocells and occupancy sensors to control classroom lights;
- Installation of CO2 sensors for DCV on specific AHU systems.
Measures of Success
The adoption of the NHSCP high-performance schools design standards and related facility planning process has initiated a whole new way of thinking among design teams, construction teams, and building operations staffs. This change in focus has not been without measurable benefit for the city of New Haven, including students, teachers, and each taxpayer. The following benefits have been recognized since the beginning of the school construction program in New Haven:- O&M savings;
- Increased student performance and less absenteeism;
- Improved teacher retention;
- Avoided more than 5.75 million pounds of carbon dioxide emissions, 27% when compared to the ASHRAE 90.1 base case design. This is equivalent to 400 passenger cars.
- Utility cost avoidance, including peak demand charge cost avoidance for both electric and gas service.
