Engineered Systems - March 2009 - (Page 52)

A New Haven For Sustainable Schools FIGURE 1. CO2 emissions: ASHRAE base case vs. modeled design. Monthly Electric Demand 500 ASHRAE 90.1 400 Current Design 300 Thermal Storage kW 200 100 0 Jan Mar May Jul Sep Nov Feb Apr Jun Aug Oct Dec FIGURE 2. Projected electric demand reduction utilizing partial thermal storage design. 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 52 En g i neer ed Sy stem s 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 STRATEGIES 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 CO2 sensors. 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 March 2009

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Engineered Systems - March 2009 Contents Editor’s Note Back2Basics Case In Point Commissioning Building Automation HVACR Designer Tips Application Checklist Teaching An Old School New Tricks Basics For Absorption Chillers A New Haven For Sustainable Schools Glossary Classifieds Advertiser Index Tomorrow’s Environment

Engineered Systems - March 2009

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