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A Model of Sustainability
Potential Sustainable Features of a New Eugene City Hall
Building Orientation
Building orientation should respond to climate resources in a way that enables excellent performance. For Eugene, this means maximizing the amount of north-facing and south-facing walls. Summertime solar heat gain is controlled in a cost effective manner with simple overhangs for the south windows while still accommodating daylighting and views. With prevailing winds from the north and south, this orientation also creates distinct high and low pressure zones on the outside of the building that can effectively promote natural ventilation systems that use wind pressure rather than mechanical fans.
Daylighting
Daylighting is a highly integrated system, where building design and lighting controls work together to reduce energy use through the size and placement of windows, shading devices (sunshades and light shelves), interior finishes (color and reflectivity of walls, ceilings, and floors) and the electrical system (lighting controls that adjust to natural lighting levels). Architectural daylighting strategies include sidelighting from windows and clerestories, and toplighting from skylights and roof monitors. The City Hall is likely to include both sidelighting and toplighting elements.
While making significant contributions to the energy efficiency of the building, daylighting also contributes to beautiful lighting conditions, excellent architecture, and increased occupancy comfort and efficiency.
Natural Ventilation
Natural ventilation is part of a climate-responsive design solution where outside air moves passively through a building to provide cooling and fresh air. Natural ventilation systems tend to focus on human comfort issues and facilitate increased occupant control (e.g. opening a window as desired by occupant). Studies have shown that building occupants adapt to a wider temperature range when in naturally ventilated buildings. Natural ventilation systems rely on air buoyancy and external wind pressure to move air through buildings without conventional mechanical means. Systems that rely on air buoyancy (stack effect) are designed to allow warm air to rise through the building and exit through air outlets located high in the building. As warm air exits the building, cool air is drawn into the building at lower locations.
Systems that rely on external wind pressurization are typically designed to accommodate cross ventilation (windows across the building on the same level). The City Hall is likely to include elements of both air buoyancy and external wind pressure, and may be fully integrated to a fan system as well.
Night Flushing
Night flushing is a climate responsive cooling strategy that introduces outside air during the coolest times of the night and early morning, which results in pre-cooling the building prior to the next day’s warm weather. Night flushing can be integrated with a natural ventilation system or a fan system. Optimally designed night flush systems include a significant amount of thermal mass to hold the cooling effect of the night air. For the City Hall, this mass could be integral to the floors and possibly some of the interior walls.
Enhanced Building Envelope
An enhanced building envelope refers to a comprehensive building-skin strategy that includes:
• increasing insulation levels in walls and roofs
• minimizing solar absorption through exterior surfaces (higher reflectivity and lighter colored choices, primarily for roof surface)
• minimizing air infiltration by tightening joints, and using high quality weather stripping and caulking to minimize leakage
• use of high-performance glass (coatings and insulation that affect thermal and optical characteristics of glass).
As an example, on a 90 degree day in Eugene, the surface of a dark non-reflective roof can heat up to 160 degrees. In contrast, a white roof may only reach 110 degrees, significantly reducing the heat gain through the roof surface into the building. Adding insulation to the roof assembly further reduces the heat gain.
Green (Eco) Roofs
A green roof is a vegetative planting layer on top of the roofing membrane. Green roofs contribute multiple benefits as part of a sustainable design strategy. They add thermal mass and moisture to the roof surface, which reduces or eliminates solar gain from roofs. They retain rainwater, which reduces and delays the water run-off into the ground during storm events. In the most developed applications, green roofs become a design feature of quality outdoor space, integrating the natural environment (plantings) with the built environment (buildings), to create an enhanced experience (roof gardens).
Enhanced Heating and Cooling
Enhanced heating and cooling systems are designed to respond to load reducing architectural features, and to incorporate natural ventilation elements. System concepts are selected to provide heating and cooling functionality at minimum energy consumption. For the City Hall, the following enhanced heating and cooling system concepts will likely be considered:
• coupling the building’s systems to the thermal mass of the earth
• heat pumping
• solar thermal systems
• energy recovery technology for pre-tempering ventilation air
• underfloor air distribution, potentially combined with radiant heating and/or cooling.
Photovoltaics (PV’s)
Photovoltaic systems convert sunlight into electric energy as an on-site energy generation strategy. There are many creative ways to integrate PV’s into the building (on roofs, in walls, on glass, etc.).
Are PV’s cost-effective? While they are one of the most expensive energy strategies, the cost benefit is steadily improving. Projects where the full slate of current tax benefits can be accessed provide particularly compelling economic returns.
Does it take more energy to make than it will provide? No, after approximately 6 years, a PV system will have generated as much energy as it took to mine, manufacture, transport, and install. After that time, it is a net-positive energy provider.
Rainwater Harvesting
Eugene receives approximately 4 feet of water annually in the form of rainfall. Rainwater harvesting is a strategy of capturing rainwater runoff (primarily from roofs), storing it over time, and re-using it – primarily for landscape irrigation and toilet flushing. This requires a cistern for water storage. Depending on the site and building footprint, this could be stored underground or incorporated as a design feature, with visual and educational benefits.
Bioswales (Bios)
Bios are planting areas that manage the water run-off from impervious surfaces (such as sidewalks and parking lots) by capturing and filtering the water through plantings and soil mixtures, reducing the water that goes into the stormwater system and “pretreating” the water that does enter the stormwater system. A bioswale is a collaborative strategy incorporating civil engineering and landscaping concepts, and typically results in an aesthetically pleasing landscape feature.
Low Carbon Emissions (LCE)
Traditional energy production and consumption creates carbon dioxide, a greenhouse gas that contributes to climate change including global warming. Building design strategies that reduce or eliminate carbon emissions start with many of the energy efficiency strategies discussed above. The purchase of wind power, or other green power, for the remaining imported energy in the building can result in “carbon-neutral” building energy operation.
In addition to the energy used by the building, carbon emissions are also created through building-related transportation. The sites currently under consideration for the City Hall have ample access to public transportation. Access to public transit was one of the selection criteria considered when narrowing the site choice. Bike parking, bike commuting accommodations (showers and lockers), alternative-fueled fleet vehicles, and staff parking policies such as carpooling are all features and strategies that are part of the design conversation for the City Hall, and represent positive encouragement to reduce transportation related carbon emissions.
When incorporating other carbon-consuming features such as interior and exterior landscaping, one can sequester carbon emissions, contributing to the environment and participating in the carbon emission solution beyond carbon neutrality.
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