Solar Today Spring 2016 : Page 30

Design Solutions Design Solutions -Site The corner site location and the design overlay requirements for street frontage, parking and articu-lation limited the design solutions for the site. The architect kept the massing as simple as possible within these constraints and to maximize east-west building orientation. Building entry and common spaces were orient-ed to respond to urban design cues such as the light rail and to efficiently stack these functions. Semi-public outdoor spaces—including benches at the main entry and an interpretive plaza near the light rail stop—commemorate the historical significance of the site. Garden spaces, picnic benches and a play area provide outdoor gathering spaces for residents. Parking is configured to incorporate drainage swales, to extend into Phase II, and to incorporate an “orchard” of trees commemorating the former nursery. Design Solutions -Envelope The team chose to remove portions of the build-ing from the Passive House envelope—including the laundry and trash rooms—due to Passive House airtightness requirements and high ventilation rates. In addition, the doors to these spaces were custom built for this project, in order to meet Passive House airtightness and provide doors with the appropriate electric hardware for accessibility and fire rating. This example speaks to how the market in North America hasn’t caught up with some of the products that are needed to build a building of this scale. Initially, the elevator was also outside of the Passive House envelope but was brought back in after preliminary blower testing determined that the air leakage at the elevator louver would not put the project over the limit. The building structure consists of three-story wood-framed construction on top of a concrete slab-on-grade foundation. Typical enclosure walls have 2x10 framing with blown-in fiberglass cavity insula-tion in the stud cavities and 1-1/2” of rigid mineral wool exterior insulation. Mineral wool was chosen specifically due to its permeability and capacity to facilitate drying to the exterior as environmental conditions allow. Plywood exterior sheathing (with taped seams) serves as the primary air barrier at the enclosure walls. A mechanically-attached spun-bonded poly-olefin sheet membrane, installed over the plywood sheathing, serves as the water-resistive barrier. The vapor barrier is located on the interior face of the wall framing. This is a polyamide membrane with variable perm rating to facilitate wall drying to the interior. The ground floor slab sits atop a 4” layer of EPS insulation, which also wraps around and under the perimeter and interior footings. Type II EPS is used under the slab and at the sides of the footings; how-ever, Type IX EPS is used under the footings for its higher bearing capacity. Capping off the building structure is a prefabricated wood truss roof with 12” of polyisocyanurate insulation and a fully adhered single-ply roof membrane. A self-adhered rubber-ized asphalt membrane is installed over the plywood roof sheathing, serving as the vapor barrier at the roof assembly (and also functioning as a temporary roof during construction). Decks and sun shades are designed to provide resident outdoor space, archi-tectural interest and summer shading. Vertical shad-ing was considered, but was not allowed by the City design commission. for the building as well as some degree of tempered cooling during the summer. The heat pump is in parallel with the ERV so that it does not create static pressure in the ventilation system. Two central, ultra-high efficiency boilers provide hot water. The piping is insulated to the dwelling units. The team determined that a temperature maintenance system with heat trace tape was more energy efficient than a recirculation pump. Fluorescent lighting was designed to meet 0.4 Watts/SF for the dwelling units. Lighting controls were used to reduce loads in corridors and stairs. Enjoying the Design REACH is benefitting from the great press of this project and meeting our commitment to creating an affordable living environment for our residents, in a beautifully designed building, and in an amenity-rich neighborhood. Our residents are benefitting from the energy savings of living in a Passive House building. Based on residents paying their own elec-tric bills, their savings are expected to be $30 to $45 per month per unit, which, for a low-income resident, is the equivalent of a 1-2% increase in their annual income. In addition, residents have expressed that they feel better living at Orchards at Orenco in hopes that their health outcomes will improve based on indoor air quality and other attributes of the building. “Every day I find a new reason to love it,” gushes Georgye Hamlin (an Orchards resident), whose one-bedroom apartment is as noiseless as a recording studio. “It’s cool, it’s quiet, and I don’t even hear the train. During the heat wave, my girlfriend came over to sleep because it was so cool. Yay for German engi-neering!” Design Solutions -MEP Systems After reviewing the respective pros and cons of centralized vs. unitized mechanical systems, the team ended up taking a “hybrid” approach, optimiz-ing the mechanical design to utilize the best qualities of those two different approaches. The mechanical design includes a central high efficiency water heat-ing system, three mechanical “pods” with large ener-gy recovery ventilators (ERVs) serving multiple units, with an air source heat pump placed in line on the supply air distribution to temper the ventilation air. Each of the mechanical pods is located within the Passive House enve-lope at the roof level. The ERV in each pod serves 18-20 dwelling units, with direct 4” dia. “home run” duct runs. These home runs are then collected into main trunk lines above the ceiling at the third floor corridor. This solu-tion eliminates the need for fire-smoke dampers at each dwelling unit. The air source heat pump provides approxi-mately 80% of the heating Lessons Learned Things we would do again 1. Use the same design, development, and construction team. In order to build a successful Pas-sive House project of this size, you need an architect, contractor, structural engineer and Passive House consultant who will help the owner/developer meet their goals. The structural engineer on Orchards at Orenco was essential to understanding how the structural details impact energy performance, and how it might take atypical structural details to elimi-nate thermal bridging or simplify construction. A well-versed Passive House consultant brought flex-ibility and willingness to examine several scenarios and iterations as to how to meet Passive House stan-dards. Our contractor and architect worked together on designing, thinking, and building something “outside of the box.” The entire team began with the premise of meeting Passive House benchmarks and being flexible as to how we were going to accom-plish this goal. Copyright © 2014 American Solar Energy Society. All rights reserved. 30 SPRING 2016 SOLAR TODAY

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