The goal of the expansion and renovation was to articulate a symbiotic relationship between the building and the natural environment. Furthermore, the renovated Co-op was to be a place to gather and learn. This required a design process that continually looked to the natural environment as a resource within the context of building’s unique program and objectives.
An efficient envelope was the starting point for a sustainable building and this resulted in eschewing traditional building design and construction practices that result in what the project designer refers to as "weak links". For example, the front door masonry slab continues from the outside to the inside of the store but is separated by an underground thermal break. This barrier inhibits the conductance of hot and cold ambient temperatures by the interior masonry via the exterior masonry thus reducing energy demand for heating and air conditioning.
This technique in isolation is relatively insignificant but represents the level of detail taken by the designer when addressing the complexity of the building envelope. "Blanket solutions are easy because you don’t have to think. But there are microbits of building that are performing differently and that all need to be considered part of the efficiency equation. R-30 everywhere isn’t going to cut it, it’s not the whole story". In general, he emphasizes that, "You have to tailor it (the envelope) to site conditions". Insulation values in the walls and ceiling vary throughout the building but average R-20 and R-40 respectively.
Such microclimatic-responsive design is also present in People’s business operations. Produce receiving and backstock storage is strategically located on the northern end of the building where solar exposure is at a minimum. This slightly reduces energy demand for keeping produce cool and is representative of the integrated "zoning" approach that the designer employed to match building program with envelope and space conditions.
Integrated space heating and cooling
Energy modeling was employed to design an integrated 3-stage HVAC system to heat and cool the building. Heating and cooling are provided in the building using a combination of passive ventilation, direct solar gain, night flushing, ground-source heat pumping and high-efficiency natural gas combustion. A radiant tubing-in-slab system on the first floor and a conventional ducted air system on the second floor deliver heating. In both cases, the primary heating energy source is ground source heat pumps.
To cool the building, a series of design elements are used in sequence to provide the necessary heat removal, beginning with passive strategies. First, a vertical shaft in the center of the building extends from the first floor ceiling through the roof allowing "stack effect" to cause warm air to flow up and out of the building, which in turn is replaced by cool night air entering the space through perimeter openings (windows) located on the ground level. In this manner, the building is passively cooled when wind and/or outdoor air temperatures permit. Next, when conditions require it, a fan installed in the ventilation shaft can be activated to assist in establishing the desired airflow. During the following day, the building openings are closed as outdoor temperatures rise. Finally, when indoor temperatures rise beyond the thermostat setpoint, cool water is circulated through the radiant tubing in the slab, providing highly efficient mechanical heat removal.
Water temperature is monitored and controlled to prevent over-cooling of the slab, which could result in condensation. The strategy employed on the second floor is similar, except that cross-ventilation between operable second floor windows provides the passive stage of cooling, and a water-to-air heat pump provides mechanical cooling.
Heat rejection and extraction from the earth is accomplished using a closed-loop piping circuit installed in a series of deep vertical bores located in the courtyard in front of the building. When winter heating requirements require additional heat, or in the event of a heat pump failure, the system is supplemented or backed up by an ultra-high efficiency condensing natural gas water heater. The water heater also provides for the domestic hot water requirements of the building.
Deadband setpoints are set at a wider than typical range of 62-75 degrees. This relaxed environmental criteria significantly reduces the amount of time the system will run and consume energy.
Project Engineer Gene Johnson notes, "When aiming for exceptional energy efficiency, we have found that it is essential to dispense with the traditional all-in-one-box HVAC unit. The best results are achieved by first designing the building to reduce heating and cooling loads as far as possible, then designing the heating, cooling, and ventilating system intelligently to make use of passive strategies first, and finally applying the most efficient mechanical equipment and controls that the project can support."
People’s worked with the local utility (PGE) to sponsor a lighting analysis exploring the most energy efficient lighting strategies for the building. Earlier energy modeling by the HVAC designer indicated that the building would consume 45,983 kWh without lighting enhancements and the utility’s analysis outlined a strategy that would provide an estimated 11,459 kWh in energy savings.
Active lighting consists of compact T-8 fluorescent tubes and zoned controls for specific tasks to minimize the number of lights in use. Daylighting comes from several south-facing windows and an open floor plan that promotes daylight penetration deep into the building. Windows are low-emissivity thus permitting beneficial daylight to enter the building while reducing the amount thermal heat gain.
People’s expressly chose to create an "L" shaped building through the expansion that would allow the center to serve as a landscaped community courtyard. Its open design invites community congregation and supports organized events such as a weekly farmer’s market. The vegetation provides some shade and evaporative cooling.
The expansion includes greater provision of community space inside the building. The "Community Room" provides a large, open, daylit and naturally ventilated area in which to hold educational events on sustainability, nutrition, and natural health.
A very pleasant community sun space on the south side of the building welcomes customers and community members to relax in its naturally crafted cob benches while enjoying a view of the outside garden. It also doubles as a heat absorber and distribution system. The space is designed to maximize solar exposure during the winter and minimize it during the summer via a significant roof overhang and strategically placed deciduous tree located on the south side of the building. During the winter, the sun passes through the window on the south façade directly and indirectly hitting the thermal mass of the masonry floors and cob walls. The heat is absorbed and re-radiated, assisting in creating a comfortable temperature within the space. As an aesthetic feature, colored glass bottles are built into the cob walls that refract the sunlight into the space during the winter when the sun is low. In the summer, the tree’s foliage and overhang shade the space from the hot afternoon sun.
Transportation & accessibility
People’s drafted a Transportation Demand Management Plan that spells out its past, current, and future efforts to promote alternative transportation to and from the store. As part of the design phase, People’s surveyed customers to assess their transportation habits and found that a majority of shoppers walk, bicycle, and bus to the store (the Co-op is within a quarter mile of 2 bus lines). The City thus exempted them from having to build any additional parking into the project. The store provides no off-street parking and patrons that drive to the store continue to park on the street. A portion of the existing driveway was replaced with a porous grass-pave surface to allow rainwater infiltration.
A new bicycle delivery service is one particularly progressive component of the Transportation Plan that exemplifies sustainability as a business strategy. Individuals can order their groceries by phone and pay a small fee to have them delivered to their home by bike. The service is currently limited to particular areas of Portland but is designed to expand according to demand. Seniors and people with special needs receive the service at a substantially discounted price.
Other elements of the Transportation Plan include installation of nearly twice the required number of covered and uncovered bicycle parking spaces; incentives such as raffles and discounts for biking, walking or public transit use; marketing; selling transit tickets; and displaying bus schedules and bike maps.
In an effort to promote accessibility, People’s installed a wheelchair elevator behind the store. This, plus wider than typical store entrances and grocery aisles, renders the entire building wheelchair friendly. Ironically, City building codes did not require the elevator but did require that People’s install paved (instead of pervious) ramps to service a back door.
All rainwater will be either harvested or infiltrated on site via a number of innovative management strategies that were integrated into the design. Starting at the top, two sections (totaling 246 ft2) of the roof are "ecoroof" planted with a large variety of drought tolerant, colorful plant species that are watered via a highly efficient drip system. The vegetated portion of the roof handles roughly 5,000 gallons of rainwater a year via infiltration, evaporation, vegetative uptake, and evapotranspiration. All rainwater landing on the roof is directed to a 1,500-gallon underground cistern buried in the courtyard and overflow is directed to landscaped areas. This water is projected to meet almost all of the landscape irrigation needs (including the ecoroof) after the plants have been established for a three-year period.
The building is plumbed to flush all of its toilets with harvested rainwater but currently does not because the City required additional plumbing inspections that would have held up the project. Other such systems have been approved in Portland but People’s opted to seek approval at a later date when it would not interfere with their construction schedule.
People’s symbolically replaced a portion of the existing driveway with a new covered bicycle parking facility that is underlain by a porous paving surface. The additional grass-covered surface will reduce runoff, promote groundwater recharge and reduce the need for curbs and other drainage features. Mud is not anticipated to be a problem despite bike and pedestrian traffic because the space is protected from direct rainfall.
People’s is currently exploring funding opportunities for a 2 kW photovoltaic array that is planned for the building’s roof. A statewide non-profit organization may fund a majority of the project because the building is an exemplary demonstration of sustainable design.
Keys to Success - Design:
- Employ climate responsive building envelope design that renders the sun’s light and heat an asset
- Design a multi-faceted, integrated heating an cooling system that prioritizes passive strategies
- Relax environmental criteria by widening the thermostat set points
- Supplement heating needs with an ultra-high efficiency condensing natural gas water heater
- Design a microclimatic-responsive building program
- Orient the building in a way conducive to positive community gathering
- Provide community space within the building
- Develop an "alternative transportation"-friendly transportation management plan
- Reduce automobile parking and increase covered bike parking
- Vegetate portions of the roof to mitigate stormwater runoff
- Harvest rooftop runoff for landscape irrigation
- Engage City inspectors and permitting staff early in the project to plumb the building for toilet flushing with rainwater
- Replace impervious surfaces with pervious materials
- Use computer modeling to optimize the building’s lighting plan
- Preference daylight, specify high efficiency light fixtures, and use low-emissivity windows
- Install operable windows