In Depth Case Studies

People's Food Co-op

Energy

An integrated design approach enables People's to consume 16% less energy than mandated by the strict Oregon Energy Code and save roughly $1,700 each year in energy costs. These features include daylighting, low-emissivity windows, insulation values above commercial and residential requirements (average R-22 in walls, R-44 in ceilings), integrated space heating and cooling, efficient lighting, and energy monitoring.

Building Envelope

An efficient envelope was the starting point for a sustainable building and 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 intentionally separated by an underground thermal break. This barrier inhibits the conductance of heat either into or out of the building, thus reducing the 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 needs to be considered part of the efficiency equation. R-30 everywhere isn't going to cut it, it's not the whole story," he said. Such micro-climatically responsive design is also present in People's business operations. Produce-receiving and backstock-storage space 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 level of the integrated "zoning" approach that the designer employed to match the building program with envelope and space conditions.

People's was without heat until Christmas of 2002, and the project designer indicates that the focussed attention on the envelope paid off: "The energy (HVAC) engineer came for a visit and was really surprised by the heat load in the winter." The prioritization of passive heating and cooling measures substantially reduced the building's dependence on mechanically driven systems.

Integrated Space Heating and Cooling

Heating and cooling are provided in the building using a combination of passive ventilation, direct solar gain, night flushing, ground-source heat pumping, and highly efficient natural gas combustion. A radiant tubing-in-slab system on the first floor and a conventional ducted 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, beginning with passive strategies. First, a vertical shaft in the center of the building extends from the first floor ceiling through the roof, allowing a "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 on the ground level. In this manner, the building is passively cooled when wind or outdoor air temperatures permit. Next, when conditions require it, a fan installed in the ventilation shaft can be activated to assist in establishing desired airflow. During the following day, the building openings are closed as outdoor temperatures rise. Finally, if indoor temperatures rise beyond the thermostat setpoint, cool water is circulated through the radiant tubing-in-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 building's front courtyard. When winter heating requirements necessitate additional heat, or in the event of a heat-pump failure, the system is supplemented or backed up by an extremely efficient 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. These relaxed environmental criteria significantly reduce 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."

Passive Solar Heating

People's designed a south-facing community sunspace designated 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 a strategically placed deciduous tree located on the south side of the building. During the winter, sunlight passes through the window on the south facade, directly and indirectly hitting the thermal mass of the masonry floors and cob walls. The heat is absorbed and slowly 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 the roof overhang shade the space from the hot afternoon sun.

Lighting

People's worked with the local utility (Portland General Electric) 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 kilowatt hours without lighting enhancements, and the utility's analysis outlined a strategy that would provide an estimated 11,459 kilowatt hours in energy savings. The system is estimated to yield $573 in annual energy cost savings and an estimated 6.1-year payback, including the rebate (or 6.7 years without the rebate).

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.

Photovoltaics

People's is currently exploring funding opportunities for a two-kilowatt photovoltaic array that is planned for the building's roof. A statewide nonprofit organization may fund a majority of the installation because the building is an exemplary demonstration of sustainable design.

 

Energy Data Set: Simulation: Units: English Metric

Annual Purchased Energy Use
Fuel	Quantity	Cost($)	MMBtu	kBtu/ft2	$/ft2
Electricity	116,000 kWh		396	73.4
Natural Gas	4,250 kWh		14.5	2.69
Fuel Oil (No. 2, diesel)	0 kWh		0	0
Biomass (wood or other)	0 kWh		0	0
Other	0 kWh		0	0
Total Annual Building Energy Consumption
Fuel		Cost	MMBtu	kBtu/ft2	$/ft2
Total Purchased			411	76.1
Grand Total			411	76.1

Annual End-Use Breakdown
End Use	Quantity	MMBtu	kBtu/ft2
Heating	20,200 kWh	68.9	12.8
Cooling	2,000 kWh	6.83	1.27
Lighting	34,500 kWh	118	21.8
Fans/Pumps	24,300 kWh	82.9	15.4
Plug Loads and Equipment	35,200 kWh	120	22.2
Domestic Hot Water	4,250 kWh	14.5	2.69
Other

Data Sources & Reliability

Simulation software
DOE2 & eQUEST Building Energy Simulation Program

Reliability
The analysis is based upon a simplified DOE2 model of the building in its newly renovated configuration, with the HVAC measures modeled as a single package. The baseline and EEM models do not include any lighting system or envelope enhancements. The energy analysis of the building was performed using the eQUEST Building Energy Simulation Program. Statistical weather data was input from typical meteorological weather data for Portland, Oregon.

 

Green Strategies

• Wall Insulation
  • Achieve a whole-wall R-value greater than 25
• Ground-coupled Systems
  • Use ground-source heat pumps as a source for heating and cooling
• Solar Cooling Loads
  • Shade south windows with overhangs
  • Shade building walls and roofs with trees
• Non-Solar Cooling Loads
  • Provide high-low openings to remove unwanted heat by stack ventilation
• Water Heaters
  • Use water heaters with energy efficiency ratings in the top 20%
• Cooling Systems
  • Use a gas-fired absorption chiller/heater
• Light Sources
  • Use high-efficacy T8 fluorescent lamps
• Heating Systems
  • Use mass-wall passive solar heating
  • Use sunspace passive solar heating
  • Use high-efficiency, condensing oil or gas boilers and furnaces
  • Use hot water heat distribution
  • Replace existing heating system
• HVAC Controls and Zoning
  • Provide sufficient sensors and control logic
  • Create zones that unite spaces with similar thermal requirements

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