Oregon Solar Cottage Shares a Ground-Source Heat Pump with Its Neighbors
General Specs and Team
Location: Salem, OR
Living Space : 1350 sqf
Cost (USD/sq. ft.): $320/sqf
Completed: June 2007
Architect: James Meyer, AIA LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify.
, Opsis Architecture
Builder: Bilyeu Homes, Inc.
Developer: Sustainable Development, Inc.
Interior designer: Jessica Helgerson Interior Design
Landscape architect: DeSantis Landscapes
Engineer: Catena Consulting Engineers
Energy analysis: Oregon Department of Energy
Foundation: short basement; 4-in. concrete slab; 6-in. poured concrete wall; 2-in. XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. insulation on inside (R-15)
Walls: 2x6 studs at 24 in. o.c.; vented rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. : housewrap (Tyvek), vertical XPS battens 12 in. o.c.; dense-packed blown cellulose; 1-in. R-5 foil-faced polyisocyanurate over sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. (R-28 total)
Windows: cedar-frame, double-pane, low-E2, argonInert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows. -filled (U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. < 0.32, SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. 0.41, Jeld-Wen)
Roof: cool-color standing-seam metal roof (Taylor Metals); 3/4-in. ply sheathing, waterproofing membrane; 9 1/2-in. I-joists at 24 in. o.c., open-cell spray foam (R-36, Sealection 500)
Garage: one-car detached
Heating/cooling: vertical-loop ground-source heat-pump system, neighborhood-shared, with 2-ton heat pump (WaterFurnace), forced-air heat, and (initially) three-zone ERVs; no cooling system
Water heating: Two evacuated-tube solar collectors, two 120-gal. storage tanks, 4,500-W backup electric heating element
Annual energy use: 13.3 MMBtu/yr. (8,900 kWh gross-5,000 kWh PV production). Note: Air handler was upgraded, so current energy use could now be less.
Photovoltaic: 2-kW, grid-tied
- Passive solar orientation
- Building-integrated shade
- Short, semi-conditioned basement
- High-performance insulation
- Reflective metal roofing
- Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. kitchen appliances
- CFLs throughout
- Sealed ducts, ERVs, and whole-house fan
- Low-flow fixtures
- Dual-flush toilets
- Rainwater harvesting (1,500-gal. underground tank)
- Drought-tolerant landscaping
- Drip irrigation
Indoor Air Quality
- Energy-recovery ventilator (ERV)
- Operable windows (natural ventilation)
- Formaldehyde-free sheet goods
- Low-VOC interior finishes, sealants, and adhesives
- 100% wool carpeting
Green Materials and Resource Efficiency
- Minimal site disturbance
- All stormwater remains on-site
- Concrete contains 35% fly ash
- Advanced framing
- 95% of construction waste recycled
- Fiber-cement siding
- 100%FSC-certified construction-grade lumber & plywood sheathing
- Locally sourced hardwood flooring, paint, and windows
- Biodegradable foundation form-release oil
- Community-wide measures:
- landscape irrigation integrated into GSHP system
- biofiltration swales
- permeable-surface roads, sidewalks, paths
LEED for Homes: Platinum (101 points)
Earth Advantage: platinum
This LEED Platinum-certified home is a model of sustainability on a community level
This small house on reclaimed institutional grounds in Salem, Oregon, is just the first of many to come in a project that puts equal importance on energy efficiency, environmental conservation, and quality of life. Though the Pringle Creek cottage uses some cutting-edge technology to produce its heat and electricity, the essential principle of its design is an efficient use of space and resources.
Part of a whole
Many elements—from the ground-source geothermal loop to 12 acres of open space—are shared at Pringle Creek, thus weaving a fabric of experience and intent for people living here. There really is a Pringle Creek, too. As part of the original master plan for some 275 acres, the creek was cleaned and restored; the aquifer that underlies the property was protected through multiple swales, percolation beds, roads with permeable surfaces, and much more. This house may not exist apart from the community it’s in.
A large ground-source heat pumpHome heating and cooling system that relies on the mass of the earth as the heat source and heat sink. Temperatures underground are relatively constant. Using a ground-source heat pump, heat from fluid circulated through an underground loop is transferred to and/or from the home through a heat exchanger. The energy performance of ground-source heat pumps is usually better than that of air-source heat pumps; ground-source heat pumps also perform better over a wider range of above-ground temperatures. (GSHP) satisfies the space heating loadRate at which heat must be added to a space to maintain a desired temperature. See cooling load. of more than half the homes in the complex. The heat pump system is around 50% more efficient than standard forced-air heating. The heat is delivered through pipes that loop through the community in an underground right-of-way. A two-well system supplies the GSHP with nonpotable water; it also supplies water for irrigation of common areas. More than 90% of stormwater remains on-site due to an all-porous street system and network of rain gardens.
The very tightly built house pulls fresh air through an energy recovery ventilation unit (ERVEnergy-recovery ventilator. The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV.) to further conserve energy.
The city provides water for domestic use, which flows through all the low-flow fixtures and low-usage appliances. Nonpotable rainwater is harvested from roof runoff and stored underground in a 1,500-gal. concrete tank. This supplies occasional irrigation needs (plantings around the house are native and drought-tolerant) and exterior uses, such as washing the car.
The scale of experience
It’s not common for a house this small to be equipped with a sprinkler system, but this high measure of safety was the serendipitous trade-off with the fire marshal for granting the planners narrower streets at better human scale. This scale ties in to the house, which was designed with large windows that provide “eyes on the street.” The open flow of the plan blends the living energies of back and front and makes the house feel larger than its 1,350 square feet.
Oriented for passive solar benefit, the house is equipped with solar screens and generous eaves to optimize light in winter and manage it gently in summer. A grid-tied 2.0-kWh photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. (PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.) array feeds any excess electricity back to the utility grid, and a visually subtle evacuated-tube solar collectorSolar collector consisting of a series of glass vacuum tubes in which an inner tube containing fluid (or in some types, a metal plate) absorbs heat energy and transfers it for practical use, usually water heating. on the roof provides domestic hot water. On cloudy days, an electric water heater backs up the solar thermal system.
Crafted with the exterior proportions of an evolving “traditional” Northwest architecture, fiber-cement siding and roofing contribute to durability, as does modest detailing. Low-VOCVolatile organic compound. An organic compound that evaporates readily into the atmosphere; as defined by the U.S. Environmental Protection Agency, VOCs are organic compounds that volatize and then become involved in photochemical smog production. paints, adhesives, and finishes are employed throughout, as are locally sourced structural FSCNonprofit organization that promotes forestry practices that are sustainable from environmental and social standpoints; FSC certification on a wood product is an indicator that the wood came from a well-managed forest. lumber, exterior paints, and Pacific madrone wood flooring. The very high indoor air quality is further protected through a detached garage, which keeps away auto pollutants.
Structure addresses conditions
A rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. works to keep the building dry. Essentially, such an arrangement divides the function of weather resistance into two parts. The exterior protective claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. of fiber-cement clapboards, usually nailed to housewrap and sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , is held away from these by polypropylene battens, which provide a ventilation space—a layer of air over the entire inner wall. Water may get under the siding through gravity, capillaryForces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules. action, or the force of winds, but it never condenses on the housewrap (in this case, also polypropylene) or enters the structure beneath it. In the rainy Northwest, this strategy eliminates problem leaks and the unhealthy molds that can grow as a result.
Architect and community master planner James Meyer intended to dispel myths that thoughtful design and technology were not compatible or doable. This house came together in about four months using local contractors. Meyer says, “The technology needed for a green house already exists—all that’s needed is the will.” He feels that “the new paradigm has arrived” and that builders are willing, but they need a helping hand—they tend to stay with what they’re used to and may confuse this with responding to what the market demands. Current home buyers are alert as never before to sustainability but have tremendous confidence in what builders say, so it’s important that builders “embrace green technologies.”
The benefits of integrated design
Addressing the community's various priorities, such as aesthetics and indoor air quality, holistically rather than independently was an important design strategy. Not only did this contribute to the overall efficiency of the project, it ensured that the cottage (and the whole Pringle Creek community) would be a pleasant, durable, and healthy place to live.
—Jesa Damora is a freelance writer in Somerville, Mass.
- James Meyer
- Opsis Architecture
- Rob Wotzak
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