Oregon Home Approaches Net-Zero With PV/Thermal System

By Douglas R. Boleyn, P.E.

Published: July 29, 2010

South façade of Oregon home at winter solstice.

Designing homes for near net-zero-energy consumption in the cloudy Pacific Northwest is a challenge. But "Morning Sun," built in 2009, is a residence designed to do just that.

The home is located in a suburb of Portland, Ore., and uses energy-efficiency strategies along with a combined photovoltaic (PV)/solar thermal energy system to reach for the "net-zero" goal.

The design and construction of net-zero-energy buildings is near the top of the global energy agenda. The climate of the western portions of the Pacific Northwest provides particular opportunities and challenges. The primary opportunity is working with a mild climate with few extremes, hot or cold. This climatic feature enables energy-efficiency strategies such as insulation and air-source heat pumps to be very effective.

The primary challenge for the climate is capturing enough utilizable solar energy to provide the energy-producing part of the equation. Winter tends to be very cloudy, yet is the season with the largest energy demand, primarily for space heating. Capturing the maximum amount of energy when rare winter solar radiation is available is key to improving winter performance. Harvesting maximum amounts of electricity (running the meter backwards) in the summer months is also key to moving toward annual net-zero-energy consumption.

The "Morning Sun" residence and its energy features and systems were designed to be a comprehensive integration of energy-efficiency features and high energy-yield solar features that work with the climate.

The homeowner had previously lived in a 1970s-era solar-powered home for over 30 years. The earlier home was approximately 2,800 square-feet and had a solar water heater, a 2.6-kilowatt PV system and a sun room with lots of south windows. These features, combined with a high-efficiency heat pump for heating and cooling, enabled the house to consume a net of 9,000 kilowatt-hours per year from the utility company. This resulted in an Energy Utilization Index (EUI) of approximately 10 kilo British thermal units per square foot per year (kBTU/ft2/yr).  While this EUI is just 25 percent of the U.S. home average of 46 kBTU/ft2/yr, the owner wanted the new "Morning Sun" residence to have an EUI of less than half the previous residence, with a design goal EUI of 4 for the household.

The result was a 2,836-square-foot home located on a south-facing hillside on a steeply sloping lot. The lot was selected for solar access (90 percent) as well as for the beautiful mountain views to the east and south, so extensive window areas were included to capture sun and views. The house consists of two levels and an open loft. The main level (1,788 square-feet) contains the great room/living area, the master suite and a home office. The lower level (879 square-feet) consists of two bedrooms, a bathroom and a recreation room. The open loft (169 square-feet) is a sun room with views.

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