The one story, two-bedroom house is 870 square feet and sits on a rectangular 4,000 square foot lot that faces west. The home is long and narrow in shape (19 feet wide) with the longer sides oriented north and south. The roof is relatively steep with a pitch of 8:12.
Alan is an architect and did his own design work with frequent input from Ana. Together, the owners worked within the structure’s siting and configuration to find ways to further benefit from the sun and reduce energy and water consumption. Being an old house with historic character worth preserving, the opportunities for a complete passive solar makeover were limited. For example, eliminating west-facing windows, significantly increasing south facing glazed area, and adding mass were not realistic options. The Scott’s thus integrated a number of small measures that have minimal impact on the aesthetic of their historic home. The major projects include a new heating system, toilet replacement, and a 160 square foot addition to their master bedroom.
To heat their home, the Scotts replaced their old forced-air furnace with an in-floor, hydronic radiant heating system. The system consists of crosslink polyethylene (PEX) and copper piping that is tacked onto the subfloor throughout the house and circulates warm water on demand. Cardboard sheathing with a reflective coating is installed below the pipes that reflects heat upward as the water travels and radiates heat throughout the home’s floor. The heat then naturally rises up into the living space with no electrical assistance. The benefits of this system are improved energy efficiency, better indoor air quality, warm floors for children and bare feet in the winter and very quiet operation. Pipes were also installed in some of the bathroom walls, which helps warm the air near the bath towels and claw-foot tub.
The system has two pumps that break the house up into two different heating "zones". This enables the Scott’s to heat only the occupied zones and reduces superfluous heating and energy consumption. In addition, a programmable thermostat allows the owners to further optimize system performance by pre-specifying the timing and temperature of the system throughout the day.
A 30-gallon, 94% efficient condensing gas water that is vented directly outside supplies hot water for the radiant heating system and domestic use. This water heater, in turn, is supplied with preheated water from a solar water heater that Scott installed on the roof. The 20-gallon solar water heater consists of four evacuated tubes and contains no pumps or storage tank. In the summer it pre-heats the water to 160 degrees using the sun’s energy. Alan purchased the solar water heater from Mister Sun Solar and installed it in one week. President of Mister Sun Solar John Patterson recommends solar hot water heating over solar electric as a first step towards harvesting renewable energy; "The conversion of solar energy into thermal energy (i.e. solar hot water heating) is approximately twice as efficient as conversion to electrical energy (i.e. photovoltaic panels)." In other words, you get twice as much bang for your buck.
Heat recovery fresh-air ventilators were put in the existing and new bathrooms and kitchen. As the warm, moist indoor air is exhausted, its heat is absorbed by a heat exchanger and fresh air is brought in from the outside. The fresh incoming air passes through the heat exchanger to warm it up thus making use of what would otherwise be wasted heat. Heat exchangers are very valuable in cold climates but less useful in Oregon’s temperate climate. However, the ventilator is very quiet and works well to restore air quality in the Scott’s house.
The window addition to the south side of the house facilitates passive heating and reduces the demand on the radiant floor heating system. This strategy enables the home to realize some of the benefits of "sun tempering", in which homes allow direct solar heat gain but do not have enough south facing windows and thermal mass heat storage to be primarily heated by the sun. Moving closer towards the notion of passive solar in which homes store solar heat energy, Alan had a contractor install Tyvek sheeting to the joists and blow cellulose insulation into the walls, roof, and floor, which greatly decreased heat loss and improved comfort. Additional insulation was added in the attic and in the basement below the radiant floor heating system after the addition was competed.
The house is principally cooled by virtue of thoughtful integrated design. A solar powered attic ventilation fan combined with the double glazed low-E windows, well-insulated walls and attic, and a shade tree at the southwest corner of the house keep interior temperatures comfortable even when outside temperatures reach the low 90's. These measures, combined with the occupants relaxed comfort criteria, eliminated the need to install an air conditioning unit.
One double-glazed, low-e window was added to the south side of the house (a 50% increase) to augment daylight penetration and reduce electrical lighting demand. Existing window sashes were also replaced with new double-glazed low-e sashes and the new window’s characteristics help mitigate overheating in the summer and condensation in wet conditions. All existing light fixtures were replaced with fluorescent bulbs and luminaries to further reduce household energy demand.
Once their home's energy loads were reduced through the small changes to the building envelope and landscape and variety of passive and active energy efficient measures, Alan and Ana purchased a 3kW solar photovoltaic system to produce energy on-site. The system is metered and tied to the grid so the Scott's only pay for the energy they use beyond what they produce. In the first five months, the system produced over 1,400 kWh, which amounts to 80% of the electricity they used during that period. In April and May, the system produced 40-50% more electricity than they used.
The home's ability to be a net producer of energy is principally due to the integration of several different measures the Scott's took in their home. The positive impacts of any of their energy efficient strategies in isolation are minimal; however, as they continue down their list of green "to dos" their home's energy performance is increasingly impressive.
To reduce household potable water consumption the Scott’s made a couple of simple changes inside and outside the house. Alan specified dual flush, low-flow Coroma toilets for both the existing and new bathrooms. Two buttons on the top allow a choice of either a 0.8-gallon flush or a 1.6-gallon flush, depending on need. This results in water savings of approximately 40%. The toilets have adjustable rough-ins and were available at Environmental Building Supplies and Keller Plumbing.
When replacing their washing machine, they chose a front-loading washer that uses less water than a top loader. They also replaced their existing showerheads with low-flow fixtures. On the outside, all gutter downspouts drain to rain barrels which are used for irrigation. Most importantly, the couple reduced the amount of lawn on their property and has stopped irrigating it in the dry summer months- one of the most water consumptive practices in the residential sector.
Future plans include the installation of a 2,000-gallon cistern that will significantly increase their rainwater harvesting storage capacity. This system will collect rainwater for irrigation and possibly some domestic uses (ie: toilet flushing) as well.
Keys to Success - Design:
- Design a radiant heating system with multiple zones to reduce waste heating
- Pre-heat hot water with a solar hot water heater
- Recover waste heat from inside air to heat incoming outside air in ventilators
- Enhance the building envelope to take advantage of solar heat gain and daylighting
- Select low-flow and high efficiency when replacing showerheads, toilets, and washing machines
- Reduce lawn size and do not irrigate it with potable water during the dry summer months
- Disconnect downspouts and drain them to rain barrels to be used for irrigation