Big Thunder Residence
Site characteristics or focus during construction or remodel:
The intent of the design was to reflect the ecotone in which the house sits; namely the ecotone between the Sierra Nevada mountains and the Great Basin desert. The most important sustainable design idea was the solar heating and power that was driven by wanting to capitalize on a climate with over 290 sun-days per year amid 5,600 heating degree-days. This was expressed architecturally in the orientation with the long east-west axis and materials and colors to optimize passive solar gain. The split Trombe wall holding the stairs between them was the most unique sustainable design innovation, providing a second function and better use of space than other Trombe wall designs.
Building Construction Type:
Mixed; timber frame, cast-in-place concrete, conventional stick-frame and LVL framing.
Site Use and &Protection Measures Before & During Construction (LEED Cat I):
Big Thunder stands as an example of what can and should be done when sustainable and creative design is allowed. The re-creation of ecosystems destroyed by construction and the creation of new ecosystems was critically important to this project, reflecting especially the owner’s fields of study and their interest in minimizing their local impact. The house footprint is approximately 5,300 sq. ft., or about 10% of the total site. The development fits perfectly within the master plan for this area. The site was planted almost entirely with native species, emphasizing water efficiency and creating natural spaces. The density and land use is suburban/rural with a minimum of one acre per home. The goal of maximizing permeable spaces to absorb local precipitation is an important part of the project.
Big Thunder’s design incorporates and responds to the bioclimatic area through orientation and passive heating and cooling. The home sits at 5,770 feet in elevation on the eastern slope of the Sierra Nevada Mountains. The summers are characterized by hot days, with relatively cool nights and down-slope evening breezes. This was capitalized on by use of operable windows and thermal mass. Opening windows in the evening cools the mass of the building; closing window blinds and windows when the owners are away in the daytime prevents heat build-up, and excellent insulation coupled with reflective glazing on the west side also prevent heat build-up. There is no mechanical cooling system and only a radiant heating system that is designed to work with the passive solar features of the house. The orientation of the house, with the long axis aligned east-west, allows for maximizing solar gain while also allowing the owners to watch the changing pattern of sun- and moon-light as the various shadows thrown by windows change with the season. The ability to follow these seasonal patterns in the design of the house brings the owners more in touch with those patterns and cycles.
Outdoor & Indoor Water Efficiency Measures in Project (LEED Cat II):
All drip irrigation. Native, and regional plants. Grey water recovery and re-use for irrigation. Low flow indoor fixtures, energy star rated dishwasher, frontloading clothes washer.
Energy Efficiency & Renewable Energy Measures Used in Project (LEED Cat III):
There are large operable windows in all living areas. The majority of the windows are south-facing, thus providing illumination during daylight hours: percent of total building area that is daylit: 96.2%.
Big Thunder is intimately concerned with the use of energy and our energy future. The goal of the home is to be“net zero” in energy impact. There was also a goal of being CO2 neutral, thus any propane consumed must be balanced by a CO2 reduction- equivalent of PV electricity generated. Currently, the owners expect to generate about 2,500 kWhs of electricity more than they consume, equal to about 5,000 pounds of CO2 not emitted via electricity production. This more than offsets the approximately 2,700 pounds of CO2 emitted via consumption of propane.
The home was designed to be very efficient for both heating and general electrical use. The HVAC systems are small befitting the size of the building; most heat comes from the solar thermal system, and the backup boiler is EPA Energy Star rated, as are the major appliances. Energy-efficient fluorescent lighting is used in many areas of the home.
According to energystar.gov, the house is in the second percentile in terms of single-family home energy use (i.e., 98% of US homes use more energy than Big Thunder does). The home uses on average 27% of the baseline case (average home) in terms of total energy use (heat and electricity). This is based on actual metered power use for 2004-2005. In absolute terms, it uses 2.5 kWh/sq. ft./year of electricity (all PV generated) and about 6,000 BTU/sq. ft./year in propane. The balance of the thermal energy use is provided by an active solar thermal system and passive solar space heating. These systems are all designed to work in harmony and have demonstrated excellent performance over the last two winters.
The base case home was based on data from a variety of web sources that concluded for our area an average of 42,000 Btus/sq. ft./year in gas and 17,060 Btus/sq.ft./year in electricity (5.0 kWhs/sq. ft./year) are reasonable estimates of energy use. These were compared to actual meter uses of energy for Big Thunder. The “net zero” calculations assume an energy content of 28 kWhs/gallon propane, a density of 4.24 pounds/gallon propane and use our local electrical utility’s (Sierra Pacific Power) published emission rate of 1.9 pounds of CO2 per kWh.
Space & Water Heating Systems:
Solar, flat plate collectors, open loop drain-back with propane backup via Munchkin high efficiency (Energy Star-rated) boiler.
Green Materials & Green Measures Implemented in Project (LEED Cat IV):
Recycled/reused materials, easily recyclable materials, locally produced/harvested materials.
Indoor Environmental Considerations Used in Project (LEED Cat V):
No forced air ventilation. All natural fiber rugs, no wall-to-wall carpet. Low toxicity/low VOC finishes used where possible. Water-based concrete stains.
Subjective Evaluation/ Design Considerations: How well has the structure achieved its design goals? What would be done differently the next time?
The evaluation process is an ongoing one (see Feedback Loops, below) with systems continuously monitored and evaluated. The building itself has served the owners very well. The only thing that would be considered for the future is a larger solar hot water storage tank.
The owners’ commitment to the project and the ideas embodied in it have led them to create several outreach and educational efforts related to it. The owners created a website through which they shared the process of designing and building Big Thunder (www.big-thunder.com) and most recently have begun adding performance data on the photovoltaics (Solar PV) to the web site. They answer questions sent through the website and try to assist people considering similar projects. Several presentations have been given at local green building conferences and energy expos regarding the project, its performance, and how to incorporate green building in to other projects. The house is continuously monitored and data-logged; this data is used to help assess performance. Power data from both inverters, and temperature data from five locations (three in floor, two in the trombe walls) is logged every 10 seconds. The temperature sensors were installed during construction and home-run wiring was done by the owner. The owners recently worked with the heating contractor to modify the control signals to improve the overall system efficiency related to the use of the solar thermal storage tank heat. Several sensors used in the solar water tank have failed, and custom sensors were recently ordered to replace these.