The first ZNE remodel – or Deep Energy Retrofit – project in Boulder, Colorado was designed with the overarching goal of creating a home capable of producing enough energy to satisfy domestic needs, power a future electric car, and still have a net-negative annual energy balance. Challenged again with a building site with relatively low passive solar gain, the mechanical systems engineers had to design a building that could “charge” up during sunny days by solar hot water-heated radiant floor systems, and could “coast” through cloudy cold-snap days without needing more energy.
With the addition of a 6.02-kW solar array installed by Namaste Solar Electric, the home is expected to achieve 120-130% of it’s net-zero energy goal within the first year with a net excess greater than 1,500 kWh.
What our clients think: Coming soon!
This home was featured on the 2007 Boulder County Tour of Solar & Green Homes and was gracefully designed by Andy Johnson of DAJ Design.
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Location: Boulder, CO
SF: 2,700 ft2 conditioned space
Year Retrofitted: 2007
Projected HERS Performance: 0
Confirmed HERS Index: Not rated
Electricity
Grid-tied 6.02 kW roof-mounted PV array, producing 8,300 kWh per year with expected household consumption at 7,600 kWh per year
Primary Heat Source
Solar thermal hot water feeding radiant floor heat systems in basement slab, and staple-up in new addition
Backup Heat Source
8 kW Thermolec electric boiler boosting water temperatures in the solar storage tanks
Primary Hot Water Source
180 evacuated tubes
Solar Thermal Storage
Two 168-gallon stainless steel tanks (photos) insulated with 12″ open-cell foam on all sides
Exterior Walls
Existing Structure
(Outside to inside) 1/2″ OSB over 2×4 stud wall, set off from existing wall by 1/4″, filled with 3.25″ Icynene insulation, separated from interior 2×4 stud wall filled with 3.5″ cellulose insulation by 1 layer Tyvek. Thermally broken R-28
New Addition
2×4 stud wall with 1.5″ resilient channel on interior, 7″ Icynene insulation in cavity. Thermally broken R-27
Roof
At existing structure: 8″ Icynene + 8″ blown cellulose between ceiling joists. Estimated R-70. (cold attic)
At new addition: 6″ SIPS with 3.5″ Icynene sprayed on underside at dropped ceiling. Estimated R-55
Exterior Finish
Stucco with faux-stone trim
Foundation
At existing basement: 4″ concrete slab + 1.5″ Gypcrete, covered by 1″ natural wool carpet
At new addition: 8″ Greenblock insulated concrete forms. R-30
Windows
Duxton fiber glass frames with 2 layers Heat Mirror TC88 by Serious Windows (formerly Alpen Energy Group). Average whole-unit U-value: U-0.15 (R-6.7); Center of glass (COG) U-value: U-0.07 (R-14.3)
- Energy Monitoring LIVE! (Web Energy Logger)
- Case Study from GreenBuildingAdvisor.com
- Finished photos (Flickr)
- Construction photos (Flickr)
- Full color poster detailing all the homes’ features (PDF)
Want to see how the home is performing right this minute? Check out its live Web Energy Logger (WEL) installed by Sunnyside Solar Colorado.
Ready to learn more about us? Read about our whole-systems approach to building and why we should be your choice for a new or retrofitted zero net energy home. Don’t take our word for it, though. Check out what our clients have to say about us.