Net-Zero Home| Austin, TX

Energy Efficiency Improvement 75% – 100%+

Net-zero with energy - Austin, TXKaren and Dan Cripe designed and built their custom home in Round Rock, Texas with the expertise and support of Solluna Builders, a custom home builder who specializes in net-zero projects. Their home has been viewed by thousands of people, and is an exemplary project of a high-performance building located in a conventional planned-unit development.

Due to the lender‘s guidelines, the owners were unable to finance their renewable upgrades. Their financial plan was to reduce their loan amount and pay cash, so this barrier did not pose a challenge.

The Cripe‘s co-op utility company does not pay net-energy rebates, but they do credit surplus amounts that can be used later if additional power is needed. In cases of net energy revenues not being paid by the utility, you can plan to use your excess energy by powering an electric vehicle (see Case Study #5).

The property value was not supported in their region due to a lack of recent custom home sales and the only available comparables were production built homes, at a much lower price of $110 per square foot; they paid approximately $157 per square foot, excluding the land costs.

The Cripe’s main goal was to produce enough energy to power their home and hopefully exceed surplus energy. Over the first year they accomplished their goal. They included a geo-thermal HVAC, Heat Pump and rain-harvesting system, which decreased energy costs, reducing their water bills by $70 per month.

“Green” Lawn: a Whole New Meaning

Karen reports, “we have the greenest lawn in our neighborhood, and our water bills have averaged about $20 per month. During the worst drought Texas has seen with over 100 days of temperatures over 100 degrees, that’s a statement.”

The Cripes offer a great blog covering their project’s development process and have quantified their savings further with Dan’s weather station data.

Green Building Features:

  • Roof- Galvalume standing seam metal roof
  • Insulation- Bio-Based spray foam insulation
  • Windows- Andersen 100 Series
  • Geothermal heat pump- 26.0 EER Carrier Puron R410A
  • 722 square feet of living space per ton of cooling, also provides hot water
  • 5kW grid-tied solar electric system. 24 Sunpower 215 watt modules with Enphase M190-72 micro-inverters. Online monitoring system.
  • Energy-efficient appliances, lighting, ceiling fans, convection oven, magnetic induction cook top.
  • Plumbing- centralized plumbing runs. Insulated hot water lines.
  • Fixtures- dual-flush toilets, low-flower showerheads, high-efficiency washer.
  • Rainwater- 500-gallon rainwater collection system tied to hose bibs to irrigate the garden.
  • Low- and no-VOC paints and finishes. Custom cabinets made with formaldehyde-free plywood. Exhaust fans. Fresh air intake on the heating/cooling system
  • Polished concrete floors. Optimal framing using finger-jointed studs. ZipSystem exterior wall sheathing with built-in moisture barrier. Local limestone and HardiPlank on exterior.
  • No turf grass. Native plants reduce the need for watering and fertilizing. Gutters and rain chains channel front runoff to rain gardens. Composting.

Energy Efficiency Case Study Data

COST OF CONSTRUCTION $291,000 Less equipment
COST OF LAND $55,000
EXISTING PROPERTY VALUE $346,000 * see footnote
COST OF RENEWABLES $61,400 5kWh System; GeoThermal Heat Pump & Water Recycle
Utility (Elec) kWH rate $0.12 Encore/Green Mountain Energy
Monthly utility savings $178
Yearly utility savings $2,136
Energy Production N/A Green Mountain Energy does not pay net energy fees
2010-2011 Usage (KwH) Generation (KwH) Net (KwH) Energy Banked
November 815 451 87 -$10.44
December 1100 727 363 -$43.56
January 572 580 -8 $0.96
February 758 560 198 -$23.76
March 632 640 -8 $0.96
April 586 734 -148 $17.76
May 552 767 -215 $25.80
June 581 762 -181 $21.72
July 916 865 51 -$6.12
August 897 783 114 -$13.68
September 924 810 114 -$13.68
October 728 769 -41 $4.92
Total Electricity Costs -$39.12
Formula 1, PV @5% 20 yrs $26,619
Formula 2, SQ Ft *$20 $42,720 HERS Index not available, no power generation @ $20
*Total Upgrade Investment $40,400
NEW PROPERTY VALUE $380,670 baseline of $346k+ IPV $34,670
Traditional Payback $40,400 @ 20 years interest paid $23,589
**GEM Payback Method $40,400 @ 11.4 years $100 extra payment + Bi-weekly interest $12,595
FV @ 5% 20 years $70,629
Appraised value in 2010 @ $206,000

Custom home prices @ $200-$225 sq ft were not available in subdivision of production homes
Comparables @ $143 per square foot used by the appraiser in 2010 evaluation
*Owner had to pay higher down payment to offset renewable measures and other costs.
They chose to keep their bldg sq footage smaller than other homes in the neighborhood, making ithe appraisal comparison process more difficult to evaluate.
**GEM Payback Method includes extra energy savings pmt + Bi-Weekly payment
Utility prices expected increases of 30% in next 5 years not used in calculation