7 Steps to a Mainstream Net-Zero House
Fortunately for those of us concerned about the planet, net-zero-energy homes are not a new concept—and not even rare. What’s new about houses that produce at least as much energy as they consume is the systems they use to accomplish the goal. And when you can get there with mainstream stuff, you know net zero is coming to a neighborhood near you.
When John Wesley Miller designed a 2,267-square-foot mainstream net-zero home, his goal was to get the house’s HERS score into the negatives. And he succeeded. The VISION House Tucson—one in an illustrious line of high-performance demonstration projects presented by Green Builder Media—received an astounding -17 HERS rating. The HERS Index is a nationally recognized system for inspecting and calculating a home’s energy performance.
A net-zero energy home generates as much energy as the home needs over the course of a year. During the day, photovoltaic panels on the VISION House make electricity. Any electricity the home doesn’t need goes back to Tucson Electric Power (TEP). During the night, the electricity needed is taken from TEP. Electric bills for net-zero homes most months are less than $10, which is essentially a monthly connection fee for access to the power grid.
The total cost of owning a net-zero home (including mortgage and utilities) is less than the cost of owning a similarly priced home that only meets the minimum requirements of the building code.
Here’s the 7-step how-to guide for achieving an ultra-energy-efficient house. With tweaks for regional differences, this power combo of products and systems can be replicated by any builder for any market:
- Structure. The structure is standard masonry concrete block filled solid with concrete. The walls are insulated with two inches of Johns Manville AP Foil-Faced polyiso foam sheathing, and then clad with a three-part stucco finish. This all sits on top of a 12”-thick steel reinforced slab. Walls and floor have thermal mass that holds and greatly slows temperature extremes, something Miller calls “the thermal flywheel effect.”
- Insulation. Walls and floors store warmth during the winter, and they store “coolth” (a word Miller likes to use) in the summer. The house achieves roof R-ratings as high as 50 by using foamed-in-place insulation on the top of the ceiling, and filling the attic with blown-in Johns Manville fiberglas. Because the house is built so tightly, Miller spec’d Panasonic’s WhisperGreen Energy Star rated ventilation fans, with their highly energy efficient DC motors.
- HVAC and Hot Water. Rheem’s Net-Zero Air and Water System was used for the first time at VISION House Tucson. The system includes a Rheem classic 15 SEER heat pump, a hydronic air handler and Rheem’s solar hot water heating system with storage tank and electric tankless water heater to serve as back up. “What’s innovative about this system is how it was custom tailored and integrated specifically for the Tucson Vision House," says Tim Shellenberger, corporate vice president of product engineering for Rheem. "These are off-the-shelf products that make up the integrated system that helps drive down the cost of energy for the home using renewable solar energy as the primary source for domestic hot water and space heating. Soon Rheem will have even higher efficiency heat pumps and air conditioners that can be applied to further drive down energy use and achieve lower than a -17 HERS rating.”
- Solar. Since the home uses approximately 5.5 KW of energy much of the time, a 7.4 KW grid-tied solar array, provided by Hanwha Solar, and its solar leasing partner One Roof Energy, with Schneider Electric’s Conext™ TX inverter, enables the home to sell energy back to the utility. Solar hot water panels supply most of the home’s water heating load. This system sits on durable Boral Madera cement tiles, which protect the roof.
- Windows and Doors. MI EnergyCore windows are R-4, with a U-value of 0.25. Solar screens on west-facing exterior windows protect homes from heat without obscuring views. Window films can moderate damaging heat and light.
- Appliances and Lighting. The home features Whirlpool’s Gold-Series Energy Star kitchen appliances and its Smart Front Load Washer and Electric Dryer. To further keep the energy load low, all lighting is CFL or LED.
- Design. The house was sited for passive cooling. West-facing porches protect from afternoon heat gain and provide places to enjoy fabulous Tucson sunsets. North facing porches protect walls from summer heat gain, when the sun hits the north side of buildings on the longest, hottest days of the year.