Net-Zero Performance: Page 5 of 5

Year 1
Beginner

Inside this Article

The Riggins family is net-zero energy, ...including their car.
The Riggins family is net-zero energy, ...including their car.
A solar hot-air collector heats the garage space passively.
A solar hot-air collector, built from plans in Home Power (HP109), heats the garage space passively.
Low U-factor, high SHGC windows on the south side admit the sun’s energy.
Low U-factor, high SHGC windows on the south side admit the sun’s energy, which is absorbed by the concrete slab floor.
The wood heater has proven more useful for setting ambiance than as necessary for auxiliary heating.
The wood heater has proven more useful for setting ambiance than as necessary for auxiliary heating.
Closed-cell spray-on polyurethane foam was used on all inside sheathing faces for an airtight, high R-value insulation.
Closed-cell spray-on polyurethane foam was used on all inside sheathing faces for an airtight, high R-value insulation.
A water-to-air heat exchanger connected to the earth tube outlet
A water-to-air heat exchanger connected to the earth tube outlet isn’t needed, and was never connected to the solar thermal system.
From the earth tube, air passes through an ERV
From the earth tube, air passes through an ERV, which transfers energy (and humidity) from outgoing to incoming air.
The 100-foot-long earth tube was placed in a 10-foot-deep trench.
The 100-foot-long earth tube was placed in a 10-foot-deep trench. The earth tube tempers incoming air—cooling it in the summer, and warming it in the winter.
A minisplit heat exchanger was installed as a backup space heating system
A minisplit heat exchanger was installed as a backup space heating system, but has never proven necessary.
A minisplit heat exchanger was installed as a backup space heating system
A minisplit heat exchanger was installed as a backup space heating system, but has never proven necessary.
Passive space heating, solar water heating, solar electricity, solar clothes drying, and solar cooking (with a portable solar oven).
The home’s “solar side”: Passive space heating, solar water heating, solar electricity, solar clothes drying, and solar cooking (with a portable solar oven). Garage air heater not shown.
A 15-gallon drainback tank sits in the conditioned attic space.
A 15-gallon drainback tank sits in the conditioned attic space.
A 120-gallon, dual heat-exchanger storage tank with a backup electrical element.
A 120-gallon, dual heat-exchanger storage tank with a backup electrical element.
Enphase M190 microinverters installed and ready for PV modules.
Enphase M190 microinverters installed and ready for PV modules.
Properly sized window overhangs help prevent summer overheating.
Properly sized window overhangs help prevent summer overheating. A mix of good passive design and high-quality active systems make a net-zero success story.
The Riggins family is net-zero energy, ...including their car.
A solar hot-air collector heats the garage space passively.
Low U-factor, high SHGC windows on the south side admit the sun’s energy.
The wood heater has proven more useful for setting ambiance than as necessary for auxiliary heating.
Closed-cell spray-on polyurethane foam was used on all inside sheathing faces for an airtight, high R-value insulation.
A water-to-air heat exchanger connected to the earth tube outlet
From the earth tube, air passes through an ERV
The 100-foot-long earth tube was placed in a 10-foot-deep trench.
A minisplit heat exchanger was installed as a backup space heating system
A minisplit heat exchanger was installed as a backup space heating system
Passive space heating, solar water heating, solar electricity, solar clothes drying, and solar cooking (with a portable solar oven).
A 15-gallon drainback tank sits in the conditioned attic space.
A 120-gallon, dual heat-exchanger storage tank with a backup electrical element.
Enphase M190 microinverters installed and ready for PV modules.
Properly sized window overhangs help prevent summer overheating.

Conclusions

Energy design by computer modeling is only an approximation and can never completely account for variations in occupant behavior and lifestyle. Still, our Energy-10 modeling predictions came very close to reality. There is still much to be learned as we monitor the house’s performance over the long term. We can safely say, however, that we demonstrated that the Passivhaus philosophy works well, and that builders can achieve tremendous energy-efficiency improvement with just a change in techniques and a modest increase in cost (see “Cost Comparison” sidebar).

Comfort and safety are very important, too. A home like ours is not for a “hands-off” family that insists on the narrow 68°F to 72°F comfort range that Americans have grown accustomed to since the widespread use of air conditioning. A passive solar home requires getting used to slightly wider temperature swings, and requires hands-on participation to occasionally open and close shades and windows to maintain comfort.

We also were pleased that humidity problems did not occur. Because of our dry climate, we purposely used an ERV for ventilation, rather than a heat recovery ventilator, because an ERV also transfers humidity between incoming and exhaust air. This worked extremely well—throughout the winter, the house remained between 25% and 35% relative humidity, the heart of the comfort zone in cold weather.

The challenges of detailed design and frustrations during construction began fading the moment we watched the electric meter run backward—and at the first of many 0 kWh electricity bills—and the first time the outside temperature dipped below 0°F, but we could sit in a 72°F house, with no heater turned on. It has been a fun and worthwhile adventure!

Access

Jim Riggins is the owner and principal analyst of EnerSmart Energy Solutions (enersmartenergy.com), a Building Performance Institute (BPI) building analyst, EPA WaterSense home inspector, and a Residential Energy Services Network (RESNET) certified home energy rater. Jim and his wife Elise showcased Heliospiti in the 2011 Pikes Peak Tour of Sustainable Buildings to show the benefits of affordable energy-efficient construction to the Monument and Colorado Springs, Colorado, communities.

Products & Companies:

Accurate Dorwin • accuratedorwin.com • Windows

ACT • gothotwater.com • D’Mand hot water recirculator

Enphase Energy • enphase.com • Microinverters

Habitat for Humanity ReStores • habitat.org/restores • Recycled building materials

National Renewable Energy Laboratory • 1.usa.gov/PVWatts • PVWatts solar calculator

Onset • onsetcomp.com • Hobo data loggers

Passive House Institute U.S. • passivehouse.us

Professional Solar Products • prosolar.com • PV & SHW mount rails

Rampart Custom Homes • rampartcustomhomes.com • Builder

REHAU • bit.ly/ECOAIR • ECOAIR earth tube

Sharp Solar • sharpusa.com • PV modules

Sun Earth • sunearthinc.com • Solar hot water collectors

Sun Plans • sunplans.com • Passive solar building plans

UltimateAir • ultimateair.com • RecoupAerator ERV

WaterSense • epa.gov/watersense

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