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The passive path to zero energy

An administrative wing added to a large nursing home is a combination of three distinct buildings, all of which are certified by Passive House Institute U.S. (PHIUS).
Photo courtesy Sam Rodell Architects AIA

by Katrin Klingenberg

Buildings are getting tighter from both the regulatory and consumer-demand sides. As energy codes get steeper and consumers desire more sustainable options, builders face new challenges for meeting these standards and expectations without opening the door to unintended consequences. Indeed, there have been many building failures since contractors began to place putting insulation inside walls in the 1930s.

The good news is a lot can be learned from those failures. Scientific research, best practice guidelines, and certification systems can help design/construction professionals sidestep building failures while delivering high-performance buildings. When inexpensive solar panels are added to the mix, buildings that produce as much energy as they use are actually within reach.

Steps on the path to net zero
Gone are the days of 2×4 walls with batt insulation between the studs. Thicker walls are the new normal, and with them come different details for constructing buildings. The best path to a zero-energy building depends on where it is located. The climate zone is the critical first step because it defines what the project is up against—Seattle is different from Saskatoon.

The Sunshine Health Facilities resident building has 380-mm (15-in.) thick walls and can produce more energy than it uses. Photo courtesy Hamilton Studios

With blower doors and exterior insulation in the building code, it is time for builders to bone up on tight building. It is best to begin with the 2015 International Energy Conservation Code (IECC). From there, one should go to Energy Star 3 or 3.1 to drive home the importance of airtightness and thermal bridges. Further along the path is the Department of Energy’s (DOE’s) Zero-energy Ready (ZER) Home program, which exceeds Energy Star and IECC requirements while adding others, such as the U.S. Environmental Protection Agency’s (EPA’s) Indoor airPLUS certification.

The least risky path to net zero is passive building certification, because it is a complete system with quality assurance built into the system, rather than a collection of discrete programs. The most common passive building certification in North America is PHIUS+, administered by the Passive House Institute U.S. (PHIUS). All buildings certified under PHIUS+ are automatically eligible for ZER certification because the program was developed in part with the DOE to be comprehensive and scientifically sound.

Passive building principles
Fast-forwarding past the in-depth physics of passive building, the method’s five building science principles boil down to the following points.

1. Continuous insulation interrupts thermal bridges between inside and out.
By completely wrapping a building with insulation, heat can no longer sneak out through framing which has a lower in R-value than the insulation between the studs.

2. Airtight construction stops heat and moisture.
Plugging air leaks can slow heat flow, because air that moves through buildings usually carries a lot of heat with it. Further, warm air can hold more moisture than cold air, so when warm air leaks into wall cavities and hits a cold surface (such as wall sheathing or drywall), it dumps moisture, depending on the season.

3. Optimized windows let heat in when (and only when) you want them to.
Double glazing with argon gas is typical of Energy Star windows. Passive buildings usually have triple glazing. Low-emissivity (low-e) coatings applied to the surface of the glass can be fine-tuned to allow more or less heat gain. Windows with high solar heat gain coefficients (SHGCs) should be used on sides of the house where winter sun is wanted—generally, on the east and south sides. Low-SHGC windows should be used where summer sun will do the most harm (generally west-facing windows).

4. Balanced ventilation ensures fresh air and controls moisture.
All of this air tightening means dirty, moist air is not leaking into the living space, so air changes must be controlled with some sort of high-tech fan. One option is an energy recovery ventilator (ERV), which pulls new air in and pushes old air out while transferring heat and moisture in the process.

5. Minimal mechanical is all a super-tight building needs.
As the building is super-tight, super-insulated, and has ‘super windows,’ super-sized heating and cooling systems are unnecessary. This is where the upfront investment begins to pay off. Some of the money spent on insulation and windows can be recouped with much smaller mechanical systems.

When these five principles are applied to buildings, the result is predictable performance, unmatched comfort, superb indoor air quality (IAQ), and resiliency in the face of power outages due to winter storms or summer blackouts. Best of all, because passive buildings consume so little energy, zero energy is easily within reach. Just adding a small renewable energy system, such as a photovoltaic (PV) assembly, can place design/construction professionals at the end of the path to zero.

Katrin Klingenberg is executive director of the Passive House Institute U.S. (PHIUS), an organization committed to making high-performance passive building the mainstream market standard. Klingenberg holds a degree in architecture from Ball State University, and is a registered architect in Germany. In 2015, she won the Women in Sustainability Leadership Award (WSLA). Klingenberg can be reached via e-mail at info@passivehouse.us.

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