Our Net Zero HomePassive House Construction 101
Welcome to 928 NW Cedar!
My name is John Pitney and together with my wife Debbie, I’ve spent the last year of my life planning, constructing, and now moving into a “Net Zero” home in McMinnville, Oregon. It is truly our “dream house.” Not just because we love the way it looks and feels. We share the dream of a world where average people, like Debbie and I, can live in a way that contributes to the long-term regeneration of our planet. We will not be the grandparents who have to explain to our grandchildren why we didn’t do all we could when we had the chance. We want to show others that building a small home like ours is not only possible, but preferable. Below, you’ll find an overview of how we did it!
WHAT IS A PASSIVE HOUSE?
Passive House is the world’s leading standard in energy efficient construction. Passive Houses require little energy year around, making conventional heating and air conditioning obsolete. It is the best path to Net Zero and Net Positive buildings, minimizing the load renewables are required to provide.
Passive House designs go through an energy modeling process, computing: EPA appliance ratings (kwh/year), heat emissions from appliances and occupants, R-values of walls and ceilings, heat gain and loss from windows (etc)—to project annual energy load and determine the capacity of renewable energy generation (in our case, photovoltaic solar generation) needed to reach Net Zero.
OUR ENERGY MATH
Projected energy for our house and electric car = 6,900 kilowatt hours per year
Projected energy generation 5.2K photovoltaic system = 6,900 kwh/year
6,900 – 6,900 = NET ZERO!!!
Passive House Principles
The principles of Passive House construction are:
1) Seamless super-insulation: with no thermal bridging.
2) Airtight envelope: prevents infiltration of outside air & loss of conditioned air.
3) High-performance windows (typically triple-paned) and doors.
4) Heat Recovery Ventilation: operates continuously.
5) Design exploits solar energy for heating & minimizes it for cooling.
BONUS: In order to achieve Net Zero, we add the principle active solar generation.
These principles originated in the U.S. and Canada from work done in the 1970s, a reaction to the OPEC oil embargo. As interest waned here, Europeans refined the principles and application into a rigorous certification process which is quickly becoming the building code standard in the countries of the European Union.
Passive House Institute U.S. (PHIUS) was formed in 2007, committed to making passive principles mainstream here. Its roots date to 2002, when Katrin Klingenberg, a German-born, trained architect, built her own passive house in Urbana, Ill. PHIUS has trained more than 1,700 architects, engineers, energy consultants, energy raters, and builders. As of May 2015, 129 single and multifamily projects had been certified. Ours is certified with PHIUS by trained staff at Earth Advantage in Portland.
How We Applied These Principles
In partnership with our builders and designer, we applied each principle to our home in the way that best fit our goals, our latitude, climate, and budget. Below you can find an overview of how we met the challenge of each principle, including pictures and links.
#1: Seamless Super Insulation
Achieving “super” insulation in our home includes 3 steps:
- R60 Floor: Our floor is built of 12-inch thick insulation under 4 inches of concrete. Read a blog about the flooring process.
- R-54 Walls: Our 13-inch thick walls include a 10 inch layer of dense-packed fiberglass (R40) wrapped in 3 inches of a spun basalt product called Roxul Stone Wool (R-14). Read a blog post about insulating our walls.
- R-70 Attic: Blown-in fiberglass.
- Offset Studs In Double Wall: To minimize thermal bridging
#2: Airtight Envelope
- Insulated Concrete Slab Floor: Our efficient, cost-effective floor plays a double role: insulating and helping to maintain an airtight seal from the ground up. Read a blog post about our flooring process.
- Vapor Barrier Beneath Slab: We used a black plastic layer on top of insulation. (see above)
- Henry’s Blueskin VP 100: We used this air-tight/weather-tight, peel-and-stick “miracle product” to wrap the entire cube of our house, from plate and walls and across the ceiling. The blueskin is even self-sealing when penetrated by nails and screws!
- Minimizing Penetration of Blueskin Envelope: We did this by eliminating the need for our appliances to vent outdoors, using a ventless condensing dryer and circulating hood and filter above the stove/range.
- Intus Windows: These high-tech windows have super tight construction and seamless installation with Blueskin.
- Double Latching Doors: That create a tight seal on closing.
- Foam Gasket Beneath Outer Plate
- We Passed Our Blower Test! This tests the tightness of our air barrier, pressurizing and de-pressurizing the living space by inserting a blower in the front door. The Passive House standard of leakage is a maximum of .6 air changes/hour (ACH) at 50 pascals of pressure. Buildings built well using conventional construction will test at 4-5 ACH. We passed the test at 0.51 ACH!!!!
#3: High-Performance Windows
- Construction of Intus Windows and Doors:
- Triple paned
- Argon gas between the layers.
- Insulating Values:
- R-Values: 7.7
- U-Value: 0.08 (U-Value is the rate a window conducts non-solar heat: lower is better. Single glazed U-Value = 5 Double glazed U-Value = 1.6
- SHGC (Solar Heat Gain Co-efficient) = .4 (fraction solar heat admitted)
- Low-E Coatings: metallic oxide onglass surface acts like a sieve or filter:
- Some particles block long waves (heat) while allowing short waves (light).
- Other particles allow maximum light and minimize heat transmission.
#4: Heat Recovery Ventilation
The most important element in heating and cooling a Passive House is the Heat Recovery Ventilator (HRV). Ours is a Zehnder ComfoAir 350, certified by Passive House to operate at 84% efficiency. It is located in a closet, distributing air through 4-inch flexible ducts, running just above the ceiling. Our only mechanical heat source beside appliance operation is a small unit (think hair dryer) located in a duct.
Perhaps the most common misconception regarding Passive Houses concerns airflow. “A house needs to breathe”, builders might say disapprovingly, when first presented with the idea of building very tight homes. A Passive House does breath – exceptionally well. Rather than breathing unknown volumes of air through uncontrolled leaks, Passive Houses breathe controlled air by mechanical ventilation, effectively the “lung” of the building. A Passive House constantly sips fresh outside air in and exhausts stale inside air (with moisture and odors form bathrooms and kitchens) back out.
The HRV runs 24/7, replacing one-third of the house’s air every hour. Exhaust air from the bathrooms and kitchens doesn’t mix with incoming air supplied to the bedrooms and other living areas. The two streams pass each other, exchange energy, not mixing or touching, making the Passive House one of the healthiest building standards in the world.
Read a blog post about “the lungs of our Net Zero house.”
#5: Exploiting Solar Energy for Heating and Minimize for Cooling
Our house at 928 NW Cedar is positioned as far north as possible on our lot to exploit as much passive solar energy in addition to the south facing roof for active solar. The south facing wall contains 3 floor-to-ceiling glass windows and 2 doors with major glass. In the energy modeling process, the south roof overhang was adjusted to balance summer shading (to prevent overheating) with access to lower sun angles in winter for solar gain. Coupled with smart (high performance) windows these design choices provide maximizing and minimizing solar energy gain when appropriate.
Getting to Net Zero
As mentioned above, Passive House doesn’t automatically equal Net Zero House. In order to get our overall energy balance to zero, we needed to apply a few other principles to keep our energy use as conservative as possible. Check out the overviews below to see what we did!
Active Solar Energy Generation
We are using a 5.2 K Photovoltaic array to generate all of our annual electricity needs (including our Chevy Volt). Here’s a breakdown of the system:
- 16 SunPower panels on the south facing roof.
- Inverter in garage with Kindle Fire readout to monitor generation.
- Panels rated at 327 watts each, for a total 5,232 watt
- System projected to generate 6,881 kwh of electricity annually.
- Generation will operate the house and charge the electric car.
- SunPower offers a 20-year extended warranty on the inverter.
$25,899 TOTAL COST
-7,770 – Federal Income Tax Credit (30% of installed cost)
-6,000 – State Tax Credit ($1.90/installed wattage up to $6000)
-3,388 -Estimated 5-year generated energy value (5X $619)
$8,741 *ESTIMATED COST AFTER 5 YEARS
*Using SunPower’s 1-year “bridge loan,” customers delay full payment until 1 year after installation, by which time all Federal Tax credit will have been received.
*Customers of PG&E and Pacific Power are eligible to receive a substantial additional rebate through Energy Trust of Oregon.
Appliance Choices for Energy Efficiency & Airtight Envelope
The appliances we choose figure in the Passive House design in a number of ways:
- Energy efficient operation: lowest possible EPA rating for KWH/year
- Vented appliances are vented indoors to minimize holes in the envelope.
- Ventless, condensing dryer
- Recirculating hood above range
- Appliances provide indoor heating in winter and need of cooling in summer
APPLIANCE BRAND MODEL PRICE KWH/YR
Dishwasher Bosch SHP65T55UC $810 259
Refrigerator Frigidaire (20.4) FGHT2046QF $839 386
Range Samsung NE595R0ABSR $1499 no rating
Freezer GE–chest FCM15DHWW $585 297
Dryer Whirlpool Ventless WED99HEDW $1049* 531
Washer Speed Queen AFNE9BSP113TN01 $1699 68
Microwave Whirlpool WMHNC73521CS
Water Heater GeoSring Hybrid GEH50DFEJSR $1,000 1514
*Price after $450 factory rebate
Technology Advances To Note!!!
- Heat Pump Dryers: This is the first significant advancement in energy efficient dryer technology in forever!!! Whirlpool (model WED99HED) is a ventless dryer using a heat pump refrigeration system instead of a electrical coil to dry and recycle the same air. It doesn’t require outside venting so the integrity of the airtight envelope is maintained. Condensed moisture, collected inside the dryer exits into the washer drain. Typical dryers consume 900 kwh of energy/year. This heat pump dryer will use 531.
- Induction Ranges: The Samsung cooktop heats food by induction technology. The element’s electronics power a coil that produces a high-frequency electromagnetic field. That field penetrates the metal of the ferrous (magnetic-material) cooking vessel and sets up a circulating electric current, which generates heat. Induction transfers 90% of the energy from source to food, compared with 55% for gas ranges and 65% for conventional electric stovetops.
- Heat Pump or Hybrid Water Heating: The GeoSpring 50 gallon unit employs an integrated heat pump to draw heat from outside air and transfer it to water. Conventional electric tanks use (ave.) 4646 kWh/year vs. 1514 for the GeoSpring.
Household Lighting: Passive & Efficient
14% of household energy use is for lighting. In our lifetimes, we witnesses and agents of an ongoing revolution of lights, from Thomas Edison’s incandescent to light emitting diodes (LEDs). LEDs are now affordable enough that all of us can be the luminaries we’re born to be and support our neighbors in switching on a new light! Compact Fluorescent technology reduced energy use by 75% over Edison’s light breaking invention. LEDs cut CFL energy in half again! Figuring the cost of power at 12 cents/KWh, the current lower cost of LEDs and that you hardly ever have to replace an LED, even the cost/year is lower with LEDs. And significantly less heat is produced by LEDs, lowering summer air-conditioning loads.
LOCATIONS FIXTURE TYPES BULB/BULBLESS WATTAGE
Living Room Flushmount Ceiling Bulb-less 24 watts
Sewing Center Flushmount Ceiling Bulb-less 24 watts
Entry Flushmount Ceiling Bulb-less 24 watts
Dining Room 3 Pendant Lights 3 Bulbs 7 watts each
Kitchen 2’x2′ Ceiling Bulb-less 48 watts
Kitchen (cont’d) 3 Counter Undermounts Bulb-less 7 watts each
Bathrooms (2) Oversink Fixtures 5 Bulbs 13 watts each
Bedrooms (2) Flushmount Ceiling Bulb-less 20 watts
Closets/Pantry (5) Wall mounts Bulb-less 9.4 watts each
Laundry Flushmount Ceiling Bulb-less 20 watts
Garage – indoor 2 Shoplights Bulb-less 40 watts each
Outdoor lights (5) 3 Patio/2 Garage 5 Bulbs 9 watts each
2 Porch Can lights 2 Bulbs 13 watts each
TOTAL *505 watts
*3,600 watts required if house was lit by incandescent bulbs——1,000 watts for CFLs
*For a comprehensive comparison of incandescents, cfls and less, visit designrecycleinc.com