Passive House Methods Help Build for the Future
General Specs and Team
Location: Duluth, MN
Living Space : 2660 sqf
Builder: J and R Sundberg
Architect/designer: Wagner Zaun Architecture
Engineer: Krech Ojard Engineers (structural)
Consultants: Conservation Technologies (mechanical systems design, building energy modeling, building performance, technical details and supervision)
Foundation: ICFInsulated concrete form. Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above-ground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure. with 8-in. poured walls; 4-in. XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. exterior insulation (R-40); 5-in. slab over 12-in. XPS (R-60)
Walls: 2x4 at 16-in. o.c.; 14-in. deep overall; 1/2-in. exterior OSB sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , 1/2-in. interior gypsum wallboard filled with dense-pack cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection. (R-53)
Roof: 26-in.-deep parallel chord trusses with continuous vent chutes; 24-1/2--deep blown cellulose (R-88)
Windows: triple-pane, argonInert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows. -filled insulated fiberglass frame, thermal spacers, low-e2; SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.: .5 (south), .3 elsewhere; U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. : .19 (south), .17 elsewhere
Garage: Attached 2-car, continuous air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both.
—Rob Wotzak is assistant editor at GreenBuildingAdvisor.com
Heating/cooling: Evacuated-tube solar collection system (Sunda) with 275-gal. insulated tank; EPA-rated wood stove with dedicated combustion air route ($4,000); back-up heating from gas-fired Takagi; no air conditioning
Water heating: same as heating system with 80-gal. tank
Annual energy use: 19.4 MMBtu (projected); 40 MMBtu (actual)
- Ground tempering closed loops to prewarm or precool ventilation air; 300 ft. of PEXCross-linked polyethylene. Specialized type of polyethylene plastic that is strengthened by chemical bonds formed in addition to the usual bonds in the polymerization process. PEX is used primarily as tubing for hot- and cold-water distribution and radiant-floor heating. tubing with glycol solution circulates underground and then runs through a heat exchangerDevice that transfers heat from one material or medium to another. An air-to-air heat exchanger, or heat-recovery ventilator, transfers heat from one airstream to another. A copper-pipe heat exchanger in a solar water-heater tank transfers heat from the heat-transfer fluid circulating through a solar collector to the potable water in the storage tank. to temper incoming fresh air
- Fluorescent and LEDLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed. lighting
- Solar thermal domestic hot water and space heating
- Passive solar heat
- Extremely tight, superinsulated building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials.
- Dual-flush, wall-mounted toilets
- Low-flow faucets
- Rain barrels for roof water collection
- Stacked bathrooms very close to mechanical room
Indoor Air Quality
- Whole-house HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air.
- No carpet
Green Materials and Resource Efficiency
- Bamboo flooring on main floor
- Water-based concrete stain on lower floor
- Cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection.
- Standing seam metal roof
Energy Modeling and Integrated Design are Keys to Getting the Most Out of a Home
When Curt and Melissa hired Wagner Zaun Architecture to design a new home for their family, they had a clear goal: build a durable, adaptable home that uses as little energy as possible and has the smallest possible effect on the local and global environment. Designer Rachel Wagner brought in energy consultant Michael LeBeau of Conservation Technologies early to help achieve the project goals in the most integrated way possible. The history of collaboration between the two professionals combined with each firm’s strong commitment to sustainability and their experience with computer modeling of energy efficient homes well prepared them for the job. Their ultimate plan combined a heavily insulated shell with passive and active solar heating.
Make the best of the site
The narrow hillside and the commanding views of Lake Superior offered a solar orientation that was less than ideal, complicating the passive solar design. Fortunately, the sloped site also gives shelter to much of the home’s lower level. The team was careful to deal with the overall site and building design in an integrated, thorough manner, developing the overall site plan, roof forms and building orientation so stormwater runoff from the steep, in-town lot wouldn’t become someone else’s problem.
Energy modeling pays off
The design team started by modeling potential building assemblies with a helpful software package called REM:Design, but then turned to the newly acquired Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. Institute software (PHPP) to develop the design even further. In the final energy model, the house did not quite meet the Passive House standard for heating (15 kWh/m2 per year - a difficult benchmark to reach in extremely cold climates). After construction, the blower door test result was 0.7 ACH@50 Pa, a very tight house but also just over the Passive House air tightness requirement of 0.6 ACH @ 50 Pa. Nonetheless, the Passive House approach and software gave the team a very detailed and quantifiable method with which to improve the design.
The home’s final design was estimated to use 75% less energy than a comparable home built just to code, and the initial data collected from the household energy consumption suggests that the energy model was accurate.
Buy more insulation once, save energy every day
Double 2x4 walls contain 14 in. of dense-packed cellulose with a cavity R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of 53. The roof has over 2 feet of blown cellulose and there’s a foot of XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. foam under the slab. With this much insulation, the windows are bound to be the weakest link in the thermal barrier, but with triple glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill., 2 low-e coatings, and insulated fiberglass frames, they do a respectable job. Plus the big south facing windows let sunlight pour onto a massive 13 ft. high concrete wall that stores heat well into the evening, and radiates it back into the house as needed.
Energy systems work best when integrally designed
Although a good portion of the home’s heat comes from its passive solar design, there’s also an active solar thermal system that heats an 80-gallon domestic water tank before it redirects to a 275-gallon space heating storage tank. Local building codes requiring double wall heat exchangers for potable water caused Conservation Technologies to design the dual-tank system. An efficient modulating gas fired water heater backs everything up, but most of the family’s domestic hot water needs have been met by the solar thermal system so far.
An outgoing coil in the big tank sends hot water through radiant tubes in the first floor slab and to a water-to-air heat exchanger in one of two main ventilation supply (HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. ) ducts. The heat exchanger (from the solar storage tank) only heats the ductwork for the upper level of the home because the ground level is taken care of by the radiant slab heat. The concept of distributing heat through the residential ventilation ducting is popular in Passive House projects in Europe, but recent experience in North America and northern Europe has shown the mismatch between peak load heating requirements in very cold climates and the typically low air flows necessary for fresh air ventilation.
The whole mechanical system is difficult to describe (see schematic diagram), but it takes no special effort to operate. Energy consultant Michael LeBeau commented, “It was an extraordinary example of integrated design.” Based on the first year’s energy data, the house is actually 80% more efficient than the average Minnesota home. Michael is hoping to install a multi-sensor energy logging system to better study and fine tune the HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. and water heating components.
Verifying results can be as tough as making them happen
One of the biggest challenges in sustainable building is measuring success. Fortunately, the contractor put the extra time in to do a cost comparison of building the same home more conventionally. The premium was estimated at around 17% — not a bad investment when you factor in the long-term energy savings that go along with it.
With its 13 ft. tall, 13 ft. wide concrete interior wall for thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. , the passive solar design works extremely well. As Rachel Wagner put it, “It was a beautiful thing to enter the house at 7:00 pm on a cold January day with the temperature around -7°F, to find the house at 70°F with no heat source running and the thermal wall still warm to the touch from the day's solar gain.” With many sunny days in January and February, the radiant heat was rarely used and the wood stove was barely used as well.
The attempt to distribute heat through the ventilation system drove the decision to install a larger HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. than required for ventilation alone. From this project and other research, the design team has decided to focus on simpler, smaller radiant-based heating approaches in future projects, keeping the mechanical ventilation system separate.
- Rachel Wagner
- Michael LeBeau
- Toshi Woudenberg
Mar 17, 2009 4:15 PM ET
Jun 3, 2009 9:39 AM ET