Passive Houses Can Reduce Energy Use by 90% :
Keep occupants comfortable and healthy
Todd Collins and Andrew Michler
Since nearly half of U.S. energy use goes into operating buildings, saving money on utility bills and environmental sensitivity are great reasons to improve the performance of new and existing buildings. However, energy efficient buildings are about much more than just saving energy. Built properly, they are more comfortable, healthier and more durable.
Passive House is considered by many to be the most rigorous energy efficiency building standard in the world. Initiated in the U.S. as a response to the energy crisis of the 1970’s, Passive House or Passivhaus was perfected in Germany. The methodology involves high insulation values, precise detailing of every part of a building’s envelope (roof, walls, windows, floors) as well as meticulous accounting for nearly all sources of heat gains and losses.
A Passive House certified home or building is designed to meet a specific annual energy demand using software called the Passive House Planning Package or PHPP which allows designers to carefully assess the energy needs. Passive House buildings are then constructed to
The result is buildings that reduce the energy required for heating and cooling by 90% of typical construction. To many in the industry, this seems preposterous if not impossible. In Europe, though, more than 30,000 projects have been built to Passive House standards including single family homes, office buildings, residential towers, schools and even swimming pools. Several jurisdictions are planning to make Passive House a standard in their building code including Brussels, Austria and Sweden. Even Oregon is recognizing the standard in its Reach Code.rigorous air- tight standards which are 3.5 times more stringent than the new Energy Star 3 program.
Passive House is being proven viable technically, aesthetically, and economically in all regions of the U.S. Approximately 30 projects have so far been certified to Passive House standards and there are more than 15 projects pursuing certification in Colorado alone. Passive House advocates say the standard solves many issues the building community often simply ignores.
Photo Courtesy of Andrew Michler
Passive House myths:
1. “It is expensive.” While the incremental cost in the U.S. has been quoted at 5% to 20%, the incremental cost in Germany, where Passive House has been practiced for well over a decade, is 3% to 5%. A square foot cost comparison does not account for lower operation and maintenance costs.
2. “It is just for houses.” The phrase “Passive House” is a literal translation from the German language. In Europe, Passive House buildings include commercial, residential, multifamily, schools etc.
3. “You can’t open the windows.” Not only can you open the windows, but properly designed cross and stack ventilation strategies in the energy model help achieve Passive House certification.
4. “Buildings need to breathe.” People need to breathe, but buildings need to stay dry. By controlling precisely how air and moisture move through a building wall, many potential problems are resolved. Constant fresh air is provided by energy efficient mechanical ventilation.
5. “Passive House buildings are ugly.” Passive houses have been called boxy but there are many unique building examples, from ultra contemporary to more classic and traditional styles, including the winner of the AIA 2012 Cote Award and 2011 USGBC Project of the Year.
6. “You can heat them with a hair dryer.” While it is not recommended, this is partially true. Passive House buildings are so efficient that the equivalent of a hair dryer is often enough to meet a majority of a modestly sized home’s heat load.
7. “Didn’t we try passive solar back in the 70’s?” The term ‘Passive’ refers to the ability of the building to maintain temperature without dependence on HVAC (heating, ventilation and air conditioning) or active systems. Instead, temperature is maintained by keeping heat where it belongs --- in or out --- as well as capturing energy from the sun, occupants and devices.
The Building Envelope is a Big Deal
In a conventional home or building, we turn up the heat or air conditioning for a number of reasons such as leaky windows and walls, lack of sufficient insulation or poorly placed windows. For example, a room with big bank of west facing windows will likely overheat in the summer and be cold in the winter. A Passive House’s design approach focuses on building a shell or envelope that maintains comfort. The result is the near elimination of HVAC and the corresponding energy use and complexity.
In Passive House buildings, high performance windows are essential. Typically, they use triple panes to achieve a minimum of R-5 insulation value and some are over R-10. Typical homes by contrast have double pane low-E units which are usually around R-2. Passive House windows are well sealed and properly tuned for the building’s orientation.
Photo Courtesy of Andrew Michler
These windows not only save energy but more importantly, they also eliminate that feeling of cold or heat on bare skin which is why even a room whose thermostat says it is comfortable doesn’t feel like it. Right now, few U.S. window manufacturers make units that can work for Passive House, so most projects use windows from Europe or Canada.
However, U.S. manufacturers are starting to rethink their performance assumptions and develop more energy efficient options, a good sign of how pushing energy efficiency helps the industry develop higher performing products.
Unlike passive solar design, Passive House is not dependent on perfect solar exposure to work. It is possible to build passive house buildings in high density areas with less sun. However, if good solar gain is possible, window glazings are carefully selected and units are sized to allow in as much heat as needed without over heating in summer or having excessive energy losses in the winter.
Healthy Air by Design
Some worry that super efficient construction can be too tight and insist that buildings need to breathe, which in fact was the biggest problem with the first heavily insulated homes built in the 1970’s. Actually, it’s the occupants that need to breathe, but buildings need to be tight to keep out moisture and pollutant-laden air and to avoid wasting energy. Also, air leaks allow a significant amount of moisture into a wall which, under the right conditions, causes condensation. The resulting wet surface not only creates an ideal place for mold to thrive and grow, but the moisture is also one of the primary root causes for building failures and related health concerns.
Passive House wall systems significantly reduce air leaks and allow any moisture to dry out of the walls. The core piece of equipment to keep the interior healthy is an Energy or Heat Recovery Ventilation system which exhausts stale interior air and replaces it with fresh, filtered air while capturing and transferring the energy. Pollution or moisture sources like baths and kitchens are typically exhausted with the fresh air vents located in the bedrooms and living rooms.
Much of the design criteria in Passive House are based on integrated system thinking which is often a primary goal in green building but notoriously difficult to implement. Certified Passive House Consultants are required to complete a technically demanding 9-day training course and must pass a rigorous two-part exam to insure they understand the intricacies of the process and methodology. The building system thrives at developing low energy buildings by not only accounting for heat losses and gains, but also by enabling designers to model each project very accurately based on the needs of the site, materials and other specific goals.
The PHPP software is very much a balancing act. It helps the design team assess the efficacy of different strategies and products to meet the energy requirements including thermal bridging, wall and window assemblies and insulating materials. For example, the team uses the model to achieve the correct ratio of insulation without over insulating or putting it where it is not effective. Called performance- based design, the team can assess different options to choose the best and most cost effective way to achieve the required energy performance.
Cost Advantages of a Passive House
One of the largest challenges for Passive House is the perceived cost. Being so new to the U.S., the development of products cost competitive to production building is critical. The advantage of Passive House from a cost perspective is three-fold.
1. First, some of the incremental construction costs for things like high performance windows can be offset by a reduction in cost for the HVAC system. By reducing the energy required for heating and cooling, Passive House buildings have significantly smaller and less costly heating and cooling systems. Also, because these buildings have such low heating demands, it is possible to eliminate natural gas lines, a significant new construction cost. Reducing the heating loads by 90% makes electricity a more viable option for heating. Assuming there are no other natural gas requirements like domestic hot water, stoves and ovens, natural gas lines are not needed.
2. Second, Passive House utility or operational costs are significantly lower. It is critical to factor in the home or building owner’s total monthly cash outlay for living expenses to determine the suitability of a mortgage. Some banks recognize this savings and offer mortgages up-to a full point cheaper for energy efficient housing making Passive House even more cost competitive. Ultimately, the total monthly cash outlay including mortgage payment and utility payment for a Passive House can be similar to a typical house or building.
3. Finally, Zero Net Energy buildings can actually be less costly with Passive House. Because Passive House steeply reduces the building’s energy footprint, significantly fewer solar panels are required to achieve Net Zero, meaning a house generates as much energy as it needs. This reduction in required solar panels offsets the incremental costs of improving the efficiency of the building making Passive House cost neutral and possibly less costly.
In the end, performance is measured not just by the cost or energy savings but by how the home or building occupants feel when they are in the building. Comfort is built into the design and is truly one of the primary metrics to judge the success of a project.
Todd Collins is Founder of A&E Building Systems – Products for High Performance Buildings, and is Passive House Trained. Andrew Michler, LEED AP, is a founding Partner of Rocky Mountain Passive House.