Sheri Koones writes on AOL’s real estate pages on the growing trend towards passive houses. While it started in Europe, the interest is growing globally.
The ‘Passive House’ Path to Extreme Energy Efficiency
With the growing cost of fuel, increasingly stringent home construction codes, and scientific evidence that we must reduce CO2 emissions, many architects, builders and homeowners are turning to “Passive House” or “Passivhaus” specifications to design and build their new homes. Buildings consume approximately 48 percent of the energy used in this country. Passive Houses use 80 to 90 percent less energy to heat and cool.
Demand has increased, in the United States and various countries around the world, to build not only new homes using these Passive House, or PH, specifications but also for commercial structures, schools and for remodeled homes. The Passivhaus standard was developed in Germany in the early 1990s by Professors Bo Adamson of Sweden and Wolfgang Feist of Germany, and the first dwellings to be completed to the Passivhaus Standard were constructed in Darmstadt in 1991.
There are currently 30,000 Passive House structures built around the world, including in the United States. The first PH in the U.S. was built in Urbana, Illinois, in 2003 by Katrin Klingenberg, the founder of the PH Institute in the United States. According to the PH website, “The Passivhaus standards’ strengths lie in the simplicity of its approach; build a house that has an excellent thermal performance, exceptional airtightness with mechanical ventilation!” (See examples in the slideshow below.)
Energy-efficient structures are achieved meeting PH specs by creating a very efficient building envelope. PHs are so well insulated that they no longer need conventional heating and cooling systems such as forced air furnaces. They rely on keeping in the heat generated by the sun, people, computers and appliances in the winter. Vastly reducing the need for heating and cooling is achieved by substantially increasing the amount of insulation used in the ceiling, floor and walls of the house.
In most cases the walls are built much thicker than the standard house to accommodate the additional insulation. It is also necessary to seal up all of the openings, where wires, vents and pipes come into the house, to avoid air infiltration. One or more blower door tests are performed to make sure that all the openings are sealed.
High performance windows and doors are used to keep the “envelope” of the house tightly insulated. Typically, triple-pane windows are used filled with argon or kyrpton gas to reduce thermal bridges, which allow air infiltration. In order to maintain a cool interior environment in the warmer months, south-facing windows are shaded or shuttered to eliminate solar gain; natural cross ventilation is used for cooling, along with some other creative strategies.
Most PHs need a small backup heating or air conditioning system such as a mini split heat pump for extremes in hot and cold weather. PHs require that buildings use no more than 15 kilowatt hours per square meter of living space per year for heating and cooling. (Fifteen kilowatts is similar to the amount of energy used by a hairdryer or small space heater.) This energy efficiency is achieved by using energy modeling software. The Passive House Planning Package, or PHPP, an Excel-based software, is used to size ventilation systems and determine the energy effects of substituting any product or design change.
PHs focus on saving energy rather than creating energy with fossil fuel. However, in order for homeowners to achieve “0” energy homes they can include photovoltaic panels and/or hot water panels to make the home potentially independent of the grid or able to give energy back to the grid.
PH energy codes are challenging to achieve, but the rewards go beyond saving money on energy. PHs are very comfortable and healthy to live in. Because they are so tightly insulated, ventilation is required to keep the air fresh in the house. Energy or heat recovery systems continuously exchange the interior stale air in the PH with exterior fresh air, while also exchanging the heat and “cool” already created in the home.
Many additional strategies have been used to make PHs very comfortable and efficient, by the creative architects designing PHs. Stone floors are often used as thermal mass, which absorbs heat during the day and releases it in the evening when the sun is down. Interior and exterior blinds are commonly used and some retract into the structure so they are not seen when not in use. Many PHs have radiant heating with geothermal or solar panels.
One house in France uses cooling ponds to cool the air before if enters the house in the summer. All use energy-efficient appliances and low-energy bulbs to minimize energy loads.
When people decide to build a house, they need to consider the long-term cost of running their homes. Mortgages might be slightly higher on a PH home, but energy costs will be lower — creating a “wash” in monthly expenses. However at the end of the mortgage, energy costs will continue to be low for the PH.
Dr. Wolfgang Feist, founder of the Passivhaus institute in Germany, says of Passive Homes, “It’s a development of a kind of liberation, because now you can build your energy future; you do not depend on the oil, you do not depend on the nuclear energy, you just depend on your own knowledge and your work. We have seen that it is possible.”