Super energy efficiency for existing homes

 The Star Tribune has a story about the MinnePHit House in South Minneapolis.

Sometime in the next few weeks, Paul Brazelton will move his family into a 1935 Tudor in south Minneapolis that has no furnace. He’s just finished a massive renovation of the family home and even though winter’s bearing down, he removed the boiler and plans to use that basement space for his daughters’ home-school classroom.

He also took out the fireplace.

If this sounds like the most uninviting house (and classroom) in Minneapolis, there’s something else to know: Brazelton, a software engineer and passionate environmentalist, has nearly finished a retrofit of his house to the stringent engineering standards of the Passivhaus model, a German system of homebuilding that uses insulation and highly efficient doors and windows to save energy.

The finished 2,000-square-foot home could be warmed even in the dead of winter with a pair of small space heaters, Brazelton said, though the family plans to piggyback on their hot water heater and use an in-floor heating system in the basement.

The project is the renovation of an existing home to meet EnerPHit standard for energy performance. EnerPHit is a subset of the Passive House standard (hence the PH), which is an energy performance standard that requires very high levels of energy efficiency.  The Passive House Institute has a summary:

A Passive House is a very well-insulated, virtually air-tight building that is primarily heated by passive solar gain and by internal gains from people, electrical equipment, etc. Energy losses are minimized. Any remaining heat demand is provided by an extremely small source. Avoidance of heat gain through shading and window orientation also helps to limit any cooling load, which is similarly minimized. An energy recovery ventilator provides a constant, balanced fresh air supply. The result is an impressive system that not only saves up to 90% of space heating costs, but also provides a uniquely terrific indoor air quality.

Passive House is a performance standard, meaning it doesn’t specify design features like LEED, but has performance characteristics that the building must meet after construction is complete.  Namely an airtight building shell at  ≤ 0.6 ACH @ 50 pascal pressure measured by a blower door test and a total heating & cooling demand of <4.7 kBtu/sq ft/yr.  Total energy use needs to be ≤ 38.1 kBtu/ft2/yr.

In layman’s terms, this means Passive House designs are 11 times more airtight than a conventionally designed and built modern home.  As for energy use, a typical single family detached home uses 76 kBtu/sq ft/yr.  My own house was built in the 1920’s and currently has no wall insulation.  In 2010, we used 89 kBtu/sq ft/yr in total, and I think we’re fairly frugal with our electricity.  That means when the Brazelton family finishes their home, it will use less than half the total energy of my house and be 15% larger.

The Passive House standard doesn’t require or depend on renewable energy to achieve this high energy performance.  It’s focused on minimizing, to the greatest extent possible, the loss of heat and capitalizing on natural heat sources like sunlight and even body heat.  The MinnePHit house will be renewable-ready, but it won’t have renewables to start with.  Paul, the owner, puts it eloquently:

 …we decided to use our limited resources in building a house with the highest level of efficiency and durability.  If maintained correctly, solar panels can last decades.  On the other hand, insulation can last centuries.  Looking again at the long term, the best investment is using less energy, not alternate energy.

Last but not least, this home is energy efficient because it is location efficient, located in South Minneapolis with nearby access to jobs, recreation and services.  The Brazelton’s definitely don’t have to use an automobile for every trip, and they likely won’t be traveling far to their destination.  The other local example of Passive House design can’t make that claim.

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