By Melissa MacDonald

Special Contributor

DEVENS -- Last Friday, the Devens Eco-Efficiency Center hosted its quarterly Green Building Roundtable. These roundtable discussions give participants a venue to gather new information about trends in environmentally-sustainable building practices and share their own insights and experience with others who might benefit.

This quarter, the roundtable zoomed in on Passive House energy design, an energy-design standard aimed at driving residential and commercial buildings' energy consumption toward and even below zero. A U.S. take on the European Passivhaus standard, Passive House takes "buttoned up" to a new level, relying on tight construction and insulation techniques to keep the indoor climate comfortable and clean while slashing the need for power-chugging equipment to heat or cool the space.

Five elements

Neil Angus, an environmental planner with the Devens Enterprise Commission and moderator of the roundtable discussions, pointed to five key elements that make the Passive House standard what it is:

-- Superinsulation from a combination of double-wall construction and air sealing of all seams, which helps maintain consistent temperatures

-- Energy-efficient, triple-glazed windows and reduced thermal bridging (heat lost through gaps in construction or insulation)

-- Passive solar heat gain and thermal massing (using interior materials such as granite or concrete, which absorb heat and then release it slowly, as well as heat put out by other sources, like electrical equipment and even humans)

-- Avoidance of heat gain and reduction of the need for cooling via shading and well-thought-out window placement

-- Use of heat recovery ventilation (HRV) or energy recovery ventilation units to provide fresh air while conserving heat and energy already in the building

With all these methods in place, buildings can be heated or cooled with one to two small, wall-mounted units, such as the Mitsubishi Mr.


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Slim. In fact, Angus noted, the savings on mechanical systems for heating and cooling are a significant offset to additional material costs for the difference in construction techniques.

A leading-edge standard

The move for builders to adopt energy-design practices like these is accelerating. In Massachusetts, it's driven in part by Gov. Deval Patrick's Zero Net Energy Buildings Task Force, which is pushing for all new construction to be net-zero energy by 2030.

Passive House is out in front of many of the other current energy design standards, Angus added. For instance, the Leadership in Energy and Environmental Design standard calls for a finished building to use 25-30 percent less energy than a traditionally-built design; Passive House angles for a 60-90 percent reduction in energy usage.

And while a house built according to the current Stretch Energy Code (which many Massachusetts towns have recently adopted in their quest to become Green Communities) needs to meet a Home Energy Rating System rating of 70 (down from 100 for a standard code-built house), homes built using Passive House techniques typically achieve a HERS rating of no more than 20, and frequently a negative number. Angus noted that the latest of the Transformations Inc. Net-Zero Energy Homes built on Devens Green (which used Passive House methods) has a HERS rating of -36.

Angus rounded off the Roundtable discussion with two key examples of Passive House design at work:

-- The Glasswood Passive House, a commercial retrofit in Portland, Oregon

-- The Sonnenschiff , a commercial and residential complex in Freiburg, Germany

"It is really great to see these energy efficient design and construction methods catching on," said Angus, "and even better to have examples in our own backyard."