By Ken Levenson, AIA
Continued from the October issue of Green Energy Times
The Passive House Methodology: Optimize what is already required to be built. In roughly five parts:
- Part One: Use the Passive House Planning Package (PHPP) to optimize all efforts. The PHPP energy model has been optimized based on continual research and data collection. Entering all required parameters into the PHPP is the basis of assuring predictability and high quality.
- Part Two: Optimize the thermal enclosure: Enclosure orientation, shading, and volumetric proportions should be optimized given project constraints. Be sure there is a continuous and verifiable airtightness control layer without breaks at component connections such as roof-wall connections. Provide good and continuous insulation with thermal bridge-free connections. And if the thermal bridges cannot be eliminated they are accounted for in the PHPP model. Windows and doors are fully integrated into the thermal and airtight control layers.
- Part Three: Optimize the passive heat gains – both solar and internal gains. Do this with orientation, shading, and sun exposure at first. Then account for lighting, equipment and people. Always be careful to avoid summertime overheating and excessive cooling demand.
- Part Four: Optimize the ventilation system with continuous high-efficiency heat-recovery balanced ventilation.
- Part Five: To account for drastically reduced heating and cooling load requirements, use smaller and simpler systems. While the heating requirement is never eliminated entirely, the elimination of traditional heating systems becomes possible.
The Passive House Components:
- Airtightness: Houses are air-tight with a continuous air-tight layer. This is the single most critical component in achieving efficiency, more important than even thermal insulation because so much heat is lost through air leaks. Once again, perhaps counterintuitively, airtightness is essential in providing indoor air quality, because you cannot control the quality of air unless you control that air in an airtight environment. Airtightness is also critical in avoiding condensation- and moisture-related damage in well-insulated enclosures.
- High-efficiency ventilation: With an airtight environment, mechanical ventilation must be provided. Fresh outside air is continuously provided to the living spaces while stale air is continuously exhausted from the bathrooms and kitchen. To avoid costly heat losses the air streams pass through a counterflow heat exchanger that enables up to 90% of the heat of the outgoing airstream to be conserved by being passed to the incoming airstream.
- Thermal bridge-free construction: As the insulation layer is continuous, forming a sort of thermos, connections and building elements passing through the thermal enclosure need to be thermally broken, avoiding heat losses and potential condensation and the mold damage it can cause.
- High performance windows and doors: For comfort and energy balance it is important to install very good, often triple-pane, airtight, tilt-turn, or fixed-sash windows. Passive House windows ensure that the interior surface of the glass is warm, allowing even temperatures and typically eliminating the need for traditional heating and cooling perimeter distribution systems. Note that you can open the windows in a Passive House – on a nice day, by all means let the breeze blow through.
- Integrated Design: The use of high-performance products alone is not enough – they must be fully integrated, and with Passive House all parts are integrated through the PHPP. It is often noted that high performance windows can’t pay for themselves in energy saved – and this is certainly true considered in isolation. But if we also integrate airtightness and thermal bridge-free construction then the context is shifted and much greater overall savings with greater comfort is possible. The fully integrated design and construction of the Passive House is the synthesis of the scientific research preceding it and makes it a significant step forward in high performance building.
The Passive House Institute has been single-minded in measuring performance, collecting data and consequently pushing the standard forward. The first great study was the European Union funded CEPHEUS (Cost Effective Passive Houses as European Standards) project. Two hundred fifty housing units across many European countries, by different architects and builders, for different clients, validated the energy model. Today PHI is collecting data around the world. In our region, Efficiency Vermont is collecting data on a number of residential projects in the state. All this is resulting in a new appreciation for how we can further optimize our low-energy buildings going forward. This shift to Passive House can unleash new ambitious imaginative energy, making new and astonishing things possible.
Find out more about Passive House at: www.passivehouse.com.
Ken Levenson is an architect, Certified Passive House Consultant, President of the non-profit New York Passive House, a founder of the North American Passive House Network, an International Passive House Association Affiliate Council Member, and COO of 475 High Performance Building Supply.