What's So Different about a Passive House?
What makes a Certified Passive House unique in today's green building is that the home knows where it's going to......an 85% reduction in the heating and cooling load.
The way it’s done is not magical or expensive. It uses the same techniques that other green or high performance buildings use. The difference is the Certified Passive House Consultant and the PHPP. While a Green Builder may add more insulation and select higher quality materials, there is always the question of “how far do you go and where does it get you?”. A Passive House and a Passive House Consultant provide the destination as well as the path to get there. The “there” is the 85% reduction from a normal “code built house”, or a 70% reduction from an “Energy Star House”. The “there” is like nowhere else.
A Passive House is essentially a heat battery. The structure is designed to both super-insulate the envelope for heat loss due to leaks and thermal transfer, and then to exchange interior air for fresh exterior air to maintain indoor air quality without losing the heat of the interior air by using a heat exchanger.
All homes generate waste heat. Our human activity, lighting, and household appliances produce heat. The simple act of cooking a dinner noticeably warms a kitchen. In current construction standards, those sources do not generate enough heat to offset the continuous heat loss through the walls windows and doors of today's structure. A Passive House design elevates the insulation standards to the point where the heat is trapped in the home and held, to provide a comfortable temperature during occupancy.;)
While the super-insulation of the structure retains the heat generated, the next step in maintaining a warm fresh environment is to keep a continual stream of fresh air moving into the home while the stale air is exhausted. This normally happens in today's homes by the amount of air leaks in wall and roof systems and through the seals of windows and doors. Since the passive home has all of these leaks stopped or dramatically reduced, the air supply is exchanged regularly through a ventilation system. Since the air leaving the house is warm and contains heat that would preferably stay in the home, the warmth travels through a heat exchanger before it leaves the home. In the heat exchanger, the warm heat energy is essentially moved from the exiting air and put into the incoming fresh air.
Since a Passive Home is warmed by trapping the waste heat already generated from within the home and augmented by whatever solar gain is available, the design process is where the all of the gains and losses are brought together in the Passive House Planning Package (PHPP). The PHPP is essentially an “accounting” or a “thermal modeling” of all the events that either add heat or lose heat within the structure. The process starts with a clearly stated goal: A heating and cooling load of 15Kwhrs per square meters per year. From there, the Certified Passive House Consultant starts working with the variables of insulation values, window placement shading occupants and all of the variables that can be modified until the project is in balance with the stated goals. The real comfort in the process is that it is possible to reach the design goals. Projects have been built and they test out meeting the design requirements. To see the step by step process of modeling a project in the PHPP, go here to read the ABC's of the PHPP.
Brief Explanation of What it's Like Living in a Passive House
Interview with Passive House Designer Adam Cohen: Residential and Commercial Pay Back Topics
More resources to learn about Passive House building:
PBS Radio Story on Passive House Design
American Passive House Network
ABC's of the PHPP: Step by step design process of the energy modeling software
Passive House training and certification organizations: