Passive House Pre-certification Pending


Eric and I decided it was time to actually submit our paperwork for Passive House certification.  So, after a couple of weeks of hard work, we finally organized all the documentation needed for pre-certification and sent it to PHIUS (Passive House Institute U.S.) on Wednesday.  I am sure we will need to make some modifications but hopefully, they won’t be huge.

I then realized we never really discussed what it means to be a certified Passive House.  Here’s what we think it means:

The house needs to meet the three basic but very stringent requirements:

  • Air-Infiltration must be less than 0.6 ACH at 50 Pascal
  • Specific Heat Demand must be less than 1.39 kWh/sqft per year
  • Total Primary Energy Demand must be less than 11.1 kWh/sqft per year

What do those numbers mean?

Maximum Air Infiltration at 0.6 ACH at 50 Pascal:

This means air-tight construction.  You should not see daylight between your door panel and the frame, no air leakages around the windows, no random holes in walls, very few and well sealed wall and roof penetrations. If you think about it, this requirement really means high quality construction and components in addition to paying very close attention to detail.  The way this is tested is using a blower door, which inflates the home to 50 Pascals (Pascal is a unit measure for force 1Pa=1Newton/square meter), and measures the amount of air leakage. 0.6 ACH indicates that air changes per hour due to that air leakage.

Maximum Specific Heat Demand at 1.39 kWh/sqft per year: 

This means figuring out the heat loss from every components of the the thermal envelope (walls, roof, slab, windows, doors), adding any other heat loss from heat recovery ventilation, you have the Total Heat Loss figure for the entire house.  You then add up the heat gains from the sun, home appliances, people breathing out hot air, cooking, baking etc., anything that generates heat without purposely generating heat to warm up the house, you have your Total Heat Gains.  Total Heat Loss-Total Heat Gains=Specific Heat Demand.  Specific Heat Demand is the amount of energy required to actively keep the house warm.  In our case, our house is projected to have a Specific Heat Demand of 1.06kWh/Sqft.  To heat the entire house, we will need 12,609 btu/hr.  A standard hair dryer needs about 6,398 btu/hr.  We can heat the entire house with just 2 hair dryers.

Maximum Primary Energy Demand at 11.1 kWh/Sqft per year:

Primary energy refers to the total energy usage including heating, cooling, water heating, household appliances and transmission losses as the electricity travels from the power plant to the house.  This number really means the amount of energy that needs to be generated to meet the energy demand of the house.  How do you achieve this number? First the heating and cooling loads need to be minimized by building an air-tight and super-insulated thermal envelope.  Second, the heating and cooling equipment must be sized correctly to the minimized demands of a passive house.  Third, the home must be lit with energy efficient bulbs and fixtures.  So, as much as possible LEDs and CFLs are used.  Finally, use energy efficient appliances.  Whenever possible, choose from the most efficient of Energy Star certified appliances.  The Arlington Passive House is projected to consume 5.7 kWh/Sqft/yr in primary energy demand.

Passive House designers cannot dictate how the homeowner will use electricity in their house.  However, the numbers projected are based on average usage data in the United States.  There are a number of different software and hardware monitoring systems available, some of which will allow the homeowner to “fine-tune” the way they live the same way people adopt to driving a Prius more efficiently.

Beyond Passive House:

Theoretically, if the house meets all three requirements, it is a Passive House.  This means great flexibility in design, material selections, building methods, etc.  Even how you meet these requirements is something that you have the ability to decide.  i.e., if you do not like the greenhouse potential of XPS foams, you can use EPS.  If you want to completely stay away from petr0 materials, you can use cellulose.  Or if your insulation of choice is pink fiberglass batts, you can do that too, it just needs to be thick enough.

Interior finishes are designer driven as well too. You can choose to use exotic woods for flooring or you can use bamboo, cork.  You can buy your dimensional lumber from a sustainable source or you can just get the cheapest you can find from your local lumberyard.

A performance based standard like this really allows for various levels of entry.  One passive house may be built as part of a low income house project and another may be built as a speculative home for several million dollars.  Both homes will be constructed to a high construction quality and energy performance.

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3 responses to this post.

  1. you don’t technically have to meet criteria 2 (the 4.75kBTU/ft2a or 1.39kWh/m2a) – if you can achieve a peak heating load of 10W/m2 (3.71BTU/hr.ft2). although i’ve yet to see a project that meets the heat load but doesn’t meet the specific space heating demand.

    Reply

  2. Mike, I believe you are correct.

    Reply

  3. This is exactly the third blog post, of urs I personally read.
    But yet I love this particular one, “Passive House Pre-certification Pending
    Arlington Passivhaus” the very best. Thanks ,Coy

    Reply

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