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Passive House Appeals to Home Energy Raters

RESNET Conference 2012 Trade Show Energy Vanguard Booth Passive House

RESNET conference 2012 trade show energy vanguard booth passive houseThe Passive House Institute of the US (PHIUS) had a real presence at the RESNET conference this week. I felt it even before I got on the plane to Austin last Saturday, as I met John Semmelhack of Think Little while waiting to board in Atlanta. John is a Passive House Consultant in Virginia as well as a Home Energy Rater, and he and I got to talk before and during the flight.

The Passive House Institute of the US (PHIUS) had a real presence at the RESNET conference this week. I felt it even before I got on the plane to Austin last Saturday, as I met John Semmelhack of Think Little while waiting to board in Atlanta. John is a Passive House Consultant in Virginia as well as a Home Energy Rater, and he and I got to talk before and during the flight.

In case you aren’t aware, the Passive House concept began in Germany, and the idea behind it is to beef up the building envelope so much that the heat that flows into or out of a home is extremely small. And I do mean small. They like to say that the heating load can be so small you can heat your home with a blow dryer.

In fact, they have a limit for the heating load that a Passive House must be below: 4,750 Btu per square foot per year. A 2000 square foot house, then, would need to have a heating load less than 9.5 million Btu per year, which could be met by a 1500 Watt blow dryer running for 77 days. By contrast, a typical furnace with an output capacity of 60,000 Btu per hour would run only 158 hours, or less than a week. Those numbers for heating include the heat that comes from the Sun (solar gain through the windows), appliances, and the people in the house.

The Passive House standards are really strict. To qualify, a home must have a measured infiltration rate no higher than 0.6 air changes per hour at 50 Pascals (ACH50). They also require super good windows, mechanical ventilation, and no thermal bridges. Martin Holladay wrote a nice summary a while back called Passivhaus for Beginners.

I first heard of Passive House about five years ago and loved the idea of reducing the loads so drastically. You invest up front in the building envelope and then you benefit for the life of the house. When you look at cost effectiveness, however, sometimes it may be better not to improve the envelope so much and instead add photovoltaics. There’s been a lot of discussion about this program over the past few years, and the Passive House Institute of the US last year split from the German PassivHaus Institut, creating even more discusssion.

Back to my original point, the PHIUS team at RESNET, John Semmelhack and Katrin Klingenberg, were there for three main reasons. First, they went to the RESNET Technical Committee meeting on Saturday to discuss using the HERS software for Passive House projects. Second, they had a booth at the trade show. Third, they taught a two-day class for HERS raters who want to work on Passive House projects because PHIUS is going to use HERS Raters for the quality assurance.

One of our raters, Diane Milliken of Horizon Maine, took the class because of the growing number of projects she’s being asked to work on in Portland, Maine. I didn’t get a complete rundown on the class from her, but she went to the conference not knowing if she would sign up for it or not. I introduced her to John, and after discussing it with him, decided to jump in. When it was done, she was happy with her decision and especially enjoyed the field trip they took to see a Passive House project in Austin. For more on what they did at the conference, see their RESNET 2012 Recap in today’s Klingenblog.

There’s a lot to say about Passive House, so I’ll be writing more here this year. One of the big questions, at least from my mixed-humid climate zone perspective, is, how well does the program work in warmer climates? Stay tuned.

This Post Has 12 Comments

  1. I like this concept and feel
    I like this concept and feel this should be the wave of the future. 
    In our dry SoutWest climate, we can retrofit homes to be cooled or heated for about the same wattage of a hair dryer. This is one of our “Performance Retrofit” goals. We are not attempting passive house – but maybe we are getting there – I will have to look into this.

  2. Thanks for the plug, Allison!
    Thanks for the plug, Allison!  
    A couple of notes for you and your readers – 1) The annual heating demand and cooling demand requirements are even more strict than you might think…our reference floor area in the Passive House world is based on “Treated Floor Area”, or true usable floor area. For a 2,000ft2 (gross area) house, the treated floor area would typically be around 1,500ft2….bringing the theoretical run-time of the 1500W blow dryer in your example down to 58 days. 2) The annual heating/cooling demand requirements already factors in available solar gains and internal gains.  
    Regarding Passive House in the mixed-humid climates – we’ve have a quite a few projects in VA and NC already built or in progress. I’ll be happy to help you with looking at these examples as well as some theoretical case studies for the warmer areas down in Zone 3.

  3. Chris C.:
    Chris C.: I think it’s a great concept, too.  
    John S.: Thanks for clarifying. I’ve revised the article to correct the part about solar and internal gains. And yes, I’d love to learn more about the VA and NC Passive House projects you mentioned.

  4. In general Passive House is
    In general Passive House is pushing us to think differently and that’s a very good thing.  
    I have done the two day PHPP (the Passive House software) course so I know enough to say PHPP is a very good tool, even if you are not building to Passive standards, in assessing the effects of varying insulation/glazing amounts in different parts of a design . 
    However, as our instructor pointed out, it is quite possible to build a huge, Passive house with floor to ceiling glass facing north (to get the view over that way) as long as you throw enough insulation elsewhere and get the solar gain/shading right.  
    We live in a small, ninety year old, far-from Passive home but it has energy consumption of a very costly to build, 6000 square foot Passive mansion. In a world where we need to be concerned about energy consumption, energy security and GHG emissions a standard that does not penalise house size and total energy consumption still has a way to go.  

  5. I think PH is great for cold
    I think PH is great for cold climates, especially areas without access to natural gas. But in warm climates, high levels of insulation and atomic air sealing are hardly cost-justified. 
    I recently worked on a local Passive House project here in SE Arizona. Aside from obvious overkill on envelope u-factor, here are my observations: 
    PH recommended a very expensive, super high efficiency ERV, hardly an appropriate choice for our mild, dry climate. 
    PH recommended sub-slab insulation. The cost benefit of sub-slab insulation is questionable in hot climates, where the small winter benefit is traded off against loss of the passive cooling benefit of full ground contact in summer. 
    PH only assumed 1400 btu/hr internal design load for appliances and six persons. 
    Although my total heating and cooling design loads weren’t significantly different than PH’s, I was not comfortable recommending a single wall mount mini-split to condition the home. In particular, since solar gain dominated the cooling loads, it’s important to get the air to where it’s needed in hot climates. I recommended a small ducted mini-split with unducted return and super low-friction supply side.

  6. Good points David on the
    Good points David on the Energy Recovery Ventilation and the slab insulation. That would not work in the SW as well. I have also heard that the home would possibly get too hot in the winter and may need to be conditioned in this type of climate. 
    I am also starting to favor the simple ducted mini-splits with hard pipe supplies and un-ducted return. Was just looking at these yesterday. These things can sit behind a 20×40 return filter grill real nice.

  7. Chris wrote: 
    Chris wrote: 
    > These things can sit behind a 20×40 return filter grill real nice. 
    That’s exactly what my design called for. Makes the filter almost disappear.

  8. For David Butler, 
    For David Butler, 
    Regarding the Passive House in Arizona – I don’t know anything about the project. I don’t disagree with any of your comments, other than to suggest that the designer or consultant made certain recommendations…not “Passive House” or the PHPP modeling software. 
    I have a digital “test hut” (20x40x2 stories tall) that I paired up with the Tuscon climate data in the PHPP modeling tool. With just 30 minutes into it (never having previously worked on a house in the SW), I was able to get the house to meet the PH annual sensible cooling and heating requirements with the following rough performance specs paired with excellent summer shading and good passive night ventilation/cooling: 
    Slab – uninsulated 
    Walls – R-20 
    Attic/ceiling – R-40 
    Windows – U=0.30, SHGC = 0.23 
    Ventilation – HRV with mediocre heat recovery (60%) 

  9. Hi John, just to clarify, the
    Hi John, just to clarify, the builder dealt directly with Kristin on this project. To my knowledge, the recommendations came from her. Ryan worked up the climate data, and Ian did some additional modeling on the slab insulation question, but PHPP drove the recommendations. The walls were already over the top (9.25 inch TJI “stud” cavities filled with cellulose), and the window specs were 0.22/0.15. That, plus 0.6 ACH50 is just nuts for this climate (Sierra Vista). 
    The local microclimate is about 5 to 10 degrees cooler than Tucson due to higher elevation. Like Tucson, we have long periods of cloudless weather in winter, with relatively mild afternoons. This means that homes optimized for passive solar gain can offset much of the annual heating load with solar gain. I don’ believe PHPP does a good job predicting that. No software does, really. Also, the nearest TMY dataset is Douglas, AZ, which generally has colder winters and hotter summers, even though we’re at a higher elevation. Go figure. I think that contributed to the over-predictions of heating and cooling energy. 
    My own home, which was built in 2005 by a production builder, only requires ~900 kWh/yr for heat (I have a sub-meter for my 15 SEER heat pump). The house has 2,550 sf. Walls are 2×6,16oc with R19 batts and R4 EPS continuous. Attic has R30 cellulose. Ducts are tight, but in the attic. Glass is not low-e, although vinyl sliders are tight. There’s no slab edge insulation. The house tested out at about 3 ACH50 and ducts are tight. No modeling software comes close to predicting my annual heat load. 
    One final note… the builder is totally committed to getting PH certification (as well as LEED Platinum). He saw this as a challenge, which it was. We all learned something and that’s always a good thing!

  10. Having a complete passive
    Having a complete passive house means having a good air filtration system. At UltimateAir we have developed an award winning air filtration system that is complete with an energy recovery system as well as heating and cooling options. Our product has been termed “green” not only by engineers and professionals but has been recommended for health related issues such as asthma and allergies as well as respiration issues. Even without these, doctors, builders, and buyers are suggesting this product for all houses, offices and schools and most of all to complete the requirements to be called a passive house. Check out our product called the RecoupAerator at 
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    Thank you!

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