Replies

1. 
   J Chesnut | Oct 05, 2010 10:02am | #1

   If anyone has a chance to ask Dr. Feist questions I would love to hear his response to the following:

   - PassivHaus was presented to me as an optimization between a high level of energy efficiency and cost of construction. I was shown a graph (in German) that was purported to determine the criteria of PassivHaus requirements in part by the savings accrued when a boiler/furnace system was no longer required to be installed. As the US has different market dynamics than Germany should we not expect this optimization formula to chance and therefore the possibility of different US PassivHaus criteria?

   - What is the reasoning behind the .6 ACH requirement? Is it purely energy savings or does it include moisture control in wall assemblies? Is this number specific to a climatic region?

   - For us non-German speaking users of PHPP we are in part flying blind. All the critical technical references are to German DIN standards without English translation (that I am aware of). For PassivHaus to maintain its integrity and technical rigor in the US does it not need a national or regional institute to provide the scientific expertise to ensure we are not uncritically the standard? Some of the details of the energy modeling like calculating thermal bridging and determining the thermal characteristics of the soil types of the project are likely beyond the many of the users of the software and it is not certain how critical these aspects are to the accuracy of the final results.

   I don't want to sound like a critic here. I think the PHPP is an important tool and that all new construction should be energy modeled and leverage the heating contributions of the sun in heating climates. I hope that PassivHaus raises the bar of design and construction in the US but I think this requires partnering with existing US technical institutions to adopt the practice to our localities and offer the scientific expertise needed to ensure users of the software fully understand the mathematical formulas behind what they are designing.

2. 
   homedesign | Oct 07, 2010 06:22am | #2

   J
   Dr. Feist discusses the reasoning behind the .6 ACH in this video (Part 2)
   http://www.aecb.net/feist_videos.php

3. GBA Editor
   Martin Holladay | Oct 07, 2010 07:41am | #3

   Thanks, John. The relevant section is in Part 2 of the video. Here are the most interesting parts of the interview:

   Q. “We have heard that originally the concept of a Passivhaus was based around the heat loss being reduced so that the heat could be supplied through the ventilation system. Is that still a viable form of heating or do you see a move away from that method?”

   Feist: “… Nobody is forced to use a specific type of heating system. … But the basic definition of a Passivhaus is that it has an energy balance which is [so] good that it is possible to supply all services just with the supply [ventilation] air, [including] the heating and cooling. This is the basic definition.”

   Q. “The Passivhaus standard has a maximum air leakage of .6 air changes at 50 pascals. … In a warmer climate such as the UK, slightly warmer than Germany, would it be possible to raise this?”

   Fesit: “No. Not at all. The airtightness is one of the things that we really have to stick on in almost all climates. There are only a few climates where this might not be a [requirement], but very few -- like in San Francisco. In San Francisco you might not need to have it airtight, but in almost all other climates you need that. A major part of the airtightness requirement is to avoid structural damage. You have bad indoor air with humidity, and if there is an exfiltration through the construction you get really big problems of condensation in the structure. This is the major reason to make it completely airtight, and even in subtropical climates and of course in tropical climates, it has to be airtight because you get structural damage without airtightness.”

4. 
   homedesign | Oct 07, 2010 11:00am | #4

   J
   Concerning the language challenge....
   have you tried using a tranzilator?
   http://translate.google.com/translate?prev=hp&hl=en&js=y&u=http%3A%2F%2Fwww.passivhaustagung.de%2FPassivhaus_D%2FPassivhaus_Verzeichnis.html&sl=de&tl=en&history_state0=
   There is much more information in the Tranzilated German Site than the English Site
   The Grammer much more fun is.... in the Tranzilated version too ;-)

5. GBA Editor
   Martin Holladay | Oct 07, 2010 11:06am | #5

   John,
   Yes, it's fun. We learn, for example, that "The passive houses developed for high-efficiency air handling units have when used in the modernization of existing buildings also proved."

   Evidently the translator has not yet learned the trick that, when translating from German to English, it's a good idea to move the verb from the end of the sentence and place it closer to the subject of the sentence.

6. 
   J Chesnut | Oct 07, 2010 05:22pm | #6

   Thanks John and Martin for pointing out these references.

   I had assumed the rigorous airtightness limit was primarily a heating/cooling savings measure.
   Now I wonder about the differences between wall assemblies typical in our regions versus those typical in Germany. I understand they use more masonry but also have developed composite wall systems like Agepan (?spelling) with MDF structural panels glued to natural fiber board insulation.

   Its hard enough for me to obtain and wade through US technical standards. I hope that some entity can make the referenced standards behind the PassivHaus formulas and determinations more accessible.

   Dr. Feist is also a featured speaker at the upcoming PassivHaus conference in Portland.