in pursuit of energy efficient minimalism
Salem ain’t no Bonn
The latest post on the PHIUS blog is a somewhat decent overview of the monitored results for the 16th & Nebraska Passivhaus in Salem. I say decent because there are some aspects of the post with validity, and others that I struggle with. The biggest issue for me revolves around the comparisons of climate (sans discussion on insolation). We’ve spent a fair amount of time taking projects and moving them around in PHPP, curious as to how things actually perform in ‘comparable’ climates. It’s an oft-quoted statement that Europe is milder than the US, and therefore easier to achieve Passivhaus. But in our experiments w/ PHPP – it’s rare when that is the case.
The map shown on the PHIUS blog is a Koeppen Climate Classification map – which is decent but not without valid criticisms (especially for here in the NW). A big standout for me is that Philadelphia, Savannah, Tampa and Mobile are all in the same classification. Now I’ve spent time in Philly during winter, and even a few winters in Tampa… These aren’t in the least bit ‘comparable’ – otherwise we’d have no need for snowbirds. But I digress…
Katrin claims that a climate directly comparable to Salem is Bonn (DE). Which is all fine and dandy, except that when you look closer at the Koeppen-Geiger map, the EU equivalent of Salem’s climate (csb – which also includes San Francisco, oddly enough) is… Porto! Per the Koeppen-Geiger map above (click it!), Bonn’s US comparison is actually a sliver around the Appalachian mountains (oddly enough, possibly Blacksburg). Also interesting to note, most of eastern and northern Europe match the climate classifications of eastern and northern North America (which is also not by accident). The Trewartha maps attempt to correct some of the problems w/ the Koeppen-Geiger map, and so most of Europe and the more populated regions of North America fall under the same classifications (Do, Dca, Dcb, E). I believe this is a better comparison between continents… But it’s still not reflecting the insolation deficit faced by the EU.
It is also not enough to state that Salem and Bonn are comparable based on a climate map and infer that the project would have similar numbers in both locales, it needs to be validated. This is a task accomplished by ‘migrating’ the 16th & Nebraska PHPP to Koeln, which at 20 miles/36 klicks is the closes PHPP data set to Bonn. When I’ve taken projects we or others have modeled, the Koeln/Bonn numbers are coming back significantly higher. If the project is modeling just under 4.75kBTU/ft²a in Salem or Portland, the Koeln/Bonn Specific Space Heat Demand has been anywhere from 1.5-4x higher. That’s far from an insignificant difference for such a ‘comparable’ climate. I attempted to broach this topic after the PHNW conference last year, and again with a follow up post. Basically, we were trying to show that even though the EU is ‘milder’ – due to increased insolation in the US (and in some places, increased avg. ground temps) the ‘colder’ US climates get quite a boost.
While Katrin’s statement, “generally, the climates of North America and Central Europe are not directly comparable,” is factually accurate, I believe it to be misleading in content. “Generally, the climate of North America and Western Australia are not directly comparable,” would also be correct – but similarly, fails to see the larger picture. It would be valid to say that nearly 90% of the North American population lives in a climate that is as ‘similar’ to Europe (north, south, east, west & Russia) or milder. Furthermore, a significant majority of the US population lives in climates that are easier to achieve Passivhaus than here in Seattle! That’s not to say there aren’t outliers – places like Fairbanks or Yellowknife are ridiculously difficult on the PH front – but these are also some of the least inhabited regions of the country. If the Poles and Danes aren’t tweaking the definition of Passivhaus to make it easier – why are we?
Additionally, with the USDA releasing new plant hardiness maps – it’ll be interesting to see if there is a corresponding shift in the climate maps, as the Koeppen-Geiger maps are directly informed via vegetation distribution. And no, I’m not a cartophile (meh, on second thought, I probably am…)
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Wow, I think with the new USDA Plant hardiness map, with part of Virginia and Maryland in zone 8, I should be able to leave my banana trees outside!
Comment by Roger Lin — February 16, 2012