Insight PassivHaus Becomes Active—Further Commentary on PassivHaus

Here is an interesting Comment by John Straube, which was responded to by the Passiv Haus people here.. His comments give good US insights into a German standard. His points are that Passiv Haus standards are not brand new and that US and Canada have had them for a while. Not that many have implemented them in the least, but some have.

We like Passiv Haus standards in relation to Brooklyn green building. But we are not bound by them. We want to build a good green brownstone above all else. Getting certified or a nice plaque on the wall is not important to us.

So we use benchmarks like Passiv haus, LEED, Living Building Challenge etc to guide us in the millions of decisions needed to make a green Brownstone in Brooklyn.

Below is Johns comment about Passiv Haus. He also points out the importance of local building.
By John Straube

Building Science Insight 026: last updated 2009/10/05

I have recently written about some aspects of the German Passiv  Haus1housing  standard (see BSI-025:  The Passive House  Standardand the as it applies to cold climates (that is DOE Climate Zones 5 and higher) housing. The response to these ideas has been startling in its intensity and anger. I have received literally hundreds of emails and online forum postings. There are some who have tried hard to explain the intentions and science behind what is a very good low-energy house standard, and a remarkable number that have expressed outrage that someone like myself has the temerity to question the “Gospel according to Wolfgang.”2

How can we, or anyone really, argue with houses that consume less energy by
building with high levels of insulation, good airtightness, reduced thermal
bridges, good windows, all while ensuring comfort, healthy air quality and
cost-effectiveness? Of course we are not. This author personally, and
Building Science Corporation through the US Department of Energy’s Building
America program ,  have been fervent advocates of this approach to housing for more than 15
years. The Building America program and others have sponsored millions of
dollars of research that has resulted in literally hundreds of peer-reviewed
scientific presentations and reports as well as tens of thousands of homes
built exploring and developing exactly these attributes, and how far to
exploit them, throughout all the climates zones of America.

The use of energy conservation in the building enclosure, and trading off
these increased costs with lower heating and cooling systems cost is
integral to our work. In fact, the “systems engineering approach” or “house
as a system” has been promoted for 25 years in North America and pioneered
in Canada by a BSC principal, Dr Joe Lstiburek. No less than Dr Amory
Lovins has championed this approach to building low-energy buildings.

Research and field experience over the last two decades in all climate zones
of the US have shown how to insulate and airtighten buildings. Research
projects have built houses that demonstrate walls of R60, roofs of R100,
airtightness levels of 0.3 ACH@50Pa, and triple-glazed windows. Although
window performance has improved dramatically over time, the cost of high
performance windows needs to improve further and this is one area where
innovation is likely to drive costs down and performance up.

Much research work North America was begun 30 years ago, largely inspired by
two or three projects. The influential Lo-Cal House, a 1976 design, and the
1977 Saskatchewan House, used very high-levels of insulation, airtight
enclosures, triple-glazed windows, and air-to-air heat exchangers: the
latter house even dispensed with a conventional furnace in a climate with 10
000 HDD (65°F). Experience with the many house designs inspired by these
prototypes has taught us much about what does work, and what does not. The
research in the last decades has been directed at delivering these types of
houses economically while avoiding performance and durability problems that
were identified.

All of the above is to point out that the German PassivHaus approach is in
most of its general technical aspects neither unique nor innovative. Its
primary distinction (and this important is that it prescribes a very low
total primary energy consumption limit, 120 kWh/m2/yr (38 kBtu/ft2/yr), a
separate site energy consumption limit of 15 kWh/m2/yr (4.7 kBtu/ft2/yr) for
space heating/cooling, and an airtightness target of 0.6 ACH@50 Pa. Despite
claims that the PH standard is climate sensitive, these three absolute
requirements are exactly the same in Miami as Minneapolis, Berlin, or
Barcelona. There are potential arguments for and against setting
climate-independent energy targets. I have just not seen them articulated.

Although not strictly required by the three performance targets, PH has been
innovative in recommending the use of the ventilation air delivery system as
the heating/cooling system and using heat recovery ventilation with more
than 80% efficiency (this could now be a requirement in the
These recommendations have varying impacts on a home design, but the reasons
why a design should not be acceptable without meeting these recommendations
are not clear.

My apparently dangerous and provocative questions of the PH standard arise
from the reasoning behind the choice of these targets and “requirements.”
The choice of 120 kWh/m2/yr is essentially arbitrary, but that is fine: most
other programs are also arbitrary in their aims such as 50% less than
current housing (, or a 40% reduction over some code
benchmark, or zero net energy consumption over a year (the Building America
program goal). There are many homes that have achieved the 120 kWh/m2/yr
target by generating renewable energy on site, but this is not allowed in
the Passiv Haus. Why not?

Relying on the purchase of large swaths of subsidized photovoltaic’s or
complex and expensive heating/cooling systems to reduce the energy signature
of a building before using more economical strategies such as efficient
appliances, good insulation, windows, and airtightness is widely accepted as
a waste of resources (materials and money). Relying on excessive levels of
insulation, airtightness, and window performance rather than considering the
use of environmentally sound and more economical supplies of energy is also
wasteful of resources and uneconomical (although until recently this has
rarely been a problem).

Deciding on the optimum mix of conservation and generation is difficult
because there are a range of costs and technologies available that depend on
a building’s location and occupancy. Compounding this challenge, the
technology and cost of conservation and generation have changed over time
and are expected to change in the future.

Renewable energy sources, such as photovoltaic (PV), wind, hydro, biomass,
concentrating solar (CSP) and tidal are developing rapidly, and recent
history suggests that the cost of these technologies will reduce the cost of
renewable energy over time. Many expect the cost of PV and CSP to drop by
half in the next 5 to 10 years as economies of scale are achieved. Wind
power is already affordable. The Smart Grid being developed will allow
widely dispersed, and millions of small power producers (such as homes) to
distribute energy through the grid. The future for the vastly enhanced scale
and lower cost of renewable energy look bright.

In contrast to PH, the Building America research program does not prescribe
how a design in a specific climate should be assembled, only the primary
energy target that must be reached. This focuses the design on reducing
non-renewable energy depletion and minimizing environmental damage. It does
require an economic analysis to demonstrate that efficiency measures have
been fully exploited before renewable energy supply is added (e.g. all
efficiency measures that are less expensive than the cost of generating
renewable energy). Like PH, the goal is to provide cost-effective
low-energy housing.

However, the requirement to limit the heating energy demand to only 15 kWh/m
2/yr is perplexing: depleting energy resources and environmental damage are
already limited by the 120 number, why constrain the design further with no
reduction in energy? And what is special about 0.6 ACH@50Pa? If a builder
can deliver a house that uses less than 120 kWh/m2/yr, with 1.5 ACH@50, why
does this matter? Wolfgang himself offers some clues, as he states in an
interview in the UK (at that the
exceptionally low number is intended is to avoid interstitial condensation
that can damage the structure. Far too many superinsulated homes of the past
suffered this fate. Of course, we now have the practical and technical
knowledge to completely avoid interstitial condensation in a house with 2
ACH@50 Pa and also know that dangerous rot could still occur at 0.6
ACH@50if a double stud wall design is used. Again, there appears to
be other
lower-cost paths to reaching a low energy house target that are blocked by
these prescriptive restrictions.

If cost is important to PH, why constrain designers? It should not come as a
surprise that the relative cost of different strategies will be different in
Minneapolis Minnesota than in Darmstadt, Germany (where the PassivHaus
standard was developed) than in Bangor Maine or Boston Massachusetts. The
rules of thumb that guide the “low cost” recommendations of the PH standard
are often not low-cost in America.

When we have investigated the use of PassivHaus standards for some of our
cold climate projects, we have found that the cost of some of the mandated
conservation measures exceeded the cost of energy supplied by the lowest
cost renewable energy source. In other cases, mandating the use of specific
PassivHaus Institut approved products (imported from Germany) dramatically
increases the cost while reducing the energy consumption by a trivial
amount. The cost of local off-the-shelf equipment is often lower with
essentially the same performance.

BSC is not the only research group to find that the PH standard may not
always result in an optimal design. Two other Building America research
groups, IBACOS and the Florida Solar Energy Center have concluded the same.
Danny Parker’s paper4found
that “the Passivhaus concept risks overinvestment in conservation if a
point is reached in the optimization process where adding solar electricity
is a lower cost option than adding the next unit of insulation or air
tightness.” He also points out, as we have, that many other net-zero energy
homes have over-invested in PV or ground-source heat pump technology. John
Broniak of IBACOS presented the results of detailed energy analysis of
typical American house design to Passiv Haus standards in six different US
conclusion was that following the PH Standard in the cold and
climate zone was “very challenging.” Not surprisingly, these are the two
climate zones that are the most different than the German climate where PH

Another challenge is the PH program’s use of German standards. While this is
sensible in Germany, it causes confusion in North America. The floor area is
measured according to a German standard, which was developed for different
types of homes6than
in America. The air leakage test referenced is EN 13829, rather than
the very widely used ASTM test, the HRV efficiency is measured by the
PassivHaus Institut in Germany rather than the HVI CAN/CSA C439, the window
U-value is measured by ISO 12567, not the widely-used NFRC 500, ventilation
is not by ASHRAE 62, and thermal comfort seems to differ from ASHRAE 55.
Some of these standards are different in significant ways. For example, the
German window U-value are based on an exterior temperature of 0°C, whereas
the NFRC is based on an exterior temperature of -18°C (0°F ). Likewise, the
HRV ratings in Germany are not at -13°F (-25 °C). The use of German or Euro
standards result in small but sometimes significant impacts. Why would one
not accept products based on North America standards if they are shown to be
equal or better? There appears to be an assumption that all German
standards are superior to North American ones, whereas in many cases the
North American standards are just as strenuous or more so and more relevant
to local conditions.
As I have repeated numerous times in numerous venues, the Passiv Haus
standard has many excellent features. However, there are constraints to
designers that raise the cost and complexity of delivering a house that do
not result in lower energy consumption. The target of primary energy
consumption before renewable energy use is rather strict, and appears to
over emphasize conservation over energy generation in cold climates. Just
as much a concern is that there appears to be a belief that the PH standard
has some magic recipe or innovative approach that will make affordable
low-energy houses. A discussion of the science and philosophy behind the PH
standard can only help improve the standard and inform others, while an
unquestioning belief that “it must be better” is helpful to no one. Lets
hope the discussion can begin, and the dogma ends.

About the author: Gennaro Brooks-Church

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