Calculating the Embodied Energy Payback for Passivhaus Buildings
The payback period for the embodied energy of the incremental construction materials needed to meet the Passivhaus standard is surprisingly short
A common Passivhaus topic that rears its head every now and again is the embodied energy of construction. While this can be an important issue, we generally feel it’s a moot point for Passivhaus projects – especially the ones we design (owing to better optimized assemblies and less insulation!).
This was what prompted a previous blog post (“Operational Energy Trumps Embodied Energy Unless Efficiency is Achieved”). However, as this topic has come up again and again, and since the Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. Institute U.S. (PHIUS) has strangely floated the idea that embodied energy calculations could be required for certification, we figured a few research papers could add more credibility to the topic.
The Passivhaus approach differs from the LEED approach
First, our take is that the embodied energy issue is mostly a holdover from programs like LEED – where operational energy has largely been ignored in favor of “greener/lower-embodied energy” materials. Up to 2003, some of the least utilized credits were for energy efficiency greater than 30% or for the inclusion of renewables; I’d imagine that’s still probably pretty accurate (but can’t verify, as this info isn’t readily available).
We’ve never shied away from the fact that we believe that the inverse should take priority. To really make an impact in cumulative embodied energy (construction + operational), focus on the operational side first. Then, once you’ve gotten that significantly reduced (e.g., by meeting the Passivhaus standard), set your sights on the construction embodied energy.
Feist: Incremental embodied energy has a one-year payback period
Second, this issue has already been addressed by the Passivhaus Institut in Germany and presented at multiple PH conferences. Wolfgang Feist’s research showed that the “primary energy investment” of a Passivhaus compared to typical construction was not necessarily greater, and could even be lower — and that on average, the incremental embodied energy is paid back in under a year. This is due to the significant operational energy savings achieved by meeting the Passivhaus standard.
Given that U.S. energy codes aren’t as strict as those in central Europe, that could mean the embodied energy might be higher here… Could – although we’re finding that even on a small project, when optimized like crazy, the delta betwixt code minimum and Passivhaus can be relatively small.
The Passivhaus Institut report also notes that the cumulative primary energy of an “Autarkic” building (that is, a self-sufficient off-grid building) is higher than that of a Passivhaus building. This is owing to the increased embodied energy of the renewable energy system (the photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. array, batteries, etc.) over 80 years, resulting in a higher total energy than a Passivhaus building. Another win for Living Building Challenge projects meeting Passivhaus!
An Oregon study says that the payback period is seven years
Third, a recent University of Oregon study completed for a multifamily project compared Passivhaus construction to typical construction, and ended up with fairly comparable results to other Passivhaus life cycle analyses. The Daily Journal of Commerce reported, “According to the life-cycle analysis, the energy savings born out of the Passive House building will outweigh the materials’ added climate change potential in about seven years.”
So even in the U.S., where our energy codes are less strict, the environmental payback should be relatively short.
Some Passivhaus buildings have lower embodied energy than conventional buildings
Finally, as alluded to above, it’s entirely plausible to construct a Passivhaus with lower embodied energy than a “code minimum” house — especially if your Passivhaus utilizes natural materials (e.g. straw, cellulose, wood, etc). But even if you don’t use all-natural materials — maybe you’re a modernist with a hankering for concrete and glass — it’s really not the end of the world as long as your house is über-efficient.
The bigger takeaway: When comparing similar construction types, Passivhaus clearly comes out on top in the long run because of lower operational costs, lower environmental footprint, and lower cumulative primary energy… If you toss in superior comfort and great indoor air quality, it’s a no-brainer. So we consider the issue pretty much settled, and furthermore believe that requiring a life-cycle analysis to obtain certification would be a waste of time and money.
So, on to the literature… Here is a brief assortment of papers on the subject of Passivhaus embodied energy, though there are plenty more for those who really want to get wonkish:
- Life Cycle Assessment of Passive Buildings with LEGEP – A LCA-Tool from Germany (pdf): “The application to passive buildings shows clearly the advantages of these types of buildings over conventional buildings both in the short and long run.”
- Life Cycle Assessment of a Single-Family Residence built to Passive House Standard (pdf): “This means that when constructing a passive house and assuming both houses are using the same electrical heating system, it takes only 5 years before the increased material production and transport for the passive house are equalized to the TEK07 house [that is, a house meeting current building codes and standards, presumably in Norway] climate change impacts.”
- The life cycle race – silver and bronze – go to … Passive house and low energy house by Andreas Hermelink (pdf): “…The passive house is the clear winner in this comparison either from environmental perspective or from economical perspective.”
The interesting result from the last paper (and the point referenced in the title) is that while Passivhaus leads to better environmental and economic results – the grid is still too dirty, and thus a combination of renewables (or greening of the grid) + Passivhaus would get the “gold.”
Mike Eliason is a designer at Brute Force Collaborative in Seattle, Washington.
- Gruppe Angepasste Technologie
- Passivhaus Institut
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