How important are embodied energy and embodied carbon?

This two-part article appeared in Green Building Magazine in Spring and Summer 2012.

I looked at the relative importance of embodied and operational energy and carbon – very much a subject of ongoing debate. I found that operational emissions were still relatively ‘bigger’ and should remain a priority – though embodied emissions should certainly not be ignored, and indeed may be more significant than sometimes appreciated, if their timing is taken into account. This is because they tend to happen ‘up front’, leading to more cumulative emissions in our current era.

However, I found reassuring advice from a number of sources that in general there should be no need to compromise operational performance when designing buildings, even if you are set on minimising the embodied impact too – in other words, fabric efficiency needs not have a high embodied cost. Indeed, as Mark Siddall (of LEAP) pointed out, low embodied impact and low operational impact can go hand in hand when it comes to the basics: compact, uncomplicated, modestly-sized buildings.

(There may be an exception when it comes to attemtping to “cut” operational emissions by adding renewables, which may have a significant embodied impact, despite the lifetime “savings”.)

Although rules of thumb can never substiute for ‘doing the numbers’, deriving figures for the embodied impact is not straightforward, with competing calculation methods and more and less transparently-derived data on offer, and little consensus. Progress is being made though, including some work that has been done since these articles first appeared; I gave a few examples of projects that were just getting under way a year ago, which may well be worth following up now.

In the second part of the article I also considered another sort of “offsetting” – the idea that the carbon sequestered in biological building materials such as timber and hemp might be subtracted from, or claimed as credits against, the operational emissions of a building.

I was not  (and continue not to be) keen on this idea, resting as it does on the presumption that ‘replacement’ plants will be grown elsewhere (ie probably not on the roof of the building!) – and to be punctilious, it also assumes that those plants would not have grown, had the materials not been used. This is the same line of argument that has led me to challenge the presumed carbon neutrality of biomass burning – see other posts on this site.

However, there is no need to cite the sequestered carbon to justify the use of many ‘natural’ materials (notably timber), as they can have a remarkably low embodied impact compared to their manufactured alternatives – though as suggested above, glib assumptions are never a substitute for checking the figures wherever you can.

The article is in two pdfs, to view or download here.

Embodied energy – a ticking time bomb? Part 1

Embodied energy – a ticking time bomb? Part 2


Can Passivhaus teach the policymakers to love the occupant?

Ventilation was much in my mind as I dipped in and out of conversations and seminars at Ecobuild this week. And I began to notice a disturbing tendency for airtightness measures and ventilation to be discussed quite separately, with the costs and benefits of each addressed almost as though the two were unrelated.

Again and again, ventilation appeared to be an afterthought, or a problem, instead of an integral part of the assessment of building performance. Several people also lamented that  “well, you can get draft proofing done on a Green Deal, but ventilation doesn’t meet the golden rule, so who will pay for it? – it can’t be funded”. And alarmingly, this dangerous split seems to be reflected in the very structure of the Green Deal.[1]

This strikes me as rather like saying “you can get this operation that you need, but there is no money to sew you up afterwards”.

Ventilation seemed almost to be resented, an ‘obstacle’ in the way of deeper carbon cuts, limiting what could be achieved. All that fresh air spoils the building performance, it seems.

This put me in mind of a similar flavour you find in discussions about ‘comfort taking’. Once again, the pesky needs of the occupants are getting in the way of the true goal of carbon cutting. Thus in its Green Deal Impact Assessment  DECC complained that “comfort taking” leads to “underachievement in real-world energy savings”.[2] Is it really an “underachievement” to make someone’s house more comfortable?

In both these instances, there is a not-so-hidden subtext that the base animal needs of building occupants are a real hindrance to the low-energy, zero carbon perfection we are seeking. And in a way, you can see how if your job is to achieve these goals, a building with no occupiers would solve a lot of your problems.

So it might be unexpected in a way, that it takes Passivhaus, possibly the most shamelessly geeky and science-based standard of them all, to be the one that not only embraces the occupant, but actually starts from the occupant perspective. My understanding of Passivhaus design is it is built from the premise that occupants want comfortable, healthy buildings that are cheap to run. And yet, somehow, it looks as though Passivhaus manages to deliver the lowest energy and (I think you could easily argue) lowest emissions buildings of the lot of them.

Which is why (or at least one of the reasons why), as I remarked on Twitter this morning, I found that Passivhaus crept into my mind quite often, when I was pondering my uneasiness with what was being said outside the Passivhaus sessions. I think the Passivhaus lot are on to something.

[1]  I was told that for post 1919 buildings there is not anything in the Green Deal that requires the advisors to assess ventilation, even when they recommend draftproofing. There are especially serious concerns about the mass-scale installation of solid wall insulation, where the installer alone is responsible for the ventilation strategy, with no back-stop liability resting with a Green Deal provider. This is an issue that needs more than a blog to tackle – hopefully I will get the chance to come back to this soon.

[2] DECC June 2012 Green Deal Impact Assessment

Institute for European Environmental Policy report challenges “misleading” biomass GHG accounting

The Institute for European Environmental Policy (IEEP) has reviewed current thinking about the life cycle analysis conventions for bioenergy (and woody biomass in particular) and found that the routinely used metrics are “increasingly recognised as flawed”.  “This applies particularly to commonly used approaches to life cycle analysis that presume carbon neutrality of the bioenergy feedstock,” the Institute says.

Without a better system for evaluating the greenhouse gas impacts of our policies, they conclude, we cannot know if (or when) our bioenergy use might actually cut greenhouse gas emissions.

The review, The GHG Emissions Intensity of Bioenergy (56pp pdf) was published in October 2012.

The authors reviewed a wide range of recent papers on the subject of the greenhouse gas balance of biomass burning, and found that far from being generally accepted that bioenergy is ‘carbon neutral’ there was now “a general appreciation that increasing the intensity of forestry management and increasing biomass extraction rates over time will lead to a carbon deficit.”

“This then needs to be ‘repaid’ before the exploitation of bioenergy from such resources can deliver emission savings compared to burning fossil fuels,” they say. For example, a paper published in 2011 by McKechnie and colleagues calculated that even over 100 years, and even eschewing whole trees and only burning residues, biomass energy only delivered 73 per cent of the savings anticipated in conventional assumptions (as used by the EU and UK government).

According to this and many other analyses, if whole trees are burned, if a different (lower carbon) energy source is displaced, or if the focus is on a shorter timescale, these presumed savings are eroded still further, and may indeed be eliminated, IEEP warn. (The McKechnie paper was cited by the UK Committee on Climate Change in its 2011 Bioenergy Review.)

IEEP warn that to begin with, when biomass is burned “there is an excess of GHG emissions from the burning of a source of bioenergy over that from the fossil fuel reference energy source.” They also point out that the eventual savings are usually predicated on the source of the biomass being left to return to its pre-harvest state, whereas “in reality, successive episodes of bioenery exploitation may well occur, and keep creating a GHG emission debt.” In other words, we’re not talking about a discrete bioenergy harvesting event, but a new mode of intensified extraction, to feed a new industry.

The report also echoes the concern highlighted in the report for DECC by Forest Research and North Energy Associates (Carbon impacts of using bioenergy in energy and other sectors: forests) that burning biomass might not be the best way to use it to reduce carbon emissions, if that same biomass is being diverted from manufacturing, which then turns to higher-carbon substitutes such as steel, concrete or plastic.

IEEP conclude that we urgently need new ways to evaluate the best way to use land and biomass products to reduce carbon emissions – that have a stonger basis in the evidence. “Utilisation for energy represents only one potential use of diverse biomass materials within society … in a variety of situations other uses will be prefereable purely in terms of climate impact … irrespective of other considerations.”

“Policies based on misleading LCAs need to be revisited and revised as appropriate,” and “the evidence base for making informed decisions about bioenergy in relation to climate change needs to be strengthened considerably as a matter of urgency.”

They end: “It is not currently possible to define the emissions profile and savings associated with Europe’s expanding use of biomass for energy, nor is there any policy process currently in place to secure this. As a consequence, at present there is only the certainty of commitment to bioenergy use up to 2020, but no associated guarantee of emission reduction.”