Who Counts Engineers | Stuart McPherson
- 1. Who Counts?Carbon Accounting in Option AppraisalsStuart MacPhersonSenior Partner, Irons Foulner Consulting EngineersandChairman, CIBSE Scotland
- 2. The ProblemOption appraisals for developments now usually must include consideration of the environmental impact.There are assessment methods for this, the two major systems being:The Building Research Establishment Environmental Assessment Method (BREEAM) – developed in the UKLeadership in Energy and Environmental Design (LEED) – developed in the US
- 3. Limitations of these and other similar methodologiesThese methodologies allocate points on a scoring system to developments in a variety of criteria.They are useful in general terms in that they encourage better environmental design, but they do not specifically address development life cycle carbon dioxide emissions.Assessments like these leave me in doubt as to whether I (and my clients) are doing the right thing in carbon dioxide emissions terms.
- 4. What do I need?I, and my clients, need to know which option in a range of options has the lowest life cycle carbon dioxide emissions.That is, we need to be able to assess the carbon dioxide emissions associated with:the initial construction projectthe energy consumption of the development over its lifethe ongoing maintenance and replacement cycle of the development over its lifethe ultimate decomissioning and removal of the development at the end of its life.
- 5. An illustrationA responsible, semi public sector client wants to improve their office facilities.The design team have suggested an appraisal of options ranging from a minimal scheme to replace the building services installations but only carry out basic maintenance to the fabric of the existing building through to relocating to a new building on a green field site.There were five notional options sketched to characterise the range. These were reduced to two leading options in a high level initial appraisal.
- 6. OptionsOption ARetain structure and main fabric elements and upgrade the energy performance of the building fabric and services as much as possible.Option BDemolish 70% of the building (the rest is listed) and create a substantially new building with excellent energy performance and possibly a ground source heat pump.
- 7. Option A
- 8. Option B
- 9. What do I need to make a decision?I need to be able to assess the carbon dioxide emissions associated with:the initial construction projectthe energy consumption of the development over its lifethe ongoing maintenance and replacement cycle of the development over its lifethe ultimate decomissioning and removal of the development at the end of its life.
- 10. Who can count with any confidence?The only part of this that I am confident in approaching is the energy consumption of the building.There are debates about the details of even this element of the assessment but the tools exist to make a reasonable approach to that component of the life cycle carbon dioxide emissions assessment.There are tools which purport to enable assessments of other elements but there are many questions over the basis for these and I do not believe that anyone can currently claim an adequate level of confidence in these other parts of the assessment.
- 11. Key questions for those who countIn the context of option appraisals....How accurate do we need to be?How do we treat boundaries?Is there any case for applying a discount (or escalation) factor to future carbon emissions?
- 12. AccuracyAccurate enough....Option appraisals need an adequate and equivalent basis for comparison. It is not so important that data is highly accurate in absolute terms so much that it gives the correct relative answer across the options.Sensitivity analyses of the outcomes can reveal those elements of the appraisal that may require further investigation.
- 13. BoundariesCradle to grave....Who is responsible for what part of the carbon dioxide emissions in a supply chain is not so important for option appraisals. What is important is that all options are assessed on an equivalent basis and that no important emissions element is missed out.
- 14. Discounting or escalation factors?For the climatologists....Is the environmental impact of a kilogramme of carbon dioxide emitted today the same as a kilogramme emitted in 30 years time? If not then which is worse?For the policy makers....Is there any case for ‘investing’ carbon emissions today to save carbon emissions in future years or vice versa?I suspect the issue is neutral, but I think it is worth asking the question.
- 15. In conclusionThe issues for those of us who need to make decisions on developments via option appraisals are different to the issues relating to ‘global’ carbon accounting.The difference is analogous to the difference between macro and micro economics.We need practical guidance on minimising life cycle carbon emissions of developments. Our concern is with comparing options on an equivalent basis with no glaring omissions, not with obtaining absolute figures for emissions.We need this guidance urgently. We are making decisions now that will determine impacts from individual projects for between 20 and 60 years.
- 16. In conclusionThe guidance needs to be practical to use. This may seem difficult given the complexity of the matter, but if a methodology is difficult to use it will not be applied.The guidance needs to be based on data in which we can all have confidence, be transparent and be authoritativeResearch is ongoing currently under the direction of Scottish Building Standards as well as other agencies, and we hope that this will lead to some authoritative practical guidance.