By Dr Samantha Mudie, Head of Technical Development
In my various roles as an academic, an energy-carbon reduction consultant and even as a parent I find I am always arguing the case for change towards the sustainable. What I am frequently met with, in business and at home, is a position of paralysis when it comes to cutting carbon. When we are scared, we can freeze. When the problem becomes insurmountable, if there is no hope, (as is sometimes the view of my friends and clients when discussing dangerous climate change) then there is no reason to take action.
In this vein, one aspect of sustainability that I have discussed frequently in the past year or two is the ‘unintended consequences’ of carbon reduction. Take the classic example of tree planting, long touted by government and industry as the carbon sequestration tool required to remove carbon from the atmosphere. Sadly, many have not accounted for the full environmental consequences which may, in fact, outweigh the benefits of afforestation. On top of the fact that trees often have larger water demands than crops and pastures, causing reductions of 38% in water supply (13% streams drying up completely, both at site and downstream), higher nutrient demands often increase soil salinization and acidification. Popular species of pines and eucalyptus rapidly pull CO2 out of the atmosphere, but support a paltry biodiversity. Arguably the biggest issue with tree-planting as our saviour is that once the trees die they rot; when they catch fire, they burn, releasing the carbon back into the atmosphere; we are simply buying a few decades to transform our economies, not solving the problem.
Another brutally alarming unintended consequence I have come across in the search for carbon reduction solutions in the built environment involves heat pumps. The installation of heat pumps to replace natural gas boilers in the past often increased carbon in the first instance (see below table from the last decade grid make-up). Thankfully with grid-decarbonisation and improvements in heat pump coefficient of performance (COPs) the situation is improving and will continue to improve.
A ground source heat pump (GSHP) also used for cooling or water heating sees much more significant savings, but often the remainder of water heating load is met with an immersion coil or similar, adding further carbon into the mix.
The second issue is that of refrigerant leakage. A review of heat pumps undertaken by DECC in 2014 found 9% of non-domestic heat pumps leak each year at a rate of 2-8% of refrigerant per year on average. This tips the global warming potential of such systems significantly towards the unfavourable. Taking a typical non-domestic GSHP with a typical refrigerant (R134a), a mean refrigerant charge of 24.53 kg and a median leakage of 4%, this gives an outrageous 1,403 kg CO2 per year. The table below shows this can easily be double the global warming potential of the gas boiler scenario above.
I could continue. Probably the most hideous of all is the dreadful fact that from 1990 to 2005 Britain’s CO2 emissions went down by 15% while sadly at the same time the CO2 emitted in producing all the products consumed in Britain increased by 19%. There are hundreds of situations where slight tweaks can make all the difference between a successful carbon abatement strategy and a disaster of unintended consequences (glass jars vs single use plastics, disposable vs cloth nappies, working from home vs workplace energy savings).
BUT….
The take home is that planting trees is not a bad thing, but schemes that are not well thought through can be environmentally harmful. Success depends on management and careful research in the initial phase, site history, native species, soil texture and the availability and quality of ground water. In terms of heat pumps, the levels of emissions from leakage are relatively small compared to the total emissions reductions which might be delivered by heat pump technologies through the displacement of fossil fuelled heating alternatives in the grand scheme over the coming decades. Careful maintenance and analysis of logbooks and incentivising low GWP refrigerants will help to realise the overall benefits still further.
Turning inaction through hopelessness, and the fear of unintended consequences on its head; with holistic life cycle analysis and full operational impact assessment we can be as sure as we can be that we are doing the right thing.
In one energy reduction study concerning a large pub and restaurant operator, I modelled the energy consumption of commercial catering appliances in 7 energy reduction scenarios. The sophisticated and award-winning model took account of all energy using appliances in the food preparation operation from ventilation, food storage, cooking equipment, hot holding appliances, right down to the cutlery polishers. The food items cooked were run, at ingredient level, on a minute-by-minute basis (from till receipt data) to produce the full energy use profile (validated against monitored data). The most lucrative scenario studied the replacement of fryers, chargrills and standard microwave combi ovens with combi steam ovens, as well as moving the majority of frozen food storage to chilled storage. The use-phase energy consumption was reduced by 58.08% per year. Overall, the operation emissions per meal were reduced from 2.12 kg CO2 per meal to 1.16 kg CO2 per meal and the holistic view showed 64.45%, 40.58% and 55.27% from the cooking, food storage and extraction and ventilation use phases respectively. Savings for the whole restaurant chain of 37.77 million kWh, 10.71 million kg CO2 and £2 million per year were achievable from these relatively straight forward swaps. Incidentally, scaled across the other restaurants the operator managed, savings increased to £18.3 million, and across the whole UK pub-restaurant sector, £1.27 billion per year savings are up for grabs.
But the real success was in ensuring the absolute minimisation of unintended consequences. A full stakeholder consultation was performed throughout every stage of the study and as a result quantifiable outputs included; staff training requirements, user behaviour, cooking times, appliance utilisation, maximum food throughput vs appliance capacity, space requirement and uniformity and consistency of product were all managed to exceed expectations. While cook times increased slightly in the most favourable scenario, these were measured, assessed and viewed as a worthwhile sacrifice in light of the many benefits to the operation in addition to the massive energy and carbon savings.
At Carbonxgen we pride ourselves on performing a thorough operational impact assessment to ensure we have considered any positive or negative attributes outside of energy use impacts on the overall running of your operation. We strive to help operators realise any positive benefits are highlighted and any negative outcomes are managed within acceptable limits so that, in our aim of creating a more sustainable environment, there are no surprising unintentional consequences.
References:
1 – Moulton & Kelly (2009), The physical risks of reforestation as a strategy to offset global climate change. Critical Reviews in Environmental Science and Technology (https://www.tandfonline.com/doi/abs/10.1080/10643389709388523?journalCode=best20)
2 – Department of Energy and Climate Change (DECC) (2014). Impacts of Leakage from Refrigerants in Heat Pumps (https://www.ammonia21.com/files/decc-refrigerants-heat-pumps.pdf)
3 – Dieter Helm (2015) The Carbon Crunch. Yale University Press; Second edition. ISBN-10 : 0300215320
