Reducing energy demand and emissions

Professor Savvas Tassou of Brunel University discusses opportunities for reducing energy demand and emissions in the UK food chain.

Introduction

The food chain comprises agricultural production, manufacturing, distribution, retail and consumption (Figure 1).

Figure 1 - Schematic diagram of main stages in the food chain

In the UK it involves approximately 300,000 enterprises, employs 3.9 million people representing 14% of national employment and, including catering, accounts for £201 billion in consumer expenditure. The food chain is also responsible for 18% of total UK energy use, 176 MtCO2e emissions and 15 Mt of food waste. It is predicted that by 2030, the growth in global population and the impacts of climate change will increase food production needs by 50%, energy demand by 45% and water demand by 30%. To ensure food security in the face of these challenges it is important to:

1. reduce the food system’s resource use and GHG emissions,
2. reduce, reuse and reprocess food waste,
3. ensure a resilient, profitable and competitive food system.

In recent years, progress has been made in the reduction of energy consumption and emissions from the food chain in response to government initiatives and legislation, rising fuel prices and the desire of many companies to improve social and environmental performance. This has been achieved primarily through the application of well proven energy conservation technologies and projects that could lead to quick return on investment. However, much more radical solutions will be needed to further reduce energy demand in the food sector and mitigate the related climate change impacts. The National Centre for Sustainable Energy Use in Food Chains (CSEF), led by Brunel University London and partnered by the Universities of Manchester and Birmingham, is making a contribution to this effort by working closely with key stakeholders, industry, government, trade associations and funding bodies to develop innovative approaches and technologies to effect significant energy demand and GHG emissions reduction. Technological approaches are complimented by socioeconomic research designed to influence corporate and consumer behaviours towards sustainable food production and consumption ^[1]. Emissions from the different activities in the food chain are illustrated in Figure 2. A variety of strategies has been used to effect reductions in emissions and energy demand at different stages along the food chain.

Figure 2 - Greenhouse gas emissions from the UK agri-food sector (source DEFRA, 2013)

Energy demand and reduction in agriculture

A significant portion of emissions in the food chain come from agriculture (Figure 2). Most of hese emissions are from enderic fermentation in ruminant livestock and nitrous oxide released from tilled and fertilised soils. The aggregate primary energy consumption for agriculture is approximately 12.0 TWh if forestry and fisheries are included ^[2], corresponding to approximately 0.6% of the total UK consumption and associated with approximately 4.7 MtCO2e (0.8% of total UK GHG emissions).  Energy use in agriculture is primarily for heating (36%), field operations (36%) and ventilation (~14%). Heating is mainly needed for glasshouse production using fossil-fuelled boilers as well as crop drying and storage. Field operations require oil and diesel for machinery, while ventilation is required for temperature and humidity control of glasshouses, crop drying and storage facilities and intensive livestock housing. The remainder is for refrigeration (~6%) for the cooling of dairy products, potatoes and horticultural field crops, lighting (~4%) and motive power (~4%) mainly for pumping.

Substantial energy reduction, up to 20%, can be achieved in the sector through technological improvements, such as decentralised boiler plants and higher efficiency boilers, increased use of natural ventilation and CHP systems, the use of more efficient lighting systems and higher efficiency motors. In recent years, an approach for emissions and energy demand reduction in agriculture has been the use of anaerobic digestion (AD) of animal manure and agricultural and food waste for biogas production for heating or combined heat and power generation. The trend so far has been in the establishment of large AD plants that have benefited from government incentives from export of surplus electricity generated on site to the grid and renewable heat incentives. Expansion in the future is likely to be in small single farm plants and integration of anaerobic with aerobic digestion to maximise resource use and value from the simultaneous production of energy and biofertiliser. The National Centre for Sustainable Energy Use in Food Chains (CSEF) at Brunel is working with a number of stakeholders on the development of a packaged integrated dry anaerobic-aerobic system for small farms suitable for both developed and developing countries. 

Energy demand and reduction in food processing

The UK food and drink manufacturing sector includes primary processing (such as milling, malting or slaughtering) as well as processing complex prepared foods. It is the single largest manufacturing sector in the UK, with a turnover of £81.8 billion and gross value added (GVA) of £21.9 billion, accounting for 16% of the total manufacturing sector by turnover ^[3]. The sector also employs close to 400,000 people and is the fourth-highest industrial energy user in the country with 34 TWh final energy demand. The type of fuel used by the sector has remained fairly constant in recent years: 61% natural gas, 31% electricity, 6% petroleum, with fuel oil and coal accounting for the rest ^[4]. A small number of products is responsible for 80% of the carbon emissions. The most prominent of these are manufacture of bread and fresh pastry goods, cheese and other dairy products, meat and poultry products and beer and alcoholic beverages. This therefore points to the need for improvements in technologies used by these sectors, such as processing equipment, refrigeration, boilers, ovens, pumps, space heating and lighting. Food manufacturing is also responsible for 3.2 Mt of food waste, which is mainly landfilled. This presents opportunities for more efficient resource use through the minimisation of waste, the manufacture of co-products or by-products and the improved use of waste to recover energy through efficient incineration, gasification, pyrolysis or anaerobic digestion technologies. Energy can be saved at the processing plant level by:

1. design, optimisation and validation of new and modified processes including process integration and intensification,
2. better understanding of how processes work and use of advanced sensors and equipment for on-line measurement and intelligent adaptive control of key parameters,
3. reduction of processing requirements to improve quality without compromising safety,
4. minimisation of waste through better use of by-products and energy recovery.

A project currently being undertaken by CSEF in collaboration with a large chilled food manufacturer, an air distribution system manufacturer and co-funded by Innovate UK and Research Councils UK (RCUK) has demonstrated that improved air distribution in chilled food manufacturing facilities can provide energy savings of the order of 10% compared to conventional cooling systems. The innovative air distribution system supplies air at low level and low velocities to increase temperature stratification, floor-to-ceiling, in high ceiling manufacturing spaces. This effectively reduces the volume of air to be cooled to low temperature in the space, resulting in energy savings in excess of 10% and reduced thermal discomfort of the occupants of the space. Figure 3 shows simulation results of temperature stratification that can be achieved with low level and low air velocity distribution in the space.

CO₂ emissions reduction in food transportation

Commercial food transport, excluding food shopping, is responsible for emissions of the order of 12.0 MtCO2e per year ^[4]. Of this, nearly 6.0 MtCO2e is for food freight in the UK, more than 80% of which is performed by Heavy Goods Vehicles (HGV). It is also estimated that approximately a third of food freight is temperature controlled. On board refrigeration can account for substantial, ~ 25%, vehicle fuel consumption. Various approaches can be employed to reduce transport emissions, which include: food chain optimisation and reduction in food transport intensity, modal shift, improved vehicle fuel efficiency, electrification of transport with zero or low carbon electricity and alternative refrigeration technologies.

A small number of products is responsible for 80% of the carbon emissions.

Energy demand and reduction in food retail

In developed economies, food retail accounts for between 3% and 5 % of total electricity consumption. Food retail is also responsible for approximately 11% of CO2 emissions, a sizeable portion of this, up to 20%, being direct emissions from refrigerant leakage. The energy consumption of supermarkets depends on business practices, store format, product mix, shopping activity, the equipment used for in-store food preparation, preservation and display. The electrical energy consumption can vary widely from around 500 kWh/m2 sales area per year in hypermarkets to well over 1200 kWh/m2 sales area per year in convenience stores.

In general, refrigeration systems account for between 30% and 60% of the electricity used (taking into consideration smaller stores), whereas lighting accounts for between 15% and 25% with the HVAC equipment and other utilities, such as bakery, for the remainder. Gas is normally used for space heating and domestic hot water in larger supermarkets. The current trend in convenience stores is to use all electric systems, such as air source heat pumps for space heating and cooling.

The introduction of doors on chilled food cabinets  can lead to energy savings in refrigeration energy consumption of up to 40%.

Significant energy savings can be achieved by improving the efficiency of refrigeration systems, refrigeration and HVAC system integration, heat recovery and amplification using heat pumps, demand side management, system diagnostics and local combined heat and power generation and trigeneration. Energy saving opportunities also exist from the use of low energy lighting systems, improvements in the building fabric, integration of renewable energy sources and thermal energy storage. Another area that provides significant opportunities for energy savings is the design of more efficient refrigerated display fixtures and reduction in the infiltration loads that can account for up to 75% of the cooling load of low front chilled food cabinets. The introduction of doors on chilled food cabinets can lead to energy savings in refrigeration energy consumption of up to 40%.

Energy demand and reduction in food consumption

Catering 
Energy use by catering processes in the UK is estimated at 6.24 TWh ^[2]. A rough breakdown of this energy is presented in Figure 4, which shows that in contract catering approximately 40% of the energy used in kitchens is for cooking, 28% for refrigeration, 17% for air extraction and 5% for dishwashing, with estimated carbon emissions at approximately 1.3 million tonnes CO2 per year.  Opportunities for energy reduction include the use of more efficient refrigeration systems and cooking equipment, improved ventilation and exhaust hood extraction, integration of operation of refrigeration, ventilation and air conditioning systems and behaviour changes with respect to the food consumed and food preparation practices. 

Figure 4 - Energy use and CO₂ emissions by end-use in four catering sites (source: AEA, 2012)

Home 
Food consumption in the home is estimated to be responsible for 18 MtCO2e emissions ^[4]. Major contributors to this include refrigeration, cooking and food shopping.  Even though the diffusion of energy efficient large appliances, such as refrigerators and freezers, is improving, total energy use by appliances is increasing due to an increase in the number of small items of electrically powered household equipment. Savings can be achieved from the use of more efficient appliances and food preparation methods, such as microwave rather than oven cooking, the use of more temperature stable foods and changes in consumer diets and behaviour.

Unavoidable food waste and its utilisation for energy 
It is estimated that the post farmgate is responsible for around 15 Mt of food waste, which accounts for more than 20 MtCO2e emissions. Household waste is responsible for 7.0 Mt of this; manufacturing, retail and wholesale account for 4.3 Mt and the hospitality and foodservice sectors 0.92 Mt. The remainder is attributed to the service and other sectors of the chain, including 2.2 Mt of by-products from the manufacturing sector used for animal feed. Alongside food waste, non-recycled packaging waste accounts for an additional 3.6 Mt of waste amounting to approximately another 6 MtCO2e emissions ^[9].

Part of the food waste (≈ 6 Mt) is avoidable and can be reduced through changes in food labelling and consumer behaviour and a relaxation of quality standards, but also through technological changes, such as improved manufacturing processes and logistics and better temperature control across all sectors of the food chain.  Unavoidable food waste from the food chain can be effectively used as an energy resource at different stages of the food chain through digestion (anaerobic or aerobic) or gasification. Such technologies can also provide additional benefits of producing valuable bio-fertilisers.
 
Conclusions

Energy is an important input in growing, processing, packaging, distributing, storing, preparing and disposing of food. It is estimated that the energy consumption of the food chain is responsible for approximately 18% of total UK primary energy use. The food chain is also responsible for 176 MtCO2e emissions and 15 Mt of food waste.

In agriculture, even though the direct energy consumption is not very high compared to the whole food chain, energy savings of up to 20% can be achieved through renewable energy generation, including energy from waste biomass and the use of more fuel efficient equipment, such as tractors. In food processing, energy can be saved at the processing plant level by optimising and integrating processes and systems to reduce energy intensity. In the food retail sector, significant progress in energy efficiency has been made in recent years but substantial potential still exists through further improvements in the efficiency of refrigeration systems, refrigeration and HVAC system integration, heat recovery and amplification using heat pumps and demand side management.

Energy demand and emissions reduction can be achieved from the use of more efficient equipment and appliances and behavioural changes with respect to type of food consumed and food preparation practices

Energy consumption in catering facilities and the home is primarily from cooking and refrigeration. Energy demand and emissions reduction can be achieved by the use of more efficient equipment and appliances and behavioural changes with respect to type of food consumed and food preparation practices.

Food consumption is affected by many factors including food availability, disposable income, urbanisation, marketing, religion, culture and consumer attitudes. All these factors should be taken into consideration in devising approaches and technologies to effect significant reduction in energy consumption and resource use in food chains.

Professor Savvas A Tassou, Director Institute of Energy Futures, Director RCUK National Centre for Sustainable Energy Use in Food Chains (CSEF), Brunel University, London Web: www.foodenergy.org.uk   Email: savvas.tassou@brunel.ac.uk

References
1. Tassou, S.A., Kolokotroni, M., Gowreesunker, B., Stojceska, V., Azapagic, A., Fryer, P.J., Bakalis, S. (2014). Energy Demand and Reduction Opportunities in the UK Food Chain, ICE Proceedings, Energy, Vol. 164, 162-170.
2. DECC (2013). Digest of United Kingdom Energy Statistics 2013 – DUKES. 248 pgs.
3. FDF (Food and Drink Federation) (2013). http://www.fdf.org.uk/statsataglance.aspx
4. DEFRA (2013). Food Statistics Pocketbook 2013. 71pgs.
5. Campden BRI (2011) Scientific and Technical Needs of the Food and Drink Industry. Campden BRI, Chipping Campden, Gloucestershire. See http://www.campden.co.uk.
6. Tassou, S.A., De-Lille, G., Ge, Y.T., (2009). Food transport refrigeration - Approaches to reduce energy consumption and environmental impacts of road transport, Applied Thermal Engineering, 29, 1467-1477.
7. Tassou, S. A., Ge, Y. T., Hadawey, A., Marriott, D. (2011). Energy consumption and conservation in food retailing, Applied Thermal Engineering, 31, 147-156.
8. http://www.sustainable-systems.org.uk/files/Energy_demand_in_food_chains...
9. WRAP (2013). Handy Facts and Figures on food waste; www.wrap.org.uk/household-food-waste, Accessed on 31Mar-2014. 

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