Reducing greenhouse gas emissions from TRUs

Some reductions in the environmental impacts of transport refrigeration are possible using conventional technologies. For example, manufacturers such as Carrier offer systems that replace F-gases with CO2 as the working fluid. This eliminates the impact of leaks of high-GWP refrigerants, but has several drawbacks. To work as a refrigerant, CO2 requires more compression than F-gases, meaning the TRU engine consumes more fuel, and therefore emits even more CO2, NOx and PM. The TRU in any case emits far more CO2 – up to 50 tonnes per truck per year – from burning diesel than from leaking F-gas, which at an estimated annual leakage rate of 25%64 is likely to equate to low single digit tonnes of CO2 per year.

As for NOx and PM, TRUs' unregulated and disproportionate emissions could be reduced by upgrading the TRU diesel engine to a lower-emitting model, but these are larger, more expensive, and may also consume more fuel. In response to a European Commission proposal to tighten emissions standards on Non Road Mobile Machinery, organisations including Transfrigoroute International, the European cold-logistics trade association, pointed out that such cleaner engines do not fit within the tight space constraints of refrigerated trailers, which are regulated by EC directive.65

TRUs on vans and some rigid trucks are driven from the vehicle's propulsion engine, the emissions of which are regulated in the US and EU, and it might be possible to convert more TRUs to this notionally cleaner source of power. But this would mean more propulsion engines would be left idling to provide refrigeration when the vehicle is stationary while unloading etc; and engines operating at low power tend to produce disproportionate amounts of NOx and PM.

So while incremental improvements can be made using existing technologies, it is difficult to escape the conclusion that to address all the challenges of refrigerants, CO2, and NOx and PM emissions, and make a decisive reduction in the environmental damage caused by transport refrigeration, diesel needs to be eliminated altogether.

Rapidly rising carbon emissions from transport refrigeration would be in addition to those from non-refrigerated freight, as trade expands and growing volumes of goods are transported longer distances. The International Transport Forum (ITF) of the OECD has forecast that global emissions from road freight will rise 300% by 2050 to more than 4.5 billion tonnes.66 Emissions from all freight transport, including air and sea, will top 8 billion tonnes and exceed those of passenger traffic. The ITF has proposed a series of measures to mitigate freight emissions, but we suggest that the additional energy demands and air pollution of transport refrigeration require especially urgent attention.

64 Sustainable Refrigerated Road Transport, 21st Informatory Note on Refrigerating Technologies, International Institute for Refrigeration, Dec 2011,

65 Consultation on the revision of Directive 97/68/EC on emissions from non-road mobile machinery engines, European Commission,

66 Freight emissions set to skyrocket as trade routes widen, study finds, Business Green, 29 January 2015,