ShareCO2, one of the options for reducing the carbon footprint of refrigerated transport
Comparison of CO2 emissions from refrigerated transport units using R744 and HFC-134a and overview of solutions that could reduce the carbon footprint of this sector.
The IIR estimated that the number of refrigerated transport units worldwide stood at 3.4 million in 2017 and that associated emissions amounted to around 50 MtCO2eq, or almost 25% of total food cold chain emissions (1). Additionally, a recent study found that Europe's road refrigeration fleet consumes more than 3,500 GWh of primary energy annually and that an improved fleet – with better insulation, units using natural refrigerants, electrification and improved controls – could potentially lead to a reduction in primary energy consumption of more than 28% and a reduction of more than 66% in equivalent CO2 emissions (2).
Among the options studied to reduce the energy and environmental impact of refrigerated road transport, it is worth highlighting thermal energy storage and the use of renewable energies. Incorporating phase change materials as a cold storage medium to transport food products can lead to a reduction of between 22% and 56% in the total carbon footprint compared to the conventional vapour compression system (3). Reducing overall engine fuel consumption through hybridisation with renewable energy sources, such as through the integration of solar panels mounted above the vehicle body, can play an important role in increasing sustainability of road transport refrigeration systems, as documented in several studies.
Furthermore, an analysis of the scientific literature highlights that the choice of refrigerant has a significant impact on the total carbon footprint over the life cycle of a refrigeration system for road transport. Replacing R404A – the most widely used refrigerant in refrigerated transport but which has a very high GWP of 4808 – with R452A (GWP of 2336), which is currently the dominant option, can lead to a total reduction in emissions of between 5% and 15% over the system’s entire lifecycle (4).
In an open access article (5) published in the March 2024 issue of the International Journal of Refrigeration by Italian researchers from the National Research Council of the Institute of Construction Technologies in Padua, a dynamic numerical simulation is used to assess and compare the annual performance of a unit using HFC134a (GWP of 1470) and a new model using R744 (CO2), both designed to provide medium-temperature cooling. The main innovations of the R744 unit compared to a classic vapour compression cycle are the presence of a two-phase ejector and the possibility of including an auxiliary evaporator.
The two units were compared both in terms of their annual performance on urban delivery missions and in terms of their carbon footprint over their entire lifecycle. They were installed on a light utility vehicle with an insulated body and an interior volume of 11.9 m3. The lifespan of the refrigeration unit was set at 12 years.
The results show that the R744 unit has a substantially higher Coefficient of Performance (COP) in the hottest months of the year, while its performance deteriorates in the colder months, due to the large difference between cooling capacity and cooling demand for low ambient temperatures. In total, on an annual basis, the COP of the R744 unit is 27.5% higher than that of the R134a unit.
It should be noted, however, that the higher weight of the R744 unit (186 kg) leads to indirect emissions, linked to fuel consumption, that are slightly higher (+9.3%) than those of the R134a unit (84kg). This difference in weight can be attributed to the presence of additional components in the R744 system, such as the auxiliary evaporator, the internal heat exchanger and the separator, which are not necessary in the R134a unit due to the presence of the thermostatic valve. However, R134a, due to its high GWP, contributes significantly higher direct emissions – due to refrigerant leaks – than those attributable to R744, which are negligible.
Taking into account the total emissions over the lifespan of the units, the R744 option comes out clearly ahead, with a carbon footprint that is 31.9% lower.
The authors conclude that, from a lifecycle sustainability perspective, significant reductions in the carbon footprint of transport refrigeration units can be achieved by carefully selecting materials and designing lighter components to reduce the weight of the cooling unit. Furthermore, they underline that it is crucial to meet the challenge of developing and making available components designed specifically for R744 refrigerated transport applications.
Sources:
(3) https://www.sciencedirect.com/science/article/abs/pii/S0959652622030943
(4) https://www.sciencedirect.com/science/article/abs/pii/S2213138816301370