Energy demand and environmental impacts of food transport refrigeration and energy reduction methods during temperature-controlled distribution

Abstract

The growing demand for temperature-controlled food distribution is driving the growth of transport refrigeration units (TRUs). The majority of these TRUs are powered using auxiliary diesel engines of less than 19 kW power output. These engines are currently not covered by European regulations on emissions. The emissions from TRUs are instead regulated by the Non-Road Machinery (NRMM) standard which is considered insufficient to adequate control emissions. The reliance of most TRUs on diesel fuel which contributes to both greenhouse gas and particulate emissions has heightened the need for more energy efficient and low carbon alternatives. In this work, a model has been developed to determine the fuel consumption and GHG emission of auxTRUs for the distribution parameters obtained from a survey study conducted as part of research to quantify the energy usage and emissions associated with auxiliary engines for transport refrigeration units in London. Using the model, different alternative technologies have been investigated, which include, cryogenic systems using LN2, cryogenics systems using LCO2, all-electric TRU and hydrogen fuel cell powered TRU. Both production and operation related GHG emissions were considered for the studies. The production related emissions for electricity are lower than the emissions from the production of hydrogen and cryogenic fluids by almost 60%. For this reason, the all-electric TRU was found to be the most suitable alternative to diesel auxTRU in respect to GHG emissions and current infrastructure. The infrastructure for both hydrogen and cryogenic fluids does not exist as yet to support frequent refilling of the transport vehicles. Infiltration of ambient air during door openings has been identified to be a major source of refrigeration load in multi-drop temperature controlled food distribution. Plastic strips curtains are inconvenient to use as they impede loading and unloading. For this reason, even when they are fitted on the vehicle they are not utilised by the drivers. Air curtains can avoid the use of a physical barrier but have not been previously investigated sufficiently for this application. For this reason, extensive experimental and numerical investigations were performed to establish the effectiveness of air curtains to reduce air infiltration into the refrigerated space of distribution vehicles. The air curtain discharge velocity was identified to be an important design parameter for the air curtain. Optimising the discharge velocity and angle has shown to produce an energy savings of 50% in distribution vehicles.