Defining energy efficiency indicators for refrigerated shipping vessels

A working group from the International Maritime Organisation (IMO) has proposed new energy efficiency indicators for ships. Shipping companies challenge their applicability to the reality of energy consumption on refrigerated shipping vessels.

According to the International Maritime Organisation (IMO), greenhouse gas (GHG) emissions from shipping have increased by 9.6%, from 977 million tonnes in 2012 to more than one billion in 2018. [1] IMO aims to reduce carbon emissions from international shipping by 40% by 2030, compared to 2008. [2] Initiatives to achieve this goal should include using energy-saving technologies, reducing the speed of ships as well as using low-carbon alternative fuels. [1]


An IMO working group has agreed on draft guidelines introducing two new energy efficiency indicators for all ships, pending final adoption:

  • a new Energy Efficiency Existing Ship Index (EEXI), which measures the technical requirement for energy efficiency (how the ship is equipped and retrofitted)
  • a new Carbon Intensity Indicator (CII) which measures the operational requirement for energy efficiency (how the ship is operated) [2]


The upcoming CII will determine the annual reduction factor needed to ensure continuous improvement in the operational carbon intensity of the ship. The CII rating will be given on a scale from A to E. According to the drafted guidelines, a ship graded D or E for three consecutive years, will have to submit a corrective action plan to achieve the required grade of C or better.


Several major shipping organisations have pointed out that CII ratings can penalise ships that consume power and therefore fuel to maintain low temperatures when transporting refrigerated foodstuffs or gases. Energy consumption also varies greatly depending on whether the cargo needs to be chilled or frozen, the length of the voyage, the time spent in port, and the ambient temperature since higher ambient temperatures and longer voyages require more energy.

According to shipping companies, electricity consumption for cooling on board could represent up to 51.5% of the total consumption for a container vessel with 1,121 plugs for reefer containers, or up to 70% for a vessel with 2,024 plugs for reefers. Simply put, the shipping companies argue that a vessel carrying refrigerated cargo should not be classified as less energy efficient. [3]

Preliminary meetings are being held to review the arguments presented by the shipping companies. [3]


For further information on energy efficient cooling technologies for maritime applications, we recommend the following documents in FRIDOC: