EEDI calculation
Concept of EEDI
The Attained EEDI is the actual value of EEDI for a ship and represents the amount of CO2 generated by a ship while doing one tonne-mile of transport work. In simple term, it may be represented by equation (1):
Figure 8: EEDI calculation formula (MariEMS 2017).
Attained EEDI is calculated using the “EEDI formula” as shown below:
Figure 9: Main terms in EEDI formula
The items that primarily influence EEDI are:
- Main engine and energy needed for propulsion; this represented by the first term in the nominator of the formula.
- Auxiliary power requirements of the ship; this is represented by the second term in the nominator.
- Any innovative power (electric) generation devices on board such as electricity from waste heat recovery or solar power. These are represented by the third term in the nominator.
- Innovative technologies that provide mechanical power for ship propulsion such as wind power (sails, kites, etc.). This is the last term in the nominator.
- In the denominator of the formula, ship capacity and ship speed are represented that together gives the value of transport work.
Various terms in equation are fully defined in the relevant IMO guidelines summary of which is given in table below.
Table 3: Parameters for EEDI formula (MariEMS 2017).
More details of the important parameters are given below:
- SFC (Specific Fuel Consumption): The specific fuel consumption (SFC) is for engines and represents their fuel efficiency (fuel used) in g/kWh. The value for SFC is determined from the results recorded in the engine’s NOx Technical File; determined as part of the engine NOx certification. The SFC for main engine is generally taken at 75% load and for auxiliary engines is generally taken at 50% load.
- CF (Carbon Factor): This factor specifies the amount of CO2 generated per unit mass of fuel used. Table below provides the standard value for marine fuels. The type of fuel used for the NOx Certification test (to be taken from NOX Technical File) should be used to determine the value of the CF conversion factor (MariEMS 2017).
Table 4: Standard values of CF for marine fuels
It is important to note that EEDI is calculated for a single ship’s operating condition. This single operating condition is referred to as “EEDI Condition”. The EEDI Condition is as follows:
- Draught: Summer load line draught.
- Capacity: Deadweight (or gross tonnage for passenger ships, etc.) for the above draught (container ship will be 70% value).
- Weather condition: Calm with no wind and no waves.
- Propulsion shaft power: 75% of main engine MCR (conventional ships) with some amendments for shaft motor or shaft generator or shaft-limited power cases, where applicable.
- Reference speed (Vref): Is the ship speed when measured/estimated under the above conditions.
To calculate EEDI, all the measurements and data used should be corrected to the above conditions (MariEMS 2017).
EEDI Technical File
For verification purposes and subsequent implementation and enforcement purposes by flag and port States, it is a requirement that all the relevant terms and their values shall be recorded in an “EEDI Technical File” and then submitted to the verifiers (normally Recognized Organization on behalf of flag State) that will carry out the certification on behalf of flag Administration. Also, the “EEDI Technical File” needs to be kept on board and forms a supplement to International Energy Efficiency Certificate (MariEMS 2017).