*3.5. EEDI Candidate 2: EEDI Considering the Energy Density of LH2*

EEDI candidate 2 considers the energy density difference between LH2 and LNG. As shown in Table 4, the density of LH2 is 16% of that of LNG. This low density of LH2 makes the attained EEDI of an LH2 carrier calculated using Equation (10) smaller than that of an LNG carrier with the same volumetric capacity. Conversely, LH2 has a heating value that is 2.58 times that of LNG. This indicates that LH2 can carry more energy within the same mass as LNG. EEDI candidate 2, therefore, considers this energy density factor. The energy density is used to introduce the "re-scaled deadweight" concept shown in Equation (19) in place of the mass density. Using this rescaled deadweight, Equation (20) defines the "energy-based EEDI", which applies the energy density concept to the attained EEDI. In EEDI candidate 2, it is compared with the required EEDI of LNG carriers with the same volumetric capacity.

$$\text{DWT} = \text{DWT}\_{\text{carggo}} + \text{DWT}\_{\text{other}} \tag{18}$$

$$\text{DWT}\_{\text{re-scaled}} = \frac{\text{LHV}\_{\text{LH2}}}{\text{LHV}\_{\text{LNG}}} \text{ DWT}\_{\text{cargo}} + \text{DWT}\_{\text{other}} \tag{19}$$

$$\text{EEDI}\_{\text{energy}-\text{based}} = \frac{\text{P}\_{\text{ME}} \cdot \text{C}\_{\text{ME}} \cdot \text{SFC}\_{\text{ME}} + \text{P}\_{\text{AE}} \cdot \text{C}\_{\text{AE}} \cdot \text{SFC}\_{\text{AE}}}{\text{DWT}\_{\text{re}-\text{scaled}} \cdot \text{V}\_{\text{ref}}} \tag{20}$$

DWTcargo: Deadweight of cargo DWTother: Deadweight without cargo DWTre−scaled: Rescaled deadweight LHVLH2: Lower heating value of LH2 LHVLNG: Lower heating value of LNG EEDIenergy−based: Energy-based EEDI

**Table 4.** Densities and lower heating values of LH2 and LNG.


#### *3.6. EEDI Candidate 3: No Restrictions Using LNG as a Fuel*

EEDI candidate 3 refers to the case in which LH2 carriers have no restrictions regarding their CO2 emissions provided that conventional clean fuels such as LNG are used. Unlike other gas carriers that carry CO2-rich fuels, such as LPG and LNG, LH2 carriers are used to transport CO2-free hydrogen. The strong regulations on CO2 emissions from LH2 carriers, such as those considered in EEDI candidates 1 and 2, may thereby be impartial to liquid hydrogen, ultimately preventing the shipping of this clean fuel. It would therefore be fair to impose no restrictions on CO2 emissions if these ships utilize relatively clean fuels such as LPG or LNG. In this case, the practicality of BOH re-liquefaction can be determined purely on an economic basis.
