It needs to be noted that there are also non-carbon dioxide greenhouse gases generated in fuel combustion, mainly methane (CH4) and nitrous oxide (NO2). They are produced due to incomplete combustion of hydrocarbons in fuels, but the contribution of fuel combustion to global emissions of these gases is minor and the uncertainty is high (IPCC, 1996). Therefore, emissions of non-carbon dioxide greenhouse gases are not estimated in this study.
Based on the emission factors determined and energy consumption of the hotels, CO2 emissions from the 29 surveyed hotels were estimated. The CO2 emissions indicators (CEI) were calculated by dividing the total emissions with the selected normalizing denominators, namely GFA and number of room nights (Table 3). While floor area normalization is like a convention in building energy studies, the number of room nights was selected because it is a frequently used indicator and normalizing factor in hospitality management. A comparison of the two metrics shows that variation in CO2 emissions in kg/m2 is much smaller than that in kg/room night. Hotel 3, for example, appears more like an outlier when its carbon intensity in terms of kg/room night is compared to that of other hotels. But an investigation shows that it is simply because this 5-star hotel has lots of large suites catering for the needs of luxurious travelers. As can be seen in Table 3, its carbon intensity in terms of kgCO2/m2 is more comparable to that of others. Selecting an appropriate normalization factor in GHG emissions accounting is of vital importance and can be notoriously difficult. Thomas et al.(2000) pointed out that each industry sector has its own peculiarities and normalization factors must be industry specific. Since a widely accepted normalization factor is lacking for the hotel industry, the carbon intensity estimated must not be interpreted in an arbitrary manner.