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Aircraft retrofitting is a challenging task involving multiple scenarios and stakeholders. Providing a strategy to retrofit an existing platform needs detailed knowledge of multiple aspects, ranging from aircraft performance and emissions, development and conversion costs to the projected operating costs. This paper proposes a methodology to account for retrofitting costs at an industrial level, explaining the activities related to such a process. Costs are mainly derived from three contributions: development costs, conversion costs and equipment acquisition costs. Different retrofitting packages, such as engine conversion and onboard systems electrification, are applied in the retrofitting of an existing 90 PAX regional turbofan aircraft, highlighting the impact on both aircraft performance and industrial costs. Multiple variables and scenarios are considered regarding trade-offs and decision-making, including the number of aircraft to be retrofitted, the heritage of an aircraft and its utilization, the fuel price and the airport charges. The results show that a reduction of 15% in fuel demand and emissions are achievable, considering a fleet of 500 platforms, through a conspicuous investment of around EUR 20 million per aircraft (50% of the estimated price). Furthermore, depending on the scenarios driven by the regulatory authorities, governments or airlines, this paper provides a useful methodology to evaluate the feasibility of retrofitting activities.

AbstractThe United States Postal Service (USPS) Pacific Area implemented an employee trip reduction program (ETRP) in 1991. By the end of 1994, the Pacific Area was successful in increasing average vehicle ridership (AVR) from an initial level of 1.09 to approximately 1.15, against an ultimate goal of 1.50. (AVR is defined as the ratio of the number of employees arriving at the worksite to the number of vehicles arriving at the work site. Further, the ultimate goal is only a target. There is no penalty for not achieving the goal.) The total cost for administration and operation of the program during the same period was approximately $5.6 million. The apparent high cost of the program in comparison to the results achieved, coupled with similar results attained by other major employers within the same geographic area, prompted management to look toward alternatives to trip reduction which might provide equal or greater environmental benefit at reduced cost. The alternative selected for analysis was conversion of USPS gasoline‐powered fleet vehicles to compressed natural gas (CNG). The approach used was to first determine the number of employee vehicle miles eliminated under the ETRP. Emissions factors in grams per mile were then applied to determine the corresponding amount of targeted pollutants (i.e., reactive organics, CO, and NOx) that were eliminated. By using ducumented emissions factors for gasoline‐and CNG‐fueled fleet vehicles, a comparison was drawn to estimate the appriximate number of vehicle conversions that would have been required to achieve the same net reduction of pollutants.The results of this analysis showed that conversion of roughly 569 fleet gasoline‐powered vehicles to CNG would have achieved an equivalent reduction in emissions over the same four‐year period. This, in turn, would have cost only $4.4 millin (78 percent) over trip reduction. The economics of this analysis strongly suggest that some type of emissions reduction equivalency credit (EREC) should be applied to ETRP programs (particularly for thos organizations that have implemented comphrehensive ETRP and fleet fuel conversion programs) to enable more cost‐effective reduction of air emissons.

One option to decarbonise residential heat in the UK is to convert the existing natural gas networks to deliver hydrogen. We review the technical feasibility of this option using semi-structured interviews underpinned by a literature review and we assess the potential economic benefits using the UK MARKAL energy systems model. We conclude that hydrogen can be transported safely in the low-pressure pipes but we identify concerns over the reduced capacity of the system and the much lower linepack storage compared to natural gas. New hydrogen meters and sensors would have to be fitted to every building in a hydrogen conversion program and appliances would have to be converted unless the government was to legislate to make them hydrogen-ready in advance. Converting the gas networks to hydrogen is a lower-cost residential decarbonisation pathway for the UK than those identified previously. The cost-optimal share of hydrogen is sensitive to the conversion cost and to variations in the capital costs of heat pumps and micro-CHP fuel cells. With such small cost differentials between technologies, the decision to convert the networks will also depend on non-economic factors including the relative performance of technologies and the willingness of the government to organise a conversion program.