# Green Spare Parts Evaluation for Hybrid Warehousing and On-Demand Manufacturing
## 4 Conclusions  
The results obtained by the simulation model help us to conclude that the hybrid warehouse can offer a green and cost-effective option to manage critical spare parts. Physical or digital warehouse options alone may not offer this, which is in line with other studies [32; 33]. Hybrid warehousing offers better availability rates, shorter and more resilient supply lead times, and smoother and less crowded inventory stocks. Although this study has not covered the social benefits of reinforcing local manufacturing with the digital warehouse option and the ability to deal with the global supply crisis, these are benefits that must always be highlighted. The spare parts evaluation analysis for several simulated scenarios indicates that the digital warehouse is not sufficient by itself to maintain production availability at the highest levels; however, it is effective in reducing the amount of stock, simplifying inventory management, and making the supply process more resilient. Although digital warehousing without physical stock has lower production availability than other scenarios, it can be the best scenario (in terms of operating cost and CO2 emissions) for spare parts that do not directly affect production availability. In addition, this study demonstrates how simulation modeling can be useful for SPIR engineers in determining reasonable subscription fees for digital warehoused items. This study highlights the need to update the SPIR analysis to consider the option of digital warehousing and on-demand manufacturing during the project phase. From an \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Warehouse Type** & **Consequence Demand Rate** & **Location** & **Price Per Unit NOK** & **Delivery Time** & **Qy Commissioning** & **Qy Oper-** & **Reorder** \\ \hline Physical Stock & Critical & 1.5 per month & Minimum stock at site & 1500 & 20 days & 7 & 7 & 6 \\ Hybrid Stock & Critical & 1.5 per month & Minimum stock at site & 1500 & 7 days & 4 & 4 & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: SPIR worksheet for physical and hybrid warehousing. asset management point of view, considering digital warehousing and on-demand manufacturing options in the project phase is a cost-effective option compared to modifications and changes in inventory concept in the utilization phase. Moreover, early consideration at the project phase also allows warehouse stakeholders to establish resources (manufacturing rights and contracts with local manufacturers) to be able to offer a digital warehouse and on-demand manufacturing. Switching physical warehouses to offer digital warehousing and on-demand spares requires considerable investment, effort, and time. This paper contributes to the field of spare parts analysis and offers valuable information on the benefits and implications of digital warehousing, on-demand manufacturing, and hybrid warehousing. It provides a model that helps SPIR engineers quantify the impacts of considering digital and hybrid warehousing. The developed simulation model handles several conflicting key performance indicators (e.g., availability against holding cost) and enables trade-off analysis. The paper proposes upgrading the existing SPIR process by incorporating the simulation model developed to enable evaluating the options for digital and hybrid warehouses. The findings underscore the potential to improve availability and create a green spare parts inventory and supply, particularly under the hybrid warehousing option. The study also recommends updating the spare part risk matrix and SPIR worksheets. Simulation analytics using various assumptions and simplifications such as those that were used as a tool to illustrate the effect of spare parts policy on asset availability, operating expenses, and CO2 emissions is still better than performing SPIR analysis in the current naive way.