## 1 Introduction
### Literature Overview  
The present section overviews recent studies, offering a perspective on the current state and future directions for the sustainability of data centers. [PERSON] et al. [14] offer a systematic literature review on DC technologies, focusing on cooling systems, renewable energy integration, and waste heat recovery. The study stands out for its holistic view of data center operations, emphasizing the importance of developing advanced control methods and performance metrics to maximize energy efficiency. In line with this, [PERSON] et al. [17] discuss the adoption of renewable energy sources and thermal management strategies, providing a strategic six-step process for creating sustainable and energy-efficient data centers. The energy consumption and reliability modeling in data centers are other critical areas of research. An article [16] surveys recent studies on modeling data center energy consumption, concluding with the organization of a taxonomy. [PERSON] et al. [10] adopt a systematic literature review methodology to dissect contributions related to energy consumption, providing a foundational tool for future research in this domain. Similarly, a study [18] examines power models for virtual machines and software applications, investigating strategies to maximize the quality of service. Numerous reviews and research papers populate the literature in the WHR field. Already in 2014, the question of recovering DC waste energy arose: [PERSON] et al. [12] reviewed techniques for recovering waste heat, assessing various methods, including district heating, absorption cooling, and direct and indirect power generation. The study identifies absorption cooling and the ORC as highly promising for data center applications for cooling purposes and electric generation, respectively. In particular, to the best of the authors' knowledge, ORC technology represents the most suitable solution for electric production from DC waste heat from an energy and economic point of view, considering the corresponding low-grade thermal level and the typical operating conditions of data centers. In fact, alternative solutions based on piezoelectric and thermoelectric generation exhibit lower efficiencies, lower power, and higher costs [12]. Furthermore, comparing the Kalinacycle, trilateral Rankine cycle, and organic Rankine cycle for waste heat reuse confirms that the ORC is the proper choice for low-quality thermal energy exploitation due to its energy and economic performance [1; 19]. The literature review highlights that Stirling engines can also exploit low-grade thermal sources [20; 21]. However, the corresponding electric efficiency is always lower than 1% considering the typical operating conditions of DCs with source temperatures lower than 60-85 \({}^{\circ}\)C [22; 23], suggesting that ORC adoption for the reuse of the DC low-quality waste heat is a viable option. In a similar vein, another work [3] evaluates the integration of micro-ORC systems into data center cooling systems through experimental analysis, showcasing the potential of harnessing waste heat effectively. At the RISE ICE Data Center, research has evaluated the potential direct exploitation of the data center's excess heat [24]. The investigation has developed a matrix illustrating different options based on the DC cooling characteristics (i.e., air-cooled, liquid-cooled), demonstrating that data centers are essential to promote industrial and urban symbiosis (IUS) through district heating, direct heating, and industrial applications. In this framework, [PERSON] et al. [25] investigated the possible adoption of low-grade excess heat from data centers as a thermal source for a small-scale mealworm farm, and [PERSON] et al. [26] suggested directly utilizing the low-grade heat for fruit- and berry-drying processes in food industries. The solutions improve the value and the benefit of the electric energy used in data centers by exploiting the excess heat and reducing the energy dissipation.