The metal-organic frameworks (MOFs) MIL-101(Cr) and NH 2-MIL-125 offer high adsorption capacities and have therefore been suggested for sustainable energy conversion in adsorption chillers. Herein, these MOFs are benchmarked to commercial Siogel. The evaluation method combines small-scale experiments with dynamic modeling of full-scale adsorption chillers. For the common temperature set 10/30/80 C, it is found that MIL-101(Cr) has the highest adsorption capacity, but considerably lower efficiency (À19%) and power density (À66%) than Siogel. NH 2-MIL-125 increases efficiency by 18% compared with Siogel, but reduces the practically important power density by 28%. From the results, guidelines for MOF development are derived: High efficiencies are achieved by matching the shape of the isotherms to the specific operating temperatures. By only adapting shape, efficiencies are 1.5 times higher. Also, higher power density requires matching the shape of the isotherms to create high driving forces for heat and mass transfer. Second, if MOFs' heat and mass transfer coefficients could reach the level of Siogel, their maximum power density would double. Thus, development of MOFs should go beyond adsorption capacity, and tune the structure to the application requirements. As a result, MOFs could to serve as optimal adsorbents for sustainable energy conversion.

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Globally, heat demand accounts for 71% of industrial energy consumption. [1] For example, the industry in the US requires 3416 PJ heat between 40 and 260 C, with 1755 PJ already in the temperature range between 120 and 160 C, and the industry in the European Union requires 626 PJ heat for temperatures below 150 C, with 116 PJ in the temperature range between 100 and 150 C. [2] Examples of such industrial processes and their process temperatures were summarized by Arpagaus et al. or Brückner et al. (Table 1). [2,3] Simultaneously, the global industry releases 31902 PJ of waste heat, with 42% occurring below 100 C as low-grade heat. [4] Transforming this low-grade waste heat from temperatures below to above 100 C could enhance industrial energy efficiency. Thereby, heat transformation has the potential to reduce both primary energy consumption and greenhouse gas emissions. [5] The low-grade waste heat can be transformed into useful heat with higher temperatures by mechanically driven vapor compression heat pumps or thermally driven heat transformers. However, classical heat pumps currently available are restricted to a maximum gross temperature lift of 50 K and a maximum condensing temperature of 130 C. [2,6] Vapor compression heat pumps for higher temperatures suffer from the lack of suitable working fluids. [2,6] Designs are often challenging for both the cycles (e.g., multi-stage cycles) and components (e.g., multi-stage compressors) due to high discharge pressures and temperatures. [2,6-8] To overcome these limitations, many researchers screen working fluids or improve the thermodynamic cycle design. For example, Mikielewicz and Wajs screened working fluids with low global warming potential for upgrading heat from 50 to 130 C. [6] Ethanol was identified as a promising working fluid in a singlestage cycle design, whereas multi-stage cycles generally seemed