<p>  </p> <p>Environmental challenges, increasing energy costs and demand, and upcoming regulations (e.g., new equipment performance ratings, phase-down of HFCs) are a few of the main drivers behind the research on advanced HVAC&R equipment. The HVAC&R systems are one of the largest energy consumers in both commercial and residential buildings and their operation is essential to ensure thermal comfort as well as other industrial needs. Within this context, large chillers provide chilled water to condition commercial buildings and the new generation of smart chillers feature variable speed compressors that enable active capacity modulation. In turn, variable speed operation along with other factors can contribute to performance degradation. Understanding mechanisms of degradation and developing models that enable predicting the decrease in performance with respect to the rated values are still open topics in the literature. </p> <p>The overarching goal of this research is to investigate the performance degradation of a water-cooled variable-speed screw chiller under long term operation and to gain insights on the behavior of the chiller under accelerated life testing. In particular, this thesis covers the initial task of designing an experimental test setup that enables performance testing according to the AHRI 550/590 standard. Once the experimental setup was commissioned, a set of four standard-conform baseline tests was conducted to map the rated performance of the chiller at both full and part-load conditions. After completing the baseline tests, an accelerated life test cycle procedure was developed and implemented in order to conduct 24/7 automated testing on the chiller. To this end, two test modes were established to simulate a real-life use of the chiller and induce high level of thermo-mechanical stresses on the compressor. Furthermore, eight recurring baseline tests were conducted to determine the performance behavior after 1000 operating hours. Finally, a preliminary system model was set up. This thesis describes the design of the system, the commissioning and control and provides insights on the performance testing as well as long-term testing methodology and the modeling work that was done so far. </p>