The world needs reliable, sustainable, and longer duration energy storage solutions as the share of intermittent renewable energy increases in energy systems. Carnot batteries are a promising, emerging technological class of energy storage that store electricity in the form of thermal exergy. They can be made from abundant materials and existing technology, are durable, have a low specific cost, store energy for medium-to-long periods, and cogenerate heat and power. Previous studies have simulated thermodynamic components, optimized system design and control, and investigated application potential of Carnot batteries at different scales and environments with promising findings that suggest the energy storage can be competitive and even outperform mature energy storage technologies on the market. Carnot battery potential in the metropolitan environment is still being explored and specific case- studies are needed to further validate the functional utility of the technology. The aim of this research is to investigate Carnot battery potential for a practical use-case with an existing building through a research-for-design approach. Data is gathered through literature, commercial sources, and interviews with experts informed the design and application of the energy storage system in an urban context in the Netherlands. With the goal of net-positive energy building performance, an analysis based on energy balance, hypothetical onsite renewable energy potential, spatial considerations, and two different scenarios was conducted on an existing building using real energy data. The implementation of Carnot batteries to existing buildings can manage electricity and heat services, provide a cost-competitive energy storage option, and reduce carbon emissions released into the environment when coupled to renewable energy systems over the lifetime of the technology. The findings indicate massive potential for Carnot batteries to contribute to urban energy storage needs.