Performance and Profitability Perspectives of a CO2 based District Energy Network in Geneva’s City Center

A new type of district energy network capable of providing simultaneously heating and cooling is being investigated. It is based on the use of CO2 as a heat transfer fluid by taking advantage of the latent heat of vaporization, to store and transfer heat across the network. The goal of the present study is to determine the performance of a CO2 network when applied to a real urban area. It focuses first on determining the requirements for the various thermal energy services for a part of Geneva’s city centre. The energy consumption is first computed for the energy conversion technologies now in place in this area - namely fuel boilers and vapour compression chillers. Then the new energy consumption is computed if a CO2 network were used instead of the existing technology. Finally a profitability analysis of the CO2 network variant is done accounting for investment, energy purchasing, equipments replacement, operation, and maintenance costs. For an interest rate of 6% and a price of the delivered heating/cooling energy at 0.13 CHF per kWh, a net present value of 82.8 million CHF after 40 years is achieved, while the break-even is reached after 5 years of operation.