Performance and profitability perspectives of a CO2 based district energy network in Geneva's City Centre

• Evaluation of the cooling and heating requirements for an area in Geneva (CH).
• Two systems compared, a CO2 network and a conventional decentralized system.
• Comparison shows 84% energy consumption reduction for the CO2 network.
• Comparison shows cheaper delivered services for the CO2 network.

A new type of district energy network providing simultaneously heating and cooling services 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 final energy consumption is first computed for the energy conversion technologies now in place in this area – namely heating oil boilers and air cooled compression chillers. Then the new final energy consumption is computed considering that a CO2 network is used instead of boilers and air cooled compression chillers. For the area considered the CO2 network's variant leads to a final energy consumption of 10,968 MWh of electricity. It represents a reduction of 84.4% when compared to the boilers and chillers case. A comparative profitability analysis of the two cases is also presented. The analysis takes into account investment, heating oil and/or electricity, equipment replacement, operation, and maintenance costs, as well as the sales of energy services.For an interest rate of 6%, a price of the delivered heating/cooling services at 0.108 € kW h−1 and a lifetime of 40 years, the conventional technology does not reach profitability while the CO2 network achieves a profit in present value of 69.59 million € and the break-even point is reached after 5.5 years of operation.