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

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 e 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 V 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 V and the break-even point is reached after 5.5 years of operation.

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

Daniel Favrat, Samuel Henchoz, Céline Weber

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.

2012

Key Energy and Technological Aspects of Three Innovative Concepts of District Energy Networks

Patrick Chatelan, Daniel Favrat, Samuel Henchoz, François Maréchal

Energy needs in urban areas are heterogeneous by their nature, spatial distribution and temperature level required. Three concepts of district energy networks that could provide the energy services efficiently to a city centre are compared. The focus is on the energy and technological aspects. These networks are characterized by similar temperature levels; between 9.5 °C and 18 °C, rely on free cooling for most of the cooling services and use a combination of centralized and decentralized heat pumps to provide the heating services. Two of these concepts exploit the latent heat of evaporation/condensation of CO2 and of the refrigerant R1234yf to store and transfer heat. The third concept is more conventional and uses the sensible heat of liquid water, however with a small temperature spread. The proposed networks allow the waste heat emitted by the users requiring cooling to be transferred and valourised by the users requiring heating, thus reducing the load on the central plant. For the area considered, where the annual heating and cooling demand are 53.1 GWh and 49.4 GWh respectively, the annual electricity required to supply the thermal services amounts to 10.87 GWh for CO2, 10.52 GWh for water and 9.60 GWh for R1234yf. © 2016 Elsevier Ltd. All rights reserved.

2016

Key energy and technological aspects of three innovative concepts of District energy networks

Daniel Favrat, Samuel Henchoz, François Maréchal

In urban areas, the use of thermal energy services is intensive and relatively heterogeneous by their nature, spatial distribution and temperature level required. In this study three concepts of district energy networks that could provide these services very efficiently to a specific area representative of mid Europe (Geneva) are compared. The focus is on the energy and technological aspects related to each of the proposed networks. These networks are characterized by similar temperature levels; between 9.5°C and 18°C, rely on free cooling for most of the cooling services and use a combination of centralized and decentralized heat pumps to provide the heating services. Two of these concepts exploit the latent heat of evaporation/condensation of CO2 and of the HFO refrigerant R1234yf to store and transfer heat across the network. The third concept is more conventional as it uses the sensible heat of liquid water, however with a small temperature spread (2 - 8 °C). The three proposed networks allow the waste heat emitted by the users requiring cooling to be collected, transferred and valorised by the users requiring heating, thus reducing the load on the central plant. For the area considered, where the annual heating and cooling demand are 53.1 GWh and 49.4 GWh respectively, the annual final energy (electricity) consumption required to supply the thermal services amounts to 10.87 GWh for the CO2 variant, 10.52 GWh for the water variant and 9.60 GWh for the R1234yf variant.

2015