District heating and cooling energy network using CO2 as a heat and mass transfer fluid

The 5th generation compact district heating and cooling networks in a temperature range of 10 to 16 °C have a great potential for energy savings by providing a heat source for decentralized heating heat pumps, a cold source for air-conditioning and a heat sink for refrigeration or cogeneration units. The energy balance of the network is achieved by a central plant equipped with a heating heat pump in winter operation and a heat dissipator in summer operation. They typically facilitate the synergy between users and allow the concept of a city without chimneys or cooling towers in the various buildings. One such concept is based on using the latent heat of the transfer fluid (CO2), with one saturated CO2 vapor pipe and one saturated CO2 liquid pipe. Studies show that up to 80 % of the final energy can be saved in urban areas, at a cost that is lower than the conventional technologies.

Novel district heating and cooling energy network using CO2 as a heat and mass transfer fluid

Daniel Favrat, Luc Girardin, Samuel Henchoz, François Maréchal

Compact district energy networks in a temperature range of 10 to 16°C have a great potential for energy savings by providing a heat source for decentralized heating heat pumps, a cold source for air-conditioning and a heat sink for refrigeration or cogeneration units. The energy balance of the network is done by a central plant equipped with a heating heat pump for Winter operation and a heat dissipater for Summer operation. They typically facilitate the synergy between users and allow the concept of a city without chimneys or cooling towers in the various buildings. One such concept is based on using the latent heat of the transfer fluid (CO2),with one saturated CO2 vapor pipe and one saturated CO2 liquid pipe, in which the flow is bidirectional in the function of the predominance of the heating or cooling demands. While the concept has already been published this paper discusses some of the potential dynamic phenomena as well as further extension to allow those networks to collect CO2 from hybrid decentralized SOFC-GT cogeneration systems for either further disposal, use or contribution to power to gas concepts. Additional extensions to using reversible supercritical CO2 heat pump or ORC is also mentioned. A reminder of the technico-economic results obtained on the actual demands of an existing district is also done including the evaluation of the uncertainty margins.

2017

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

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