===== District heating network =====

The implementation of a district heating system depends on the heat demand density [kWh/(year*m<sup>2</sup>)] of the area under study.

| ^Not suitable ^Limited ^Optimal ^
^Heat demand density [kWh/(year*m<sup>2</sup>)] [[#Sources|[1]]] |<50 |50-70 |>70 |

The city of Genève has been selected as a model for calculating the environmental impact and cost of a district heating network. The information regarding the heat demand density [kWh/(year*m<sup>2</sup>)], area [km<sup>2</sup>] and number of buildings is from Fazlollahi et al. [[#Sources|[4]]]. Next table contain the data for a predefined area in the center of Genève.

^Heat demand density [kWh/(year*m<sup>2</sup>)]|91.25|
^Area [km<sup>2</sup>]|35.2|
^Number of buildings|378|

Girardin [[#Sources|[3]]] proposes a preliminary estimation for the network length (//L<sup>dn</sup>//), considering the land area (//S<sub>z</sub>//), the number of buldings (//n<sub>b</sub>//) and a topological factor (//K//). The value //K// = 0.23 has been calculated from an existing network in Genève.

$L_{dn}=2(n_b-1)K\sqrt[]{ \frac{S_z}{n_b}}$

The estimated network length for the area in Genève would be 380 km. So taking into account the area, the heat demand density and the network length, it is possible to calculate the required meters of network per unit of heat: 118.3 m/MWh<sub>th</sub>.

Olivier-Solà et al. [[#Sources|[2]]] list the components and materials that are necessary for the construction of 1 meter of district heating network. The combination of this list with the data in Ecoinvent [[#Sources|[5]]] provides the emissions (IPCC07-10a and Deposited waste) for 1 meter of district heating network. The values are shown on the next table.

^IPCC07-100a [kg CO<sub>2</sub>-eq]|283.11|
^Deposited waste [UBP]|21038|

The life time of the static elements (pipes, trench and insulation) is assumed to be 50 years, while the life time for the pumps is 25 years.
===== Sources =====

[1] [[http://www.afo.eu.com/GetItem.asp?item=digistorefile;374837;1434&params=open;gallery|AFO - Operating figures, quality parameters and investment costs]]

[2] J. Olivier-Solà, X. Gabarrell, J. Rieradevall, "Environmental impacts of the infrastructure for district heating in urban neighbourhoods", //Energy Policy//, vol. 37, pp. 4711-4719, 2009.

[3] L. Girardin, //A GIS-based Methodology for the Evaluation of Integrated Energy Systems in Urban Area//. PhD thesis, Ecole Polytechnique Federale de Lausanne, Switzerland, 2012.

[4] S. Fazlollahi, G. Becker and F. Maréchal. Multi-Objectives, Multi-Period Optimization of district energy systems: III-Distribution networks, submitted to Computers & Chemical Engineering, 2013.

[5] [[http://www.ecoinvent.ch/|Ecoinvent]]