**8. Heat demand**

District heating demand may be seen as a valuable resource itself because it enables the uti‐ lisation of energy resources that without this demand would be difficult to use. The districtheating demand also makes combined heat and power production possible.

District heating is more suitable the larger the heat load density is (i.e., heat demand per ground area, e.g. [18]) because more heat can be delivered per meter of pipe buried in the ground and network costs can be spread on a larger energy amount. Therefore, district heat‐ ing is primarily used in larger buildings, for example multi-family residences and service premises, such as hospitals, schools and larger office buildings. But the heat load density that is required for district heating to be economically favourable depends on the heat pro‐ duction cost [2]. If the *heat sink* that district-heating users constitute enables power produc‐ tion or waste reception that yield revenues, it is profitable to build district-heating grids in areas with lower heat load density than if biomass or oil is used to produce the district heat separately.

In some places, heat prices vary in a similar way as the heat production cost during the year (Sect. 1.1) to give consumers a signal on when it is most desirable that they reduce their heat demand. Houses with district heating may, for example, be less suitable for solar heating be‐ cause district heating often comes from surplus resources, such as waste or waste heat, when there is most solar radiation.

houses to the district-heating grid was studied with MODEST. These changes would not af‐ fect global carbon-dioxide emissions if there is interplay with coal-fired condensing power plants. But heat production plants and fuels used have crucial importance for the environ‐ mental impact of district heating. In this case, the heat demand changes would, for example, decrease the use of a CHP plant fuelled with carbon-rich peat, which cause similar carbondioxide emissions as coal. The larger impact on CHP production compared to the previously mentioned study is also shown by an electricity-to-heat output ratio for the system that de‐

District Heating and Cooling Enable Efficient Energy Resource Utilisation

http://dx.doi.org/10.5772/51837

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To make it favourable to use district heating in areas with low heat demand and, thus, to enable utilisation of the energy sources that can only be used through a district-heating sys‐ tem, as much district heating as possible should be used in such an area while still using the

Besides the traditional purposes domestic hot water and space heating, district heating can be used for industrial processes and all heat supply to household appliances (e.g. dish wash‐ ers, washing machines, tumble dryers and towel dryers), which now often, at least partly, use electricity for heating. Solar rooftop energy extraction could yield electricity instead of

Henning [22] outlined scenarios for more sustainable energy supply for a development in a Swedish town. In two cases, the buildings were supplied by district heating. In one of these scenarios, district heating was used only in the traditional way for domestic hot water and space heating in normal, but not inefficient, houses. In the other scenario, there were lowenergy buildings where district heating also was used for household appliances. Energy that in the first case only disappeared out of the buildings was in the other case utilised for heat supply to dish washers, washing machines, tumble dryers and towel dryers. The first sce‐ nario meant more climate-dependent space-heating demand partly covered by expensive high-load fuels (mainly forest wood chips in this town), whereas the latter scenario included more base load in the household appliances, which could be covered by fuels with lower

Many industrial processes have heat demand that partly or wholly can be covered by dis‐ trict heating but now is supplied through fuel or electricity. When required, district heating can be supplemented by boilers to obtain desired high temperatures. Heat demand in indus‐ trial manufacturing processes is often more or less independent on outdoor temperature and only has little seasonal variations (besides holidays) in the same manner as domestic hot wa‐ ter. Industrial processes can, therefore, constitute a base demand, which favourably could be

With lower heat demand, the temperature in district-heating networks can be lower, which means that surplus heat of lower temperature can be utilised. Also, more electricity can be produced in CHP plants because the heat that is extracted after electricity generation can be

covered by base-load plants, such as waste incineration or CHP plants [23].

heat, because the latter would reduce the demand for district heating supply.

clines with heat demand [21].

heat efficiently.

costs (wood waste, [22]).

**8.2. Using district heating at low demand**
