Heat supply in cities comprises a significant contribution to climate change. Heat supply to buildings requires low temperature heat, which most efficiently can be produced with heat pumps, geothermal heat or the cogeneration of heat and power, and through urban district heating networks. District heating is an established technology, which covers roughly 50% of the Danish heat supply to the built environment. Future district heating systems will have to face several challenges: heat sources need to be less carbon intensive, which can be achieved using renewable energy or waste heat sources. As these sources generally are limited and characterised by higher costs, investments in these sources may need to happen alongside investments in energy savings in the built environment. Finally, heat distribution may be subject to efficiency measures. What is common to all these factors is that they depend on the geography of urban areas and regions. An analysis of the potentials, costs and policy requirements must therefore be based on a highly detailed, large scale model of urban heat demand and supply. This paper presents the design and the use of an urban Heat Atlas for Denmark, which is composed of publicly available data on the built environment and urban heat supply. Three cases are presented, which 1) describe the conversion of predominantly oil boilers and 2) of individual natural gas heating to collective heat supply in climate conscious cities, as well as are used for 3) designing carbon-neutral heat supply infrastructures. The results of applying Heat Atlases deliver important quantitative data and information for urban decision making processes. Not only are the potentials of converting to district heating mapped and available as numerical data, but also the investment costs associated to the establishment or the expansion of district heating networks are calculated. Potentials and costs are then composed to continuous cost-supply curves, which facilitate the political process of converting urban energy systems. In addition, the Heat Atlas methodology delivers data for the required investments in additional heat supply capacities; and returns maps of CO2-emissions caused by several forms of individual and collective heat supply. In addition to the applications sketched in the present paper, further use of the methods described here are within urban carbon accounting, the reconstruction of urban areas in environmentally benign manner, as well as integrative studies of urban climate change mitigation. The Heat Atlas hence comprises a practical tool for renewed urban heat supply planning, which in the present form is applicable for all Danish towns, cities and regions.
Heat Atlas design
The heat atlas presented here quantifies and locates the heat demand in the built environment. It specifies the heat installations of buildings (boilers, district heating, heat pumps etc.), the fuels used in individual heating (natural gas, oil, biomass etc.) and the existing collective heat supply technologies found in an area (district heating, natural gas or none). For each building, the net heat demand for room heating and hot water is calculated using registered building data, complemented with empirical building and user data. Also, the potential for heat savings by insulating existing buildings is assessed based on these data. The costs of connecting buildings to new or existing district heat systems can be calculated using data on heat demand density and distance to existing infrastructures, combined with empirical data from actual installation works. Together with information on the energy plants used to produce district heating, a heat atlas may cover the entire process chain from end-use heat demand to useful, or secondary, heat and to primary energy or fuels. As all these parameters are specified by geography, the heat atlas is designed as a geographical database using geographical information systems (GIS). The completed heat atlas comprises a geographical database of heat demand and supply, which can be used for spatially explicit analyses of changes to the geography of heat supply. For every new setup of supply, as specified in the next chapter, the heat atlas will yield data on the potentially connectable buildings and their heat demand, the affiliated costs, and the additional heat to be produced by the existing district heating plants.
Spatial analysis of urban heat supply
A geographical or spatial model of the urban heat supply, demand and future supply options forms the basis for spatially explicit analyses of potentials for carbon free heat supply and its associated costs. For cost-supply analysis of the conversion of individual natural gas to district heating, the potential for district heating and estimated investment costs were included in a spatially explicit economic model with the single building as the smallest entity. A potential for district heat exists for all buildings, which are not currently connected to district heat and which are located within areas of sufficient heat demand density and within reach of existing infrastructure. The costs are consequently calculated for each building not currently connected and located in a neighbourhood without district heat distribution network. The neighbourhood is specified as a 1 hectare standard square cell of the Danish Square Grid. If there is at least one building in one of these cells, a district heating network must exist nearby, and costs of local distribution networks and transmission radials are avoided. The reason to have this rule is that district heating areas in the heat plan typically exceed the extent of actual installations. Also, municipalities have used different ways to delineate these district heating areas, which therefore are unfit for being used here.