Heat Mismatch of future Net Zero Energy Buildings within district heating areas in Denmark

The long-term goal for Denmark is to develop an energy system solely based on renewable energy sources (RES) in 2050. To reach this goal energy savings in buildings are essential. Therefore, a focus on energy efficient measures in buildings and net zero energy buildings (NZEBs) have increased. NZEBs are characterized by having a greatly reduced energy demand that on an annual basis can be balanced out by an equivalent generation of energy from RES.
Most buildings in Denmark are connected electricity grids and around half to district heating (DH) systems. Connecting buildings to larger energy systems enables them to send or receive energy from these systems. This is beneficial for NZEBs because even though they have an annual net exchange of zero, there is a temporal mismatch in regard to the energy consumption of buildings and the production from the renewable energy units added to them. In other words, situations occur where the renewable energy units produces more energy than
the building consumes. If the building was not connected to a grid, the energy produced would have to be either stored or unused. By connecting the building to a grid it is possible to sell the energy to the grid instead of wasting the energy. The objective in this paper is find how large an area of NZEBs is to be built within DH areas and how the heat mismatch of NZEBs influence different types of Danish DH systems. In the analyses nine different scenarios are analyzed. The examination is from a technical perspective, looking into how the overall heat production within DH areas is affected by the NZEBs excess heat production from solar thermal collectors. The resource consumption, primarily biomass, is used as an overall indicator of the effect on the DH system. The main findings are that the heat mismatch in general is positive in DH systems, decreasing the production from CHPs and boilers and thereby fuel consumption. This however, is not the case in systems where the heat demand in summer months is covered by solar thermal already. By adding seasonal heat storages to the DH systems, the situation can be prevented.