Smarta fjärrvärmenät - En simuleringsstudie av prosumers inverkan på tekniska parametrar i distributionsnät

Environmental awareness increases, with demands for environmental certifications of new communities and buildings as a result. The introduction of climate friendly energy solutions is an important part of this sustainability development. Some examples of such solutions are solar collectors and heat pumps, which is why E.ON wants to investigate ways to combine small-scale, local solar collectors or heat pumps among customers, called prosumers, with district heating. The studied area is the Western Harbour (Västra Hamnen), which is a part of the district heating network of Malmö-Burlöv. This study focuses on how technical parameters, especially velocity, supply temperature, flow and differential pressure, change in district heating networks when prosumers, in this case with heat production in solar collectors and heat pumps, are introduced. Periods when prosumers produce and when they consume district heating has also been investigated. Heat contribution to the district heating network from solar heating occurs primarily during the summer and only during daytime, with a peak at midday. The heating demand among customers is, however, greatest during the winter, with peaks primarily in mornings and evenings. The solar collectors thus deliver heat when the need is at a minimum in the network. Heat pumps can, technically, deliver heat around the clock and during the greater part of the year but they require electrical energy. Since solar collectors and heat pumps have higher efficiency when they supply cooler water, it is desirable to have as low supply temperature as possible. This means that the supply temperature in the district heating network drops when a prosumer delivers heat to the distribution network. The supply temperature should however not be too low, since that can cause problems with insufficient heating and risk of bacterial growth in the domestic hot water. The cooler water from prosumers may also cause migratory temperature fronts, which leads to increased fatigue of the pipes. However, this has generally no impact on the lifetime of the pipes, since corrosion remains to be the limiting factor. The flow in the pipes increases as the temperature is lowered. This may be important to consider when dimensioning the pipes, since excessive velocities lead to unwanted noise. The flows from prosumers may also be larger during summer when the solar collectors produce much heat, than the flows to prosumers during low outdoor temperatures. Therefore, some of the supply pipes may have to be redimensioned. The results show that the differential pressure increases inside a prosumer’s pressure cone and in areas not reached by their cooler supply water. The latter can be used to optimise the pumping power and thus save money. On the other hand when water from the prosumers is mixed with supply water from the rest of the network, the differential pressure will instead decrease due to increased flows and thus higher pressure losses in the areas reached by this mixed water. What mainly needs to be regulated when introducing prosumers into a district heating network is the requirement of a minimum supply temperature from prosumers. It may also be necessary to control when prosumers are allowed to deliver heat to the network in order to avoid, for example, problems with too low differential pressures. The results have mainly been developed through simulations in NetSim, a network calculation program. Both static and dynamic simulations were conducted