Lågtempererad fjärrvärme i Umeå

Sammanfattning: People in today’s society are becoming more and more aware of how important it is to use energy as efficiently as possible. This is clearly noticeable by an increase in home produced heat with e.g. solar panels or heat pumps heating systems. These changing customer demands forces district heating technology to be redesigned, which is why there is an ongoing research regarding the next generation of district heating - low temperature district heating (LTDH). Umeå Energi is a district heating company which has noticed these changed customer requirements and are in the need to gain knowledge about the technology of LTDH and how it could affect their existing distribution networks. The purpose of this study is therefore to examine the conditions surrounding the integration of LTDH in parts of Umeå. The technology of LTDH as well as its advantages and disadvantages are first described in this thesis. The next step was to decide the dimension of a secondary low temperature network by calculating heating requirements for domestic hot water demands as well as pipeline dimensions. To be able to create a low temperature part of the network, a heat exchanger was used. Simulations were then performed in the program NetSim to see how this network affected the existing primary net at Umeå Energi. The results showed that the existing network is not affected in any significant way. The next step was to investigate how the so-called prosumers affected on the secondary network but also on the existing primary net at Umeå Energi. A prosumer is a costumer who is partly a consumer, who buys heat from Umeå Energi, and partly producing its own heat via e.g. heat pumps. Umeå Energi is meeting these changing customer requirements by allowing such a prosumer to store their eventual excess heat into the district heating network, and is also given the opportunity to buy heat at shortfall. The flow temperature of the water (60⁰C) that a prosumer wants to deliver to the network falls below the temperatures on the existing network, which is about 100⁰C but can also be higher than that. This is the biggest reason why prosumers must deliver their waste heat to a low temperature network. A study in which waste heat from Akademiska Hus was delivered to the network was made to analyze how a prosumer may affect the district heating network. To be able to do that a simulation were made in NetSim based on different seasonal basis. The results showed that a prosumer does not affect the network in a noticeable way. However, during the summer months, the district heating network already has excess heat due to the use of waste as fuel. This means that the connection of prosumers will increase the excess heat in the net and therefore an investigation of the possibilities of using seasonal storage in the form of boreholes stock was made. Various cases were analyzed, and the biggest focus was on a case about the amounts of waste heat obtained from Akademiska Hus added to the excess heat Umeå Energi have in the current situation. The result shows that an investment of boreholes stock cannot primarily be seen as profitable for Umeå Energi, but this solution may meet the changed customer demands and may by that generate economic benefits in the long run.  Based on the results of this analysis, it appears that Umeå Energi's existing distribution network is capable of connecting to a secondary low temperature network and also potential prosumers. This means that the implementation of LTDH could lead to economic benefits for Umeå Energi.