Sekundärnät för lågtempererad fjärrvärme

Sammanfattning: Lower energy use in buildings is a result of increasingly stringent energy requirements across Europe. When conventional district heating technology is used in areas with low energy consumption heatlosses do not fall even though the amount of energy delivered is reduced. This reduces income for thedistrict heating company. To maintain their economic viability the district heating companies’ majorchallenge is to implement new solutions that minimize heat loss. This report aims to provide the district heating company Eidsiva Bioenergi AS an example of thepossibilities and limitations of a secondary low temperature district heating system. Focus areas arepast and present limitations of plastic pipes and on what temperatures may be used when taking intoconsideration the potential for growth of Legionella bacteria in hot water systems.The report's goal is to present a theoretical design of a low temperature secondary network for districtheating located in Lillehammer, Norway. The report is written in collaboration with the Norwegiancompany Eidsiva Bioenergi AS.The given solution consists in a secondary low temperature district heating system built with plasticpipes supplying four apartment buildings of a total of 360 student apartments. The network shouldmaintain a supply temperature of 60 °C and a return temperature of 30 °C.A secondary network means lower pressure and temperature levels, making it possible to use plasticpipes. Plastic pipes have an advantage regarding installation as they do not require welding and can besupplied in lengths of 50,100 or 200 meters which can speed up trenching work. The authors are of the opinion that the present plastic piping technology have an adequate technicaldurability and does no longer cause problems with oxygen diffusion if installation is done correctly. Although it was possible to design a secondary low temperature district heating network with lowerheat losses, it was not the most profitable in this case even though heat losses are lower than forconventional technology. Secondary low temperature district heating network with plastic pipes aremore competitive in areas with lower energy demands. We recommend that Eidsiva Bioenergi AS to gain knowledge from this report and look foropportunities to implement the solution in areas where conventional technology is less competitive,such as in new housing developments and more heat sparse areas. The technology can also have great advantages in areas with difficult topography or where longer periods of open trenches are not wanted. In all these cases the fast and flexible installation of plastic pipes can give great financial savings.