12th International Symposium on District Heating and Cooling

The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaCHALLENGES ON LOW HEAT DENSITY DISTRICT HEATING NETWORK DESIGNM. Rämä 1 and K. Sipilä 11VTT Technical Research Centre of Finland PB 1000, FI-02044 VTT, FinlandABSTRACTWhile district heating is an energy efficient solution toprovide heating to areas with high heat consumption,mature systems extending out to more demandingoperational environment face challenges maintainingcompetitiveness over alternative heating systems. Asthe heat density falls below a certain level, districtheating is no longer economically feasible. Studying thepossibilities of extending this threshold by means ofdistrict heating system design and pointing out theoperational challenges while approaching it are themain topic of this paper.The problem is investigated in a representative case ofa low heat density area bordering a more extensivedistrict heating network. A node-and-branch typenetwork simulation model is used study the operation ofthe network and a simulation period of one year is usedto get a realistic view of the system in a normaloperational cycle.Not taking into account the characteristics of a low heatdensity area in network design can result in inefficientdistribution system. Operational problems, especiallymaintaining the temperature level in summertime, mustbe solved. Only concentrating on minimizing the heatlosses will not result in best possible design.The temperature level issue can be solved with a bypassvalve, auxiliary heating or accumulators, but inoverall more efficient system requires steps to be takenin the houses. Floor heating and a heat pump coupledwith an accumulator enables the use of low temperaturedesign where the heat losses can be cut significantly.heating. The expansion of mature and large scalesystems take place in areas with lower heatconsumption. This transition to more demandingoperational environment both technically and financiallyrepresents challenges to district heating network design.This is also true in small scale systems of limitedconsumption separated from a larger system.A careless network design in these circumstances canlead to deterioration of the advantages of districtheating; efficiency and reliability. An annual heat loss of5% in district heating distribution is considered a goodresult, but the case in question the heat losses caneasily reach 10% or even tens of percents if thecharacteristics of low heat density areas are not takeninto account in design.LOW HEAT DENSITY AREAA detached house area consisting of 56 identical 150m 2 houses with energy consumptions in compliance oftoday‘s building standards is studied. Dedicated heatexchangers between the network and the consumerexist for both heating and domestic hot water. Totalenergy consumption for the houses is 18.75 MWh/yearof which domestic hot water has a share of 20 percent.The district heating network studied is presented inFigure 1. The detached house connections are markedas green dots and the connection to the main districtheating network as a red rectangle. The connectionshave 1, 2 or 6 detached houses as consumers,indicated by the size of the dot.INTRODUCTIONDistrict heating remains to be one of the most efficientalternatives to provide heating mostly due to its hightotal efficiency especially when utilizing combined heatand power production or waste heat from industrialfacilities or other sources. A wide choice of productiontechnologies, based on fossil or renewable fuels orother sources of heat, provide flexibility to districtheating systems and enable the benefits from theeconomy of scale unlike most consumer specificheating systems. From the consumer point of view,district heating is considered as a reliable and carefreesource of heating energy and is also often aneconomically sound choice.Areas with high heat consumption i.e. economically themost attractive areas will be connected first to district50 mFigure 1. District heating network studied.The total trench length in the area is 2 390 m of whichthe service pipes (DN 15-25) account for 1 300 m. Thepipe size distribution is illustrated in Figure 2. The darkblue coloured bar (DN 65) represents the pipeconnecting the area to the main district heating network.69