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, EstoniaSpecific pumping energy (electrical power/ heat supply)Fig. 7b. Electricity used for pumping in relation to thelength of the district heating network, 0–500 km.Specific pumping energy (electrical power /heat supply)1.7 %1.5 %1.3 %1.1 %0.9 %0.7 %0.5 %0.3 %1.6 %1.4 %1.2 %1.0 %0.8 %0.6 %0.4 %0.2 %Fig. 7c. Electricity used for pumping in relation to thelength of the district heating network, 0–70 km.For big companies the proportional pumping energy isalmost constant 0.5 per cent of heat supply.The longer the DH network, the smaller the proportionalpumping energy. The result is partly the same as in theprevious chapter: the bigger companies have smallerproportional pumping energies.If a company seems to have a high proportionalpumping energy in figures 7a–7c it may be due to poorheating density (lots of pipes in areas with not so muchconsumers).3. Heat densitySpecific pumping energy vs. length of the DH netLength 0 - 70 km0.1 %0 10 20 30 40 50 60 70Length of the DH net, kmSpecific pumping energy vs. length of the DH net0.0 %0 200 400 600 800 1000 1200 1400Length of the DH net, kmHeat density is the heat supply divided by the length ofthe district heating net.Fig. 8. Electricity used for pumping in relation to the heatdensity.It is natural that in a DH network with not too manypipes in proportion to sold heat the need for pumping ofDH water is lower.FURTHER INFORMATION:Pöyry Finland OyPL 93 (Tekniikantie 4 A)FI-02151 EspooFinlandantti.hakulinen@poyry.comCONCLUSIONDistrict heating networks enlarge and changecontinuously and therefore the conditions of pumpingwill also change. For that reason, it is important tocheck every now and then if the actual operating pointof the pump is as designed and what the efficiency ofthe present operating point is. The pumping could stillwork technically well but the pumps could be operatingwith low efficiency.The most important issues in designing and operatingof district heating pumping are:Specific pumping energy (electrical power /heat supply)1.7 %1.5 %1.3 %1.1 %0.9 %0.7 %0.5 %0.3 %Specific pumping energy vs. heat density0.1 %0 1 2 3 4 5 6 7Heat density, GWh/kmA sufficient but not too big pressure differencemust be guaranteed for customers.There must be enough pressure in all parts of thenetwork at all circumstances and at the same timethe maximum pressure level must not beexceeded.When designing pumping it is important to studyall possible pumping cases.Good operating point should be verified whendesigning and operating pumps.Pumping energy is dependent on certain parameters.The best parameter is considered to be heat density onwhich pumping energy is clearly dependent. And this isa quantity every district heating company measures.286