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, Estonia60Column radiator P fan= 2.2 W110DH primary supply temperature5550T ss,0T sr,0T ss,Fan100T s[C]454035T sr,FanT ps[C]9080307025200 0.2 0.4 0.6 0.8 1601 0.8 0.6 0.4 0.2 0 0rel heatloadFig. 13 Modified temperature program for column radiator,P fan=2.2 W.Q relINFLUENCE ON DH NETWORKKnowing the reduced temperature level on thesecondary side of the HEX, the impact on the DHnetwork can be estimated. The impact is calculatedbased on two different strategies:1. Primary supply temperature (T ps ) is kept at thesame level as before2. The primary flow (m p ) through the HEX is keptconstantBy applying the first strategy, both T pr and the mass flowin the DH network is reduced. The second strategyresults in a reduced T ps and T pr without changing theflow rate in the DH network.Results so far will now be applied to a DH substationdimensioned as recommended by the Swedish districtheating association [1]. The calculations are made witha parallel connected DH substation serving a buildingwith 20 apartments. The substation is providing thebuilding with heat and domestic hot water (DHW) andDHW circulation. The assumed DHW usage is125 l/apartment&day, space heating load at DOT is3 kW/apartment. The heat loss from DHW circulation isassumed to be 0.1 kW/apartment. For each spaceheating load a flow-weighted mean value for T ps and T pris calculated for a time period of 24 h, including heatload from both DHW and DHW circulation. Thereference DH supply temperature, dependent on thespace heating load, is assumed as illustrated in Fig. 14.Fig. 14 DH primary supply temperature.ResultsThe first control strategy is in Fig. 15 – Fig. 20 noted as„T ps unchanged‟, and the second strategy is noted as„m p unchanged‟.In Fig. 15 and Fig. 16 the possible reduction of DHsupply temperature is shown.T pssaving [C]15105Panel radiator T pssavingP fan= 2.7 W m punchangedP fan= 1.9 W m punchanged01 0.8 0.6 0.4 0.2 0rel heatloadFig. 15 Resulting T ps reduction with panel radiator.T pssaving [C]15105Column radiator T pssavingP fan= 3.0 W m punchangedP fan= 2.2 W m punchanged01 0.8 0.6 0.4 0.2 0rel heatloadFig. 16 Resulting T ps reduction with column radiator.In Fig. 17 and Fig. 18 the reduction of T pr is shown. Asseen the reduction of T pr is of the same magnitudeindependently of which control strategy is used.27