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, Estoniaheating water is supplied by pipe 1 to substation,circulated through HEX or external by-pass (seeFig. 3) and then sent back to district heating network(DHN) supply by pipe no.3. This concept is in earlystage of investigation but it looks promising. The mainquestion will be related to flow of DH water in branchpipe in order not cool it down too much before will besent back to DH supply pipe in the street.lower heat loss. On site measurements were started inLystrup to evaluate performance of both types of DHsubstations, but no detailed measurements requiringshort time steps are performed to evaluate level ofusers comfort. The measurements more focused touser‘s comfort are planed to be performed this year inDanish Technological Institute and TechnicalUniversity of Denmark (DTU) on DH systemssimulating the conditions in Lystrup. The DH systemswill consist of branch pipes, substation and DHWbuilding installations and different control approaches(external or internal by-pass, different set up by-passtemperatures, possibility of supply-supply recirculation,etc.) will be studied for DH substations supplied byLEDH. Measured data will be used for evaluation ofperformance of different control concepts, level ofusers comfort and lately also for validation ofnumerical model which is aimed to be developed foroptimization LEDH systems.Fig. 3 Supply – supply recirculation with external by-passThis solution is expected to be favourable mainly forcircular shapes of DH networks, but it should bementioned, that re-heating stations will be probablyneeded in point of DH network, where temperature ofDH water decrease bellow defined value.Full scale demonstration of LEDHFull scale demonstration of LEDH is recently running inLarch Garden in Lystrup, Denmark [11], where 40 lowenergy houses class 1 and 2 are connected to LEDHsystem, with designed forward temperature from heatplant 52 °C. For primary side of substation, forwardtemperature of 50 °C and return temperature of 25 °Care designed. The DH network is built from highlyinsulated single pipes (for main pipes) and main pipeswith smaller diameter, distribution and branch pipesare built from twin pipes. Two types of district heatingsubstations providing houses with DHW and spaceheating are tested by customers in real conditions. Thefirst concept is 29 Instantaneous Heat Exchanger Units(IHEU), second is 11 District Heating Water Units(DHWU). IHEU is classical concept of substation withinstantaneous heat exchanger, only with enlargednumber of plates. IHEU units have external by-pas,with set point temperature of 35 °C for customerssituated not at the end of street and 40 °C forcustomers situated at the end of the street. DHWU isnew concept of DH substation, reported e.g. byPaulsen [13]. DHWU consist of buffer tank for districtheating water and when DHW is needed, DHW isheated in instantaneous heat exchanger as in previouscase. Advantage of concept with buffer tank is peakshaveddemand of DH water during charging and useof branch pipes with lower diameter, connected with64TEST OF TEMPERATURE PERFORMANCEAs a first part of measurements planed to beperformed at DTU, the time needed for IHEU toproduce DHW with temperature of 42 °C and 47 °Cwas measured, after tapping of DHW was started. Thetap delay was investigated for two control strategies,one using internal and second using external by-pass.The measurements were performed for different initialconditions before tapping was started to simulate inrealistic way users behaviour. Finally, the periodbetween two by-pass flow operations was measured.Experimental setup and instrumentsTested DH substation was prototype of InstantaneousHeat Exchanger Unit (IHEU) developed specially forLEDH pilot project in Larch Garden – Lystrup,Denmark. The IHEU is a type of district heatingsubstation consists of a heat exchanger (HEX) withoutstorage tank. DHW is heated instantaneously in HEXonly when tapping is performed and then supplieddirectly to DHW taps by individual feeding pipes, whilespace heating is using direct connection without heatexchanger, i.e. concept typical for Denmark.Substation is same concept as regular IHEU fortraditional DH. The difference is in increased numberof plates in heat exchanger assuring better heattransfer. Water volume of primary and secondary sideis 1.1 L each and the heat exchanger is not insulated.The experiments were focused only on dynamicbehaviour of substation related to DHW heating andthus space heating loop wasn‘t connected and spaceheating valves in substation closed. Desiredtemperatures of DHW were chosen in accordance withrequirements in DS439 for temperature of DHW forkitchen sink and other fixtures. Required temperaturesmentioned in DS 439 are 45 °C and 40 °C. In order to