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, EstoniaFinally, the outdoor climate affects the length of theheating season. Usually, the lower the average outsidetemperature, the longer the heating season. Thishowever, does not affect the DHW since this is more orless steady all the year along.Positioning of substationFigure 2 shows the positioning of the substation. Theheat is delivered from the district heating pipelinesthrough two separate heat exchangers, one for heatingthe water in the storage tank for DHW by a circulatingloop, and the other for the air heating and spaceheating system. The main reason for having two heatexchangers is due to the different needs of temperaturelevels. In the calculations dealing with the production,the used heat demand used is the total demand, whilefor the distribution the heat is divided into heatdistribution for SH and for DHW.In order to calculate losses related to the storage tank,it is assumed that the tank is of a common type with acommon value for the stand by heat loss. The systemdesign consists of the coupling in series of 289 litresstorage tanks. There are considered two tanks for theapartment building of 1000 m 2 but one more tank if thecase is dealing with hospitals, educational and hotelbuildings. For other sizes the number of tanks isadjusted according to the demand.temperature is here constantly at the designed point of60 o C.When dealing with distribution of SH, the losses areconsidered dependent on the kind of insulation materialand the ambient and the mean water temperature inthe supply and return pipes.The heat emission to the room from the DHW draw-offtap discharge cocks is considered to be negligible incomparison to the total heat consumption.Dealing with space heating a distinction is done withrespect to the kind of emission. Two major groups areconsidered: the emission by floor heating and byradiators. The first has a low temperature distribution of35/28 ˚C. As for the radiator system, the analyzed basecase is 80/60 ˚C for supply/return design values.Besides the temperature level, the placing in the roomaffects the stratification efficiency and the loss throughthe outside wall. Furthermore, another point related tothe temperature is the regulation of the roomtemperature, which in our case, is assumed to be aPI-regulator, even if in a lot of apartments thisregulation is quite often done by on/off regulation.RESULTSProduction efficiencyEfficiencies to be studiedFor the present paper, as written previously, thesystem is divided in three smaller system parts whichare independent. For every component, the efficiencyis calculated following different standards: Production; according to EN 15316-4-5:2007[4]Distribution; according to EN 15316-2-3:2007 andEN 15316-3-2:2007[5] Room emission; according to EN 15316-2-1:2007[6]The efficiency of the production includes the lossesdepending on the thickness of the insulation material,the insulation material itself, the storage tank, thecomplete local piping system of the substation systemand the temperature difference between the two mediaand the ambient. It takes into account the thermal lossof the total substation. For this case the substation isconsidered to be in an unheated part and therefore thelosses are considered as unrecoverable.In case of the distribution, the efficiency depends onthe use of the heated water. In case of being a part of aDHW system; the energy used for heating the waterwhich is not drawn-off and which slowly gets cold in thepipelines, has to be considered as loss. Moreover, heatis used to heat up the pipes and fittings. Since thebuilding is large enough to need a circulation loop thisloop is considered to be a source of loss? The water240The production efficiency is shown in Figure 3. By usingthe losses on the heat demand and the temperaturedifference as basis for calculation, the values inTable 1 are obtained.System efficiencyProduction efficiencies for the different types of buildings according to theEN 15316-4-5 :2007 (Oslo climate) with a distribution temperature 80/600,9900,9800,9700,9600,9500 250 500 750 1000 1250 1500 1750 2000 2250Building floor area [m 2 ]Apartment blockOffice buildingHotel and restaurantbuildingEducational buildingHospital buildingSingle familyFigure 3 Production distribution of the 80/60 ˚C districtheating for different buildingsAs Figure 3 shows, the bigger the building, the higherthe efficiency. This effect is due to the reduction of therelative losses when the size of the substation (kW)increases. The curve profile is decreased slightly from2000 m 2 and downwards, and then decreasing rapidlyfrom about 1000 m 2 down to 500 m 2 .