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, EstoniaA DIRECT HEAT EXCHANGER UNIT USED FOR DOMESTIC HOT WATER SUPPLY INA SINGLE-FAMILY HOUSE SUPPLIED BY LOW ENERGY DISTRICT HEATINGMarek Brand 1 , Jan Eric Thorsen 2 , Svend Svendsen 3 and Christian Holm Christiansen 41Ph.D. student, Technical University of Denmark2Senior project manager, Danfoss District Energy, Nordborg, Denmark3Professor, Ph.D., Technical University of Denmark4Danish Technological Institute, DenmarkABSTRACTThe increasing number of new and renovated buildingswith reduced heating requirements will soon maketraditional District Heating (DH) systems uneconomic.To keep DH competitive in the future, the heat loss inDH networks needs to be reduced. One option is toreduce the supply temperature of DH as much aspossible. This requires a review of the behaviour of thewhole domestic hot water (DHW) supply system withfocus on the user comfort and overall costs. This paperdescribes some practical approaches to theimplementation of this Low Energy District Heating(LEDH) concept. It reports on the testing of the dynamicbehaviour of an Instantaneous Heat Exchanger Unit(IHEU) designed for DHW heating and space heating indetached family houses supplied by LEDH ensuring anentry-to-substation temperature of 51 °C. We measuredthe time it takes for the IHEU to produce DHW with atemperature of 42 °C and 47 °C when the tap isopened. Measurements were made for controlstrategies using internal and external by-pass and noby-pass. Our results show the importance of keepingthe branch pipe warm if comfort requirements are to befulfilled, but this involves higher user costs for heating.To increase user comfort without increasing costs, wepropose the whole-year operation of floor heating inbathrooms, partly supplied by by-pass flow.INTRODUCTIONDistrict Heating (DH) is a well known concept ofproviding buildings with heat for space heating (SH) andDomestic Hot Water (DHW) heating in economical andenvironmentally friendly way. Nowadays, buildingregulations have been introduced worldwide and arepushing to reduce energy consumption in buildings,because 40% of all energy consumption takes place inbuildings. The energy policy of European Union isrecently focused on energy savings, reducingproduction of CO 2 and increasing the ratio of renewableenergy [1]. DH is one of the most suitable solutions toachieve these goals for building sector and it gives highpriority for further development of DH. But recenlty usedtraditional high and medium temperature DH systemsare not optimal solution for the future. Sooner or later,energy consumption of all buildings will be inaccordance with low energy building regulations and it60will form areas with lower heat demand than nowadays.Currently used DH networks will not be able supplythese areas in economical way, because the ratiobetween network heat losses and heat consumption inbuildings would be unacceptable and thus cost of heatfor end users will increase and DH systems will looseconcurrency with other solutions, e.g. heat pumps.Recently, research in DH is focused to find the way howto use DH in areas with low energy buildings and how toincrease ratio of heat produced by renewable sources ofenergy as solar heat plants or heat pumps driven byelectricity from renewable sources.One of interesting application of renewable energy inDH is use of decentralised heat sources as e.g. solarcollectors installed on roofs of individual buildings,supplying heat to DH network, but it still needs moretime and work to develop new substations and newconcept of DH networks to be able to handle these newfeatures. The solution for future development of DH is toreduce heat losses of DH networks by means of pipeswith better insulation properties e.g. twin pipes, usebetter concepts of network design (circular networkconfiguration, possibility of using circulation line for mainpipes) and to reduce the supply temperature of districtheating water to lowest level as possible.The District Heating Systems designed due to thisphilosophy are called Low Energy District HeatingSystems (LEDH). The main focus in LEDH system is toreduce heat losses from network as much as possible,exploit more sources of renewable energy for heatsupply and still maintain or improve level of comfort forusers, because without high level of comfort thisconcept can‘t be successful. LEDH concept wasreported e.g. in project ―Development andDemonstration of Low Energy District Heating for LowEnergy Buildings [2], where theoretical case studydocumented, that LEDH concept is a good solution forfuture and even in sparse housing areas is fullycompetitive to heat pumps. This article is focused onapplication of LEDH for DHW heating. Considerationsrelated to use of LEDH for space heating will bereported in future in another article.