The Use of tap water as a heating medium for combined hot tap water and radiator system

Reducing the world usage of fossil fuels and the CO2 emissions from its\ncombustion, are among the main goals of the world’s governments.While in 2011\nthe world’s total primary energy supply was 13113 Mtoe (basically oil, coal and\nnatural gas), in Sweden was 49 Mtoe (nuclear, oil, biofuels, waste and hydro).\nTherefore, Sweden is trying to use renewable and clean energy instead of the\nfossil fuels.\nDistrict heating (DH) is one of the possible ways to produce heat, and in 2010,\nSweden used 45 TWh from this energy carrier. It is an environmental and efficient\ntype of energy, due to the fuel’s flexibility (Biofuel and Waste accounts for 70%\nof the fuel used for DH). It is mainly used in residential and services (91%), while\nthe rest is used in industry (9%). It is the most important energy carrier delivered\nfor heating purposes, representing the 50% of the total heating demand. While in\nmulti-dwelling buildings and non-residential premises DH accounted for 86% and\n69%, respectively, for one- and two-dwelling buildings the corresponding\nproportion was 10%.\nThe project uses DH as energy carrier, and studies the costs of two possible\nheating system designs for a one-dwelling building in Sweden. A comparison\nbetween the investments and the determination of how both cases affect the\nLegionella growth are the aims of this project. This thesis could be beneficial for\nthose who want to know the background of the house’s heating system.\nThe two mentioned ways are the actual one, that is being used nowadays (the\nspace heating and hot tap water system are independent); and the second one,\nwhich is an implementation of this, consists of joining the circuits. Thus, the\npotable water for the production of domestic hot water will be the working fluid\nfor the space heating circuit. With this change the heating system is reduced,\nusing just one heat exchanger for both space heating and hot tap water, while in\nthe conventional configuration there are two (one for each circuit).\nDue to the fact that the piping and radiator system destined for the space heating\nwill work with normal tap water (which has dissolved oxygen, which is an\nimportant iron corrodant) the elected material for the alternative system will be\ncopper. The material used in the conventional space heating system is steel.\nDue to this differentiation in the material, the costs for both cases differ; being\nmore expensive for the alternative design than for the conventional one. While for\nthe first case the cost rises to 224600 SEK, for the second one the cost is 179700\nSEK. These costs include all the material and installation costs.\nSince in this thesis, both systems consider the production of hot water as\ninstantaneuos (not storaged water), the possibility of Legionella positive\nspecimens is non existent and so both are free of this bacteria.\nTherefore, it can be concluded that it makes no sense at all to implement the\nalternative case for the heating system. From Legionella growth point of view, the\npossibility of positive specimens in the water is non-existing for both systems\nstudied. From an economical point of view, the reduced system would imply a\n25% of increase in the investment, with respect to the conventional heating\nsystem.