7As existing buildings are renovated and energy-efficiency measures are implemented to meet requirements 8 for reduced energy consumption, it becomes easier to heat our homes with low-temperature heating. This 9 study set out to investigate how much the heating system supply temperature can be reduced in typical 10Danish single-family houses constructed in the 1900s. The study provides a simplified theoretical overview 11 of typical building constructions and standards for the calculation of design heat loss and design heating 12 power in Denmark in the 1900s. The heating power and heating demand in six typical Danish single-family 13 houses constructed in the 1900s were estimated based on simple steady-state calculations. We found that 14 the radiators in existing single-family houses should not necessarily be expected to be over-dimensioned 15 compared to current design heat loss. However, there is considerable potential for using low-temperature 16 space heating in existing single-family houses in typical operation conditions. Older houses were not always 17 found to require higher heating system temperatures than newer houses. We found that when these 18 houses have gone through reasonable energy renovations, most of them can be heated with a supply 19 temperature below 50 °C for more than 97% of the year. 20

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Document Version Peer reviewed version Link back to DTU Orbit Citation (APA):Tunzi, M., Østergaard, D. S., Svendsen, S., Boukhanouf, R., & Cooper, E. (2016). Method to investigate and plan the application of low temperature district heating to existing hydraulic radiator systems in existing buildings. Energy, 113,[413][414][415][416][417][418][419][420][421] This study presents a method to adapt existing hydronic systems in buildings to take advantage of low temperature district heating (LTDH). Plate radiators connected to double string heating circuits were considered in an optimization procedure, based on supply and return temperatures, to obtain the required logarithmic mean temperature difference (LMTD) for a low temperature heating system. The results of the analysis are presented as the average reduction of LMTD over the heating season compared to the base case design conditions. Two scenarios were investigated based on the assumption of a likely cost reduction in the end users' energy bills of 1% for each 1 °C reduction of return and average supply and return temperatures. The results showed possible discounts of 14% and 16% respectively, due to more efficient operation of the radiators. These were achieved without any intervention in the thermal envelope or to the heating systems, through simply adjusting the temperatures according to demand and properly controlling the plate radiators with thermostatic radiator valves (TRVs).

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The efficiency of district heating systems is greatly affected by network supply and return temperatures. However, the opportunities to lower the temperatures and thereby increase network efficiency are restricted by customer installations. Very little is known about the customer installations, because heating system operation is only rarely monitored in detail. In this study, we therefore investigated the operation of the heating systems in five houses. The study had two aims: first to investigate how much of the heating season the houses could be heated with supply temperatures as low as 55 °C, and second to investigate whether occupant behaviour and heating system malfunctions caused unnecessarily high return temperatures. The results showed that all the houses were compatible with low-temperature supply, and in two of the houses return temperatures were even as low as the preferred 25-30 °C. Two main causes were found for unnecessarily high return temperatures in the remaining houses: a few radiators were found to be too small, and thermostatic radiator valves did not always ensure proper water mass flow. In conclusion, if these errors were corrected, the study indicates that it would be possible to heat the investigated houses with district heating temperatures of 55/30 °C.